EPA-650/4-74-005-L
NOVEMBER 1974
ng Serbs
PRQll
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EPA-650/4-74-005-L
GUIDELINES FOR DEVELOPMENT
OF A QUALITY ASSURANCE PROGRAM
VOLUME XII -
DETERMINATION OF PHOSPHORUS
IN GASOLINE
by
Daniel E. Gilbert, Denny E. Wagoner, and Franklin Smith
Research Triangle Institute
Research Triangle Park, N. C, 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
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
November 1974
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This report has been reviewed by the Environmental Protection Agency
and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Agency,
nor does mention of trade names or commercial products constitute
endorsement or recommendation for use.
11
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ABSTRACT
This document presents guidelines for developing a quality assurance
program for the determination of phosphorus in gasoline by the Federal
reference method. These guidelines include:
1. Recommended operating practices and techniques,
2. Procedures for assessing performance and qualifying data, and
3. Procedures for identifying trouble and improving data quality.
This document is an operations manual, designed for use by laboratory
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 November 1974.
ill
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TABLE OF CONTENTS
SECTION
I
II
INTRODUCTION
OPERATIONS MANUAL
2.0 GENERAL
2.1 EQUIPMENT SELECTION
2.2 CALIBRATION
2.3 ANALYSIS
2.4 CALCULATIONS
2.5 DATA REPORTING
2.6 PHOSPHORUS CONTENT EQUALS OR EXCEEDS
FEDERAL STANDARD
PAGE
1
3
3
6
11
19
27
27
29
III
IV
APPENDIXES
A
B
C
D
QUALITY ASSURANCE PROCEDURES
3.0 GENERAL
3.1 FUNCTIONAL ANALYSIS OF THE DETERMINATION
METHOD
3.2 COLLECTION OF INFORMATION TO IDENTIFY
TROUBLE - -..,,
3.3 INDEPENDENT PERFORMANCE AUDIT
3.4 DATA QUALITY ASSESSMENT
METHOD FOR THE DETERMINATION
OF PHOSPHORUS IN GASOLINE
GLOSSARY OF SYMBOLS
GLOSSARY OF TERMS
CONVERSION FACTORS
30
30
32
38
40
42
50
51
55
57
59
iv
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LIST OF FIGURES
FIGURE NO. PAGE
1 Operational flow chart of the determination
process 5
2 Phosphorus calibration curve 11
3 Sample receiving record 20
4 Flow chart for the analysis of phosphorus
in gasoline 21
5 Illustration of the addition of sample
to the zinc oxide 23
6 Laboratory test record 28
7 Sample control chart for duplicate
determinations of gasoline samples 39
8 Sample control chart for the determination
of standard samples 41
9 Example illustrating p < 0.10 and
satisfactory data quality 48
10 Example illustrating p < 0.10 and
unsatisfactory data quality 48
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LIST OF TABLES
TABLE NO. PAGE
1 List of equipment 7
2 Computation of mean difference, d, and
standard deviation of differences, s, 46
3 Sample plan constants, k for P{not detecting
a lot with proportion p outside limits L and
U> < 0.1 49
vi
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SECTION I INTRODUCTION
This document presents guidelines for developing a quality assurance
program for the manual (noncontinuous) determination of phosphorus in
gasoline by the molybdenum blue method. This method was published by the
Environmental Protection Agency in the Federal Register, July 8, 1974,
and is reproduced in appendix A of this document.
This document.is divided into three 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, calibration, and operating procedures
to insure the collection of data of high quality and instructions for
performing quality control checks designed to give an indication or warning
that invalid or poor quality data are being collected, allowing for corrective
action to be implemented before future determinations are made.
Section III, Quality Assurance Procedures. The Quality Assurance
presents information relative to the test method, a functional analysis
to identify the important operating variables and factors, and statis-
tical properties of and procedures for conducting an independent assessment
of data quality.
The objectives of this quality assurance program for the molybdenum
blue method of determining phosphorus in gasoline are to:
1. Provide recommended operating procedures and techniques,
2. Identify and minimize systematic errors to maintain the
precision 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
5. Provide the necessary information to describe the quality of
the data.
To accomplish these objectives, a quality assurance program must
contain the following components:
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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 accept-
able quality.
The scope of this document has been purposely limited to that of a
laboratory manual.
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SECTION II OPERATIONS MANUAL
2.0 GENERAL
This operations manual sets forth recommended operating procedures for
the spectrophotometric determination of phosphorus in-gasoline by using the
molybdenum blue method (ref. 1). This method is reproduced from the Federal
Register in appendix A of this document. Quality control procedures and
checks designed to give an indication or warning that invalid or poor
quality data are being collected are written as part of the operating pro-
cedures and are to be performed by the operator on a routine basis.
In this method the gasoline sample is adsorbed on zinc oxide and
ignited. The phosphorus is determined in the presence of the zinc using the
molybdenum blue method, which was studied extensively by Mellon and
Kitson (ref. 2). The color obtained is stable and reproducible in the
presence of zinc and lead ions, tetraethyllead, scavengers, antioxidants,
metal deactivators, sulfur, or manganese antiknock compounds (ref.3).
The color development results from the condensation of orthophosphoric
and molybdic acids to heteropoly complex compounds, the molybdophosphoric
acids (refs. 4,5). The reduction of these molybdophosphoric acids
produces a blue color; the color intensity is proportional to the amount
of orthophosphate ions incorporated in the complex. The exact constitu-
tion of these reduction products is uncertain, but their formation is
reproducible (ref. 6). Complex formation is carried out in an acidic
solution at pH less than 1. The color intensity is stronger in a less
acidic solution, but the color developed by the reagents is also much
greater. The color intensity does not increase in the presence of excess
reducing agent, hydrazine sulfate.
In measuring the intensity of a heteropoly blue solution, the color,
once developed, cannot be diluted or concentrated because the intensity
depends on the pH, the molybdenum-acid ratio, and the amount of molybdate
(refs. 7,8). With a given concentration of molybdate, a minimum concen-
tration of acid is required to prevent color development in the absence of
phosphate. Just above this critical concentration there is a limited range
in which the intensity of the color is proportional to the phosphate con-
tent almost independently of the acidity. Further increases in acidity
cause a decrease in color intensity (ref. 5).
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The accuracy of data obtained from this method depends upon equipment
calibration and the proficiency with which the operator performs his vari-
ous tasks. This determination 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, Vol. 39, No. 131, Part 80, July 8, 1974
(reproduced as appendix A of this document for convenience of reference).
Instructions throughout this document are directed primarily toward an
8-hour determination period—i.e., an 8-hour workday in which it is assumed
that approximately 8 P determinations can be made. Also, an auditing or
checking level of a minimum of once a week or every time a field sample ex-
ceeds the Federal standard is recommended (see subsection 3.3.2). Sampling
period durations and auditing levels are subject to change by the supervisor
and/or manager. Such changes would not alter the basic directions for per-
forming the operation. Also, certain quality 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
specifications and that the manufacturer's recommendations will be fol-
lowed when using a particular instrument (e.g., spectrophotometer).
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 spectrophotometer calibration are performed period-
ically. The remaining operations are performed during each determination
period. The operations are classified as equipment selection, calibration,
sample analysis, and data processing. Each operation or step in the
process is identified by a block. Quality checkpoints in the determination
process, for which appropriate quality-control limits are assigned, are
represented by blocks enclosed by heavy lines. Other checkpoints involve
go/no-go checks and/or subjective judgments by the analyst with proper
guidelines for decisionmaking spelled out in the procedures. These opera-
tions 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:
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EQUIPMENT SELECTION
1. Select the equipment according to
specifications given in the reference
method (section 4, appendix A) and
according to subsection 2.1.
2. Perform visual and operational checks
of equipment according to subsection
2.1.1.
3. Record new equipment in a receiving
record file according to subsection
2.1.1.
CALIBRATION
4. Calibrate the equipment according to
subsection 2.2.
SAMPLE ANALYSIS
5. Identify the sample and document it
according to subsection 3.2.1.
6. Prepare reagents according to sub-
section 2.2.
7. Analyze samples according to sub-
section 2.3.3.
DATA PROCESSING
8. Perform calculations to determine phos-
phorus content according to subsection
2.4.
9. Validate "data by comparing determined
value of reference sample to the known
value according to subsectjojjo:2.|>_. _ ,,
10. Report data according to subsection
2.5.
EQUIPMENT
SELECTION
EQUIPMENT
INSPECTION
EQUIPMENT
RECORD
FILE
EQUIPMENT
CALIBRATION
SAMPLE
IDENTIFICATION
REAGENT
PREPARATION
SAMPLE
ANALYSIS
PERFORM
CALCULATIONS
VALIDATE
DATA
10
REPORT.
DATA
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1. Receiving Record Log Book. This book contains a description of
the item received, its serial number or catalog number when ap-
propriate, and results of the acceptance test, signed and dated.
2. Calibration Record Log Book. This book contains the phosphorus
calibration curves, standard sample data, and the calibration
of all the equipment.
3. Sample Receiving Record Log Book. This book contains the test
station sample and laboratory identifications data for each
test station sample received.
4. Laboratory Test Record Log Book. This book contains the test
station sample and laboratory identifications, calculation
data and test information.
The Sample Receiving Record Log Book can, if desired, be combined with
the Laboratory Test Record Log Book.
2.1 EQUIPMENT SELECTION
A listing of the required equipment with certain pertinent specifica-
tions is given in table 1 and in section 4 of appendix A. 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 equip-
ment are presented. In addition, a descriptive title and the identification
v\
number of new equipment should be recorded in the receiving record log book.
2.1.1 Spectrophotometer
2.1.1.1 Specifications . The spectrophotometer should be an instrument
equipped with a tungsten lamp, a near-infrared-sensitive phototube capable
of operation at 820 nm with a maximum spectral bandwidth of 10 nm and with
a cell compartment capable of holding cells with a 5-cm pathlength. The
radiation beam should be perpendicular to the cell window when placed in
the cell holder.
2.1.1.2 Acceptance Check. The instrument should be checked out according
to the manufacturer's instructions and the wavelength calibrated according
to the instructions set forth in subsection 2.2.
2.1.1.3 Documentation . Record in the receiving record log book a description
of the spectrophotometer, its serial number, and the results of the acceptance
check, except the wavelength calibration which is recorded in the calibration
record log book. Sign and date the entry.
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Table 1. List of Equipment.
Apparatus Quantity
Spectrophotometer, instrument equipped with
a tungsten lamp and a near-infrared-sensitive
phototube capable of operating at 820 nm with a
maximum spectral bandwidth of 10 nm and with absorp-
tion cells that have 5 cm pathlengths. 1
Absorption cells, equipped with windows that are
transparent to infrared radiation at 820 nm and
possessing a light pathlength of 5 cm. 2
Constant-temperature bath, capable of maintaining
the temperature at 82 to 88 C and equipped
to hold ten 100 mil volumetric flasks submerged to
the mark. 1
Cooling bath, equipped to hold ten 100 mH volu-
metric flasks submerged to the mark in the ice
water. 1
Oven, capable of maintaining a temperature at
105 to 110°C for 3 hours. 1
Muffle Furnace, capable of heating camples to
704°C. 1
Filter paper, Type II, Class G, as designated
in ASTM Standard Specification D1100, 12.5 cm
diameter. 1 box
Filtering Funnel, bowl with 60 angle,
depressed flutings^ and 75 mm diameter. 1
Ignition disk, porcelain evaporating dish,
glazed inside and outside, with pour-out size
number OOA, inside diameter of 75 mm and
capacity of 70 mfc. 1
o
Thermometer with range 10 to 105 C. 1
Volumetric flask, 0.100 H volume with ground
glass stopper. 10
Volumetric flask, 1.000 £ volume with ground
glass stopper. 2
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Table 1 (continued),
Apparatus
Syringe, 10 mi, volume equipped with a 5 cm,
22 gauge needle.
Buret, 10 mX. volume with 0.05 m£ subdivisions.
Graduated cylinder, 1.000 £ volume.
Graduated cylinder, 225 m£ volume.
Glass flask, 1.000 £ volume.
Pipet, 10 mi volume.
Pipet, 25 m£ volume.
Glass beaker, 1.5 £ volume.
Reagents
Sulfuric acid, reagent grade.
Distilled water.
Ammonium molybdate tetrahydrate.
Ethylene glycol, technical grade (or other
suitable high-boiling bath liquid with a
boiling point greater than about 100 C).
Hydrazine sulfate.
Potassium dihydrogen phosphate.
Zinc oxide, with density of approximately
0.5 g/cm
Bunsen burner.
Propane gas.
Face shield.
Rubber gloves.
Rubber apron.
Quantity
1
1
1
l
1
l
1
•l
225 ml
3.2 £
20 g
4 gal
1.5 g
5 g
Several liters
1
1
1
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2.1.2 Constant-Temperature Bath
2.1.2.1 Specifications. The constant-temperature bath should be equipped
to hold ten 100 m£ volumetric flasks submerged to the mark. The bath must
have a large enough heat reservoir or water capacity, about 4 gallons, to
O O
keep the temperature between 82 and 87 C during the entire period of sample
heating, which will be about 25 minutes. A good bath should maintain the
O
temperature within ±2 C.
2.1.2.2 Acceptance Check. The bath should be checked out according to the
manufacturer's instructions and calibrated according to instructions set
forth in subsection 2.2.
2.1.2.3 Documentation. Record in the receiving record log book a
description of the bath, its serial number and the results of the accept-. <
ance check, except the calibration results which should be recorded in
the calibration record log book. Sign and date the entry.
2.1.2 Absorption Cells
2.1.3.1 Specifications. The absorption cell should be matched properly,
possess windows which are parallel and transparent in the near-infrared
regions, and exhibit a radiation pathlength of 5 cm.
2.1.3.2 Acceptance Check. The cells should be inspected for scratches,
and their pathlengths and parallelisms insured by the manufacturer.
Note 1: As long as the use of an absorption cell is dedicated to either
a reference or sample, the pathlength and parallelism will be invariant,
thus precluding measurements of their values.
2.1.3.3 Documentation. Record in the receiving record log book a
description of the cells, the numbers inscribed on the cells (performed
by operator, if necessary), and the results of the acceptance check.
Sign and date the entry.
2.1.4 Glassware
2.1.4.1 Specifications. All glassware shall be class A, volumetric
glassware (ref. 9).
2.1.4.2 Acceptance Check. The volumetric glassware is inspected for
cracks, scratches, and damage before it is calibrated according to the
instructions set forth in subsection 2.2.
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2.1.5 Oven
2.1.5.1 Specifications. The oven should be capable of maintaining a
temperature of 105 to 110 C for 3 hours.
2.1.5.2 Acceptance Check. The proper operation and temperature stability
of the oven should be demonstrated according to manufacturer's instructions.
2.1.5.2 Documentation. Record in the receiving record log book a.
description of the oven, its serial number, and the results of the accept-
ance check. Sign and date the entry.
2.1.6 Reagents
2.1.6.1 Specifications. Reagent-grade chemicals shall be used in all tests.
Unless otherwise indicated, it is intended that all reagents shall conform
to the specifications of the Committee on Analytical Reagents of the American
Chemical Society, where such specifications are available (ref. 4). Other
grades may be used, provided it is first ascertained through measurement of
samples of known concentrations that the reagent is of sufficiently high
purity to permit its use without lessening the accuracy of the determination.
2.1.6.2 Acceptance Check. Ascertain that the chemicals are reagent grade
and conform to the specifications of the Committee on Analytical Reagents
of the American Chemical Society.
2.1.6.3 Documentation. Record in the receiving record log book a descrip-
tion of the reagent, its lot number, manufacturer, and results of the
acceptance check. Sign and date the entry.
2.1.7- Distilled Water
2.1.7.1 Specifications. Distilled water shall be understood to mean water
free from organic and phosphate materials. It should preferably be double-
distilled from all-glass apparatus.
2.1.7.2 Acceptance Check. The purity,.,afjBtb,^ water should be ascertained
when the water is purchased or prepared and before preparing reagent solutions
for analysis, according to the instructions published in subsection 2.2.
2.1.7.3 Documentation. Record in the receiving record log book the source of
the water and the results of the acceptance check. Sign and date the entry.
10
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2.1.8 Syringes
2.1.8.1 Specifications. Syringes should be 10 m& volume with 5 cm,
22 gauge needles.
2.1.8.2 Acceptance Check. The syringes should be inspected for scratches
and cracks before calibration according to the instructions for glassware
in subsection 2.2
2.1.8.3 Documentation. Record in the receiving record log book the
description of the syringe, its manufacturer and catalog numbers, and the
results of the acceptance check, except the calibration data which should
be recorded in the calibration record log book. Sign and date the entry.
2.2 CALIBRATION^
2.2.1 Glassware Cleaning
All glassware for this method must be dedicated to this experiment.
No commercial detergents must be used in cleaning the glassware because
these compounds often contain alkali phosphates which are strongly adsorbed
by the glass surfaces during an 8-hour soak and are not removed by ordinary
rinsing.
An initial wash for all glassware should consist of an 8-hour soak in
1+1 (Vol to Vol) solution of sulfuric acid and water, maintained at about
o
82 C, and followed by several rinses with distilled water.
2.2.2 Glassware Calibration
The accuracy of certain glassware is critical to determining the
true quantity of phosphorus in gasoline. This glassware would includie the
apparatus used for delivering a known quantity of gasoline to the zinc oxide
and for preparing standard solutions. Class A volumetric glassware pur-
chased from^reliable manufacturers is generally sufficiently accurate. It
is suggested that glassware need not be calibrated unless its capacity is
in doubt as a result of not bein'g^atri'e ^-td •'measure the concentration of a
reference sample (a gasoline sample of known concentration) within
0.05 mg'P/£ of its known value.
The calibration of the volumes of this glassware, when necessary,
should be performed according to the following procedure or o.ther acceptable
11
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methods (ref. 4). The glassware to be calibrated must be scrupulously
cleaned as described previously. The distilled water and glassware
should be allowed to stand for a couple of hours in the room in which
the calibration is to be made before operations are begun, in order that
the glassware may assume the temperature of the air. The room temperature
should be as constant as possible to preclude the possibility of volume
changes during the calibration. Ordinary distilled water is used; it
need not be air free. A thermometer graduated in single degrees is
suitable for obtaining the temperature of the water. Temperatures
o
should be read to the nearest 0.5 C.
The glassware is calibrated by weighing the amount of distilled
water contained or, if applicable, delivered at the standard temperature
o o
of 20 C and calculating the volume from the density of water at 20 C,
0,9982 g/cm3.
2.2.2.1 Documentation. Record the description of the calibrated glassware
and its calibration, if required, in the calibration record log book.
Sign and date the entry. I
2.2.3 Distilled Water
2.2.3.1 Test for Phosphate. To 2-3 drops of the distilled water add
5.r2 drops of nitric acid; add 10 drops of ammonium molybdate solution as
O O
discussed in subsection 2.2.4.1; warm to 60 -80 C (keep below boiling);
and look for the formation of a bright yellow precipitate (NH,).,-P(Mo.,0..0)..
If a yellow precipitate forms, the remaining water should be
redistilled.
2.2.3.2 Test for Purity. Distilled water can be tested for purity from
oxidants in the following manner:
1. Add 0.20 ml of KMnO, solution (0.316 g/fc) to a mixture of
500 mX- of the distilled water and 1 mfc of H-SO, in a stoppered
bottle of chemically resistant glass.
2. If the permanganate color (blue) does not disappear completely
after standing 1 hour at room temperature, consider the water
suitable for use.
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3. If the permanganate does disappear, the water must be purified
before using.
2.2.3.3 Purification Procedure. Water failing the purity test can be
purified as follows:
1. Add one crystal each of potassium permanganate and barium
hydroxide for each liter of distilled water.
2. Redistill the water in an all-glass still.
3. Perform the test for/ purity as'described above.
4. Repeat the purification procedure and the test for purity
until the water checks pure.
This distilled water, free of oxidants, is used whenever water is required
in preparing reagents for sampling or analysis.
2.2.3.4 Storage of Distilled Water. Oxidant-free water should at all
times be protected from atmospheric contamination by storing in containers
made of material that has been proven to be resistant to solvation by or
reaction with water. Also, any tubing used during reagent preparation
should be of high resistant material. Also, when removing water from
the storage container, the replacement air should be drawn through a
vent guard (e.g., a drying tube filled with equal parts of 8-20-mesh
soda lime, oxalic acid, and 4-8-mesh calcium chloride, each compound
being separated front the other by a glass wool plug).
2.2.3.5 Documentation. Record in the calibration record log book the
source of the distilled water and the tests for phosphate and purity.
tt
Sign and date the entry.
2.2.4 Reagent Preparation
The analytical balance should be checked before preparing a batch
of reagents by weighing a standard weight between 1 and 3" grams". If the
measured and actual weights agree within ±0.2 mg, proceed with the
preparation. Record the actual and measured weights" fnTthe calibration
record log book. If the weights differ by more than ±0.2 mg, report to
the supervisor that the balance calibration needs checking before
continuing. The balance should be repaired and/or calibrated by a
qualified repairman.
13
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2.2.4.1 Ammonium Molybdate Solution. Wearing a face shield, rubber
gloves, and a rubber apron, add slowly, with continuous stirring, 225 ml
of concentrated sulfuric acid (assay as H_SO, at 95 to 98 percent) to
500 mi of distilled water contained in a liter beaker placed in the
cooling bath. Cool the solution to room temperature and add 20 g of
ammonium molybdate tetrahydrate ((NH4)6Mo702^,-4H20). Stir the solution
until the tetrahydrate is completely dissolved and transfer the solution
to a 1.000 I volumetric flask. Dilute to the mark with distilled water
and store in the volumetric flask stoppered with glass.
2.2.4.2 Hydrazine Sulfate Solution. Dissolve 1.5 g of hydrazine sulfate
(H-NNH- • HLSO.) in 1.000 I of distilled water, measured with a graduated
cylinder. This solution is unstable. Store it in a tightly glass-
stoppered 'amber-colored or opaque glass container and in the dark.
Prepare a fresh solution after 3 weeks or at any sign of the solution's
turning light brown.
2.2.4.3 Molybdate Hydrazine Reagent. Pipet 25 mi of ammonium molybdate
solution into a 100 mi volumetric flask containing approximately 50 mi
of water, add by pipet 10 mi of N-NNH. • H2SO, solution and dilute to
100 mil with water. This reagent is unstable but has been reported as
stable up to 4 hours. It is our recommendation that the.reagent be
prepared immediately before use ~in analysis. The flask should be
stoppered with a glass plug except when transferring to the sample.
r .
Each determination (including the blank) uses 50 mi.
2.2.4.4 Phosphorus, Stock Standard Solution (1.000 mg 7/mi). Dry
approximately 5 g of potassium dihydrogen phosphate (KH_PO,) in an oven
at 105° to 110°C for 3 hours. Dissolve 4.393 ± 0.002 g of the dihydro-
gen phosphate reagent in 150 mi, measured with a graduated cylinder, of
-..-» <=,-n , i'it.5. J10£ji . -
H^SO, (1 volume acid to 10 of water) contained in a 1.000 i volumetric
flask. Dilute with water to the mark and store in the volumetric flask
* •'••>•••* f •..., J.'j"" 30IfiV •
plugged with a glass stopper.
2.2.4.5 Phosphorus, Standard Solution (10.00 yg P/mi). Prepare by
pipetting 10 mi of stock standard phosphorus solution into a 1.000 i
volumetric flask and dilute to the mark with distilled water. Keep
the flask plugged with a glass stopper. It is unnecessary to prepare
14
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the standard phosphorus solution daily because it keeps well. Prepare
the solution weekly.
2.2.4.6 Sulfuric Acid (1+10, volume of acid to water). Wearing a face
shield, rubber gloves, and a rubber apron, add slowly, with continuous
stirring, 100 m£ of concentrated sulfuric acid (H~SO,, sp gr 1.84),
measured with a graduated cylinder, to a liter of distilled water
contained in a 1.5 H beaker placed in the cooling bath.
2.2.4.7 Documentation. Record in the calibration record log book the
dates of the preparations of the reagent solutions, the source and lot
numbers of the reagent chemicals. Sign and date the entry.
2.2.5 Constant-Temperature Bath
The constant-temperature bath shall be calibrated by operating the
o '
bath filled with ethylene glycol at 85 C for 25 minutes, during which
time the temperature should be recorded every 5 minutes. The bath
o
should maintain this temperature to within ±2 C.
2.2.5.1 Documentation. Record in the calibration record log book a
description of ,.Jthe., constant-temperature bath and the results of the
calibration.
2.2.6 Spectrophotometer
2.2.6.1 Wavelength Calibration. Convenient wavelength calibration
points for the near-infrared, 600 to 2500 nm, are furnished by 10 cm
lengths of gaseous ammonia which has bands at these wavelengths: 1513,
1967, and 2264 nm (ref. 10).
2.2.6.2 Absorbance Calibration. The calibration curve of pg of phosphorus
versus absorbance is quite reproducible. Once this curve is obtained,
it should only be necessary to check its calibration each time that it
>
is used by measuring the absorbance of the standard sample and comparing
the measured value of phosphorus with its known value. The phosphorus
calibration curve must be recalibrated when new stock reagent solutions
are prepared, when the spectrophotometer receives major maintenance,
and/or when the standard sample fails the performance check.
The absorbance of the spectrophotometer shall be calibrated as follows:
1. Transfer by buret, or a volumetric transfer pipet, 0.0,
15
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0.50, 1.00, 1.50 and 2.00 m£ of phosphorus standard solution
into 100 mH volumetric flasks.
2. Pipet 10 m£ of H^O^ (1 + 10 by volume) into each flask.
Mix immediately by swirling.
3. Prepare the molybdate-hydrazine solution. Prepare sufficient
volume of reagent based on the number of samples being
analyzed.
4. Pipet 50 m£ of the molybdate-hydrazine solution to each
volumetric flask. Mix immediately by swirling.
5. Dilute to 100 mJl with distilled water.
6. Mix well and place in the constant-temperature bath so that
the contents of the flask are submerged below the level
of the" bath. Maintain bath temperature at 82° to 88 C for
25 minutes.
Note 2: If the temperature of the constant-temperature bath
Q
drops below 82 C, the color development may not be complete.
The flasks'can either be clamped in the bath, or a lead ring
can be placed on the neck of the flask to prevent their turning
over in the bath. The liquid of the sample should be completely
submerged.
7. Transfer the flask to the cooling bath and cool the contents
rapidly to room temperature. Do not allow the samples to
cool more than 2.8 C below room temperature.
Note 3: Place a chemically clean thermometer in one of the
flasks to check the temperature. Remove the samples from the
o
bath when their temperature is 5 above room temperature.
If the samples are chilled, they will fog the windows of the
spectrophotometer, and if the samples, once removed, are allowed
to stand, restopper the flasks to prevent oxidation in air.
8. After''cooling the flasks to room temperature, remove them from
the cooling water bath and allow them to stand for 10 minutes
at room temperature.
9. Using the 2.0 mil phosphorus standard in a 5 cm cell,
determine the wavelength near 820 nm that gives maximum
absorbance. The wavelength giving maximum absorbance
should not exceed 830 nm.
16
-------
10. Using a red-sensitive phototube and 5 cm cells, adjust
the spectrophotometer to zero absorbance at the wavelength
of maximum absorbance using distilled water in both
cells. Use the wavelength of maximum absorbance in the
determination of calibration readings and future sample
readings.
Note 4: The sample and reference cells must be dedicated
solely to this function and must be reproducibly positioned
in the cell holder to attain satisfactory precision. It is
essential that all measurements be made at the same value
of the exit slit width.
11. The use of 1 cm cells for the higher concentrations is
permissible.
12. Measure the absorbance of each calibration sample including
the blank (0.0 mi phosphorus standard) at the wavelength
of maximum absorbance with distilled water in the
reference cell.
Note 5: Great care must be taken to avoid possible contamination.
If the absorbance of the blank exceeds 0.04 (for 5 cm cell),
check for source of contamination. It is suggested that the
results be disregarded and the test be rerun with
fresh reagents and clean glassware.
13. Correct the absorbance of each standard solution by subtracting
the absorbance of the blank (0.0 m£ phosphorus standard).
14. Prepare a calibration curve, as shown in figure 2, by plotting
the corrected absorbance of each standard solution against
micrograms of phosphorus. One milliliter of phosphorus
standard solution provides 10 yg of phosphorus. . _ ..iJH
15. Use regression analysis to obtain a best-fit line to the
data points. Check the plotted points; ana that-deviate .more
than 0.4 ng P should be rerun and the average of the two used.
16. Forward the calibration curve and related data to the supervisor
for his approval.
17
-------
Graph No.:
Laboratory Name:
Laboratory Address:
Technician Name:
Technician Signature:
Date:
Wavelength: 820 run
Slit Width: 0.04 mm
Cell Length: 5.000 cm
ABS.
0.004
0.214
0.441
0.656
0.876
yg
Blk.
5.00
10.00
15.00
20.00
0.210
0.437
0.652
0.872
Phosphorus calibration curve
18
-------
2.2.6.3 Documentation. Record in the calibration record log book the
spectrophotometer wavelength and absorbance calibrations.
2.3 ANALYSIS
2.3.1 Sample Receiving Procedure
Samples as received from the field must be labeled with at least
the following information:
1. Time of station test,
2. Date of station test,
3. Location of station,
4. Sample number,
5. Inspector's name and title,
6. Inspector's signature.
These data should be recorded in a sample receiving log book as shown in
figure 3. At this time, each sample should be assigned a laboratory
analysis number. This number should be placed in the sample receiving
log book and on the chain-of-custody label.
2.3.2 Sample Handling Procedure
The sample should be handled and stored in accordance with safety
procedures for flammable liquids. Since light fractions of a gasoline
sample evaporate easily, it is recommended that the samples be stored in
an explosion-proof refrigerator. Before analysis, the sample should
attain room temperature. The sample must be tightly covered at all
times except when removing aliquots for analysis.
2.3.3 Sample Analysis Procedure
*
"Hie sample analysis procedure is illustrated in figure 4 and is
listed in the following steps:
1. Selection of the size of the sample to be tested depends on
the expected concentration of phosphorus in the sample. If a
concentration of phosphorus is suspected to be less than 1.0
rng/A, it will be necessary to use 10 m£ of sample.
Note 6: Two grams of zinc oxide cannot absorb this volume of
gasoline. Therefore, the 10 m£. sample is ignited in aliquots
A looseleaf, oversized flow chart for wall mounting is supplied in the
,,rear of the report.
19
-------
SAMPLE RECEIVING RECORD
1. Test Station Sample Identification
Test Station Sample Number:
Test Station Location:
Region:
Date of Station Test: / /
MO DA YR
Time of Station Test: :
HR MIN
Inspector's Name:
Inspector's Title:
2. Laboratory Identification
Laboratory Name:
Laboratory Address:
Laboratory Analysis Number:
3. Laboratory Technician
Name:
Signature:
Date:
Figure 3. Sample receiving record
20
-------
DELIVER
GASOLINE SAMPLE
TO ZINC
OXIDE (2.3.3)
COVER SAMPLE
WITH ZINC
OXIDE
(2.3.3)
t
PREPARE
< 2 * 0.2 g
~"ilNU OXIDE
(2.3.3)
'
SELECT
SAMPLE SUE
(2.3.3)
IGNITE SAMPLE
(2.3.3)
PREPARE ZINC
OXIDE BLANK
(2.3.3)
RECORD ALL
KtASUREO
VALUES
(2.3.3)
CALCULATE
PHOSPHORUS
cwTEitr
(!.«)
MEASURE
ABSORBAKE
OF STANDARD
SAMPLE (2.3.3)
645
o
K PKOCED
ICAL FAB
D
O
CHECK PROCEDURES DECISION BLOCK
OR PHYSICAL PARAMETERS
MEASUREMENT SYSTEM
Figure 4. Flow chart for the analysis of phosphorus in gasoline.
-------
of 2 mi in the presence of 2 g of zinc oxide.
2. The table in section 7.2 of appendix A should be used in
determining the required sample size.
3. Transfer 2±0.2 g of zinc oxide into a conical pile in a clean,
dry unetched ignition dish as illustrated in figure 5.
Note 7: In order to obtain satisfactory accuracy with the small
amounts of phosphorus involved, it is necessary to take extensive
precautions in handling. The usual precautions of cleanliness,
careful manipulation, and avoidance of contamination should be
scrupulously observed also, all glassware should be cleaned before
use with cleaning acid or by some procedure that does not involve
use of commercial detergents.
Note 8: It is recommended that a standard sample of the stock
standard solution of phosphorus (10.00 ]jg P/m£) be run during the
analysis. This standard sample (1.3 mg P/fc) should be prepared
according to the instructions in subsection 2.2.6.2 wherein 1.30 m£
of the stock standard solution of phosphorus is transferred into
a 100 m£ volumetric flask in step 1. Complete steps 2 through 13.
4. Make a deep depression in the center of the zinc oxide pile
with a stirring rod.
5. Pipet the gasoline sample into the depression in the zinc
oxide. Record the temperature of the fuel if the phosphorus
O
content is required at 15.6 C and make corrections as directed
in subsection 2.4.
Note 9: For the 10 m£ sample, use multiple additions and a syringe.
Hold the tip of the needle at approximately two-thirds of the
depth of the zinc oxide layer and slowly deliver 2 mH of the sample;
fast sample delivery may give low results. Give sufficient time
for the gasoline to be absorbed by the zinc oxide because fast
delivery from the syringe will cause evaporation from expansion.
When adding the gasoline, watch the gasoline migrate to the edge of
the ZnO and then stop. In some cases, even a 2 m& aliquot cannot
be added. The idea is not to saturate the zinc oxide. Before
ignition, allow the gasoline to soak into the ZnO. After the
initial ignition, carbon material will result, and the amount of
22
-------
Syringe
Gasoline Sample
Stop Adding
Sample When
Gasoline Appears11
Around the Base
of the ZnO Pile.
Ignition
Dish
Depression
in Tip of Cone
Conical Pile
of ZnO
Figure 5. Illustration of the addition of sample
to the zinc oxide.
23
-------
gasoline that the ZnO will hold is less. Safety: After flashing
the sample, allow the crucible and contents to cool to room
temperature (check temperature of crucible to the touch) before
making another addition of gasoline.
6. Cover the sample with a samll amount of fresh zinc oxide from
the reagent bottle (use the tip of a small spatula to deliver
approximately 0.2 g). Tap the sides of the ignition dish to
pack the zinc oxide.
Note 10: The amount of zinc oxide should be <2 g; too much
zinc oxide can result in a high blank (see next step). The
amount of zinc oxide waste should be consistent between samples.
7. Prepare a blank of zinc oxide using the same amount of
zinc oxide in an ignition dish.
8. Ignite the gasoline using the flame from a bunsen burner.
Allow the gasoline to burn to extinction. For 10 m£ samples,
repeat the addition and ignition of 2 m& aliquots until all
the sample has been burned.
9. Place the ignition dishes containing the sample and blank in
o o
a hot muffle furnace set at a temperature of 621 to 704 C
"' for 10 minutes. Remove and cool the ignition dishes. When
cool, gently tap the sides of the dish to loosen the zinc
oxide. Again place the dishes in the muffle furnace for 5
minutes. Remove and cool the ignition dishes to room temper-
ature. The above treatment is usually sufficient to burn the
carbon. ' If the carbon is not completely burned off, place the
dish in the oven for additional 5-minute periods until it is
completely burned off.
Note 11: The-decomposition of organic matter may also be accomplished
by heating the ignition dish with a Meker burner, gradually increasing
the intensity" of1'heat'ikntll-. the carbon from the sides of the dish
has been burned and then cooling to room temperature. However, the
muffle furnace is recommended.
10. Pipet 25 mi of H-SO, (1+10, volume acid to volume water) to
each ignition dish. While pipeting, carefully wash all traces
of zinc oxide from the sides of the ignition dish.
24s
-------
11. Cover the ignition dish with a borosilicate (Pyrex) watch
glass and warm the ignition dish on a hot plate until the zinc
oxide is completely dissolved.
Note 12: Place the sample plus acid on the hot plate at a low heat
Do not overheat or try to hasten the dissolution process. Allow
30 to 45 minutes for the dissolution.
12. Transfer the solution through filter paper to a 100 m£
volumetric flask. Rinse the watch glass and the dish several
times with distilled water (do not exceed 25 mfc) and transfer
the washings through the filter paper to the volumetric flask.
The flask must be kept stoppered with a glass plug.
Note 13: The filtration usually requires a half hour. Use 12.5 cm
filter paper to transfer the solution; this allows the transfer and
the rinse to be made in one concerted step. In addition, it provides
a good measure of the rinse water. Use a small orifice wash bottle.
Wash the crucible, not the filter paper, because the P will be in
solution.
13. Prepare the molybdate-hydrazine solution as described in
subsection 2.2.4.3
14. Add 50 mi of the molybdate-hydrazine solution by pipet to each
100 mH volumetric flask. Mix immediately by swirling.
15. Dilute to 100 mfc with water and mix well. Remove stoppers
from flasks after mixing.
16. Place the 100 mJ- flasks in the constant-temperature bath for
25 minutes so that the contents of the falsks are below the
liquid level of the bath. The temperature of the bath should
be 82° to 88°C. See note 2.
17. Transfer the 100 mJl flasks to the coolingjbath and cool the
contents rapidly to room temperature.
18. Replace stoppers and allow the samples:;jt
-------
letter to insure accuracy in the resultant value of phosphorus.
The importance of slowly delivering the samples of gasoline to the
zinc oxide cannot be stressed enough.
19. Set the spectrophotometer to a wavelength of 820 nm. Allow at
least 5 minutes for the spectrophotometer to warm up. If
necessary, adjust the zero control to bring the meter needle
to 0 on the percent absorbance scale. Standardize the radia-
tion source by inserting 5 cm pathlength cells filled with
distilled water into the sample and reference cell holders and
by adjusting the radiation source as required until the meter
reads 0 percent absorbance.
Note 16: Care must be taken that the sample and reference cells
are not interchanged. In addition, each cell should be positioned
reproducibly in the cell holder.
Note 17: The infrared absorption cells must be handled very care-
fully. Do not breathe onto or touch the window material with your
fingers. By means of a hypodermic needle, transfer a portion of
the liquid sample to the absorption cell. Wipe away any( excess
with a lint-free tissue or cloth. Place the cell in the sample
compartment; close the cover,
20. Measure the absorbance of the reagent blank and, it is rec-
ommended, that of the standard sample (1.3 mg P/£) before each
set of determinations. Record the absorbance value of the
reagent blank and the total ug P measured for the standard
sample in the laboratory test record log book with the time to
the nearest hour. If the absorbance of the reagent blank is
within ±0.04 absorbance unit for a 5 cm cell of the calibration
curve absorbance intercept and if the measured value of the
standard sample is within ±0.4 yg P of the actual value,
proceed to analyze the field samples. If the absorbance value
of the blank is not within these limits, clean the glassware
and rerun the test with fresh reagents. If the absorbance
value of the standard sample is not within these limits,
recalibrate the phosphorus calibration curve and check the
complete absorbance scale with a calibrated set of filters
from the National Bureau of Standards.
26
-------
21. Measure tHe absorbance of the samples at the wavelength of
maximum absorbance with distilled water in the reference cell.
22. Subtract the absorbance of the blank from the absorbance of
each sample (note 5).
23. Record all measured values (i.e., reagent blanks, standard
samples, samples) in sequential order in the laboratory test
record log book. The date and time should be recorded with
each set of determinations. The reagent blank should only be
used with the set of determinations in which it was measured.
2.4 CALCULATIONS
Determine the micrograms of phosphorus in the sample using the
calibration curve from subsection 2.2 and the corrected absorbance.
Calculate the milligrams of phosphorus per litter of samples as follows:
mg P/liter = P/V
where P = total micrograms of phosphorus in the ignited sample, read
from the calibration curve, and
V = total milliliters of ignited gasoline sample.
If the gasoline sample was taken at a temperature other than
o
15.6 C, make the following temperature correction:
mg P/S, at 15.6°C = [mg P/S, at t] [1 + 0.001(t - 15.6)]
o
where t = observed temperature of the gasoline, C.
The calculations are complete when the calculation data are recorded
or a copy is filled in the Laboratory Test Record Log Book, shown in
figure 6.
2.5 DATA REPORTING
Concentrations of phosphorus below 2.50 mg/£ should be reported to
the nearest 0.01 mg/£.
The concentration of phosphorus is to be recorded in the laboratory
test record log book in the format shown in figure 6. The data reporting
is not complete until the laboratory test record is filled out.
27
-------
LABORATORY TEST RECORD
1. Test Station Sample Identification
Test Station Sample Number:
Region:
Date of Station Test: / /
MO DA YR
Time of Station Test: :
HR MIN
2. Laboratory Identification
Laboratory Name:
Laboratory Address:
Laboratory Analysis Number:
3. Test Information
Date of Lab Test: / /
MO DA YR
Time of Lab Test: :
HR MIN
P, mg/£ : .
4. Laboratory Technician
Name:
Signature:
Date:
Figure 6. Laboratory test record
-------
2.6 PHOSPHORUS CONTENT EQUALS OR EXCEEDS FEDERAL STANDARD
If the determined value of phosphorus in the field sample equals o
\y exceeds the value promulgated in the Federal Register, 1.3 mg P/&,
analyze the phosphorus content of a reference sample supplied by the
/
/ supervisor. Concomitant with this analysis, analyze the phosphorus
/ / content of a second aliquot of the field sample which exceeded the
/
Federal standard. Both analyses should be performed simultaneously
according to the instructions in subsection 2.3.3. When the analyses
are completed, report the results to your supervisor.
-------
SECTION III QUALITY ASSURANCE PROCEDURES
3.0 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 analyst conscientiously adheres to the procedures
and checks of section II, then the precision and accuracy of the phosphorus
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
phosphorous 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 analyst, the operating
3j.qn?z ff-r
procedures used, and the measured values that he reports may be challenged
in a court of law.
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. With the exception of
the independent audit, all functions could be performed by the analyst, if he is
properly trained.
The purposes of this section are to:
1. Present ^information relative to the determination method (i.e., a
functional analysis) to identify the important operations and
factors,
2. Present techniques for the collection of information to identify
trouble,
-------
3. Present an independent performance audit procedure for use in
quantifying data quality on an interlaboratory basis,
. 4. Present techniques for data quality assessment.
These four purposes will be discussed in the order stated in the subsections
that follow. The first subsection (3.1) will contain a functional analysis
of the determination 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 measurements resulting from equip-
ment and analyst errors.
Subsection 3.2 will contain suggestions for the collection and
analysis of information to identify trouble. This will involve the use
of control charts for the duplicate measurement of gasoline samples and
for measurement of standard samples with appropriate criteria for decision
making concerning whether the operation is in control and should be left
alone or if it is out of control and corrective action is required.
Subsection 3.3 contains a discussion of an independent performance
audit. Such an audit involves randomly inserting reference samples (i.e.,
NBS or otherwise certified samples) into the determination process. Such
3 .'
an audit, if feasible, could serve as an independent check of the determina-
tion process from sample handling through the final calculations. It would
provide a means of assessing data quality as a function of bias and preci-
sion and serve as an independent verification of data quality for future
users of the data.
Data quality assessment is discussed in subsection 3.4. 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.
31
-------
3.1 FUNCTIONAL ANALYSIS OF THE DETERMINATION METHOD
The determination of phosphorus in gasoline requires a sequence of
operations and measurements that yields, as an end result, a number that
serves to represent the mass of phosphorus in a unit volume of gasoline.
The degree of agreement between the determined and the true value of a
sample can be estimated from the agreement between determined and known
or accepted values of reference samples. Precision and accuracy of the
determination' process are reduced to and/or maintained within acceptable
limits by identifying and, where feasible, eliminating systematic errors.
The importance of a variable on the precision and/or accuracy of a measure-
ment process is a function of the variable's mean value and variance, how
it is related to the dependent variable, and its probability of occurrence
under normal operating conditions.
The objectives of this subsection are to:
1. Evaluate variables and estimate error ranges,
2. Determine, through a variance analysis, the variability to expect
in the phosphorus in gasoline determinations,
3. Estimate, through a bias analysis, the expected bias,jif any, in
phosphorus in gasoline determinations. . • . . ....
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 quality is characterized by measures of
precision and bias. In subsection 3.1.1 variables believed to be important
to the determination method are discussed. Estimates of the mean, variance,
and probability distribution a"re made using data from published reports when
available, and using engineering judgments when documented data are not
available. These data are then used in a variance analysis (subsection 3.1.2)
to determine the resulting^variability of the measured value i.e., the mass
of phosphorus per unit volume of gasoline. The data from subsection 3.1.1 are
32
-------
also used in subsection 3.1.3 to estimate the potential bias of the
determination process.
3.1.1 Variables Evaluation and Error Range Estimates
The milligrams of phosphorus per liter of sample at 15.6°C is
calculated from the following relationship
Pc = [VV] [1 + 0-001(t - 15-6)] (1)
where P = the concentration of phosphorus in gasoline at 15.6°C, mg/£.
P = mass of phosphorus in the aliquot of gasoline sample as read from
calibration curve at t°C, jig P.
V = volume of the gasoline sample at t°C, m-t
t = temperature of the gasoline sample at analysis, °C.
Error sources then can be grouped according to whether they affect the
determination of total mass of phosphorus, P , or the volume of the gasoline
sample, V.
3.1.1.1 Potential 'Errors in Determining the Sample Volume, V. A sample,
at the time it is collected, will contain a specific but unknown quantity
of phosphorus per. unit volume. The difference in the phosphorus content
of the sample at the time of collection and that determined at some later
time is due to error in the determination process. Following a hypothetical
unit of volume of gasoline from collection through analysis, the following
operations and/or measurements could, if not properly controlled, adversely
influence the measurement results.
1. Evaporation during shipping and handling.
2. Measurement error in the 10 m£ aliquot for analysis.
3. Evaporation losses while delivering the gasoline sample to the
zinc oxide from a syringe.
4. Vaporization during the ignition process.
5. Incomplete transfer or loss of sample during filtering and rinse.
33
-------
Of the potential errors listed above, error 1 would result in an
apparent or measured volume smaller than the true volume, thus resulting
in a higher than true measured phosphorus content. Errors 3, 4, and 5
would result in a lower than true phosphorus content. Error 2 would
probably be randomly distributed about a zero mean value.
There are no data available for estimating the error associated with
each of the above operations. However, a judgment can be made from the
values given for repeatability and reproducibility of the method as written ..
in the Federal Register (see appendix A).
For concentrations below 1.30 mg P/£ the repeatability and reproducibility
of the determination method at the 95 percent confidence level are given as
0.05 mg P/£ and 0.13 mg P/£, respectively. The above values mean that, on the
average,* duplicate results should agree within 0.05 mg P/£ 95 percent of the
time when the determination process is operating properly. Also, results of
two laboratories determining the same sample should agree within 0.13 mg P/£
95 percent of the time when both laboratory determination processes are in
control.
It is felt that at least half of. the difference in. ther repeatability and
reproducibility values is due to variability in analyst technique in perform-
ing the above listed operations.
3.1.1.2 Potential Errors in Determining Total Phosphorus, P. The quantity
of phosphorus in a sample at the time of collection can differ from the
determined value due to:
1. Contamination during sample handling and analysis,
2. Incomplete color development from the use of poor reagents and/or
inadequate temperature control during color development,
3. Error in the calibration curve,
4. Inprecision of"'thfe'spectrophotometer, including reading errors.
These sources of variability are estimated to account for less than
half of the total determination 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 contamination would act as a positive bias.
3.1.2 Variance Analysis
Many different factors may contribute to the variability of a deter-
mination method, for example:
34
-------
1. The analyst,
2. Apparatus and reagents used,
3. Equipment calibration,
4. The environment (temperature, humidity, pollutant concentration,
etc.).
The variability will be larger when the determinations to be compared
are performed by different analysts and/or with different equipment than
when they are carried out by a single analyst using the same equipment.
Many different measures of variability are conceivable according to the
circumstances under which the determinations are performed.
Only two extreme situations will be discussed here. They are:
1. Repeatability, r, ds the value below which the absolute difference
between duplicate results 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..
2. Reproducibility, R, is the value below which the absolute difference
between two determinations made on the same sample by different
analysts-1 in-different laboratories using different equipment may be
expected to fall with a 95 percent probability.
The above definitions are based on a statistical model according to which
each determination is the sum of three components:
P = P + b + e (2)
c
where
P = the measured value, mg P/£,
P = the general average, mg P/£,
b = an error term representing the differences:between laboratories,
mg P/l,
e = a random error occurring in each determination, mg P/£.
In general, b can be considered as the sum
b = b + b (3)
r s
35
-------
where b is a random component and b a systematic component. The term
IT S
b is considered to be constant during any series of determinations performed
under repeatability conditions, but to behave as a random variate in a
series of determinations performed under reproducibility conditions. Its
variance will be denoted as
var b = OL , (4)
the between-laboratory variance including the between-analyst and between-
equipment variabilities.
The term, e, represents a random error occurring in each determination. Its
variance
2
var e = a
will be called the repeatability variance.
For the above model the repeatability, r, and the reproducibility, R, are
given by
r = 1.96 »/2 a = 2.77 a (5)
and R = 2.77Jcr2 + a2 = 2.77 o_ . (6)
/ v IT Li K.
where cr_. will be referred to as the reproducibility variance.
K.
Values of a and a can be obtained from the values of repeatability and
r K
reproducibility respectively as given for the reference method in the Federal
Register (see appendix A). The repeatability, r, is given as 0.05 mg P/£ for
concentrations below about 1.3 mg P/&. Using this value in equation (5)
gives a = 0.018 mg P/£. Reproducibility is given as R = 0.13 mg P/£ then from
equation (6) an = 0.047 mg P/£.
R ' - o
As can be seen the reproducibility standard deviation is larger by almost
a factor of 3 than the repeatability standard deviation. It is felt this
large difference is due primarily to differences in analyst techniques for
performing the operations (listed in subsection 3.1.1.1) contributing to the
variability in determining the true sample volume. From equation (1) the
-------
coefficient of variation of P is given by
CV{P } = JcV2{P } + CV2{V} (7)
c i m
and the standard deviation then is
CT{P } = CV{P } x p .
c c c
From the discussion in subsection 3.1.1.2, it can be assumed that for
repeatability conditions the variability in determining the total phosphorus
content in a gasoline sample in mg P/£ is primarily due to the variability
in the spectrophotometer. This should be relatively small, say on the •
order of o{Pm> = 0.1 yg P. Then taking O{PC> = ar = 0.018 mg P/£ and
using values of P = 1.3 mg P/£, Pffi = 13 yg P and V = 10 ml, equation (7)
gives
CV{V} = 0.012 ,
and at V = 10 ml,
o{V} = 0.12 ml .
If the above assumptions are reasonable, then it is obvious that control
actions should be directed toward the operations listed in subsection 3.1.1.1
as the most effective means of controlling and assuring data of acceptable
quality.
3.1.3 Bias Analysis
There are no data available for estimating the bias of the deter-
mination process. However, most of the error sources listed in the previous
subsections act as positive biases. Therefore, it would seem reasonable to
assume that in general, the determined results will be higher than the actual
values. The bias could be evaluated by measuring reference samples if and
when they become available.
Assuming that the true or acceptable value, P , of a sample is known,
then from equation (2)
P - PT = T (8)
which represents the bias of the determination method. An estimate of the
bias can be obtained from audit results as discussed in section 3.3.
37
-------
3.2 COLLECTION OF INFORMATION 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. Certain visual and operational checks
can be performed by the analyst while the measurements are being made to
help insure the generation of data of acceptable quality. These checks
are written as part of the routine operating procedures in section II.
The use of control charts is recommended as a method for monitoring
and documenting the performance level of the determination process. Recom-
mended quality control charts are:
1. A cdntrol chart for duplicate results to monitor analyst technique
and equipment stability,
2. A control chart for the determination of standard solutions to
monitor calibration stability.
A sample control chart for each of the above parameters with suggested
limits is given in the following subsections. Control charts are discussed
in textbooks, such as refs. 11 and 12.
3.2.1 Control Chart for Duplicates ' ' '
A sample control chart for -the difference in duplicate measurements of
"•*• *:
a gasoline sample is given in figure 7. It is recommended tKat a duplicate
determination be made once a week or once for every 40 samples analyzed,
whichever occurs first. The second determination should be separated by at
least 2 days or 20 samples from the original determination.
Take the absolute difference in the duplicates and plot the point on
the graph of figure 7. Connect each point to the previously plotted point
by a straight line. A point falling outside the UCL indicates that an
actual change has occurred in the determination process. Such a change could
be due to poor technique, equipment change, and/or sample deterioration.
As long as the plotted points remain within the UCL, the determination process
is considered in contrbl and I no action is required.
When a point falls outside the UCL, a quick check would be to prepare
and measure a standard sample of about the same absorbance to check the
phosphorus calibration curve. If the calibration curve has not changed, the
38
-------
Q. _
Check No.
Date
Analyst
Problem and
corrective
action
* UCL = R+ 3d3 or = 0.02 + 3(0.853)(0.018) = 0.066
t R=cl,or = 1.128 X 0.018 = 0.02
Figure 7. Sample quality control chart for duplicate determinations of gasoline samples.
39
-------
most likely cause of the excess variability is poor technique. The sample
should be measured again after reviewing the analysis procedures. Plot
the difference in the original and third determinations and if it is below
the UCL continue the operation.
3.2.2 Control Chart for Standard Samples
Duplicate determinations of a standard sample should agree closer
than duplicate determinations of a gasoline sample because a major portion
of variability due to analyst technique is eliminated. The calibration
curve should be suspect if the determined value of a standard sample differs
more than 0.4 yg P from its known value. This value is taken as the action
limit in constructing a sample control chart for the differences in the
determined value and the known v.alue of standard samples (fig. 8). As each
standard sample is determined the difference should be computed and plotted
on the graph. Each point is connected to the previously plotted point with
a straight line. Corrective action such as cleaning the glassware, preparing
new standard solutions, and/or recalibrating the spectrophotometer should be
taken anytime:
• 1. One point falls outside the action limits.
2. Two out of three points fall between the warning and action lines, and
3. Seven consecutive points fall on the same side of the average or
zero line.
Analysis of gasoline samples should not be attempted until a atandard sample
can be measured to within ±0.4 yg P.
3.3 INDEPENDENT PERFORMANCE AUDIT
If implemented properly an independent audit can be used to evaluate
the total determination process through the use of reference samples. A
reference sample; is defined as a gasoline sample whose phosphorus content
is accurately known (preferably NBS certified) to the auditors but unknown
to the analyst being audited. Results from an audit provides an independent
assessment of data quality by providing a means of estimating the precision
and bias of the reported results.
3.3.1 Procedure for Performing A Quality Audit
The individual or organization responsible for performing the audit
should obtain a supply of gasoline samples with known phosphorus concentrations.
40
-------
•a
a
•a
B O.
i a
8
g
Action limit
Warning limits
0.4
0.5
Warning Lim its
Action Limit
LCL
Check No.
Date
Analyst
Problem and
corrective
action
i I I i 1 I i i i i ^
1
2
3
4
5
6
7
8
t
9
10
* UCL = 3o = 0.04 ng P (estimated, not derived from actual data)
t Warning Limit = 2o = 2.7
Figure 8. Sample control chart for the determination of standard samples.
41
-------
Samples should be placed in sample containers identical to the containers
used in the field. If possible the reference sample should not be dis-
tinguishable from regular field samples. These reference samples should
be shipped or delivered to the analysis laboratory in the same manner that
is used for field samples.
3.3.2 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. The repeatability and reproducibility of this method
appear small enough to indicate that precision of the method will not be
a big problem. 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 of a minimum of once a week or everytime a
field sample exceeds the Federal standard is required. For an analyst
analyzing about 8 samples a day, this would result in a minimum of 13' audits
per calendar quarter. If the data for the first audit period indicate that
only good quality data are being reported the auditing level could be reduced
but probably should not be lower than six to seven audits per calendar
quarter.
3.4 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 determinations. The second consideration is that of
testing the data quality against given standards using sampling by vari-
ables. For example, lower/ and upper limits, L and U, may be selected to
include a large percentage of the determinations and outside of which it is
desired to control the percentage of determinations to, say, less than 10
^percent. If the data quality is not consistent with 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 and/or feasible.
42
-------
3.4.1 Estimating the Precision/Accuracy of the Reported Data
This section will indicate how the audit data collected in accor-
dance with the procedure described in section 3.3.1 will be utilized to
estimate the precision and accuracy of the determination of interest.
Similar techniques can also be used by a specific firm or laboratory to
assess their or its own determinations. The audit data collected as a
I
result of following the procedures in the previous section are the
determined and known values of P and the difference.
c
d. = P . - P .
J cj aj
where P . = Determined value of phosphorus in the reference sample,
mg P/£,
P . = Known value of phosphorus in the reference sample, mg P/£, and
aj
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,
n
d = ^ d./n,
j=l J
and
1)1
n - 1 J
1/2
3.4.2 Statistical Tests
The mean d is an estimate of the relative bias in the determinations
(i.e., relative to the known or accepted value). Assuming the audit value
to be unbiased, the existence of a bias "in the laboratory datancan be
checked by the appropriate t-test, i.e.^
t
n - 1
, <—
s ,//n
d
See ref. 13 for a discussion of the t-test. If t is significantly
large in absolute values, i.e., greater than the tabulated value of t with
43
-------
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, its calculated
value will be reported with the laboratory data for that audit period.
The standard deviation, s,, is a function of both the standard devia-
Q
tion of the laboratory determinations and of precision with which the
reference sample value is known. Assuming the reference sample values are
known with much greater precision than the laboratory determinations, then
the calculated s, is an estimate of the standard deviation of the laboratory
determination. Table 2, contains an example calculation of d and s,,
starting with the differences for a sample size of n = 12.
The calculated-standard deviation can then be utilized to check the
reasonableness of the assumption made in subsection 3.1.2 concerning
a {P } = a = 0.047 mg P/A, under reproducibility conditions. The calculated
C K
standard deviation, s , may be directly checked against the assumed value,
cr_, by using the statistical test procedure
K
2
X2 Sd
f ~o2{P>
c
2
where X /f is the value of a random variable having the chi-square distri-
2
bution with f = n - 1 degrees of freedom. If X /f is larger than the
tabulated value exceeded only 5 percent of the time, then 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, standard deviation, s,,.the number of audits, n, and the total number of
determination periods (number of days analyses were performed) N, sample
(n _<_ N). Estimates$Hive>» s, and d, which are significantly different
44
-------
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 P = 1.30 mg P/£ for one of the N field tests not
audited, then that determination would be reported as
1. Determined value, P = 1.30 mg P/t
2. Calculated bias, d = T = -0.133 mg P/£
3. Calculated standard deviation, a{P } = s = 0.12 mg P/£
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.
o
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 determined by the percent of determination deviations outside
prescribed limits, it is accessary to use the approach described below.
3.4.3 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., see
refs. 13-17. The discussion below will be given in regard to the specific
problem herein which has some unique features as compared with the usual
variable sampling plans.
The difference between the analyst-determined and the known value of P
is designated as d., and the mean difference over n audits by d, that is,
-------
Table 2. Computation of mean difference, d, and
standard deviation of differences, s.
General Formulas
. d'PdJ-P.J
dl dl
d2 d2
d3 d2
d4 d4
d5 d5
d6 d6
d7 d7
dfi ds
o o
d9 d9
dio dio
dll dll
d!2 d!2
zd2
d = Ed./n
22.
„ Ed. — (Zd.) /n
2 j n
Sd ~ n - 1
Specific Example
Data (mg P/&)
-0.05 0.0025
-0.02 0.0004
0.00 0.0000
-0.03 0.0009
-0.06 0.0036
0.01 0.0001
0.02 0.0004
-0.03 0.0009
-0.04 0.0016 .
0.01 0.0001
-0.03 0.0009
o-.oo o.oooo
-0.16 0.0114
d = -0.133
a n m /,£.i
s — u.ujmoj
d
s, = /T sj = 0.12 mg P/£
d s, d •
46
-------
n
d = - 2
Theoretically, Pc. and Pa. should be measures of the same phosphorous
«J J
concentration, and their difference should have a mean of zero on the
average. In addition, their differences should have a standard deviation
approximately equal to that associated with determinations of P separately.
Assuming three standard-deviation limits (using the assumed a{P } =
0.047 mg P/& as derived in the variance analysis of subsection
3.1.2), the values -3(0.047) = 0.141 mg P/& and 3(0.047) = 0.141 mg P/£
define lower and upper limits, L and U, respectively, outside of which it
is desired to control the proportion of differences, d.. Following the
method given in ref. 14, a procedure for applying the variables sampling
plan is described below. Figures 9 and 10 illustrate examples of satis-
factory and unsatisfactory data quality with respect to the prescribed
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 percent of the individual differences outside L and U) and if the
sample size n = 12, then the value of k can be obtained from table 2 of ref.
14. The values of d and s, 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 with the
following criteria:
1. If both of the following conditions are satisfied:
d - k sd >_ L = - 0.141 mg P/£
d + k s, < U = 0.141 mg P/£
Q ~—
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 defi-
ciencies exist in the determination process as carried out for that
47
-------
p = Pl + p < 0.10
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.
48
-------
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 = -0.133 - (2.045)(0.12) = - 0.38
-------
SECTION IV
1. "Standard Method of Test for Phosphorous In Gasoline," American
Society for Testing and Materials, Method D 3231-73 (1973).
2. M. G. Mellon and R. E. Kitson. Ind. Eng. Chem., Anal.•Ed. 16,
466 (1944).
3. M. E. Griffing e^ al. Anal. Chem. 32. 374 (1960).
4. I. M. Kolthoff et^ al_. Quantitative Chemical Analysis. 4th ed.
Toronto, Ontario: The MacMillan Co., 1969.
5. F. D. Snell and C. T. Snell. Colorimetric Methods of Analysis,
3rd ed., Vol. II. New York: Van Nostrand, 1949, pp. 630-81.
6. D. F. Boltz and M. G. Mellon. Anal. Chem. 19, 873 (1947).
7. H. H. Willard and L. J. Center. Ind. Eng. Chem., Anal. Ed. 13, 81
(1941).
8. J. R. Woods and M. G. Mellon, Ibid., 13, 760 (1941).
9. Natl. Bur. Std. Circ. 434, 1941; 602, 1959.
10. H. H. Willard et_ a^. Instrumental Methods of Analysis, 4th ed.
New York: D. Van Nostrand Co., Inc., 1965, p. 153.
11. E. L. Grant and R. S. Leavenworth. Statistical Quality Control,
4th ed. St. Louis: McGraw-Hill, 1972.
.an
12. D. A. Simons. Practical Quality Control. Reading, Mass.: Addison-
Wesley Publishing Company, 1970. pp. 131-150.
13. A. Raid. Statistical Theory with Engineering Applications. New York:
John Wiley and Sons, 1952.
14. D. B. Owen. "Variables Sampling Plans Based on the Normal Distribu-
tion." Technometrics 9, No. 3 (August 1967).
15. D. B. Owen. "Summary of Recent Work on Variables Acceptance Sampling
with emphasis on Non-normality." Technometrics 11 (1969):631-37.
16. Kinji Takogi. "On Designing Unknown Sigma Sampling Plans Based on a
Wide Class of Non-Normal Distributions." Technometrics 14 (1972):
669-78. ' "' '
17. C. Eisenhart, M. Hastay, and W. A. Wallis, eds. Techniques of Statistical
Analysis. Statistical Research Group, Columbia, University.
New York: McGraw-Hill, 1947.
50
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APPENDIX A
TEST FOR THE DETERMINATION OF PHOSPHORUS
IN GASOLINE
FEDERAL REGISTER, VOL 39, NO. 131—MONDAY, JULY 8, 1974
APPENDIX A
.TEST FOR THE DETERMINATION OF PHOSPHORUS
' .IN GASOLINE
1. Scope. 1.1 This method was developed
for the determination of phosphorus gen-
erally present as pentavalent phosphate
esters or salts, • or both, In gasoline. This
method Is applicable for the determination
of phosphorus in the range from 0.0008 to
0.15 g P/U.S. gal. or 0.2 to 49 mg P/lltre.
2. . Applicable documents. 2.1 ASTM
Standards:
D 1100 Specification for Filter Paper fog
Use In Chemical Analysis.
8. Summary of method. 3.1 Organic mat-
ter In the sample Is decomposed by Ignition
in the presence of zinc oxide. The residue
Is dissolved In sulfurtc acid and reacted with
ammonium molybdate and hydrazlne sulfate.
The absorbance of the "Molybdenum Blue"
complex Is proportional to the phosphorus
concentration In the sample and Is read at
approximately 820 nm In a E-cm cell.
4. Apparatus. 4.1 Buret, 10-ml capacity,
0.06-ml subdivisions.
4.2 Constant-Temperature Bath, equipped
to hold several 100-ml volumetric flasks sub-
merged to the mark. Bath must have a large
enough reservoir or heat capacity to keep
the temperature at 180 to 190* F (82.2 to
87.8* C) during the entire period of sample
heating.
NOTE 1: If the temperature of the hot
water bath drops below 180* F (82.2° C) the
color development may not be complete.
4.3 Cooling Bath, equipped to hold several
100-ml volumetric flasks submerged to the
mark In ice water.
4.4 Filter Paper, for quantitative analysis,
Class O for fine precipitates as defined In
Specification O 1100.
4.5 Ignition -Dish—Coors porcelain evap-
orating dish, glazed Inside and outside, with
pourout (size no. OOA, diameter 76mm. ca-.
paclty 70 ml).
4.6 Spectrophotometer, equipped with a
tungsten lamp, a red-sensitive phototube
capable of operating at 830 nm and with ab-
sorption cells that have a 5-cm light path.
4.7 Thermometer, range 50 to 200* F (10
to 105' C). >
4.8 Volumetric Flask, 100-ml with ground-.
glass stopper. "
4.9 Volumetric Flask, 1000-ml with ground-
glass stopper.
.4.10 Syringe, Luer-Lok, 10-ml equipped,
with 6-cm. 22-gage needle.
5. Reagents. 6.1 Purity of Reagents—Re-
agent grade chemicals shall be used in all
tests. Unless otherwise Indicated, it Is In-
tended that all reagents' shall conform to
the specifications of the Committee on Ana-
lytical Reagents of the American Chemical
Society, where such specifications are avail-
able. Other grades may be used, provided It
Is first ascertained that the reagent is of
sufficiently high.purity to permit its use
without lessening the accuracy of the deter-'
initiation.
6.2 Purity of Water—Unless otherwise In-
dicated, references to water shall be under-
stood to mean distilled water or water of
equal purity.
6.3 Ammonium Molybdate Solution—Using
graduated cylinders for measurement add
slowly (Note 2), with continuous stirring,
226 ml of concentrated sulfurlc acid to 600
ml of water contained In a beaker placed In
a bath of cold water. Cool to room tempera-
ture and add 20 g of ammonium molybdate
tetrahydrate ((NH4)^to,OM-4H2O). Stir until,
solution is complete and transfer to a 1000-
ml flask. Dilute to the mark with water.
NOTE 2: Wear a face shield,, rubber gloves.
and a rubber apron when adding concen-
trated sulfurlc acid to water.
6.4 Hydrazlne Sulfate Solution—Dissolve
1.6 of hydrazlne sulfate (H1NNH1-H1SO1) In
1 litre of water, measured with a graduated
cylinder.
NOTE 3: This solution Is not stable. Keep It
tightly stoppered and in the dark. Prepare a
fresh solution after 3 weeks.
5.6 Molybdate-Hydraztne Reagent—Pipet
25 ml of ammonium molybdate solution Into
a 100-ml volumetric flask, containing ap-
proximately 60. ml of water, add by pipet
10 ml'Of NjNNH.-HjSO, solution, and dilute
to 100 ml with water.
NOTE 4: This reagent Is unstable and
should be used within about 4 h. Prepare It
immediately before use. Each determination
(including the blank-) uses 60 ml.
6.6 Phosphorus, Standard Solution (10.0
pS P/ml)— Pipet 10 ml of stock standard
phosphorus solution into a 1000-ml volu-
metric flask and dilute to the mark with
water.
6.7 Phosphorus, Stock Standard Solution
(1.00 mg P/ml)—Dry approximately 6 g of
potaslum dlhydrogen phosphate (KHjPOO
In an oven at 221 to 230* F (106 to 110* O)
for'8 h. Dissolve 4.393±0.002 g of the reagent
In 150 ml, measured with a graduated
cylinder, of H^SO.O + IO) contained In a
1000-ml volumetric flask. Dilute with water
to the mark.
6.8 Sulfurlc Acid (1 + 10)—Using gradu-
ated cylinders for measurement add slowly
(Note 2), with continuous stirring, 100-ml of
concentrated sulfurlc acid (H,SOJ, sp gr 1.84)
to 1 litre of water contained In a beaker
placed In a bath of cold water.
5.9 Zinc Oxide.
Non '5: High-bulk density zinc oxide may
cause spattering. Density of approximately
0.6 g/cm» has been found satisfactory.
6. Calibration. 6.1 Transfer by buret, or a
volumetric transfer pipet, 0.0, 0.6, 1.0,1.5, 2.0,
3.0, 3.6, and 4.0 ml of phosphorus standard
soultlon Into 100-ml volumetric flasks.
0.2 Pipet 10 ml of H,SO. (1 + 10) Into each
flask. Mix Immediately by swirling. '
6.3 Prepare the molybdate-hydrazlne so-
lution. Prepare sufficient volume of reagent
based on the number of samples being ana-
lyzed.
51
-------
6.4 Pipet 50 ml of the molybdate-hydra-
Elne solution to each volumetric flask. Mix'
Immediately by swirling.
6.5 Dilute to 100 ml with water.
6.6 Mix well and place In the constant-
temperature bath BO that the contents of the
flask are submerged below the level of the
bath. Maintain bath temperature at 180 to
180°P (822 to 87.8'C) for 25 mln (Note 1).
6.7 Transfer the flask to the cooling bath
and cool the contents rapidly to room tem-
perature. Do not allow the samples to cool
more than 6'F (2.8°C) below room tempera-
ture.
NOTTS 6: Place a chemically clean thermom-
eter In one of the flasks to check the tem-
perature.
6.8 After cooling the flasks to room tern-,
perature, remove them from the cooling
water bath and allow them to stand for 10
mln at room temperature.
63 Using the 2.0-ml phosphorus standard
In a 5-cm cell, determine the wavelength
near 820 nm that gives maximum absorbance.
The wavelength giving maximum absorbance
should not exceed 830nm.
6.9.1 Using a red-sensitive phototube and
5-cm cells, adjust the spectrophotometer to
zero absorbance at the wavelength of maxi-
mum absorbance using distilled water In
both cells. Use the wavelength of maximum
absorbance In the determination of calibra-
tion readings and future sample readings.
6.9.2 The use of 1-cm cells for the higher
concentrations Is permissible.
6.10 Measure the absorbance of each cali-
bration sample Including the blank (0.0 ml
phosphorus standard) at the wavelength of
maximum absorbance with distilled water in
the reference cell.
NOTE 7: Great care must be taken to avoid
possible contamination. If the absorbance of
the blank exceeds 0.04 (for 6-cm cell), check
for source of contamination. It Is suggested
that the results be disregarded and the test
be rerun with fresh reagents and clean glass-
ware.
6.11 Correct the absorbance of each stand-
ard solution by subtracting the absorbance
of the blank (0 ml phosphorus standard).
6.12 Prepare a calibration curve by plot-
ting the corrected absorbance of each stand-
ard solution against mlcrograms of phos-
phorus. One mlllllltre of phosphorus stand-
ard solution provides 10 Mg of phosphorus.
7. Sampling. 7.1 Selection of the size of
the sample to be tested depends on the ex-
pected concentration of phosphorous In {he
sample. If a concentration of phosphorus la
suspected to be less than 0.0038 g/gal (1.0
mg/Utre), It will be necessary to use 10 ml
of sample.
NOTE 8: Two grams of zinc oxide cannot ab-
sorb this volume of gasoline. Therefore the
10-ml sample Is Ignited In allquota of 2 ml in
the presence bf 2 g of zinc oxide.
12 The following'table serves as a guide
for selecting sample size:
Phosphorus. ' Equivalent, grams Sample
milligrams per liter • per gallon rite,
mllllUter
an to0.15..;
1.3 to 20 ,... O.OOS to 0.076..
0.0 to 13 0.0037 to O.OS..
lorless_. 0.0038 or less..
1.00
2.70
3.00
10.00
8. Procedure. 8.1 Transfer 2±0.3 g of zlno
oxide into a conical pile in a clean, dry, un-
etched Ignition dish.
NOTE 9: In order to obtain satisfactory ac-
curacy with the small amounts of phosphorus
Involved, it is necessary to take extensive pre-
cautions in handling. The usual precautions
of cleanliness, careful manipulation, and
avoidance of cortemlnatlcn should be
scrupulously observed; also, all glassware
should be cleaned before use, with cleaning
acid or by some procedure that does not
Involve use of commercial detergents. These
compounds often contain alkali phosphates
which are strongly adsorbed by glass surfaces
and are not removed by. ordinary rinsing. It
is desirable to segregate a special stock of
glassware for use only in the determination
of phosphorus.
8.2 Ma a deep depression' In the center
of the z' oxide pile with a stirring rod.
8.3 Pipet the gasoline sample (Note 10)
(see 72 for suggested sample volume) Into
the depression in the zinc oxide. Record the
temperature of the fuel If the phosphorus
content Is required at 60° F (16.6° C) and
make correction as directed in 9.2.
NOTE 10: For the 10-ml sample use multiple
additions and a syringe. Hold the tip of the
needle at approximately % of the depth of
the -zinc oxide layer and slowly deliver 2 ml
of the sample: fast sample delivery may give
low results. Give sufficient time for the gaso-
line to be absorbed by the zinc oxide. Follow
step 8.6. Cool the dish to room temperature.
Repeat steps 8.3 and 8.6 until all the sample
has been burned. Safety—cool the Ignition
dish before adding the additional aliquots
of gasoline to avoid a flash fire.
8.4 Cover the sample with a small amount
of fresh zinc oxide from reagent bottle (use
the tip of a small spatula to deliver approx-
imately 0.2 g). Tap the sides of the Ignition
dish to pack the zinc oxide.
8.5 Prepare the blank, using the same
amount of zinc oxide In an Ignition dish.
8.6 Ignite the gasoline, using the flame
from a bunsen burner. Allow the gasoline
to burn to extinction (NOTE 10).
8.7 Place the Ignition dishes containing
the sample and blank in a hot muffle furnace
set at a temperature of 1150 to 1300* F
(621 to 704° C) for 10 mln. Remove and cool
the Ignition dishes. When cool gently tap the
sides of the dish to loosen the zinc oxide.
Again place the dishes In the muffle furnace
for 6 min. Remove and cool the ignition
dishes to room temperature. The above treat-
ment Is usually sufficient to burn the carbon.
If the carbon Is not completely burned off
place the dish into the oven for. further
6-mln. periods.
NOTE 11: step 8.7 may also be accomplished
by heating the ignition dish with a Meker
burner gradually increasing the Intensity
of heat until the carbon from the sides of
the dish has been burned, then cool to
room temperature. .
8.8 Pipet 26 ml of H.SO. (1 + 10) to each
ignition dish. While plpetlng, carefully wash
all traces of zinc oxide from the sides of the
Ignition dish.
8.9 Cover the Ignition dish with a boro-
slllcate watch glass and warm the ignition
dish on a hot plate until the zinc oxide is
completely dissolved.
8.10 Transfer the solution through filter
paper to a 100-ml volumetric flask. Rinse the
watch glass and the dish several times with
distilled water (do not exceed 25 ml) and
transfer the washings through the filter
paper to the volumetric flask.
8.11 Prepare the molybdate-hydrazlne so-
lution.
8.12 Add 60 ml of the molybdate-hydra-
zlne solution by plpet to each 100-ml volu-
metric flask. Mix Immediately by swirling.
8.13 Dilute to 100 ml with water and mix
well. Remove stoppers from flasks after mix-
ing. .
8.14 "Place the 100-ml flasks In the oon-
stant-temperature bath for 25 mln so that
the contents of the flasks are below the
liquid level of the bath. The temperature of
the bath should be 180 to 190°P (88.2 to
87.8-C) (Non 1).
-------
8.1S Transfer the 100-ml flasks to the
cooling bath and cool the contents rapidly to
room temperature (NOTE 6).
8.16 Allow the samples to stand at room
temperature before measuring the absorb-
ance.
NOTE 12: The color developed is stable for
at least 4 h.
8.17 Set the epeotrophotometer to the
wavelength of maximum absorbance as deter-
mined In 6.9. Adjust the spectrophotometer
to zero absorbance, using distilled water In
both cells.
8.18 Measure the absorbance of the
samples at the wavelength of maximum ab-
sorbance with distilled water In the reference
cell.
8.19 Subtract the absorbance of the blank
from the absorbance of each sample (NOTE
7).
8.20 Determine the mlcrograms of phos-
phorous In the sample, using the calibration
curve from 6.12 and the corrected absorbance.
9. Calculations. 9.1 Calculate the milli-
grams of phosphorus per litre of sample as
follows:
P, mg/lltre=P/V
where:
P=mlcrograms of phosphorus read from
calibration curve, and
Vrrmlllllltres of gasoline sample.
To convert to grams of phosphorus per UJ5.
gallon of sample, multiply mg P/lltre by
0.0038.
9.2 If the gasoline sample was taken at a
temperature other than 60*F (15.6'C) make
the following temperature correction:
mg P/lltre at 15.6'C
= [mgp/iitreatt][l+0.001 (t-
where:
t=observed temperature of the gasoline,
•C.
9.3 Concentrations below 3.5 mg/Utre or
0.01 g/gal should be reported to the nearest
0.01 mg/lltre or 0.0001 g/U.S. gal.
9.S.1 For higher concentrations, report re-
sults to the nearest 1 mg P/lltre or 0.008 g
P/TT.S. gal.
10. Precisian. 10.1 The following criteria
should be used for Judging the acceptability
of results (95 percent confidence):
10.2 Repeatability—Duplicate results by
the same operator should be considered sus-
pect If they differ by more than the follow-
ing amounts:
g P/UJS. gal (mg
P/litre)
0,0008 to 0.005 (0.3 to
1.3).
0.005 to 0.18 (1.8 to
40)
10.3 Eeproduclblllty—The results sub-
mitted by each of two laboratories should
not be considered suspect unless they differ
by more than the following amounts:
Repeatability
0.0005 g P/DJ9. gal
(0.13 mg P/lltre),
13% of the mean.
g P/V-S. gal (mg
P/litre)
0.0008 to 0.005 (0.2 to
1.3).
0.005 to 0.15 (1.3 to
40)
Rcproducibilitg
0.0002 g P/0.S. gal
(0.05 mg P/lltre).
7% of the mean.
-------
FEDERAL REGISTER, VOL. 39, NO, 135—FRIDAY, JULY 12, 1974
Title 40—Protection of Environment
CHAPTER I—ENVIRONMENTAL
PROTECTION AGENCY
SUBCHAFTER C—AIR PROGRAMS
PART 80—REGULATIONS OF FUELS AND
FUEL ADDITIVES
- Lead and Phosphorus Test Procedures
Correction
In FB Doc. 74-15449 appearing at page
24890 In the Issue of Monday, July 8,
1974, make the following changes:
1. On page 24891:
a. In the seventeenth line of the first
paragraph In the first column, the word
"result" should read."results".
b. In the first line of paragraph 4.7
hi the third column, the figure "200"
should read "220".
2. On page 24892:
a. In paragraph 6. In the first column,
the word "solultlon" in the last line.
should read "solution".
b. In the table in the second column.
the second figure "2.70", under the bead-
ing "Sample size, millillter", should read
"2.00".
c. The formula under the heading "Re-
peatability" in the third column should
be transferred to appear under the
heading ".Reproducibility", which ap-
peared in the first column on page 24893
and the formula which appeared under
the heading "Reproducibilitv" should be
transferred to appear under the heading
"Repeatability". The formulas should
read as follows:
Repeatability
0.0002 g P/TJJ3. gal
(0.06 mg P/lltre)
7% of the mean
neproducibllitu
0.0005 g P/TT.S. .gal
(0.13 mg P/lltre)
18% of the mean
3. In the second'column on page 24893,
delete the word, "and" which appeared
in the fifth HnVbf paragraph 4.11.
54
-------
APPENDIX B GLOSSARY OF SYMBOLS
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
cm Cubic centimeter
cm Centimeter
gal Gallon
g Gram
h Hour
£ liter
m£ Milliliter
mm Millimeter
nm Nanometer
P Phosphorus
sp gr Specific gravity
p Micron
yg . Microgram
/ Per
N Lot size—i.e., the number of determination periods to be
treated as a group
n Sample size for the quality audit (section 3,3)
r Repeatability of the measurement method at the 95-percent
confidence level
o{X} Assumed standard deviation of the parameter X (population
*
standard deviation)
s Computed standard deviation of a finite sample of
A
measurements (sample standard deviation)
Pv Assumed mean value of the parameter X (population mean)
A
X Computed average of a finite sample of determinations
(sample mean)
f>.
TV Computed bias of the parameter X for a finite sample
A
(sample bias)
55
-------
APPENDIX B
GLOSSARY OF SYMBOLS-CONTINUED
SYMBOL
R
R
k
p{Y}
0
r
°R
Vl
L
U
CL
LCL
UCL
P
c
P
m
DEFINITION
Reproduclbility of the determination method (section 3.0)
Range; i.e., the difference in duplicate determinations of
a gasoline sample (section 3.2)
The difference in the audit value and the determined value
arrived at by the analyst for the j audit
Mean difference between known and determined values of
reference samples for n audits.
Computed standard deviation of difference between known
and determined values.
Percent of determinations outside specified limits L and U
(section 3.4)
Constant used in sampling variables (section 3.4)
Probability of event Y occurring
Repeatability standard deviation
Reproducibility standard deviation'
Statistic used to determine if the sample bias, d, is
significantly different from zero (t-test)
2
Statistic used to determine if the sample variance, s ,
2
is significantly different from the assumed variance, a ,
of the parent distribution (chi-square test)
Lower quality limit used in sampling by variables
Upper quality limit used in sampling by variables
Center line of a quality control chart
Lower control limit of a quality control chart
Upper control limits %>-f*3a ^quality control chart
Determined phosphorus in a gasoline sample in yg P/l
ToLtal phosphorus°asr'readlrgrom the calibration curve in
yg P
56
-------
APPENDIX C
GLOSSARY OF TERMS
The following glossary lists and defines the terms as used in this
document
Absorbance
Accuracy
Bias
Chain of custody
label
Determination
method
Determination
process
Liter
Lot
Population
Precision
Quality audit
Quality control
check
The logarithm to the base 10 of the reciprocal of
transmittance.
A measure of the error of a process expressed as a
comparison between the measured value and the true
value.
The systematic or nonrandom component of system
error.
The seal placed on the container which contains
the gasoline sample from the test station.
A set of procedures for making a determination.
The process of making a determination including
method, personnel, equipment, and environmental
conditions.
Special name for. the cubic decimeter.
A specified number of objects to be treated as a
group.
A very large number of like objects (i.e., measure-
ments, checks, etc.) from which the true mean and
standard deviation can be deduced with a high degree
of accuracy.
The degree of variation among measurements on a
homogeneous material under controlled conditions
and usually jexpressedi ascra standard deviation or
as a coefficient of variation.
A management*: Ftool for independently assessing data
quality.
Checks made by the operator on certain items of
equipment and procedures to assure data of good
quality.
57
-------
APPENDIX C
GLOSSARY OF TERMS (CONTINUED)
Reference sample
Sample
Spectral
bandwidth
Standard sample
Test station
Sample submitted to the laboratory for quality con-
trol check (concentration unknown to the analyst).
Objects drawn usually at random from the lot for
checking.
The range of wavelengths between the two points
at which the absorbance is one-half the peak
absorbance.
Sample prepared by the technician from the stock
standard solution to check the phosphorus cali-
bration curve.
Retailer gasoline station or distributor serving
the public.
58
-------
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
nanometer (nm)
milligrams (mg) of
phosphorus/liter
degree Celsius (°C)
absorbance (A)
MULTIPLY BY
0.001
0.1
-7
micron (y)
Angstrom (A)
centimeter (cm) 10
g of phosphorus/gal 0.0038
degree Fahrenheit (°F) °F =
transmittance (T) T = 10
(1.8)(°C) + 32
-A
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.
59
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-6 50 A-7l*-00 5-1
3. RECIPIENT'S ACCESSIOF+NO.
4. TITLE AND SUBTITLE
Guidelines for Development of a Quality Assurance
Program: Volume XII - Determination of Phosphorus
in Gasoline.
5. REPORT DATE
November 1Q7U
6/PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Daniel E. Gilbert, Denny E. Wagoner, Franklin Smith
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Research Triangle Institute
P.O. Box 12191*
Research Triangle Park, North Carolina 27709
10. PROGRAM ELEMENT NO.
1HA327
11. CONTRACT/GRANT NO.
68-02-123H
12. SPONSORING AGENCY NAME AND ADDRESS
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D. C. 20U60
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This document presents guidelines for developing a quality assurance program for
the determination of phosphorus in gasoline "by the Federal reference method. These
guidelines include:
1. Recommended operating practices and techniques,
2. Procedures for assessing performance and qualifying data, and
3. Procedures for identifying trouble and improving data quality.
This document is an operations manual, designed for use by laboratory personnel.
17.
KE.Y WOR.DS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COS AT I Field/Group
Quality Assurance
Quality Control
Air Pollution
Gasoline
Phosphorus
13H
13B
21D
7B
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (ThisReport/
unclassified
21. NO. OF PAGES
66
20. SECURITY CLASS (Thispage)
unclassified
22. PRICE
EPA Form 2220-1 (9-73)
60
U.S. GOVERNMENT PRINTING OFFICE: 1975 - 640-880/645 - Region
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