EPA-650/4-74-005-n
February 1975 Environmental Monitoring Series
GUIDELINES FOR DEVELOPMENT
OF A QUALITY ASSURANCE PROGRAM:
VOLUME XIV -
SCREENING DETERMINATION
OF LEAD IN GASOLINE
U.S. Environmental Protection Agency
Office of Research and Development
Washington, 0. C. 20460
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EPA-650/4-74-005-n
GUIDELINES FOR DEVELOPMENT
OF A QUALITY ASSURANCE PROGRAM:
VOLUME XIV -
SCREENING DETERMINATION
OF LEAD IN GASOLINE
by
D. E. Gilbert, F. Smith, and D. E. Wagoner
Research Triangle Institute
Research Triangle Park, North Carolina 27709
Contract No. 68-02-1234
ROAP No. 26BGC
Program Element No. 1HA327
EPA Project Officer: Steven M. Bromberg
Quality Assurance and Environmental Monitoring Laboratory
National Environmental Research Center
Research Triangle Park, North Carolina 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
WASHINGTON, D. C. 20460
February 1975
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EPA REVIEW NOTICE
This report has been reviewed by the National Environmental Research
Center - Research Triangle Park, Office of Research and Development,
EPA, and approved for publication. Approval does not signify th^it the
contents necessarily reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S . Environ-
mental Protection Agency, have been grouped into series. These broad
categories were established to facilitate further development and applica-
tion of environmental technology. Elimination of traditional grouping was
consciously planned to foster technology transfer and maximum interface
in related fields. These series are:
1. ENVIRONMENTAL HEALTH EFFECTS RESEARCH
2 . ENVIRONMENTAL PROTECTION TECHNOLOGY
3. ECOLOGICAL RESEARCH
4. ENVIRONMENTAL MONITORING
5. SOCIOECONOMIC ENVIRONMENTAL STUDIES
6. SCIENTIFIC AND TECHNICAL ASSESSMENT REPORTS
9- MISCELLANEOUS
This report has been assigned to the ENVIRONMENTAL MONITORING
series. This series describes research conducted to develop new or
improved methods and instrumentation for the identification and quanti-
fication of environmental pollutants at the lowest conceivably significant
concentrations. It also includes studies to determine the ambient concen-
trations of pollutants in the environment and/or the variance of pollutants
as a function of time or meteorological factors.
This document is available to the public for sale through the National
Technical Information Service, Springfield, Virginia 22161.
Publication No. EPA-650/4-74-005-U
11
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TNLE OP CQNIENTS
SECTION PAGE
ii OPERATIONS mm. 3
2.0 GENERAL 3
2.1 EQUIPMENT SELECTION 6
2.2 PRESAMPLING PREPARATION 11
2.3 SAMPLING PROCEDURE 17
2.4 ANALYSIS PROCEDURE 22
2.5 DATA REDUCTION 26
2.6 SAMPLE SHIPPING PROCEDURE 27
2.7 PROCEDURE WHEN CONTAMINATION IS DETECTED 28
III mm. FOR REGIONAL SUPERVISOR 30
3.0 GENERAL 30
3.1 ASSESSMENT OF DATA QUALITY 32
3.2 CONSTRUCTION AND USE OF A CONTROL CHART 33
3.3 SUGGESTED PERFORMANCE CRITERIA 37
IV QUALITY ASSURANCE PROCEDURE 42
4.0 GENERAL 42
4.1 FUNCTIONAL ANALYSIS OF FIELD TEST METHOD 43
4.2 PROCEDURES FOR PERFORMING A QUALITY AUDIT 49
4.3 DATA QUALITY ASSESSMENT 51
APPENDIX
A REFERENCE ICTHOD FOR THE SCREENING
DETERMINATION OF LEAD IN GASOLINE eo
B GLOSSARY OF SYMBOLS 61
C GLOSSARY OF TERMS 64
D CONVERSION FACTORS 66
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LIST OF FIGURES
FIGURE NO. PAGE
1 Operational flow chart of the determination process. 5
2 Field sampling kit. 9
3 Copy of the chain of custody label. 12
4 Photograph of the vial positioned on the ultraviolet
light. 14
5 Sample calibration curve for lead in gasoline,
using the portable colorimeter and 18-mm test
tubes. 16
6 Field inspection form. 19
7 Flow chart of the analysis of lead in gasoline. 25
8 Quality control chart for checking the calibration
curve. 35
9 Example illustrating p < 0.10 and satisfactory
data quality. 56
10 Example illustrating p > 0.10 and unsatisfactory
data quality. 56
IV
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LIST OF TABUES
TABLE NO. PAGE
1 Equipment and suppliers 7
2 Computation of mean difference, <1, and standard
deviation of differences, S, 53
d
3 Sample plan constants, k for P{not detecting a lot
with proportion p outside limits L and U} <, 0.1 58
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ABSTRACT
This document presents guidelines for developing a quality assurance
program for the screening determination of lead in gasoline by the
Federal reference method. These guidelines include:
1. Recommended operating practices and techniques,
2. Procedures for assessing performance and qualifying data,
3. Procedures for identifying trouble and improving data quality,
4. Procedures to permit design of auditing activities.
This document is an operations manual, designed for use by operating
personnel.
This work was submitted in partial fulfillment of Contract Durham
68-02-1234 by Research Triangle Institute under the sponsorship of the
Environmental Protection Agency. Work was completed as of February 1975,
Vi
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SECTION I IfJTRODUCTION
This document presents guidelines for developing a quality assurance
program for the screening determination of lead in gasoline by using a
portable colorimeter. This method was published by the Environmental
Protection Agency in the Federal Register, November 12, 1974, and is
reproduced in appendix A of this document.
This document is divided into four sections:
Section I, Introduction. The Introduction lists the overall objec-
tives of a quality assurance program and delineates the program components
necessary to accomplish the given objectives.
Section II, Operations Manual. The Operations Manual sets forth
recommended equipment selection, presampling preparation, sampling pro-
cedures, data reduction procedures, and sample shipping procedures to
insure the collection of data of high quality when contamination is
detected.
Section III, Manual for Regional Supervisor. The Manual for Regional
Supervisors discusses the assessment of data quality, suggested performance
criteria, instructions for quality control checks designed to give an
indication or warning that invalid or poor quality data are being collected,
and instructions for collecting and analyzing information to identify
trouble.
Section IV, Quality Assurance Procedures. The Quality Assurance
section presents information relative to the test method, a functional
analysis to identify the important operating variables and factors, and
statistical properties of and procedures for conducting an independent
assessment of data quality.
The objectives of this quality assurance program for the screening
of lead in gasoline are to:
1. Provide recommended operating procedures and techniques,
2. Identify and minimize systematic errors to maintain the pre-
cision within acceptable limits in the determination process,
3. Provide routine indications of and documentation for satisfactory
performance of operating personnel and/or equipment,
4. Provide for prompt detection and correction of conditions which
contribute to the collection of poor quality data, and
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5. Provide the necessary information to describe the quality of
the data.
In order to accomplish these objectives, a quality assurance program
must contain the following components:
1. Recommended operating procedures,
2. Routine training of personnel and evaluation of performance
of personnel and equipment,
3. Routine monitoring of the variables and parameters which may
significantly affect data quality, and
4. Development of statements and evidence to qualify data and
detect defects.
Implementation of a quality assurance program will result in data
that are more uniform in terms of precision and accuracy. It will enable
each monitoring network to continuously generate data that are of
acceptable quality.
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SECTION II OPERATIONS MWUAL
2.0 GENERAL
This operations manual sets forth recommended operating procedures for
the screening determination of lead in gasoline by using a portable color-
imeter (ref. 1). This method is reproduced from the Federal Register in
appendix A of this document.
This method is intended for use in the field for the quantitative
measurement of lead in unleaded gasoline in the range from 2.64 to 26.4 mg
Pb/£ (0.01 to 0.1 g Pb/gal). This method applies to all commercial gasolines
and responds to all types of lead alkyls, as well as to other organic and
inorganic forms of lead. This method is a screening test and is not to be
used as a replacement for Test for Lead in Gasoline by Atomic Absorption
Spectrometry (Federal Register. Vol. 39,.No. 131, July 8, 1974).
In a brief outline of this method, the gasoline is treated with iodine
and tetraethyl ammonium chloride in chloroform and subjected to ultraviolet
light. The lead alkyls form water-soluble lead alkyl iodides, which are
removed from the gasoline by shaking it with an aqueous ammonium nitrate
solution. The aqueous extract is filtered into a solution of 4-(2-pyridylazo)-
resorcinol disodium salt (PAR) and ammonium hydroxide. The lead is determined
by measuring its PAR complex colorimetrically at 490 nm using a previously
prepared calibration curve.
In theory, lead alkyls in gasoline react with halogens to form alkyl
lead halides. In the presence of ultraviolet light the lead alkyls react
with an iodine/tetraethylammonium chloride/chloroform solution in the
following stepwise fashion, with the alkyl lead dihalide RJ?bI_ being the
predominant species formed:
RI
R3PbI + I2 + R2PbI2 + RI
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The lead alkyl iodides are water extractable and the solution reacts
with the PAR,
OH,-.
•ONo«H20
ONa . H20
to form a red chelate.
PAR also reacts with many other metals forming highly colored com-
plexes. However, none of these are normally found present in a soluble
form in gasoline. The following metals were found to form colors with
PAR and if present may interfere to give high results: Fe II, Fe III,
Co II, Ni II, Cu II, Zn II, Cd II, Mn II, Sm II, V IV, PB II, U VI, Ti IV,
and the rare earths.
The accuracy of data obtained from this method depends upon equipment
calibration and on the proficiency with which the operator performs his
various tasks. This measurement method from reagent preparation through
sample analysis and data reporting is a complex operation. Guidelines
are presented with special emphasis on quality control checks and decision
rules applicable to known problem areas. The operator should make himself
familiar with the rules and regulations concerning the reference method as
written in the Federal Register (appendix A of this document).
Instructions throughout this document are directed toward on-the-site
determinations. A minimum auditing or checking level of one check per cal
endar week plus any time a gasoline sample is found to approach or exceed
the standard for lead in gasoline, i.e., 13.2 mg Pb/£ (0.05 g Pb/gal)
is recommended (see section 4.2). Sampling period durations and auditing
levels are subject to change by the supervisor or manager. Such changes
would not alter the basic directions for performing the operation. Also,
certain control limits, as given in this manual, represent best estimates
for use in the beginning of a quality assurance program and are, therefore
subject to change as field data are collected.
It is assumed that all apparatus satisfies the reference method speci-
fications and that the manufacturer's recommendations will be followed
using a particular instrument (e.g., colorimeter).
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EMFTENT SELECTION
1. Select the equipment according to
specifications given in the reference
method (Appendix A) and according to
subsection 2.1
2. Perform visual and operational checks
of equipment according to subsection
2.1
3. Record new equipment in a receiving
record file according to subsection
2.1
CALIBRATION
4. Calibrate the equipment according to
subsection 2.2
SAPLING
5. Sample the gasoline and document it
according to subsection 2.3
6. Prepare reagents according to sub-
section 2.2
7. Analyze samples according to sub-
section 2.4
8. Validate data by comparing measured
value of reference sample to the known
value according to subsection 2.4
DATA PROCESSING
9. Perform calculations to determine lead
content according to subsection 2.5
10. Report data according to subsection 2.5
EQUIPMENT
SELECTION
EQUIPMENT
INSPECTION
EQUIPMENT
RECORD
FILE
EQUIPMENT
CALIBRATION
SAMPLING
PROCEDURE
REAGENT
PREPARATION
SAMPLE
ANALYSIS
i
f
VALIDATE
DATA
PERFORM
CALCULATIONS
10
REPORT
DATA
Figure 1. Operational flow chart of the determination
process.
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The sequence of operations to be performed during each determination
period is given in figure 1. Certain operations such as preparation of
certain reagents and colorimeter calibration are performed periodically.
The remaining operations are performed during each determination period.
The operations are classified as equipment selection, presampling preparation,
sampling and analysis procedures , and data processing. Each operation or
step in the process is identified by a block. Quality checkpoints in the
measurement process, for which appropriate quality control limits are
assigned, are represented by blocks enclosed by heavy lines. Other check-
points involve go/no-go checks and/or subjective judgments by the analyst
with proper guidelines for decisionnaking spelled out in the procedures.
These operations and checks are discussed sequentially as one progresses
step by step through the sequence of actions in figure 1.
The analyst is responsible for maintaining certain records. Specifi-
cally, the following log books are maintained:
1. Receiving Record Log Book. This book contains a description of
the item received, its serial number or catalog number when
appropriate, and results of the acceptance test, signed and
dated.
2. Calibration Record Log Book. This book contains the lead
calibration curves, standard sample datat and the calibration
of all of the equipment.
3. Field Inspection Form Log Book. This book contains the test
station sample identification data for each retail station
inspected, calculation data, and test results.
4. Sample Shipping Record Log Book. This book contains test station
sample identification, test and sample shipping information.
2.1 EQUIPMENT SELECTION
A listing of the required equipment with certain pertinent specifica-
tions is given in appendix A. Table 1 contains a supplemental list of
sufficient equipment and suppliers. Additional specifications, criteria,
or design features are given herein to aid in the procurement of equipment
to insure the collection of data of acceptable quality. Also, procedures
and limits for acceptance checks of new equipment are presented. A des-
criptive title and the identification of new equipment should be recorded
in the receiving record log book.
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Table 1. Equipment and suppliers
Field Sampling Kit; Beckman Instruments Corporation,
U. S. Highway 22 at Summit Road, Mountainside, New Jersey.
Refill Packages for the Field Sampling Kit; Beckman
Instruments Corporation, U. S. Highway 22 at Summit Road,
Mountainside, New Jersey.
Shipping Cartons with Dividers, Tape and Dispenser, Carrolton
Products of Alexandria, Virginia.
Shipping Casp.s for Individual Samples, Improved Mailing
Case Co., Wayne, New Jersey.
Flammable Liquid Labels; Association of American Railroads,
Bureau of Explosives, Washington, D. C.
Chain of Custody Labels; Forms Office, Environmental
Protection Agency, Research Triangle Park, North Carolina.
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2.1.1 Field Sampling Kit
2.1.1.1 Specifications. Each kit, shown in figure 2, includes:
Apparatus
o
1. Ultraviolet lamp, long wavelength, 3660 A, placed in a standard
4-watt flourescent fixture.
2. A 3-min electric timer connected to the fixture.
3. Measuring block, aluminum, drilled to hold an 18- by 150-mm
test tube with a mark at a level equal to 5.0 m£ of liquid in the test tube.
4. Colorimeter, portable, capable of operating at 490 nm. Any
equivalent instrument capable of measurement near 514 nm (the optimum Pb-PAR
complex wavelength) may be used. The instrument must be capable of meeting
the precision requirements of this method; a repeatability of +2.64 mg Pb/£
(0.01 g Pb/gal) and reproducibility of +5.28 mg Pb/£ (0.02 g Pb/gal)* (see
subsection 4.1.2).
5. Test tubes, borosilicate, 18 by 150 mm.
6. Plpets, glass, dropping, capable of delivering 2.0 m£ with a
2-m£ bulb.
7. Funnel, plastic, 5 cm (2 in.) inside diameter.
8. Filter paper, ashless, 11.0 cm in diameter, which would allow the
organic layer (gasoline/chloroform) to filter through. Whatman 541 or
equivalent has been found to be satisfactory.
9. Graduated cylinder, plastic, 10 m£.
10. Glass vials, with caps, disposable, 28 g (1-oz) capacity.
Reagents
1. Purity of reagents—Reagent grade chemicals shall be used in
all tests. Unless otherwise indicated, it is intended that all reagents
conform to the specifications of the Committee on Analytical Reagents of
the American Chemical Society, where such specifications are available
(ref. 2). Other grades may be used, provided it is first ascertained that
the reagent is of sufficiently high purity to permit its use without less-
ening the accuracy of the determination.
2. Purity of water—Unless otherwise indicated, reference to water
shall be understood to mean distilled water or water of equal purity.
3. Ammonium hydroxide (sp. gr. 0.90)—concentrated ammonium hydroxide,
(NH. OH).
Figure 5 contains a conversion scale and appendix D a conversion factor
between mg Pb/£ and g Pb/gal. For the remainder of this report mg Pb/£
units are used.
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I
M
Pn
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4. Ammonium nitrate or solution (reagent B)*—15.0 + 0.1 g of
ammonium nitrate dissolved in distilled water in 1.000-£ volumetric
flask.
5. Chloroform (CHC1-) .
6. Disodium salt of 4-(2-pyridylazo)-resorcinol dihydrate (reagent C)*—
Dissolve 25.0 + 0.1 mg of PAR in 750 ml of distilled water in a 1.000-£
volumetric flask. Add 10.0 +0,1 m£ of concentrated ammonium hydroxide.
Dilute to the mark with distilled water. Store this solution in brown
bottles in the absence of direct sunlight or in the dark.
7. Gasoline, lead free—Gasoline containing less than 0.26 mg
Pb/£.
8. Iodine or iodine/TEAC/CHC!3 solution (reagent A)*, 1.000 g + 1 mg
of iodine and 1000 g + 1 mg of tetraethylammonium chloride dissolved in a
0.1-£ solution of chloroform. Add 1.000 g +1 mg of tetramethyl-
ammonium chloride (TEAC) and mix until dissolved. Dilute to the mark with
chloroform.
9. Lead standards—Known amounts of various lead alkyls added to
blended unleaded gasoline to cover the range of this method.
10. Tetraethylammonium chloride monohydrate (TEAC).
2.1.1.2 Acceptance Check. Inspect the kit to determine whether all items
are included, nothing is broken, and that they conform to the above speci-
fications. The colorimeter should be checked out according to manufacturer's
instructions and calibrated according to the instructions set forth in
subsection 2.2.
2.1.1.3 Documentation. Record in the receiving record log book a descrip-
tion of the equipment in the field sampling kit, appropriate serial numbers,
and the results of the acceptance check, except the colorimetric calibration
which is recorded in the calibration record log book. Sign and date the entry.
2.1.2 Gasoline-Sampling Containers
2.1.2.1 Specifications. The gasoline-sampling containers shall be of the
type approved by the EPA administrator.
*This solution is stable for at least 2 months.
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2.1.2.2 Acceptance Check. Inspect the containers for faulty construction,
cleanliness, and proper capacity.
2.1.2.3 Documentation. Record in the receiving record log book a
description of the containers, supplier, and the results of the acceptance
test. Sign and date the entry.
2.1.3 Shipping Cartons and Cases
2.1.3.1 Specifications. The shipping cartons shall contain dividers and
be the proper size to facilitate packaging eight sample cans. The cases
shall be suitable for packaging individual sample containers.
2.1.3.2 Acceptance Check. Inspect the cartons and cases for damage and
suitability for packaging eight cans or individual containers.
2.1.3.3 Documentation. Record in the receiving record log book a des-
cription of the cartons, cases, supplier, and the results of the acceptance
check.
2.1.4 Chain of Custody Labels
2.1.4.1 Specifications. The chain of custody label shall contain
provisions for the Environmental Protection Agency Inspector's Seal, the
sample number, date, signature, printed name and title, seal broken by,
and date. A copy of a seal is shown in figure 3.
2.1.4.2 Acceptance Check. Inspect the labels to ascertain that they
are copies of or contain the same information as shown in figure 3.
2.1.4.3 Documentation. Record in the receiving record log book a
description of the labels and the results of the acceptance test.
2.2 PRESAMPLING PREPARATION
2*. 2.1 Calibration of Colorimeter
The calibration of the colorimeter shall be performed according to
the following instructions, using at least a blank (lead-free gasoline) and
four working standard samples of known lead content which cover the range
from about 0.00 to 20 mg Pb/£. Working standard solutions of gasoline with
the above approximate concentrations should be supplied in quantity with
certified concentrations by the regional supervisor (section 3.1). They
should be stored in brown bottles and kept in the explosion-proof refri-
gerator except when being used. A blank with four working standard samples
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„<,*,,, UNITED STATES
f *^\ ENVIRONMENTAL PROTECTION AGEUCY
* \ INSPECTOR'S SEAL.
SAMPLE NO.
sTGN~AT'Jt?E~
PHINT NAME AND TITLE (Inspector, Analyst nr Tectmi
l* =
n-i
UJr
Figure 3. Copy of chain of custody label.
12
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at about 2.6, 7.9, 13.2, and 18.5 mg Pb/£ are recommended. Such spacing
of the working samples insures acceptable precision of the calibration
curve for lead concentrations in the above stated range with maximum
precision occuring for concentrations from about 7.9 to 13 ag Pb/£.
1. Rinse the 2-m£ graduated dropper three times with the standard
gasoline solution. Add 2.0 m£. of the working standard solu-
tion to a 28 g (1 oz) glass vial. Using another clean dropper,
add 2.0 m£ of reagent A to the vial containing the working
standard solution. Tightly cap the vial.
NOTE 1: Handle the 2-m£. graduated dropper as follows:
Squeeze the rubber bulb, hold i. squeezed and dip the glass
tube into the gasoline. Gently relax the squeeze and allow
the gasoline to slowly fill up the glass dropper. Completely
release the pressure on the rubber bulb; allow any excess
gasoline to drip out of the glass tip by very gently pressing
on the rubber bulb. When the upper level of gasoline is at
the 2-m£ mark on the glass dropper, squeeze the rubber bulb to
expel the entire contents of the dropper into the vial. (The
liquid must have no entrapped air bubbles). If gasoline or
any of the reagents come into contact with the rubber bulb,
discard the bulb and pipet and start again.
2. Place the vial on the ultraviolet light as shown in figure
4 and set the timer to give the sample a 3-minute exposure.
CAUTION: Ultraviolet light can be harmful to the eyes.
A protective shield has been provided. DO NOT remove it
or otherwise defeat its purpose. DO NOT stare at the light.
3. After exposure, remove and uncap the vial. Measure 10.0 m£ of
xeagent B in a graduated cylinder. Add this to the vial and
shake vigorously for 1 minute. (The timer in the kit may be
used.)
4. Place a clean 18^-mm test tube in the aluminum measuring block.
Add 5.0 m£ of reagent C to the test tube using the mark on the
block such that the upper level of liquid in the tube is equal
to the mark on the block. Place the plastic funnel in the test
tube. Fold a piece of filter paper and place it in the funnel.
The filter paper should be rinsed with distilled water prior to
13
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' '
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filtration in order to seal the edges and to prevent
migration of the PAR complex up the sides of the filter
paper and to prevent breakthough of the filter paper.
5. When the two layers of liquid in the vial have separated, pour
the entire contents of the vial into the filter paper. Tap
the tunnel to add any remaining drops of aqueous solution
to the test tube. Remove the funnel and discard its contents.
Swirl the test tube gently using a wrist action to obtain a
uniform color.
Note_2: If a few drops of the gasoline layer come through
the filter paper, this will not alter the results and can
therefore be tolerated. However, if more than 10 drops do
come through, refilter the aqueous la>er through a fresh
filter paper into a clean empty test tube.
Note 3: Swirling may cause air bubbles to be trapped in the
liquid. Wait for these to settle before continuing. Wipe
test tube off with a clean lint—free towel to remove any finger-
prints that may be present on the surface of the tube.
6. Set the colorimeter at 490 nm. Zero the absorbance scale with
distilled water in an 18-mm test tube.
7. Standardize the colorimeter by reading and recording the
absorbances obtained with the blank and the working standard
samples in 18-mm test tubes.
K/'te 4; Time limit—The solution obtained by adding the
contents of the via] to reagent C must be read within 10
minutes,
8. Prepare the calibration curve, as shown in figure 5, by plotting
the absorbance values versus concentration on rectangular
coordinate paper (figure 5 is an example of a calibration
curve provided by the manufacturer with 11 data points).
Draw a best fit line by eye. Note that the curve does not
pass throaph the origin.
No_te_5j If mg Pb/£ are to be used, the abscissa scale
should be from 0 to 25 mg Pb/£ with the major divisions
equivalent to 2.25 mg Pb/£ and the smallest divisions equal
to 0.5 mg Pb/£.
15
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1.0
.02 .03 .04 .05 .06
g Pb/gal
07 .08 .09 .10
2'64 5.28 7'92 10.56 13'20 15.84 18'48 21.12 23'76 26.40
mg Pb/£
Figure 5. Sample calibration curve for lead in gasoline
using the portable colorimeter and 18-mm test tubes.
16
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9. Record, sign, and date the lead calibration curve in the cali-
bration record log book.
2.2.2 Safety Rules
2.2.2.1 Before Test
1. Make sure that all caemicals and equipment needed are available.
2. Prepare only those chemicals and items of equipment actually
needed for the test. Check to see that all others are secure
in their proper storage locations.
2.2.2.2 In Case of Fire
1. Extinguish it if possible, but do not endanger yourself.
2. Leave the van.
3. Warn anybody in the vicinity of the possible hazard.
4. Call local fire department, if necessary.
5. Call regional headquarters immediately.
2.2.2.3 In Case of an Unusual or Heavy Concentration of Fumes. Leave
the van and air it out thoroughly before reentering.
2.2,2.4 General.
1. No smoking or open flames are permitted within or close to
the van at any time.
2. All accidents, hazardous occurrences, or potentially hazardous
conditions are to be reported to regional headquarters as soon
as possible.
3. Minimize amount of gasoline stored in bulk, put excess gasoline
in van tank.
4. Immediately wipe up all spills.
5. Maintain the van doors unblocked so that quick exit can be made.
6. Keep samples in refrigerator or explosion-proof cabinet.
7. Pour spent reagents into safety can.
8. Clean van regularly.
2.3 SAMPLING PROCEDURE
2.3.1 Filling Gasoline Sample Containers
Gasoline from a pump labeled to dispense unleaded gasoline should
be introduced directly into the sample container described in subsection
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2.1.2. A sample of approximately 4 ounces should be taken. The can
should be about one-half filled. Under no circumstances should the can
be filled above the bottom of the neck of the can. Department of Trans-
portation safety regulations applicable to the shipping of gasoline samples
require at least a 5 percent vapor space. Upon taking the sample, the can should
immediately be labeled as to date, time, pump serial number, and location
of the retail outlet. This information should be recorded in the field
inspection form log book as shown in figure 6 and discussed in subsection
2.3.2.
The gasoline retailer should always be paid for the sample taken.
If the retailer refuses payment, a signed receipt stating that the gasoline
was provided free of charge should be obtained.
If the sample will be analyzed on-site, the can should be loosely
capped and taken to the place of analysis. If the analysis is not to be
done until later, or if the sample is going to be shipped back to the regional
laboratory, the metal seal should be placed over the neck of the can before
the cap is screwed tight. A chain of custody label must be attached
to all sample cans which are to be shipped. The label attaches to
the cap and the sides of the can and will rip upon the attempted removal
of either the label or the cap,
2.3.2 Field Inspection Form
The field inspection form shown in figure 6 shall be used to
record information about the station as well as test results. The
Mobile Source Enforcement Division (MSED) will provide prenumbered
forms printed and distributed to each region. The printed forms are
in a format which facilitates key punching directly from the form for
data collection and storage purposes. An explanation of the field
inspection form is presented.
Inspection Numbers—A four-digit (0001 to 9999) number to identify
an inspection. This number will also serve as the sample number for
chain of custody purposes to be affixed to each sample container which
is retained for further testing.
18
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Inspection Number_
1. Station Information
Station Name:
Station Address:
Brand Name (of Gasoline)
2.
Station Owner:
Owner Address:
Station Lessee:
Lessee Address:
Agent In Charge:
Invoice Information
Distributor Name:
Distributor Address:
Shipping Point, Name:
Address:
3.
Date of Receipt / /
mo da yr
Inspection Information
Date / / Time
mo da yr
4.
Signs Labels_
Test Information
hr min
Nozzles
Region
Pump Serial Number_
^~^\^ Sample
P ar ame t er"--^^
Absorb ance
MR Bb/ £
Working
Standard
Gasoline
(first test)
Reference
if
Applicable
Serial
Number
Gasoline*
(second test)
5.
6.
*Required only if the first test equalled or exceeded the standard.
Fuels Inspector
Name:
Comments
Signature_
Figure 6. Field inspection form.
19
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1. Station Information—This is information which is used to identify
the station and who controls the station. Most of it should be readily
available from the station operator.
Station Name: business name of the station; e.g., Main Street
Shell.
Station Address: the street address of the service station; e.g.,
10016 Main Street, Fairfax, VA 22030.
Station Owner: the name of the person (or company) who owns the
retail outlet from which the gasoline is dispensed; e.g.,
South Arlington Oil Co.
Owner Address: the address! of the person (or company) who owns
the retail outlet from which the gasoline is dispensed; e.g.,
4615 Columbia Pike, Arlington, VA 22202.
Station Lessee: the name of the person (or company), if any,
who leases the retail outlet and dispenses gasoline through
the facilities; e.g., Thomas Jones (who leases his station
from South Arlington Oil Company).
Lessee Address: the legal address of the station lessee; e.g.,
10510 Adams Street, Fairfax, VA. 22031.
Agent in Charge: the person who is responsible for the station
while the gasoline is being sampled; e.g., Thomas Jones.
2. Invoice Information—This is information which is used to identify
the gasoline distributor. It can usually be obtained from the invoice
the distributor presents to the retail station operator for gasoline
which is delivered.
Distributor Name: the legal name of the distributor; e.g., South
Arlington Oil Company.
Distributor Address: the legal address of the distributor; e.g.,
4615 Columbia Pike, Arlington, VA. 22207.
Shipping Point Name: name of the terminal from where the gaso-
line was shipped; e.g., Bancroft Terminal.
Shipping Point Address: address of the terminal from where
the gasoline was shipped; e.g., 684 Barcroft Street,
Arlington, VA 22206.
Date of Receipt: month, day and year of the latest unleaded gas-
oline delivery; e.g., 7/1/74.
20
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3. Inspection Information—This is general information about
the inspection and items which can be visually checked.
Date: month, day, and year in which the inspection took place;
e.g., 7/2/74.
Time: time, by military hours, that the inspection began; e.g.,
2:25 PM would be 14:25.
Region: Federal Region in which the inspection took place;
e.g., 3.
Signs: a check mark (!.<-., /) indicates that the retail outlet
has the sign required by Section 80.22(d)* of the Federal
Register 38, 1254, Jan. 10, 1973, and that it is displayed
in the vicinity of each gasoline pump stand as required.
If no sign is present or the sign does not comply with the
requirements of the regulations, "No" should be entered instead
of a check mark, and the violation should be specifically des-
cribed in the space provided for comments.
Labels: This entry is to be filled out in the same manner as the
entry for "signs." Labels should be examined on both unleaded
and leaded pumps.
Nozzles: This entry is to be filled out in the same manner as the
entry for "signs." Dimensions of nozzles on pumps used to
dispense leaded gasoline as well as those on pumps used to
dispense unleaded gasoline should be checked.
Pump Serial Number: This is a serial number on the pump. It will
usually be located on the hose side of the pump in the vicinity
of the hose hanger.
4. Test Information—This provides information concerning the
results of the on-site tests for the lead content of gasoline dispensed
as unleaded.
Absorbance: This is the meter reading taken directly from the
spectrophotometer when the sample (i.e., working standard,
gasoline, or reference) whose lead content is to be measured
is placed in the instrument.
*
After July 1, 1974, every retailer shall prominently and conspicuously
display in the immediate area of each gasoling pump stand the following
notice: Federal 1a^ prohibits the introduction of any gasoline containing
lead or phosphorus into any motor vehicle labeled ''UNLEADED GASOLINE ONLY. "
Such notice shall be no smaller than 36-point bold type and shall be
located so as to be readily visible to the retailer's employees and
customers.
21
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mg Pfe/£: This is the lead content of the gasoline sample. It is
obtained from a calibration curve which converts absorbance
to lead content in milligrams per liter. A working standard
sample (13.2 mg Pb/Jt) is measured before each gasoline sample
to verify the calibration curve. A reference sample is measured
once a week plus any time a gasoline sample is found to equal
or exceed the standard (first test) before remeasuring the gasoline
sample (second test).
Pump Meter Reading: This provides the number of cumulative gallons
of gasoline dispensed through the pump from which the sample
was obtained. The meter is usually located on the face of the
pump above the price and jgallonage displays for each individual
purchase. This reading should only be taken when contaminated
gasoline is detected and a stop sale notice is issued.
5. Fuels Inspector
Name: The last name of the fuels inspector should be printed.
Signature: The fuels Inspector should sign his full name.
6. Comments—This space is provided to allow the fuels inspector
to comment on any entry contained on the field inspection form or on
other matters deemed relevant to the particular inspection. In all cases
where a violation is detected, it should be specifically described in
this space.
2.4 ANALYSIS PROCEDURE
A listing of the requiref steps in sample analysis is given. Recom-
mended quality control practices and safety precautions are also given.
2.4.1 Recommended Quality Control Practices
As part of the analysis procedures, certain checks are recommended
for quality control and for data-quality-assessment purposes. Procedures
for performing the checks are given along with recommendations for a minimum
acceptable frequency for performing the checks. If the checks indicate
problems in the analysis of gasoline samples, the frequency of the checks
should be increased until the problem is identified and corrective action
taken.
22
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To aid in understanding the following discussion, four types of samples
referred to in the analysis procedure are defined here. They are:
1. Gasoline sample: A gasoline sample collected in the field for
analysis of its Pb content.
2. Blank sample: A working standard sample containing 2.0 mH of
lead-free gasoline (<0.26 mg Pb/Jl) and no standard lead solution
(see 2.2.1) used to establish the zero or baseline for the
colorimeter.
3. Working standard samples: Samples prepared by the inspector from
working standard solutions supplied by the regional supervisor
with certified concentrations for use as calibration standards.
4. Reference Sample: Samples prepared by the fuel inspector
from reference solutions supplied by the Regional Supervisor
(prepared in the same manner as the working standard
solutions) whose Pb content is accurately known to the supervisor
but unknown to the fuel inspector. These samples are used to
assess data quality.
The following sequence of analyses is recommended as the minimum
level acceptable for quality control and data quality assessment purposes.
1. The colorimeter shall be calibrated (or the manufacturer's
calibration curve verified) by measuring a blank and four working
standard samples when:
a. The kit and/or colorimeter is first purchased,
b. After two weeks of use in the field, or
c. Any time a working standard sample (or reference sample)
can not be measured within ±2.86 mg Pb/£ of its known (or
true) value.
2. A working standard sample (13.2 mg Pb/£) shall be measured just
prior to measuring each gasoline sample. If the measured value
of the standard sample is within ±2.86 mg/PbJl of the known value,
proceed to measure the gasoline sample. If the measured value
is outside those limits, all equipment and procedures should be
checked and if no problems are found, the colorimeter should be
recalibrated as in (1) above.
23
-------
3. A reference sample, as provided by the regional supervisor (con-
centration unknown to the analyst or fuel inspector) shall be
measured once a week plus any time a gasoline sample is found to
equal or exceed the standard for lead in gasoline (i.e., 13.2 mg Pb/Jl),
2.4.2 Safety Precautions
During the analysis, observe the safety regulations promulgated in
subsection 2.2.2 and those presented subsequently.
1. Open and use each chemical or gasoline container only when it is
needed during the test. Close it and store it as soon as it has
been used.
2. Do not operate electrical switches while working with gasoline.
3. Do not interrupt the test, except for emergency.
2.4.3 Procedure
1. A flow chart of the analysis procedure is given in Figure 7.*
2. Prepare the field sample and a working standard sample containing
about 13.2 mg Pb/Jl in accordance with the directions given in
section 2.2.1, steps 2 through 6.
3. Place the test tube containing distilled water in the colorimeter
and set the absorbance to zero.
4, Place a test tube containing the working standard sample in the
colorimeter and read the absorbance. The analysis of the working
standard sample is performed to check the calibration, reagents,
and procedures. A record of the calibration check is maintained
by plotting the difference between the measured and known values
on the Quality Control Chart shown in Figure 8 of section 3.2.
Plot the concentrations as read from the calibration curve i.e.,
to the nearest 0.5 mg PbM or 0.002 g Pb/gal. if gallons are used.
5. If the concentration of the standard sample is not determined to
within ±2.86 mg Pb/Jl of its known value, prepare new solutions
of reagents and standards., and repeat the calibration procedure.
Repeat the analysis of a new working standard sample of about
13.2 mg Pb/Jl. If the concentration of a working standard sample
cannot be determined to wLthin ±2.86 mg Pb/Jl, notify your supervisor.
*An unattached 3-page foldout suitable for wall mounting is included in the
back of this document.
24
-------
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25
-------
If the concentration of the working standard sample was determined
to within ±2.86 mg Pb/Jl of its certified value, proceed to analyze
the gasoline sample.
6. Place the gasoline sample in the colorimeter and read the absorbance.
Note 6; The solution obtained by adding the aqueous phase to reagent C
must be read within 10 minutes.
7. Record the absorbances of all samples (i.e., working standard and
gasoline) on the field Inspection form, shown in figure 6, in the
field inspection form log book and record the working standard
sample data in the calibration record log book and plot on the
quality control chart provided by the supervisor (see figure 8
in section 3.2).
2.4.4 After Analysis
1. Make sure that all chemical and gasoline containers are well
closed.
2. Make sure that all items are securely stored in their assigned
van locations.
3. Wash hands thoroughly after everything has been stored.
2.5 DATA REDUCTION
1. From the calibration curve, find the lead content of the gaso-
line sample.
a. Report the lead content of gasoline samples rounded to
the nearest 1 mg Pb/£ value (or to the nearest 0.01 g Pb/gal
if these units are used).
b. For quality control purposes and for establishing or checking
calibration curves determinations of working standard samples
and reference samples should be rounded to the nearest 0.1 mg Pb/£
(or 0.001 g Pb/gal if these units are used).
2. Record the lead content on the Field Inspection Form in the Field
Inspection Form Log Book.
3. If the concentration of Lead in a gasoline sample exceeds 13.2
mg Pb/£, proceed to section 2.7 after this section is completed.
4. A summary of the results of the field inspections in the form of
copies of the Field Inspection Form (or as directed by the super-
26
-------
visor) should be sent to the Monitoring Source Enforcement Depart-
ment in Washington, B.C. at weekly intervals.
Note 7: The reference method (subsection 7.4 of appendix A) recommends
rounding to the nearest 0.01 g Pb/gal (2.64 mg Pb/£) however, for
simplicity, it is recommended that gasoline sample determinations be
rounded to the nearest 1 mg Pb/£ for reporting.
2.6 SAMPLE SHIPPING PROCEDURE
1. Fuels inspectors are required to ship the required number of
gasoline samples for phosphorus determination and any sample that exceeds
the standard for lead to the regional laboratory for analysis. Two
kinds of shipping packages as well as two methods of shipment are
available.
2. Single samples may be sent in individual shipping canisters.
The shipping canister is designed to hold one 8-ounce sample can. The
canister is closed by a metal screw-on lid.
3. Shipping cartons designed to hold a total of eight sample cans
may be used to ship groups of samples. These shipping cartons have been
sent to the regions in a collapsed form and must be assembled before use.
The cartons should be opened up and the bottom flaps sealed with the tape
which is provided. A layer of absorbent material should always be placed
on the bottom of the box. The absorbent material is packaged sheetwise
in rolls. One sheet is sufficient to cover the bottom of the box, run up
the side, and fit over the top of the cans. Dividers must be used to
separate the cans. After the cans are placed in the box, the remaining
absorbent material is placed over the cans and the top flaps should be
folded down and sealed with tape. A red "Flammable Liquid" label should
be placed on the shipping carton or canister.
4. The packages can be shipped either by United Parcel Service (UPS)
or Railroad Express Agency (REA). UPS operates in all states but Alaska,
Arizona, Hawaii, Idaho, Montana, Nevada, and Utah. In these states, REA
can be used. UPS is preferred since it is the less costly service. A
package can be shipped by UPS at a cost of less than $1, while those shipped
by REA may cost over $10.
27
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5. To ship the packages, the. name and address of the receiving
laboratory should be written on a label which should then be attached
to the shipping carton or canister. Labels are preferred since the cartons
and canisters can be used more than once. For shipment by means of UPS,
a "Hazardous Materials" label is required. The label should be filled out
as follows:
Full Shipping Name of Article - Unleaded Gasoline
For Analysis
Classification - Flammable Liquid Red Label
Weight or Volume - 8 Oz. Cans
Type D.O.T. Label Required - None
Shipping charges should be paid at the time the package is delivered to
the forewarding company for shipment.
2.7 PROCEDURE WHEN CONTAMINATION IS DETECTED
Whan the concentration of lead exceeds 13.2 mg Pb/£., the gasoline
is contaminated. In which case, proceed as follows.
1. Take another gasoline sample after flushing the nozzle and hose
by pumping one gallon of gasoline from the retailer's hose spout
into a waste receptacle. Immediately fill the sample can com-
pletely, rinse, then dump the sample into a clean waste recepta-
cle in the same manner as; the original one gallon. Immediately
fill this same sample can half full, cap and transport it to the
van for analysis.
2. Dispose of the waste material by pouring it into a gasoline tank.
3. Analyze in sequential order a working standard sample, a reference
sample, and the new gasoline sample according to the instructions
in subsections 2.4 and 2,, 5. Record the serial number of the
reference sample on the Field Inspection Form.
4. Record the results of the analyses on the Field Inspection Form
Log Book.
5. If the concentration of lead in the gasoline exceeds 13.2 mg Pb/£,
report the results of the gasoline and reference samples to your
supervisor. If your supervisor authorizes issuance of notice of
violation of the Federal Standard for lead, proceed according to
28
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his instructions or as follows: (a) place a notice of contamina-
tion on the pump, prohibiting the sale of gasoline and to each
unleaded pump supplied by the storage tank from which samples were
obtained, (b) record on the Field Inspection Form in the Field
Inspection Form Log Book the cumulative gallonage reading on the
meter of each pump to which a notice of contamination has been
applied, (c) instruct the retailer regarding procedures to follow
to have the notice of contamination removed, (d) provide the
retailer with forms for removal of notice (i.e., notice of disposi-
tion or cure and notice of satisfactory test results.), (e) send
the remaining gasoline sample to the regional laboratory, and
report the issuance of the contamination notice to the Regional
Office.
29
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SECTION III MANUAL FCR REGIONAL SUPERVISOR
3.0 GENERAL
The term "supervisor" as used, in this document applies to the indi-
vidual in charge of a field team. He is directly responsible for the
validity and the quality of the field data collected by his team.
It is the responsibility of the supervisor to identify sources of
uncertainty or error in the determination process for specific situations
and, if possible, to eliminate or minimize them by applying appropriate
quality control procedures to insure that the data collected are of accept-
able quality. These ,guidelines cannot cover all possible situations;
therefore, it is important for the supervisor to make full use of his
experience and knowledge to insure the collection of data of acceptable
quality. Specific actions and operations required of the supervisor for
a viable quality assurance program include, but are not limited to, the
following:
1. Monitor/Control Data Quality
a) Direct the Field Inspector in performing field tests according
to the proceudres given in the Operations Manual.
b) Perform or qualify results of the quality control checks
(i.e., insure that checks are valid).
c) Perform necessary calculations and compare quality control
checks with suggested performance criteria.
d) Make corrections or alter operations when suggested perfor-
mance criteria are exceeded.
e) Forward qualified data for additional internal review or
to user.
2. Routine Operations
a) Provide and maintain the Field Inspector with an adequate
supply of working standard solutions with accurately
known lead concentrations for calibration purposes.
b) Obtain from fuel inspectors immediate reports of suspicious
data or malfunctions. Initiate corrective action or, if
30
-------
necessary, specify special checks to determine the trouble;
then take corrective action. Document corrective action
taken.
c) Examine the Inspector's log books periodically for complete-
ness and adherence to operating procedures.
d) Approve Field Inspection Form and calibration sheets for
filing.
3. Evaluation of Operations
a) Evaluate available alternative(s) for accomplishing a given
objective in light of experience and needs.
b) Evaluate Inspector training/instructional needs for specific
operations.
Insuring satisfactory data quality on a day-by-day basis with the
inspector in the field and the supervisor in the regional office requires
the application of quality assurance techniques by the inspector with
rigorous monitoring and guidance from the supervisor.
Specific quality assurance procedures recommended for implementation
by the supervisor are:
1. Provide the inspector with a supply of certified working standard
solutions for colorimeter calibration and calibration checks.
2. Provide the Inspector with a quality control chart for plotting
the differences in the measured and certified values of working
standard samples along with the necessary guidelines for:
a) Judging when the data are of acceptable quality.
b) Judging when the data are not of acceptable quality and
corrective action is required.
c) Interpreting data patterns on the control chart to identify
likely causes of excess variability and/or biases.
Preparation and certification of working standard solutions and the
construction and use of a control chart for differences in measured and
known values of those solutions are discussed in the following two subsec-
tions. The third subsection titled Suggested Performance Criteria summarizes
the criteria used throughout this document, and gives the reasoning used
and assumptions made in arriving at the criteria.
31
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3.1 PREPARATION OF CERTIFIED WORKING STANDARD SOLUTIONS
Working standard solutions should be purchased or prepared and certi-
fied by the regional laboratory and supplied to the field inspector by his
supervisor. The working standard solutions can be prepared by addition of
leaded gasoline (or lead alkyls) to blended unleaded gasoline.
Note 8j The standard reference material for lead in gasoline obtain-
able from the National Bureau of Standards can not be utilized for this
screening method because a reference fuel (91 volume percent 2,2,4-trimethyl-
pentane and 9 volume percent n-heptane) rather than gasoline is used as the
substrate fuel and does not achieve the same response from the colorimeter
as does gasoline.
The following procedure is recommended
1. Purchase quantities of blended unleaded gasoline and leaded gasoline
from a reputable distributor.
2. Determine the lead content of both gasolines by atomic absorption
spectrometry (if lead concentrations are provided by the distribu-
tor use them).
3. Prepare a minimum of 4 working standard solutions with lead concen-
trations near 2.6, 7.9, 13, and 18 mg Pb/fc determining the approxi-
mate required volume of leaded gasoline using the following rela-
tionship.
'Pb,, - Pb -
V ' S ul
TPbl-Pbul
where
V = Required volume of leaded gasoline to prepare a standard sample
with a concentration of Pb,,, m£.
S
V = Total volume of the working standard sample being prepared, mi.
Pb =: The desired concentration of the working standard sample (i.e.,
s
either 2.6, 7.9, 13, or 13), mg Pb/fc.
Pb = The lead concentration of unleaded gasoline from 2 above, mg Pb/H.
Pb.. - The lead concentration of the leaded gasoline from 2 above, mg Pb/&.
4. Based on preparing a total volume of 1 liter (VT) of a working
standard solution place the volume of leaded gasoline (V1) as cal-
32
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culated from equation 1 into a 1 liter volumetric flask. Add
unleaded gasoline to bring the volume to the 1 liter mark.
Note 9: The required volume of each working standard solution
will depend upon the inspector's schedule and will have to be
estimated by the supervisor. Generally a liter of each working
standard should last about 2 weeks assuming an average of eight
analyses per day.
5. After preparation, each of the working standard solutions should
be analyzed a minimum of four times extending over a 2-day period
(i.e., two replicates per day) by atomic absorption spectrometry.
A range (i.e., the largest minus the smallest) of ^ 2.2 mg Pb/K.
for the four analyses indicates acceptable precision and the
average of the four analyses is used as the certified lead concen-
tration of the working standard solution. The remaining working
standard solution should be placed in a container suitable for
shipping and storage with the date of analysis, certified concen-
tration, and analyst's name affixed in some semipermanent manner.
If the range is > 2.2 mg Pb/fc the equipment, reagents, and proce-
dures should be checked, corrective action taken, and four addi-
tional analyses performed until the range criteria is satisfied.
Note 10: The variance of atomic absorption measurements is
approximately one fourth the variance of the screening method.
Therefore, four replications by atomic absorption should reduce
the variance in the certified value of the working standard solu-
tion to 1/16 or a negligible fraction of the variance associated
with the screening method determinations.
6. The inspector should be provided with an adequate supply of
working standard solutions at all times.
3.2 CONSTRUCTION AND USE OF A CONTROL CHART
A quality control chart for plotting the differences between the
measured and certified values of working standard samples provides a visual
check of the present calibration, a chronological record of data quality, a
corrective action record when the determination process is out of control,
and it may be used to identify trouble areas. The recommended control
33
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chart is shown in figure 8. It is assumed that the difference in measured
and certified values is normally distributed about a zero mean. Limits
for the control chart were calculated using the repeatability standard
deviation, i.e., a =0.953 mg Pb/fc for the reference method. Action
limits are defined as the + 3a values and warning limits are set at + 2a
values. The assumptions made in setting these limits are discussed in
subsection 3.3.
Each time a working standard sample is measured the inspector should
calculate the difference (d) by always subtracting the certified value (Pb1)
from the measured value (Pb), maintaining the positive or negative sign
for d. Each difference is plotted on the control chart and connected to
the previously plotted point with a straight line.
The filled-in control charts should be forwarded to the supervisor
for his review at the end of each week in the field.
3.2.1 Use of the Control Chart, to Estimate Data Quality
For any given time period, e.g., one calendar month or quarter, if
all the points (i.e., differences) on the control chart are within the
action limits and somewhat randomly distributed about the center line or 0,
it can be assumed that the precision of the field measurements for that time
period is consistent with the precision (repeatability) of the reference
method as given in 7.1.1 of appendix A.
Under these conditions the lead in gasoline determinations can be
reported with + 3 sigma limits aa
Pb + 2.86 mg Pb/Jl
where
Pb = The measured lead concentration of the gasoline sample, mg Pb/fc.
2.86 = 3o (see subsection 4.1.1), mg Pb/fc.
The utility of the above statement follows from the fact that if the
determined values of Pb are normally distributed about a true value Pb
(assuming no bias) with a{Pb) = 0.953 mg Pb/£, then on the average the
true value Pb will be contained in the internal as constructed above
approximately 99.7 percent of the time. An exact confidence statement is
dependent on the number of measurements used in estimating cr{Pb}. The
-------
JO
Pi
60
E
,0
P-l
-1
-2
-3
Action Limit =2.86
Warning Limit =1.91
UCL
Warning Limit = -1.91
Action Limit = -2.86
.CL
CHECK NO.
10
DATE
Z/J.1/T)
II*.*!
ANALYST
J.J.
J.J.
PROBLEM AND
CORRECTIVE
ACTION
1
I
Figure 8. Quality control chart for checking the calibration curve.
35
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above estimate was made from 57 measurements. As more data are obtained
for estimating a{Pb> the percent confidence will approach 99.7. This
statement is about precision; to estimate bias or accuracy requires the
use of reference samples whose concentrations are unknown to the inspector
as discussed in section 4.3.
3.2.2 Use of the Control Chart to Identify Trouble
In a quality assurance program, one of the most effective means of
preventing trouble is to respond immediately to indications of suspicious
data or equipment malfunctions. One means of assuring a fast reaction
time is to provide the inspector with objective guidelines for judging
when the determination process is out of control and corrective actions are
required or when it is in control and should be left alone.
The following criteria are recommended for judgeing when the determina-
tion process is out of control, requiring trouble shooting and corrective
action:
1. Anytime one plotted point (i.e., difference) falls outside the
action limits.
2. Two out of three consectutive points fall between the warning and
action limits.
3. Seven consecutive points fall on the same side of the mean or
zero line.
Further analysis of gasoline samples should not be attempted until the
cause is determined, corrected, and documented (on the control chart).
Indications of the source of trouble may, in some cases, be revealed
by the pattern of the plotted points on the control chart. For example,
exceeding the first or second criteria with all the previously plotted
points showing a random scatter within acceptable limits indicates a some-
what sudden shift in data quality. This could be the result of:
1. A sudden malfunction of the colorimeter,
2. A recently contaminated reagent,
3. A deviation (either on purpose or accidently) from the standard
operating procedures,
4. A mistake in colorimeter reading or in the conversion from
absorbance to concentration.
36
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Trouble shooting should take the form of visually checking the equip-
ment for obvious malfunctions, checking the colorimeter by zeroing the
absorbance scale using distilled water, visually checking the reagents for
signs of contamination, and reviewing the operating procedures.
Exceeding the fchird criterion indicates that a systematic error (bias)
has developed in the measurement process. How critical this error is depends
on the magnitude of the shift and on the sequential pattern of the plotted
points. A trend indicating a bias as large as the standard deviation of
the method should be a signal to locate and correct the cause before con-
tinuing to analyze gasoline samples. However, seven consecutive points
falling on the same side of but very close to the center line would not be
cause for interrupting the measurement of gasoline samples.
3.3 SUGGESTED PERFORMANCE CRITERIA
Performance criteria as suggested herein are based on the premise
that measurement precision consistent with that stated for the reference
method (see section 7 of appendix A) is acceptable and that measurements
exhibiting larger imprecision should be prevented and/or detected and
eliminated with high probability. In arriving at the performance criteria
as discussed in the ensuing subsections, the following subjects had to be
addressed:
1. The measure of precision to be used in calculating acceptable
limits, i.e., repeatability, reproducibility or some value between
these two extremes.
2. Uncertainty in the calibration curve.
3. The criteria for judging acceptable performance, i.e., should
action limits be set at + 2 sigma or + 3 sigma levels.
4. The minimum auditing level necessary to assess and document
the precision and accuracy of the lead in gasoline determinations.
5. The required frequency of measuring working standard samples to
verify the calibration curve.
The above subject areas are discussed in the ensuring subsections in
the same order as listed above.
37
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3.3.1 Measure of Precision
Precision is a measure; of mutual agreement among individual measure-
ments of the same property, usually under prescribed similar conditions.
The conditions under which the working standard samples will be measured
by the field inspector are: 1) different sample i.e., different
working standard samples prepared from a homogeneous working standard
solution; 2) same specimen i.e., homogen«ous working standard solution.
3) same analyst; A) same equipment; 5) different days; and.6) same labora-
tory.
Under these conditions it is felt that the repeatability standard
deviation, a , (see section 4.1. 2) is the appropriate measure of pre-
cision to use in setting criteria for judging acceptable performance. A
repeatability standard deviation of a =« 0.953 mg Pb/fc as calculated from
the value given in section 7.1.1 or appendix A for repeatability is used
throughout this document. This assumes that the statistic, 0 , calculated
from 57 data points (ref. 1) is a good estimate of the population parameter
a and that it contains components of variability from:
1. Replication error,
2. Scatter of data points about a particular calibration curve,
3. Variability among calibration curves.
The validity of these a.ssumptions and of the use of a in setting
limits must be checked and adjustments made, if necessary, when sufficient
field data become available, e.g., 50 or so determinations of working
standard solutions as reported by the field inspector.
3.3.2 Uncertainty in the Calibration Curve
There are two sources) of error associated with the calibration curve.
One source of error is the scatter of the data points about the calibration
line. The second source of error is the uncertainty of the calibration
curve, i.e., the variability between calibration curves. In setting action
limits on the control chart of figure 8 and in recommending that a blank
and four upscale points are sufficient for verifying the calibration curve
the following assumptions ware made:
1. That ar is known and is equal to 0.953 mg Pb/Jl.
38
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2. That the colorimeter calibration curve provided by the manufac-
turer is generated from a minimum of 11 data points and that
future multipoint calibrations by the field inspector act to
reduce the uncertainty in the calibration curve and does not
in essence generate a new curve each time.
Based on a calibration curve fit to N data points, the correct stan-
dard deviation to use in calculating the control chart limits and tolerance
intervals for future calibration checks is (see ref. 4 for a discussion
of tolerance limits):
1/2
(2)
.1
a - a
r
N + 1 . " o
(Pb - Pb)2 ^
N I (Pbj - Pb)2
where
1
the standard deviation for future measurements with an N point
calibration curve, mg Pb/fc.
a - known repeatability standard deviation, mg Pb/fc.
N » number of data points used to fit the calibration curve, dimen-
sionless.
Pb «= lead concentration point on the abscissa about which the tolerance
o
limit is set, mg Pb/fc.
Pb. - lead concentration of the j— calibration point, mg Pb/fc,
Pb - average lead concentration of all calibration points i.e.,
N
1/N Z Pb , mg Pb/Jl.
J-l J
From the above relationship, it is seen that for the case where
1/2
Pb = Pb the relationship becomes
o
i I " + 1
o1 = ar [ N J . (3)
For N - 11, in the case of the manufacturers calibration curve, a » 1.04 a ,
and as the field inspector continues to check and adjust the calibration
curve N increases and a approaches o fairly rapidly. Therefore, the
use of o in setting control limits seems appropriate, especially once the
determination kit has been in use for a period of time.
39
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If in practice the calibration curve shifts significantly from
calibration to calibration and an excessive number of determinations of
standard working samples are falling outside the action limits on the
control chart, the supervisor should either:
1. Provide the field inspector with additional standard working
solutions in the concentration range of interest for developing
calibration curves,
2. Keep using the same number of standard working solutions to
develop the calibration curve but broaden the action limits by
multiplying the present ones by
N + i 1/2 1/2
[N
L
Recommending a minimum number of five points for checking/verifying
the calibration curve on a once-a-week basis is based on engineering
judgement. Due to the relatively large normal variability of the process
(repeatability is + 20 percent for lead concentrations close to the
standard) it is felt that any number less than about five points could lead
to unwarranted shifting of the calibration curve by the field inspector.
3.3.3 Criteria for Judging Acceptable Performance
The three criteria given in section 3.2.2 for detecting trouble;
namely, 1) anytime one point falls outside the action limits, 2) anytime
two of three consecutive points fall between the warning and action limits,
and 2) anytime seven consecutive points fall on the same side of the center
line; are recommended as reasonable criteria for judging acceptable per-
formance.
The probability of any one of the three criteria being exceed while
the determination process is actually operating properly, i.e., the process
is in control, is approximately 0.05. Such criteria should prevent
unnecessary tinkering with the process when it is actually in control and
at the same time insure precision of measurements consistent with the
reference method.
3.3.4 Minimum Auditing Level
Performance auditing in the form of providing the inspector with
blind samples (i.e., reference samples with concentrations known to the
40
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supervisor/auditor but unknown to the inspector) for periodic determina-
tions serves as a check on the quality of the field measurements and can
be used as a proficiency evaluation of the operator.
The minimum auditing level recommended for this program is that the
inspector analyze a reference sample once a week (while in the field) and
anytime a gasoline sample is found to equal or exceed the standard for
lead in gasoline, i.e., 13.2 mg Pb/£.
Such an auditing scheme is recommended because 1) if all the gasoline
samples measured are well below the standard, a minimum auditing level of
once a week should be sufficient to assess and document data quality, and
2) by measuring a reference sample each time a gasoline sample is found
to equal or exceed the standard will provide an independent verification
of the measurement process each time enforcement action has to be taken.
The auditing scheme is designed to maximize confidence in determina-
tions where the lead concentration equals or exceeds the standard.
3.3.5 Frequency of Calibration Checks as Quality Control Checks
The recommended frequency of measuring working standard samples to
verify the calibration curve given here is based on the assumption that
gasoline samples will be analyzed on site. That is, it is assumed that
the mobile laboratory will be driven to the gasoline station for the check.
Under these conditions it is felt that the calibration curve should be
verified before analysis of each gasoline sample. However, if in practice
several gasoline samples are collected and brought to the laboratory for
analysis it may be sufficient to verify the calibration before and after
each analysis cycle or 4-hour analysis period, whichever is shorter.
-------
SECTION IV QUALITY ASSURWCE PROCEDURES
4.0 GENERAL
The control of data quality is a function of two related activities
of the quality assurance program: (1) development of standard operating
procedures including control limits, and (2) assurance of conformance to
the procedures and control limits. Standard operating procedures and con-
trol limits are recommended in the operations manual of this document. It
is emphasized that if the field inspector conscientiously adheres to the
procedures and checks of section II, then the precision and accuracy of the
lead determinations should be within acceptable limits. Assurance of data
quality basically involves collecting the information necessary to document
and demonstrate the quality of the measured data. This section of the document
will discuss the activities necessary to document and demonstrate data quality.
Verification of data quality is important in this instance because the
data generated by this method are to be used to determine if the standard for
lead in gasoline is being met. If results indicate that the standard is
being exceeded the appropriate enforcement group will be required to take
action. Thus, the professional competence of the field inspector, the
operating procedures used, and the measured values that he reports may be
challenged in legal proceedings.
The quality assurance procedures presented in this section should be
carried out or closely monitored by the individual directly responsible for
the quality of the reported data. In each laboratory one individual should
be assigned the responsibility for quality assurance.
The purposes of this section are to:
1. present information relative to the measurement method (i.e., a
functional analysis) to identify the important operations and
factors,
2. present an independent performance audit procedure for use in
quantifying data quality on an interlaboratory basis,
3. present techniques for data quality assessment.
These three purposes will be discussed in the order stated in the subsections
that follow. The first subsection (3.1) will contain a functional analysis
42
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of the measurement method with the objective of identifying the most impor-
tant factors that affect the quality of the reported data and of estimating
the expected variation and biases in the determination resulting from equip-
ment and field inspector errors.
Subsection 4.2 contains a discussion of an independent performance
audit. Such and audit involves the fuel inspector analyzing a reference sample
(i.e., NBS or otherwise certified samples) when the field sample exceeds the
value of the lead content promulgated in the Federal Register. Since the
fuel inspector is required as part of his normal operation to forward a
certain percentage of the gasoline samples to the Regional Laboratory for
phosphorus determinations, an alternative auditing procedure could be for the
laboratory to analyze these gasoline samples by atomic absorption for lead
and to compare this value to the fuel inspector's value. Such an audit, if
feasible, could serve as an independent check of the determination process
from sample handling through the final calculations. It would provide a
means of assessing data quality as a function of bias and precision and
serve as an independent verification of data quality for future users of
the data.
Data quality assessment is discussed in subsection 4.3. A method for
estimating the precision and accuracy of the reported data using the results
from the independent performance audit is given. Also, a method of testing
the quality against given standards using sampling by variables is given.
4.1 FUNCTIONAL ANALYSIS OF THE FIELD TEST METHOD
The determination of lead in gasoline requires a sequence of opera-
tions and measurements that yields as an end result a number that serves
to represent the mass of lead in a unit volume of gasoline. The degree
of agreement between the measured and the true value of a sample can be
estimated from the agreement between measured and standard or reference
values. Precision and accuracy of the determination process are reduced
to or maintained within acceptable limits by identifying and, where
feasible, eliminating systematic errors. The importance of a variable
on the precision or accuracy of a determination process is a function of
the variable mean value and variance, how it is related to the dependent
variable, and its probability of occurrance under normal operating conditions.
43
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The objectives of this subsection are to:
1. Evaluate variables and estimate error ranges,
2. Through a variance analysis determine the variability to expect
in the determination of lead in gasoline.
3. Through a bias analysis estimate the expected bias, if any in
the determination of lead in gasoline.
A functional analysis of the determination process is performed to
determine all the operations and variables that may affect the quality of
the reported measurements. Data q;uality is characterized by measures of
precision and bias. In subsection 4.1.1 variables believed to be important
to the measurement method are discussed. Estimates of the mean, variance,
and probability distribution are made using data from published reports
when available, and using engineering judgement or intuition when docu-
mented data are not available. These data are then used in a variance
analysis (subsection 4.1.2) to determine the resulting variability of
the measured value i.e., the mass of lead per unit volume of gasoline. The
data from subsection 4.1.1 are also used in subsection 4.1.3 to estimate
the potential bias of the determination process.
4.1.1 Variable Evaluation and Error Range Estimates
The milligrams of lead per liter of sample is determined from
comparison with the calibration curve. The calibration curve is constructed
from standard samples supplied by the Regional Laboratory. The Regional
Laboratory determines the concentration of the standard samples according
to the atomic absorption spectrometric method promulgated in the Federal
Register, July 8, 1974.
The error sources then can be grouped according to whether they origi-
nate in the determination of the concentrations of the standard samples or
of the gasoline samples.
4.1.1.1 Potential Errors in Determining Concentrations of Standard Samples
The potential errors in the determination of concentrations of standard
samples are expounded in detail in another document (ref. 3). In that
document it has been promulgated that the precision in the determination
of lead concentrations of gasoline samples by atomic absorption expressed
as the repeatability standard deviation is + 0.48 mg Pb/fc. For the present
44
-------
functional analysis, this value of the precision represents the potential
error in the determination of the concentrations of working standard
solutions and reference samples. Also, it is recommended that at least
4 determinations by A.A. be made thus the standard deviation of the mean
should be 0.48/2 - 0.24 mg Pb/fc.
4.1.1.2 Potential Errors in Determining Concentrations of Total Lead.
The quantity of lead in a sample at the time of collection can differ from
the measured value due to:
1. Contamination during sampling, handling and analysis.
2. Incomplete color development from the use of poor reagents or
lack of mixing.
3. Errors in the preparation of the calibration curve.
4. Inprecision of the colorimeter and reading errors.
5. Measurement error in the volumes of gasoline sample and reagents.
6. Evaporization losses-during analysis.
There are no data available for estimating the error associated with
each of the above operations. However, a judgement can be made from the
values given for repeatability and reproducibility of the method as
written in the Federal Register (see appendix A).
The repeatability and reproducibility of the measurement method at
the 95 percent confidence level are given as 2.64 mg Pb/£ and 5.28 mg Pb/*-,
respectively. The above values mean that on the average duplicate results
should agree within +2.64 mg Pb/2 95 percent of the time when the determination
process is operating properly. Also, results of two laboratories measuring
the same sample should agree within 5.28 mg Pb/£ 95 percent of the time when
both laboratory determination processes are in control.
It is felt that at least half of the difference in the repeatability
and reproducibility values is due to variability in analyst technique in
performing the above listed items (3), (4), and (5).
The sources of variability listed in items (1), (2) and (3) are
estimated to account for less than half of the total measurement process
variability. The errors introduced by items (3) and (4) over a long
period of time would tend to be randomly distributed about a zero mean.
Incomplete color development acts as a negative bias and sample contam-
ination and evaporization during analysis would act as a positive bias.
45
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4.1.2 Variance Analysis
Many different factors may contribute to the variability of a
measurement method, for example:
1. The analyst,
2. Apparatus and reagents used,
3. Equipment calibration,
4. The environment (temperature, humidity, etc.)
The variability will be larger when the measurements to be compared are
performed by different analysts or with different equipment, than when they
are carried out by a single analyst: using the same equipment. Many differ-
ent measures of variability are conceivable according to the circumstances
under which the measurements are performed.
Only two extreme situations will be discussed here. They are:
1. Repeatability, r, is the value below which the absolute
difference between duplicate results, i.e. two-determinations
made on the same sample by the same analyst using the same
equipment over a short interval of time, may be expected to
fall with a 95 percent probability. This represents the best
precision that could be achieved on an interlaboratory basis.
2. Reproducibility, R, is the! value below which the absolute
difference between two measurements made on the same sample by
different analysts in different laboratories using different
equipment may be expected to fall with a 95 percent probability.
This is representative of intralaboratory precision.
The above definitions are based on a statistical model according to
which each determination is the sum of three components:
Pb » Pb + b + e (4,
where
Pb = the determined value, mg Pb/i,
P = the general average tyt accepted value of the sample, mg Pb/£.
b = an error term representing the differences between
laboratories, mg P/Jl
46
-------
e - a random error occurring in each determination, mg Pb/8..
In general b can be considered as the sum
b - br + bfl (5)
where b is a random component and b a systematic component. The term
i O
b is considered to be constant during any series of measurements performed
under repeatable conditions, but to behave as a random variate in a
series of measurements performed under reproducible conditions. Its
variance is denoted by
var b » a (6)
2
where a is the variance between laboratories, including the variance
LJ
between analysts and between equipment.
The term e represents a random error occurring in each measurement.
Its variance is denoted by
2
var e m a , (7)
2
where a is called the repeatability variance.
For the above model the repeatability, r and the reproducibility, R,
are given by (ref. 5)
r - 1.960J2V - 2.77 a (8)
and R = 1.96oJa2 + aT2 = 2.77 OD , (9)
^ r Li K
where 1.960 is the value of the Student's equal-tails t-distribution
for an infinite number of degrees of freedom at the 95% confidence level,
2
and 0 is the reproducibility variance, i.e., the population variance under
reproducibility conditions.
Values of a and a can be obtained from the values of repeatability
r K
and reproducibility respectively as given for the reference method in the
47
-------
Federal Register (see Appendix A). The repeatability r, is given as 2.64 mg
Pb/Jl. Using this value in equation (8) gives a - 0.953 mg Pb/£. Repro-
ducibility is given as R - 5.28 mg Pb/£ then from equation (9) aR - 1.91
mg Pb/A.
As can be seen the reproducibility standard deviation is larger than
the repeatability standard deviation by a factor of 2. It is felt this
difference is due primarily to differences in analyst techniques.
The determined value of Pb cam be expressed phenomonologically as
where Pbg represents the quantity of lead in the gasoline sample and
VT represents the volume of the solution in the test tube at the time
of analysis, i.e.
VT = VS + VA + VB + VC
where Vg , VA> Vfi and VG are the volumes of gasoline sample, reagent A
reagent B, and reagent C, respectively, added to the test tube.
Using equation (10) the dependence on or variation of Pb with Pb
O
and VT will be analyzed. The coefficient of variation of Pb, CV{Pb),
(ref. 4) is given by
CV{Pb> = a{Pb}/Pb = V(a{Pbs>/ Pbg)2 + (a{VT>/VT)2
where a{V_} =\a2{V } + a2{V.} + a2{V> + a2{V^} ,
J. S A D C
and the standard deviation of Pb is given by
o{Pb}= CV{Pb) x pb, (13)
Equation (12) was derived by differentiating implicitly the natural loga-
rithm of equation (10), squaring both sides and substituting a{Pb}/ Pb and
o(V }/V for dPb/Pb and dVT/vT respectively. This derivation assumes that
the variables Pb and V are uncorrelated.
8 L
For this analysis, it is assumed that the variation in the quantity
of lead in the gasoline sample is due to the variability of the colorimeter.
48
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This variability should be relatively small, on the order of a{Pb } =
0.264 rag Pb/fc, which is only one tenth of the repeatability. Taking
Pb = 13.2 mg Pb/£, a{Pb}= a = 0.953 mg Pb/£ and VT = 19 m£, then
CV{Pb} = a{pb}/Pb * 0.072, (14)
CV{Pbg} = a{Pbn>/ Pb - 0.02, (15)
JcV2{Pb> - CV2{Pbs> = 0.069
(16)
and a{VT) = CV{VT> x VT - 1.3 mJl. (17)
From this analysis, it is obvious that control actions should be
directed toward measuring the volumes of sample and reagents as the
most effective means of controlling and assuring data of acceptable
quality. If greater precision than that given for the reference method
is desired by the supervisor it is recommended that pipets (2 ml)
capable of greater precision be used. Such pipet could be one that has
the 2 m£ mark on a small capillary such that a small reading error would
not greatly influence the accuracy of the total volume.
4.1.3 Bias Analysis
There are no data available for estimating the bias of the
measurement process. The bias can be evaluated by .measuring reference
samples -as recommended in section 4.2.
Assuming that the true or acceptable value, PbT, of a sample is
known, then from equation (4)
Pb - PbT = T (18)
which represents the bias of the measurement method. An estimate of
the bias can be obtained from audit results as discussed in section 4.2.
4.2 PROCEDURES FOR PERFORMING A QUALITY AUDIT
If implemented properly an independent audit can be used to evaluate
the total determination process through the use of reference samples or
49
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if more convenient and desirable comparison of the fuel inspectors
determination with that obtained by atomic absorption analysis of gasoline
samples sent to the Regional Laboratory for phosphorus determination. A
reference sample is defined as a gasoline sample whose lead content is
accurately known (preferably NBS certified) to the auditors but unknown
to the analyst being audited. Results of an audit provide an independent
assessment of data quality by providing a means of estimating the precision
and bias of the reported results.
4.2.1 Procedure for performing a Quality Audit
The individual or organization responsible for performing the
audit should obtain a supply of gasoline samples with known lead con-
centrations (see section 3.1). Samples should be placed in sample containers
identical to the containers used in the field. Each container should contain
an identification number which uniquely labels that container. A "lot" of
reference samples representative of the range of concentrations used to
prepare the calibration curve should be shipped or delivered to the fuel
inspector or analysis laboratory.
4.2.2 Frequency of Audit
The optimum frequency of audit is a function of certain costs and
the desired level of confidence in the data quality assessment. Also,
another consideration would have to be the quality of the data presently
being reported. However, there are no data available to estimate the
bias of the method and this could be important to the accuracy of the
reported data.
Initially an auditing level on once a week plus anytime a gasoline
sample is analyzed that equals or exceeds the federal standard for lead
in gasoline is recommended. For an analyst analyzing about 8 samples a
day this would result in a minimum of 13 audits per calendar quarter.
The maximum audit level would be a function of how many gasoline samples
were found to equal or exceed the standard. Also, the fuel inspector is
measuring a working standard sample before analyzing each gasoline sample.
These data may also be used in assessing data quality.
50
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4.3 DATA QUALITY ASSESSMENT
Two aspects of data quality assessment are considered In this section.
The first considers a means of estimating the precision and accuracy of
the reported data, e.g., reporting the bias, If any, and the standard
deviation associated with the measurements. The second consideration Is
that of testing the data quality against given standards using sampling by
variables. For example, lower and upper limits, L and U, may be selected
to include a large percentage of the measurements and outside of which it
is desired to control the percentage of measurements to, day, less than
10 percent. If the data quality is not consistenfwith these limits, L
and U then, action is taken to correct the possible deficiency as quickly
as possible and to correct the previous data when possible or feasible.
4.3.1 Estimating the Precision and Accuracy of the Reported Data
This section will indicate how the audit data collected in accor-
dance with the procedure described in Section 4.2.1 will be utilized to
estimate the precision and accuracy of the determination of interest.
The audit data results in a collection of differences between known values
of lead and the measured values. The difference d is given by
d - Pb - Pb . (19)
J 3 i.
where Pb = Determined value of lead in the reference sample,
3 mg Pb/*,
Pb™ - True or known value of lead in the reference sample, mg Pb/&, and
J » the audit number, j « 1, . . .n.
Let the mean and standard deviation of the differences d , j » 1, . . .n
audits, be denoted by d and s,, respectively. Thus,
<20>
i-l
and
,
n
£ Vn
i-l 3
- [A«. -
.1/2
5)2/(n ~
51
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4.3.2 Statistical Teats
The mean d is an estimate of the relative bias in the measurements
(i.e., relative to the known or accepted value). Assuming the audit value
to be unbiased, the existence of a bias in the laboratory data can be
checked by the Student's equal-tails t-distribution (ref. 5)
(22)
where y is the population mean which is assumed to be zero.
If t is significantly large in absolute value, i.e., greater than
the tabulated value of t with n - 1 degrees of freedom, which is exceeded
by chance only 5 percent of the time, then the bias is considered to be
real and some check should be made for a possible cause of the bias. If
t is not significantly large, then the bias should be considered zero or
negligible. However, in either case, its calculated value will be
reported with the laboratory data for that audit period.
The standard deviation, s,, is a function ot both the stanjara devi-
ation of the field and of precision with which the reference sample value
is known. Assuming reference sample values are known with much greater
precision (see section 3.1) than the field laboratory measurements
then the calculated s, is an estimate of the standard deviation of the
d
field laboratory measurements. Table 2 contains a sample calculation of
d and s,, for a sample size with eleven degrees of freedom.
d
The calculated standard deviation can be checked against the
assumption made in subsection 4.1.2 concerning a {Pb} «• a • 0.953 mg Pb/£,
under repeatability conditions. The calculated standard deviation, s^, is
2
checked against the assumed value, 0 , by using the one-sided x test for
a in a normal distribution,
., 2
*_ = 8d (23)
f a2{Pb} '
2
where x /f is the statistic for the value of a random variable having the
2
chi-square distribution with f » n - 1 degrees of freedom. If x /f i-8
larger than the tabulated value exceeded only 5 percent of the time, then
52
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Table 2. Computation of mean difference, d, and
standard deviation of differences, s.
General formulas Specific example
d - Pb - Pb data (mg Pb/£)
J J
d1 d2 -0.6
d2 d2 -1.2
d3 d23 +1.8
d. d2 -1.2
4 4
d5 d5 ~2'°
d, d2. +0.3
b o
d? d2, -1.4
d d^ +0.3
O o
d9 d^ -2.0
dio dio -1-0
dll dll +0'6
d!2 d!2 -1'1
Edj Edj2 -7.5
d" - Zd /n d" - -0.63
2 2
c«i-'J ^11A
Sj 1 S, " l.JZ
d n-1 d
0.36
1.44
3.24
1.44
4.0
0.09
1.96
0.09
4.0
1.0
0.36
1.21
19.19
rr
sd " sd sd - 1.15 mg Pb/£
53
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it would be concluded that the test procedure is yielding results with
more variability than is acceptable due to some assignable cause of large
variation.
The determined values should be reported along with the estimated
bias, d » T, the standard deviation, s,, the number of audits, n, and the
total number of determination periods (number of days analyses were per-
formed) N. Estimates, i.e., s and d, which are significantly different
from the assumed population parameters should be identified on the data
sheet. For example, based on the data of table 2, if the analyst reported
a value of Pb = 10.3 mg Pb/£ for one of the N field tests not audited, then
that measurement ..-aid be reported as
1. Measured value, Pb = 10.3 mg Pb/A
2. Calculated bias, d = T = -0. 63 mg
3. Calculated standard deviation, o{Pb} = s » 1.15 mg Pb/Jl
d
4. Auditing level, n = 12, N - 65.
From the above data, users of the data can calculate confidence limits
appropriate to what the data are to be used for.
2
The t-test and x -test described above are used to check on the biases
and standard deviations separately. In order to check on the overall data
quality as measured by the percent of determination deviations outside
prescribed limits, it is necessary to use the approach described below.
4.3.3 Sampling by Variables
Because the lot size (i.e., the number of determination periods
during a particular period, normally a calendar quarter) is small, N «= 65,
and consequently, the sample size is small on the order of n = 13,
it is important to consider a sampling by variables approach to assess the
data quality with respect to prescribed limits. That is, it is desired to
make as much use of the data as possible. In the variables approach, the
means and standard deviations of the sample of n audits are used in making
a decision concerning the data quality.
Some background concerning the assumptions and the methodology is
repeated below for convenience. However, one is referred to one of a
number of publications having information on sampling by variables; e.g.,
54
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see references 5-9. The discussion below will treat the specific problem
herein which has some unique features as compared with the usual variable
sampling plans.
The difference between the analyst-measured and the known value of
lead is designated as d,, and the mean difference over n audits by d, that
is,
n
3-1 ' (24)
Theoretically, Pb. and Pb,_ should be measures of the same lead concen-
tration, and i_neir difference should have a mean of zero on the average.
In addition, their differences should have a standard deviation approxi-
mately equal to that associated with measurements of Pb separately.
Since the standard deviation is known o{Pb} - 0.953 rag Pb/& the lower
and upper limits, L and U, respectively, outside of which it is desired
to control the proportion of differences, d , are defined by three standard
deviations. The values of the lower and upper limits are -3(0.953) -
-2.86 mg Pb/fc and 3(0.953) - 2.86 mg Pb/£, respectively. Following the
method given in reference 6, a procedure for applying the variables sampling
plan is described below. Figures 9 and 10 illustrate examples of
satisfactory and unsatisfactory data quality with respect to the pre-
scribed limits L and U.
The variables sampling plan requires the sample mean difference, d;
the standard deviation of these differences, s,; and a constant, k, which
is determined by the value of p, the proportion of the differences outside
the limits of L and U. For example, if it is desired to control at 0.10
the probability of not detecting lots with data quality p equal to 0.10
(or 10% of the individual differences outside L and U) and if the sample
size is n - 12, then the value of k can be obtained from Table II of reference
6. The values of d and a, are computed in the usual manner; see table 2
for formulas and a specific example. Given the above information, the
test procedure is applied and subsequent action is taken in accordance
wlt.h the following criteria:
55
-------
" P * P * °*10
Figure 9. Example illustrating p < 0.10 and satisfactory data quality.
p (percent of measured
differences outside
limits L and U) >-0.10
Figure 10. Example illustrating p > 0.10 and unsatisfactory data quality.
56
-------
1. If both of the following conditions are satisfied:
d - k 8(i >_ L - -2.86 mg Pb/Jl
d - k a, < U - 2.86 mg Pb/£
d —
the individual differences are considered to be consistent with the
prescribed data quality limits and no corrective action is required.
2. If one or both of these inequalities is violated, possible
deficiencies exist in the determination process as carried out for that
particular lot (group) of determination periods. These deficiencies
should be identified and corrected as soon as possible to prevent future
determinations of unacceptable quality. Data corrections should be made
when possible, i.e., if a quantitative basis is determined for correction.
Table 3 contains a few selected values of n, p, and k for convenient
reference.
Using the values of d and s, in Table 2, k = 2.045 for a sample size
n = 12, and p - 0.10 (Table 3), the test criteria can be checked; i.e.,
d - k sd - -0.63 - (2.045)(1.15) = -2.98 < L - -2.86 mg Pb/A
d + k sd - -0.63 + (2.045)(1.15) - 1.72 < u - 2.86 mg Pb/i
Therefore, both inequalities are not satisfied; specifically, the data
show a negative bias and are not consistent with the lower limits. The
laboratory or field unit responsible for generating these data have not
maintained satisfactory quality control activities. The field unit
should be notified of the need to improve its data quality. However,
the calendar quarter of data or a portion of that quarter of data need
not necessarily be invalidated especially if all the gasoline samples
analyzed were well below the standard e.g., below 10 mg Pb/JL
The above plan provides a 90 percent probability of detecting lots
with 10 percent or more defects (i.e., deviations falling outside the
designated limits L and U).
57
-------
Table 3. Sample plan constants, k for P{not detecting a lot
with proportion p outside limits L and U}_<0.1
Sample size n k(p = 0.2) k(p = 0.1)
3 3.039 4.258
5 1.976 2.742
7 1.721 2.334
10 1.595 2.112
12 1.550 2.045
13 1.533 2.02
14 1.519 1.999
15 1.506 1.981
58
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SECTION V
1. Standard Method of Rapid Field Test for Trace Lead in Unleaded
Gasoline (Colorimetric Method), American Society of Testing and
Materials, designation D3348-74.
2. "Reagent Chemicals, American Chemical Society Specifications,"
Am. Chemical Soc., Washington, D.C. For suggestions on the testing
of reagents not listed by the American Chemical Society, see
"Reagent Chemicals and Standards," by Joseph Rosin, D. Van Nostrand
Co., Inc., New York, N.Y., and the "United States Pharmacopeia."
3. D._E. Wagoner , F. Smith and D. E. Gilbert, "Test for Lead in
Gasoline ' J Atomic Absorption Spectrometry," Research Triangle
Institute under contract No. 68-02-1234, U. S. Environmental
Protection Agency, Washington, D.C. (1974).
4. F. Smith, and A. C. Nelson, Jr., "Measuring Pollutants for Which
National Ambient Air Quality Standards have been Promulgated,
(Final Report)," Research Triangle Institute under contract No.
68-02-0598, U. S. Environmental Protection Agency, Washington, D.C.
(1973).
5. A. Raid, Statistical Theory with Engineering Applications, New York:
John Wiley and Sons, 1952.
6. D. B. Owen, "Variables Sampling Plans Based on the Normal Distri-
bution," Technometries 9, No. 3 (August 1967).
7. D. B. Owen, "Summary of Recent Work on Variables Acceptance
Sampling wich Emphasis on Non-normality," Technometrics _11 (1969):
639-37.
8. Kinji Takogi, "On Designing Unknown Sigma Sampling Plans Based on
a Wide Class of Non-Normal Distributions," Technometrics 14 (1972)t
669-78.
9. C. Eisenhart, M. Hastay, and W. A. Wallis (eds.), Techniques of
Statistical Analysis, Statistical Research Group, Columbia, University,
New York: McGraw-Hill, 1947.
10. E. L. Grant, and R. S. Leavenworth, Statistical Quality Control,
4th ed., St. Louis: McGraw-Hill, 1972.
11. D. A. Simons, Practical Quality Control, Reading, Mass.: Addison-
Wesley Publishing Company, 1970, pp. 131-150.
59
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APPENDIX A
FIELD TEST IFOR DETERMINATION OF LEAD COMENT IN
UNLEADED GASOLINE
Prjuu) Turret LOAD
Awsonnx C—Fttui TEST urn Dmutnttnam
or LEAD Coitannr ur UMUABJS* QssnuBm
1. Scop*.
1.1 This method is intended for use In
the field by nontechnical people for the
quantitative measurement of lead I* un-
leaded gasoline In ttoe range from OJB1 to
0.10 g Pb/UB. gal. The method applies to
•a commercial gasolines and sssponds to Hi
types of lead alkyls as wn*l M to ottoet or-
ganic and inorganic form* of lead.
«. Summary o/ Method.
3.1 The gasoline la treated with iodine
and tetraethyl ammonium chloride in
chloroform and subjected to ultraviolet light.
The lead alkyls form . watsr-solnhta lead
alkyl Iodides, which are removed from the
gasoline by abating it with an aqueous
ammonium nitrate solution. The aqueoui
extract is filtered into a solution of 4-(3-
pyrldylaao)-resorclnol disodium salt (PAH)
and ammonium hydroxide. The lead is deter-
mined by measuring its PAR complex oolort-
metrlcany at 480 nm using a previously
prepared calibration curve.
9. Affmratu*.
3.1 "tntn.vlolet lAnapV' loaf wavelength.
MM A. ptesml la a standard 4-watt auores-
cwnt fixture.
8J HeaKirtng Block, aluminum, drilled
to hold an 18 by IM-mm test tOSe, with a
mark at • leva! equal to 8.0 ml of liquid
in the teat tube.
SJ "Ootartmeter. portable.- capable of
operating at 4*0 mm. Any equivalent instru-
ment oapabu of measurement near 614 mm
(the optimum Pb-PAR complex wavelength)
may be used.
3.4 "Test tubes" boroaUicete, U by 1M
3.8 "Plpeia," glass, dropping, capable of
delivering 3.0 ml wttb a a-ml bulb.
MOTE 1: Caution. neenllno or any of the
reagents mu»t not come to contact with rub-
ber, if ttus happens, discard the bulb and
pipet and itart again.
3.1 "Funnel," plastic. 18 Inch inside dl-
pmeter.
3.7 "Filter paper," sinless. 11.00 cm In
diameter.
»M '•Oraduated cylinder." plastic. 10-mI.
8.9 OUst Vials, with caps, disposable, 1-
OB. capacity.
4.1 Purity of refgentt. Reagent grade
chemical shall be ussd in all tests. Unless
otherwise indicated. It to intended that all
reagents conform to toe specifications of the
Committee on Analytical Reagents of the
American Chemical Society, where such spec-
ifications are available. Other grades may
be used, provided It Is first ascertained that
the reagent Is of suffldenUy high purity to
permit Its use without Insnnnlng the ac-
curacy of the determination.
4.2 Ammonium Hydroxide (sp. gr. 0.90) —
Concentrated ammonhun hydroxide
(NH.OH).
4.8 Ammonium Nitrate Solution (Re-
agent B) — Dissolve 16.0±0.1 g of i
nitrate (NH.NO.) in 780 ml of water in a 1-
litre volumetric flash. Dilute to the mark
with water.
4.4 Chloroform (CHCl,).
4.8 Disodium Salt of «-(2-pyrtd|/Joso) Kf-
torcinol Dihydrate (PAH, 2H,O) (Reagent
C). Dissolve 36.0+0.1 mg of PAR In TWO ml
of water in a 1 liter volumetric flask. Add
10.0±0.1 ml concentrated NH.OH. Dilute to
the mark with water. Store this in brown
bottles out of direct sunlight or In the dark.
NOTE 3: Caution—low results are obtained
if the mono-sodium or unsalted PAB Is ussd
in this test.
4.8 Gmtottne, Lead-Free. Gasoline con-
taining less than 0.001 g PB/gal.
4.7 Iodine.
4.8 lodine/TMAC/CHCl, Solution (Jte-
agent A). Dissolve 1.000 g±l mg of Iodine In
76 ml of chloroform (CHCl,) in a 100-ml
volumetric flask. Add 1.000 f±l tag of tetra-
ethylammonlum chloride (TKAC) and mix
until dissolved. Dilute to the mark with
CHCl,.
NOTE 3: Solutions 43, 4.8. and 4.8 have
been found to be stable for at least 9 months.
4.9 Lead Standard*. This method was de-
veloped using lead standards prepared by ad-
dition of known amounts of various lead
alkyls to be blended unleaded gasoline to
cover the range of this method.
4.11 Tetraethftommanivm Chloride ifon-
ohfdrate (TtAO).
6. OaHbratton.'
5.1 Prepare a calibration curve to be used
with the portable colorimeter. Such a curve
should be prepared as frequently as necessary
to assure that accurate test results are being
obtained. Use at least four gasoline standards
of known Isad content that cover the range
from 0.01 to 0.10 g Pb/gal. to prepare the
curve.
54.1 Rinse the a-ml graduated plpet
three times with the gasoline eampls. Add
2.0 ml of the sample to a 1-os glass vial. Add
2.0 ml of lodlne/TSAC/CHCl, solution (He-
agent A) from another pipet, to the vial con-
taining the gasoline. Tightly cap ths vial.
6.1.2 Place the vial on tfca ultraviolet
light and set the timer to give the •ample a
3-mlnute expcisure. Caution. Ultraviolet
light can be harmful to the eyes. Do not
remove any protective shields. DO NOT
stare at the llgn t.
6.1.3 After exposure, remove and uncap
the vial. Measure 10.0 ml of ammonium ni-
trate solution ; Reagent B) into tbe 10-ml
graduated cylinder. Add this to the vial
containing the iiample. Recap and shake the
vial vigorously for 1 minute.
5.1.4 Placs i. clean 18-mm test tube In
the aluminum measuring block. Add 6.0 ml
of PAR solution (Reagent C) to the test tube
using the mark on the block such that the
upper level of liquid in the tube is equal to
the mark on the block. Place the plastic
funnel In the tost tube. Fold a piece of filter
paper and plaeo in the funnel.
5.1.5 When the two layers of liquid In
the vial have separated (6.1.8), pour th»
entire contents of the vial inside tbe Alter
paper. The aquiious layer will remain in the
filter paper. Tap the funnel to add any re-
maining drops of aqueous solution to the
test tube. Remove the funnel and discard
its contents. Swirl tbe test tube gently using
a wrist action \a obtain a uniform color.
NOTE 4: The lead-PAR complex formed In
6.1JI must be :neasured within 10 minutes
after starting 6.1.8.
Non 8: A few drops of the organic layer
may come through the filter paper. This
will not alter the results and can therefore
be tolerated. However, If more than 10 drops
do come through, refllter ths aqueous layer
through a frsfh filter paper Into a clean
smpty test tube.
NOTE 8: Swirling may cause air bubbles to
be trapped in tthe liquid. Walt for these to
settle before continuing. Wipe the test tube
off with a clean towel to remove any finger-
prints that may be present on the surface of
the tube.
6.3 Zero and standardise the colorimeter
as follows:
6.3.1 Set tho colorimeter at 400 nm. Set
aero absorbanoii (100 percent tranamlttance)
with water in en 18-mm test tube. Read and
record the absorbance (or percent transnsit-
tanoe) obtained for the standards prepared
under B.1JS.
6.3.3 Plot the absorbance values versus
concentration on rectangular coordinate
paper. (If percent transmlttanee values are
used, plot them versus concentration using
semllog paper, with the percent transmlt-
tanoe value on the log scale.) Draw a best
fit line by eye. When plotting absorbanoe
versus concentration, note that the curve
does not psss through ths origin.
6. Procedure.
8.1 Prepare the sample in accordance with
the directions given in 6.1.1 through 6.1.6.
8.3 Place the test tube containing the
water in the colorimeter and set the absorb-
anoe to zero, or the transmlttanee to 100%.
8.8 Place the sample in the colorimeter
and read the, absorbanoe or percent transmlt-
tance.
NOTE 7: Time limit. The PAR-lead solution
obtained for the sample in 8.1 must be read
within 10 minutes after the step described In
8.1.6.
8.4 From tbe calibration curve, find tbe
• lead content of the sample. Determine tbe
lead content to the nearest 0.001 g/gal value.
8.4.1 Round the value obtained in 8.4 to
the nearest 0.01 g/gal value. This will be tbe
value reported.
7. Preciiion.
7.1 The following criteria should be used
for Judging the acceptability of results (96
percent confidence):
7.1.1 Repeatability. Duplicate results by
ths same operator should be considered sus-
pect If they differ by more than 0.01 g/gal.
7.1.3 Jtepro4ua
-------
APPENDIX B GLOSSARY OF SYTCOLS
This Is a glossary of symbols as used In this document. Symbols used
and defined in the reference method (Appendix A) are not repeated here.
SYMBOL DEFINITION
•
A Angstrom
3
cm Cubic centimeter
cm Centimeter
gal Gallon
g Gram
h Hour
£, Liter
«£ Milliliter
mm Millimeter
N Lot size-rl.e., the number of determination periods to be
treated as a group.
n Sample size for the quality audit (section 3.3).
nm Nanometer
P Phosphorus
r Repeatability of the measurement method at the 95-percent
confidence level.
sp gr Specific gravity
sy Computed standard deviation of a finite sample of
measurements (sample standard deviation)
X Computed average of a finite sample of measurements
(sample mean)
/ Per
y Micron
yg Microgram
a{X} Assumed standard deviation of the parameter X (population
standard deviation)
y Assumed mean value of the parameter X (population mean)
A
T Computed bias of the parameter X for a finite sample
(sample bias)
61
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APPENDIX B
SYMBOL
CL
CV{X}
j
K
L
LCL
P
Pb
Pb
PbT
Pb'
p(Y}
R
r
R
"n-1
R
GLDSSAFY OF SYlWB-ONriNUED
DEFINITION
Center line of a quality control chart.
Coefficient of variation of X,(100 a /y ).
X X
Mean difference between known and measured values of
reference samples for n audits.
The difference in the audit value and the measured value
arrived at by the analyst for the jth audit.
Tolerance interval constant.
Lower quality limit used in sampling by variables.
Lower control limit of a quality control chart.
Percent of measurements outside specified limits L and U
(Section 3.4).
Determined lead in a gasoline sample in mg Pb/Jl.
Known value of lead concentration of reference sample j.
True (but unknown) lead concentration of gasoline sample.
Known lead concentration of working standard samples.
Probability of event Y occurring.
Reproducibility of the determination method.
Repeatability of the determination method.
Mean value of the range of samples of size n drawn from
a normal population.
Computed standard deviation of difference between known
and measured values.
Statistic used to determine if the sample bias, d, is
significantly different from zero (t-test).
Upper quality limit used in sampling by variables.
Repeatability standard deviation.
Reproducibility standard deviation.
62
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APPENDIX B GLOSSARY OF SYMBOLS-GOWNED
SYMBOL DEFINITION
2 2
^ Statistic used to determine if the sample variance, s , „
f is significantly different from the assumed variance, a ,
of the parent distribution (chi-square test).
a Standard deviation of a parameter determined by two
different laboratories.
63
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APPENDIX C GU3SSM OF TERMS
The following glossary lists and defines the terms as used in this
document
Absorbance The logarithm to the base ten of the reciprocal of
transmit tarice.
Accuracy A measure of the error of a process expressed as a
comparison between the measured value and the true
value.
Audit Sample .... Sample prepared by the Quality Assurance and
Environmental Monitoring Laboratory (concentration
unknown to the analyst).
Bias The systematic or non-random component of system
error.
Chain of Custody
Label The seal placed on the container which contains the
gasoline sample from the test station.
Control Sample ... A standard sample used to check the determination
process.
Determination
Method A set of procedures for making a determination.
Determination
Process The process of making a determination including
method, personnel, equipment, and environmental
conditions.
Liter Special name for the cubic decimeter.
Lot A specified number of objects to be treated as a
group.
Population The totality of the set of items, units, measure-
ments, and. the like, real, or conceptual, that is
under consideration.
Precision The degree of variation among measurements on a
homogeneous material under controlled conditions,
and usually expressed as a standard deviation or
as a coefficient of variation.
64
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Quality Audit .
Quality Control
Check
Reference Sample
Sample
Spectral
Bandwidth . . .
A management tool for independently assessing data
quality.
Checks made by the operator on certain items of
equipment and procedures to assure data of good
quality.
Sample prepared and certified by the Regional Lab-
•wratory or the NBS (concentration unknown to the
analyst) for auditing purposes.
Objects drawn usually at random from the lot for
checking (as used in the section on auditing).
The range of wavelengths between the two points
at which the absorbance is one-half the peak
absorbance.
Working
Standard Sample
Sample prepared by the Fuel Inspector from a working
standard solution to prepare or validate the lead
calibration curve.
Working
Standard Solution
Solution prepared and analyzed by the Regional
Laboratory and supplied to the Fuel Inspector for
preparing working standard samples for calibration
purposes.
65
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APPENDIX D
CONVERSION FACTORS
Conversion factors for converting the U. S. customary units to the Inter-
national System of Units (SI) are given below.
TO CONVERT FROM
absorbance (A)
degree Celsius (°C)
grains (g) of lead/gal
milligrams (mg) of
lead/liter
nanometer (nm)
TO
transmittance (T)
degree Farenheit (°F)
milligrams (mg) of
lead/liter
g of lead/gal
micron (y)
o
Angs trom (A)
centimeter (cm)
MULTIPLY BY
T = ICfA
°F = (1.8)(°C) + 32
264
0.003785
0.001
0.1
10
-7
*Metric Practice Guide (A guide to the use of SI, the International
Systems of Units), American National Standard Z210.1-1971, American
Society for Testing and Materials, ASTM Designation: E380-70, Philadelphia,
Pa., 1971.
66
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EPA-65p/4-7_4j:On_5-n
J Till;.- '.-1 '-'JUriT I.1:
Guidelines for Development of a Quality Assurance
Program: Volume XIV - Screening Determination of Lead
G. FkHCOflMING ORGANISATION COW.
D. E. Gilbert, F. Smith, D. E. Wagoner
n PC HfC>;VI\G CP" ANI^ATIC'.'. \AME A ML* AOCJr'.t_SS
Research Triangle Institute
P. 0. Box 12194
Research Triangle Park, N. C. 27709
12. scN5^>'"NG AGLr.CY NAMfc AND AUURLSS
Office of Resep-'ch and Development
U. S. Environmental Protection Agency
Washington, D. C. 20460
;i ill C1PILN7 S
'.>. fU.PORT DATE
8. PE.RFODMING ORGANI2A1 IO,\ fit"'
10. PRCiGRAM tLtMLf. \ NO
1HA327
11. rONTHACT.'GRANT NO.
13. TYPE OF FU'.PORT AND PERIOD COvt I.
14. SPONSORING AC-fcMCY CODE
IS. SUPPL tMCN TAfi Y NOTE'S
16. At SI RAG!
This document presents guidelines for developing a quality assurance
program for the screening determination of lead in gasoline by the
Federal reference method. These guidelines include:
1. Recommended operating practices an'd techniques,
2. Procedures for assessing performance and qualifying data,
3. Procedures for identifying trouble and improving data quality,
4. Procedures to permit design of auditing activities.
This document is an operations manual, designed for use by operating
personnel.
KF> WOF1DJ AN'D OOCUV.LN7 ANALYSIS
DESCRIPTORS
Quality Assurance
Quality Control
Air Pollution
Gasoline
Lead
:i. I DENT If-" If RS'PPE.N ENDED TERMS
COSATI I icIII tjl\u:n
13H
14D
13B
21D
7B
1 1 U 'ill ill 'w-i '., ! A • :.VL N r
Unlimited
10 i.LCURI i Y CL-AOi , . .;i Hi-purl)
JJnclassjfied
20 CrCUlin Y CLAC3 f //ii!/>avv;
Unclassified
2 1. NO. Oh f'ACii-1
72
22. F'ltlCC
67
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