EPA-R4-72-003 Environmental Monitoring Series
September 1972
Analyses for Mercury in Water
A PRELIMINARY STUDY OF METHODS
National Environmental Research Center
Office of Research and Monitoring
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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95OR72006
EPA-R4-72-003
September 1972
ANALYSES FOR MERCURY IN WATER
A PRELIMINARY STUDY OF METHODS
John A. Winter and Harold A. Clements
Method and Performance Evaluation Activity
The Analytical Quality Control Laboratory
1014 Broadway, Cincinnati, Ohio 45202
Program Element 1H1327
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND MONITORING
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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FOREWORD
To find, through research, the means to protect, preserve, and
iJnprove our environment, we need a focus that accents the interplay
among the components of our physical environment -- the air, water,
and land. The missions of the National Environmental Research
Centers -- in Cincinnati, Research Triangle Park, N.C., Corvallis,
Oregon, and Las Vegas, Nevada -- provide this focus. The research
and monitoring activities at these centers reflect multidisciplinary
approaches to environmental problems; they provide for the study of
the effects of environmental contamination on man and the ecological
cycle and the search for systems that prevent contamination and
recover valuable resources.
Man and his supporting envelope of air, water, and land must
be protected from the multiple adverse effects of pesticides, radia-
tion, noise, and other forms of pollution as well as poor management
of solid waste. These separate pollution problems can receive inter-
related solutions through the framework of our research programs --
programs directed to one goal -- a clean livable environment.
This publication of the National Environmental Research Center,
Cincinnati, entitled: AnaZyees for MereJUry in Water~ A Pl'eZimina:ry
Method Study reports the results of a broad study of methods currently
in use in the United States and Canada for analysis of mercury in
waters. Federal agencies, states, municipalities, universities,
private laboratories, and industry should find this comparative study
of methods of analysis for mercury of vital importance in their efforts
at monitoring and controlling mercury pollution in the environment.
ANDREW W. BREIDENBACH, Ph.D.
Director, National Environmental
Research Center, Cincinnati
iii
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PREFACE
The Office of Research and Monitoring, EPA, coordinates the
collection of water quality data to determine compliance with water
quality standards, to provide information for planning of water
resources development, to determine the effectiveness of pollution
abatement procedures, and to assist in research activities.
In a
large measure, the success of the pollution control program rests
upon the reliability of the information provided by the data
collection activities.
The Analytical Quality Control Laboratory, NERC, Cincinnati,
is responsible for insuring the reliability of physical, chemical,
biological, and microbiological data generated in the water programs
of EPA.
Within the Analytical Quality Control Laboratory, the
Method and Performance Evaluation (M&PE) Activity conducts the inter-
laboratory studies of analytical procedures to:
1)
2)
assist in the selection of EPA methods,
evaluate the selected methods of analyses, and
3)
measure the performance of EPA analysts and laboratories.
This report describes one study in the series conducted by the
M&PE Activity.
v
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Staff of the
Method and Performance Evaluation Activity, Analytical Quality Control Laboratory
John A. Winter, Chief
Harold A. Clements, Senior
Guy F. Simes, Chemist
Everett L. Barnett, Chemist
Betty J. Smith, Secretary
Chemist
vi.i.
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Table of Contents
FOREWORD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PREF ACE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
........ .... .... ........
Staff, Method and Performance Evaluation Activity.
.. ........... ...... .....
PARTICIPATING LABORATORIES................................................
S~ARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IN1'RODUCT I ON. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DESCRIPTION OF THE STUDY..................................................
Samp 1 e De 5 i gn. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
....................
Preparation of Samples and Reporting of Results......................
True Values......................
. ..... ...... .............. ..... .....
Study P Ian and Anal yt ical Method.....................................
RESULTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Raw Data[[[
TREArrMENT OF DATA[[[
Statistical Summary...
.. .......... ............ .... ...... ........ .....
Rejection of Outliers.
..... ..... ... .............. .... ........ ........
DISCUSSION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CONCLUSIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
APPENDIX A.
EPA Method for Mercury in Water. April
1972. . . . . . . . . . . . . . . . .
APPENDIX B.
Details on Other Method
(non-EPA) . . . . . . . . . . . . . . . . . . . . . . . . . . .
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PARTICIPATING LABORATORIES
Forty-two analysts in 42 laboratories reported results of the analyses
of the mercury reference samples.
Of the 42 laboratories, 32 were non-EPA
laboratories.
The participating laboratories were:
u.S. Environmental Protection Agency Laboratories
Advanced Waste Treatment Research Laboratory
National Environmental Research Center
Cincinnati, Ohio
Analytical Quality Control Laboratory
Trace Metals Analyses Group
National Environmental Research Center
Cincinnati, Ohio
National Field Investigations Center
Office of Enforcement & General Counsel
Cincinnati, Ohio
Edison Water Quality Research Laboratory
National Environmental Research Center
Edison, New Jersey
Indiana District Office
Region V
Evansville, Indiana
National Water Quality Laboratory
Duluth, Minnesota
Pacific Northwest Environmental Research Laboratory
National Environmental Research Center
Corvallis, Oregon
Southeast Environmental Research Laboratory
National Environmental Research Center
Athens, Georgia
Surveillance & Analysis Division
Technical Support Branch
Region IX
Alameda, California
Wheeling Field Station
Region III
Wheeling, West Virginia
~
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Non-EPA Laboratories
Bohna Engineering & Research, Inc.
San Francisco, California
Deer Island Treatment Plant
Winthrop, Massachusetts
Diamond Shamrock Chemical Company
Painesville, Ohio
Diamond Shamrock Chemical Company
Sheffield, Alabama
Division of Water Resources
Charleston, West Virginia
E. I. du Pont de Nemours & Co. (Inc.)
Savannah River Laboratory
Aiken, South Carolina
E. I. du Pont de Nemours & Co. (Inc.)
Savannah River Plant, Lab. Division
Aiken, South Carolina
Georgia Kraft Research Company
Rome, Georgia
Georgia-Pacific Corporation
Bellingham Division
Bellingham, Washington
Georgia Water Quality Control Board
Atlanta, Georgia
Instrumentation Laboratory, Inc.
Lexington, Massachusetts
International Paper Company
Mobile, Alabama
Massachusetts Division of Fish & Game
Westborough, Massachusetts
Milwaukee Department of Public Works
Milwaukee, Wisconsin
Monsanto Corporation
Sauget, Illinois
National Council of Paper Industry
for Air & Stream Pollution
Gainesville, Florida
Water Quality Control Laboratory
Stanford University
Stanford, California
New Hampshire Water Supply & Pollution
Control Commission
Pesticide Surveillance Laboratory
Concord, New Hampshire
North Carolina Department of Water
& Air Resources
Raleigh, North Carolina
North Carolina State Board of Health
Laboratory Division
Raleigh, North Carolina
Oregon State Department of Environmental
Quality
Portland, Oregon
South Carolina Pollution Control
Authority
Columbia, South Carolina
T. W. Beak Consultants Limited
Toronto, Canada
Texas A & M University
Agriculture Analytical Service
College Station, Texas
Toms River Chemical Corporation
Toms River, New Jersey
U. S. Geological Survey
Denver, Colorado
U. S. Geological Survey
Ocala, Florida
Union Oil Company
Los Angeles Refinery
Wilmington, California
University of Illinois
College of Agriculture
Urbana, Illinois
University of Missouri
Environmental Trace Substances Center
Columbia, Missouri
Water Pollution Research Laboratory
Stevenage, England
Westvaco Research Center
Laurel, Maryland
xi
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ANALYSES FOR MERCURY IN WATER, A PRELIMINARY METHOD STUDY
SUMMARY
The Analytical Quality Control Laboratory, National Environmental Research
Center--Cincinnati, of the U.S. Environmental Protection Agency (EPA), conducted
a preliminary interlaboratory study on analysis of organic and inorganic mercury
by the cold vapor technique.
Sample concentrates were prepared at four mercury levels and furnished to
the analysts with the known values.
Analysts added an aliquot of each concentrate
to distilled water and to a surface water of their choice.
Single analyses
were made on the distilled and on the surface water samples with and without
the known increments, using the EPA Method and another of their choice (Other
Method).
Recoveries were compared.
The accuracy and precision of the methods
were noted as were interferences from natural water samples.
In this comparative study of the EPA Method and Other Method, the
EPA Method was equal or superior to the Other Method in accuracy and precision
in 80% of all tests.
More significantly, in those samples containing organic
mercury with or without inorganic mercury, the EPA Method was equal or superior
to the Other Method.
This study indicates that if water samples contain mercury
in organic form, a method
involving a vigorous digestion step such as that in
the EPA Method must be used to obtain a good recovery.
On pages xiv and xv a
statistical summary of this data shows the precision and accuracy measurements
obtained in this study.
xiii
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Statistical Summary
Recovery of Inorganic Mercury (HgCI2) from Distilled Waters
Sample 1 Sample 2
EPA Other EPA Other
Method Method Method Method
True Value, ~g/liter 0.34 0.34 4.2 4.2
Mean Recovery, ~g/liter 0.341 0.409 3.94 3.86
Accuracy as %
Relative Error (Bias) 0.3 20.2 -6.3 -8.0
Standard Deviation, ~g/liter 0.07 0.16 0.54 0.77
Relative Deviation, % 19.5 40.0 13.6 19.9
Range, ~g/liter 0.32 0.80 2.5 3.6
Recovery of Inorganic Mercury OfgC12) from Natural Waters
Sample 1 Sample 2
EPA Other EPA Other
Method Method Method Method
True Value, ~g/liter 0.34 0.34 4.2 4.2
Mean Recovery, ~g/liter
(By Difference) 0.351 0.369 3.99 4.34
Accuracy as %
Relative Error (Bias) 3.2 8.5 -5.1 3.3
Standard Deviation, ~g/liter 0.07 0.12 0.66 0.60
Relative Deviation, % 19.8 31.5 16.6 13.8
Range, ~g/liter 0.25 0.40 3.3 2.2
xiv
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Statistical Summary
Recovery of Organic and Inorganic Mercury (Phenyl Mercuric Acetate-HgC12)
from Distilled Waters
Sample 3 Sample 4
Organic & Inorganic Mercury Organic Mercury Alone
EPA Other EPA Other
Method Method Method Method
True Value, ~g/liter 6.3 6.3 4.2 4.2
Mean Recovery, ~g/liter 6.10 5.23 4.02 3.02
Accuracy as %
Relative Error -3.1 -17.0 -4.2 -28.0
Standard Deviation, ~g/ 1i ter 0.68 1.45 0.80 1.53
Relative Deviation, % 11.2 27.8 19.8 50.7
Range, ~g/1iter 4.0 7.0 4.5 4.8
Recovery of Organic and Inorganic Mercury (Phenyl Mercuric Acetate-HgC12)
from Natural Waters
Sample 3
Organic & Inorganic Mercury
EPA Other
Method Method
Sample 4
Organic Mercury Alone
EPA Other
Method Method
True Value, ~g/liter
6.3
6.3
4.2
4.2
Mean Recovery, ~g/liter
(By Difference)
5.61
6.15
3.83
3.30
Accuracy as %
Relative Error
Standard Deviation, ~g/liter
-10.9 -2.4 -8.7 -21. 4
1.27 1.06 1.07 1.48
22.7 17.2 27.9 45.0
5.3 3.8 5.3 4.1
Relative Deviation, %
Range, ~g/ 1i ter
xv
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1
INTRODUCTION
This preliminary study on methods of analysis for mercury in water
was conducted to develop further information on the ability of the
analytical methods to measure total mercury, i.e., organic plus inorganic
mercury.
It differs from formal method studies in that the analysts received
the true value data with the samples.
The main purpose of the study was
to make a preliminary comparison of methods for mercury analysis performed
with known concentrations of organic and inorganic mercury added to distilled
and natural water samples.
Analysts used different digestion reagents,
different volumes of reagents and varied the times and temperatures and
separation techniques.
The mercury concentration was detected and measured
by cold vapor technique using an atomic absorption spectrophotometer, Coleman
mercury meter or UVjvisible spectrophotometer.
One laboratory used an
emission spectrographic procedure.
It should be pointed out that the Other Method(s) used in this study
are really the methods of choice of the laboratories participating in the
study.
As these methods are those in routine use, familiarity and confidence
in the procedures would tend to favor the Other Method over the proposed
EPA procedure in some laboratories.
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2
DESCRIPTION OF STUDY
Sample Design
In this comparison of methods for mercury analyses, the test design was
as follows:
1.
Each sample was prepared as a stable concentrate in a sealed glass
ampul.
2.
When an aliquot of the concentrate was diluted to volume, the
mercury was present at levels found in waters and wastewater.
Several levels of concentration were tested to cover the range
of levels found in surface waters and wastewater.
3.
The sample concentrates containing known increments of organic
and/or inorganic forms of mercury were added to distilled water
and to a surface water of choice and the samples analyzed.
The
surface waters were analyzed with and without increments and the
added level determined by difference.
4.
Recoveries in distilled and surface waters were compared.
Precision,
accuracy and interferences were noted.
Preparation of Samples and Reporting of Results
Four water sample concentrates were prepared by dissolving weighed
amounts of reagent-grade chemicals in ASTM reagent-grade distilled water
to produce accurately-known concentrations of organic and inorganic mercury.
The concentrates were preserved with 0.15% nitric acid, and were checked
for stability by repeated analyses over a period of three months.
These
analyses verified the concentration and stability of each solution.
Further
confirmation of the true values was achieved with analyses by an
independent Teferee laboratory.
The true values are shown in Table 1.
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3
Table 1
True Values for Parameters*
When diluted in distilled water according to instructions, the water
samples contained the following concentrations of mercury:
Sample Mercury Form Concentration, ~g/liter
1 Mercuric Chloride 0.34
2 Mercuric Chloride 4.2
3 Mercuric Chloride
+ Phenyl Mercuric Acetate 3.15 + 3.15
4 Phenyl Mercuric Acetate 4.2
*The concentration given are those calculated and added.
on analyses which are used for verification only.
These are not based
Since dilution of the concentrates renders the acid ineffective as a
preservative, the analyst was instructed to add 1.5 ml of redistilled acid/liter
in sample make-up.
Study Plan and Analytical Method
The mercury samples were announced in a September 8, 1970 memorandum.
Cards were included with the invitation with which laboratories could request
samples.
On September 28 and 29, 1970, the first series of samples were
mailed to requesting laboratories.
Since these samples were announced again
through the quarterly AQCL Newsletter and by word of mouth, requests for
samples were received over the next 12 months.
Each requesting laboratory
was sent a set(s) of four ampuls, instructions for sample preparation,
duplicated report sheets and a statement of true values.
Because many labora-
tories are interested in efficiency of different digestion procedures used to
convert organic mercury prior to analysis, the Analytical Quality Control
Laboratory requested that data be returned from all laboratories for
preparation of an informal report to all participants.
A cut-off date of
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5
September 30. 1971 was set and all data returned to M&PE by that date are
included in this report.
The data obtained using the basic EPA Method (acid-permanganate-persulfate
oxidation) are combined.
Because the many laboratories used almost as many
method variations. there was not sufficient data to statistically- treat these
method results separately.
Therefore, all data obtained by methods other
than the EPA Method are combined as "Other Method".
However, anyone who
wishes, can retrieve any segment of data obtained using an other method and
make a separate comparison with recoveries by the EPA Method.
Each method
is specified as clearly as possible without identifying the laboratory.
The
number of significant figures used are equal to the true values which contain
two figures, or to one significant figure if so reported by the laboratory.
Any reported "less than" values were accepted but could not be used in the
computerized evaluation.
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6
RESULTS
Raw Data
The test results are reported by sample in Tables 2, 3, 4, and 5, using a
numbering of the laboratories and analysts in the order in which the data were
received.
For distilled water samples, a simple listing is given of 1abora-
tories and analysts with their reported values.
For the natural water samples,
values determined by difference were reported by each analyst and because spiking
995 m1 of natural water with 5 m1 of sample concentrate causes a 0.5% dilution
change, the reported values for natural waters were reduced by this amount
whenever significant.
To avoid premature round-off errors in computer ca1cu1a-
tions four digits were carried in the statistical tables.
However, a maximum
of two significant figures was used for all final values based on the number of
significant figures in the increment values.
When values containing only one
significant figure were returned by an analyzing laboratory, these figures are
reported as received.
It should be noted that the provisional EPA Method
as used in this study
included acid and permanganate plus potassium persu1fate to improve oxidation,
but no heating step.
However, later data have shown that heating is required
to recover methyl mercury chloride from natural waters.
The approved EPA Method now includes an acid-permanganate-persu1fate
oxidation procedure and heat, prior to reduction, to assure conversion of all
organic mercury compounds to ionic form before AA measurement.
It is given in
Appendix A and is further described in: Kopp, J. F., Longbottom, M. C., and
Lobring, L. B., " 'Cold Vapor' Method for the Determination of Mercury," JAWWA,
Vol. 64, No.1, January, 1972, pp. 20-25.
However, the heating step was not
needed to recover 100% of the particular inorganic and organic mercury compounds
used in this study.
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7
Because the analytical methods, other than EPA, varied in the kinds and
concentration of oxidizing reagent, time and temperature of oxidation, etc.,
each laboratory was asked to describe its method in detail or to furnish a
complete published reference to it.
This information is given in Appendix B.
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TABLE 2
Average Recoveries of Increment; 0.34 ~g of Inorganic Mercury/liter, (Sample 1)
Concentration, ~g/liter
Distilled Water Natural Water Description
Laboratory EPA Other EPA Other of
Code Method Method Method Method Other Method
1 <0.5 0.3 Ag wire deposition
2 0.48 Sulfuric, nitric, and
perch10ric acid reflux
3 0.52 0.39 Acid perrnanganate
4 0.2 0.2 CdS pad
5 0.4 0.3 Cu wire deposition
6 0.33 0.34 0.35 Perrnanganate
7 0.40 0.42 0.36 Acid perrnanganate
8 0.3 0.4 Acid perrnanganate
(overnight)
9 <0.5 <0.5
10 0.3 0.5 0.3 Acid perrnanganate
11 1)0.25 0.35 l)Acid persu1fate
at 55 C
2)0.45 2)Acid persu1fate
at 75 C
12 0.3 0.5 0.3 0.3 Acid perrnanganate
13 0.4 0.4
14 0.32
15 0.38 0.31 Acid + heat
16 0.4 0.3
17 0.25 0.3
18 .33 Acid perrnanganate
19 0.30 0.30
20 0.56 Acid, perrnanganate,
and persu1fate with
heating
21 <0.5 <0.5 Acid perrnangante
22 <0.5 <0.5
23 0.35 0.55
24 0.35
25 0.38 0.34
26 0.33
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TABLE 2 contd.
Average Recoveries of Increment; 0.34 ~g of Inorganic Mercury/liter, (Sample 1)
Concentration, pg/1iter
Distilled Water Natural Water Description
Laboratory EPA Other EPA Other of
Code Method Method Method Method Other Method
27 0.35 0.35
28 1)0.6 l)Acid permanganate (DOW)
2)0.8 2)Acid permanganate +
KBr (Modified DOW)
29 0.4
30 0.32 0.32 Acid permanganate
31 1)0.40 1)0.40 l)Acid permanganate (DOW)
2)0.60 2)0.60 2)Acid permanganate +
KBr (Modified DOW)
32 0.2 0 (Sewage Sample)
33 .28
34 1)<1. 0 1)<1.0 1)<1.0 1)<1.0 l)Acid permanganate
2) <1. 0 2)<1.0 2) <1. 0 2)<1.0 2)Acid permanganate
(Tap Water)
35 0.31
36 0.34 Stannous chloride
reduction
37 0.31
39 0.5 Acid permanganate
40 0.0 0.4 Acid, peroxide, and
permanganate
41 0.59 Acid permanganate
42 0.30 Modified DOW
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TABLE 3
Average Recoveries of Increment; 4.2 ~g of Inorganic Mercury/liter, (Sample 2)
Concentration, ~g/liter
Distilled Water Natural Water Description
Laboratory EPA Other EPA Other of
Code Method Method Method Method Other Method
1 4.0 4.3 Silver wire
deposition
2 4.4 Sulfuric, nitric,
and perchloric
acid reflux
3 4.2 3.9 Acid permanganate
4 4 3 CdS pad
5 4.5 4.4 Copper wire
deposition
6 3.86 3.99 3.90 Permanganate
7 3.81 4.2 4.1 Acid permanganate
8 4.0 4.0 Acid permanganate
(overnight)
9 4.5 4.5
10 3.8 5.1 3.0 Acid permanganate
11 1)3.55 4.90 l)Acid persulfate
at 55 C
2)4.30 l)Acid persulfate
at 75 C
12 3.6 3.5 3.9 4.0 Acid permanganate
(Tap Water)
13 4.5 4.2
14 4.4
15 2.0 2.0 Acid + heat
16 4.3 4.0
17 3.4 3.9
18 4.1 Acid permanganate
19 4.3 3.7
20 4.1 Acid, permanganate,
and persulfate
21 3.8 3.2 Acid permanganate
22 4.2 4.0
23 3.50 3.94
25 3.1 4.1
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TABLE 3 contd.
Average Recoveries of Increment; 4.2 ~g of Inorganic Mercury/liter, (Sample 2)
Concentration, ~g/liter
Laboratory
Code
26
27
Distilled 'Water
EPA Other
Method Method
4.2
4.30
Natural Water
EPA Other
Method Method
Description
of
Other Method
4.30
28
1)3.5
2)4.1
l)Acid permanganate (DOW)
2)Acid permanganate +
KBr (Modified DOW)
29
30
4.3
4.3
4.1
Acid permanganate
31
1)4.1
2)4.1
1)4.6
2)4.3
l)Acid permanganate (DOW)
2)Acid permanganate +
KBr (Modified DOW)
32
4.2
2.1 (Sewage Sample)
33
4.2
34
1)4.4
2)4.2
1)4.3
2)4.6
1)4.4 1)4.6
2)5.4 2)5.2
(Tap Water)
Acid permanganate
Acid permanganate
35
4.1
36
4.1
3.9
3.13 1)3.08
2) 2 . 72
3)3.69
1.5
4.0
4.6
4.4
Stannous chloride
reduction
37
38
l)Acid permanganate
2)Acid only
3)Acid only
39
40
4.4
Acid permanganate
Acid, peroxide,
and permanganate
41
42
Acid permanganate
Modified DOW
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12
TABLE 4
Average Recoveries of Increment; 6.3 ~g of Inorganic and Organic Mercury/liter
(Sample 3)
Concentration, ~g/liter
Distilled Water Natural Water Description
Laboratory EPA Other EPA Other of
Code Method Method Method Method Other Method
1 6.0 5.1 Ag wire deposition
2 6.7 Sulfuric, nitric,
and perch10ric acid
reflux
3 6.8 5.0
4 4 6 CdS pad
5 7.0 7.0 Cu wire deposition
6 6.20 3.57 5.96 Permanganate
7 6.0 4.6 6.6 Permanganate
8 4.8 4.8 Acid permanganate
(overnight)
9 7.0 7.0
10 5.8 4.1 4.4 Perman2anate
11 1)5.40 5.40 l)Acid persu1fate
at 55 C
2)6.20 2)Acid persu1fate
at 75 C
12 5.6 6.4 6.3 6.4 Acid permanganate
(Tap Water)
13 6.2 4.2
14 6.2
15 6.9 5.7 Acid + heat
16 6.4 5.4
17 5.8 5.6
18 6.3 Acid permanganate
19 6.1 5.5
20 6.4 Acid, permanganate,
and persu1fate
21 6.0 3.7 Acid permanganate
22 6.5 5.8
23 5.44 5.13
25 6.0 6.8 ...
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13
TABLE 4 contd.
Average Recoveries of Increment; 6.3 ~g of Inorganic and Organic Mercury/liter
(Sample 3)
Concentration, ~g/liter
Distilled Water Natural Water Description
Laboratory EPA Other EPA Other of
Code Method Method Method Method Other' Method
26 6.1
27 6.50 6.50
28 1)3.0 l)Acid permanganate (DOW)
2)6.1 2)Acid permanganate +
KBr (Modified DOW)
29 8.0
30 5.6 6.2 Acid permanganate
31 1)5.8 1)4.4 1)5.6 l)Acid permanganate (DOW)
2)8.7 2)6.9 2)8.6 2)Acid, permanganate +
KBr (Modified DOW)
32 6.2 1.7 (Sewage Sample)
33 6.0
34 1)4.0 1)3.6 1)5.9 1)6.0 l)Acid permanganate
2)5.2 2)5.4 2)7.0 2)6.3 2)Acid permanganate
35 6.1
36 5.9
37 6.4
38 5.33 Acid
39 1.7 Acid permanganate
40 4.9 5.4
41 5.9 Acid permanganate
42 6.2 3.8 Modified DOW
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14
TABLE 5
Average Recoveries of Increment; 4.2 ~g of Organic Mercury/liter, (Sample 4)
Concentration, pg/1iter
Distilled Water NatUral Water Description
Laboratory EPA Other EPA Other of
Code Method Method Method Method Other Method
1 4.2 0.8 Ag wire deposition
2 4.8 Sulfuric, nitric and
perch10ric acid reflux
3 4.3 4.1
4 4 4 CdS pad
5 4.4 4.2 Cu wire deposition
6 4.30 0.60 3.90 Permanganate
7 4.3 3.0 4.4 Acid permanganate
8 2.3 3.2 Acid permanganate
(overnight)
9 5.5 5.5
10 4.2 0.7 3.5 Acid perman2anate
11 1)3.70 3.20 l)Acid persu1fate
at 55 C
2)4.65 2)Acid persu1fate
at 75 C
12 4.2 4.2 4.3 4.6 Acid permanganate
(Tap Water)
13 4.6 3.8
14 3.9
15 4.7 3.9 Acid and heat
16 4.2 2.9
17 4.0 4.0
18 4.2 Acid permanganate
19 4.1 3.6
20 4.4 Acid, permanganate,
and persu1fate with
heating
21 4.1 0.6 Acid permanganate
22 4.3 4.0
23 3.50 3.31
25 4.3 4.5
-------
15
TABLE 5 contd.
Average Recoveries of Increment; 4.2 ~g of Organic Mercury/liter, (Sample 4)
Concentration, ~g/liter
Distilled Water Natural Water Description
Laboratory EPA Other EPA Other of
Code Method Method Method Method Other Method
26 4.3
27 4.10 4.10
28 1)0.7 l)Acid permanganate (DOW)
2)3.7 2)Acid permanganate +
KBr (Modified DOW)
29 5.0
30 4.1 4.4 Acid permanganate
31 1)1.0 1)0.6 l)Acid permanganate (DOW)
2)4.6 2)4.1 2)Acid permanganate +
KBr (Modified DOW)
32 3.8 0.2 (Sewage Sample)
33 4.2 Acid permanganate
34 1)1.0 1)<1. 0 1)4.4 1)3.7 l)Acid permanganate
2)3.0 2) 2.9 2)4.6 2)4.7 2)Acid permanganate
(Tap Water)
35 4.2
36 3.3
37 4.2
38 2.58 1)2.81 l)Acid permanganate
2)2.64 2)Acid
3)2.89 3) Acid
39 2.8 Acid permanganate
40 3.9 0.7 Acid, peroxide,
and permanganate
41 5.4 Acid permanganate
42 4.1 0.7 Modified DOW
-------
16
TREATMENT OF DATA
Statistical Summary
Complete statistical summaries are given in pages 18 thru 33.
Each sample
is discussed in turn with the data displayed by type of water sample and method
of analysis.
A statistical evaluation is provided for each concentration with
each set of sample-test conditions.
In addition to the statistical measurements. all data are ranked in ascending
order and are presented in a histogram using~ cell divisions.
histogram represents one analytical result for 1-15 values/cell.
Each X in the
When more than
15 values occur per cell. only 15 X's are printed and the number of values
included in the cell is printed at the base of the cell.
With the exception of accuracy. the statistical parameters: number of values,
true values, mean, range, variance, standard deviation, 95% confidence limit,
and relative deviation (coefficient of variation) are based on all of the data
received. without rejection.
Accuracy is based on retained data. that is the
data remaining after rejection of outliers.
Rejection of Outliers
To determine the accuracy of each method. it was necessary to remove
those extreme values which had only a small chance of validity and which
would make a significant change in the reported accuracy.
These values
were probably caused by gross instrumental. chemical or human error and
were rejected by applying the two-tail t-test to all values at a 99% probability
level; that is. with a 99 to 1 assurance that the data rejected were invalid
and should be rejected.
Each rejected value is indicated in the statistical
summaries by laboratory and analyst with a capital letter "R". after the
value.
-------
17
A greater spread of data round the true value causes rejection of fewer
outliers because a larger standard deviation in the denominator of the t-test
reduces the calculated t value and fewer extreme values are rejected as outliers.
Contrariwise, with better accuracy and precision, the t-test is more powerful and
more outliers are rejected.
However, the data rejected in either case are true
outliers and laboratories reporting such values should carefully review procedures
for the cause of inaccuracy.
A glossary of the statistical terms used in this
study is included at the end of this report on pages 57 and 58.
-------
J8 METHOD & PERFORMANCE EVALUATION, AQCl
PRELIMINARY STUDY, ANALYSES FOR MERCURY IN WATER
All DATA, All lABORATORIES
EPA METHOD
RECOVERY OF INCREMENT FROM DISTillED WATER
AM PU l 1
INCREMENT =
0.34 pg/llter, INORGANIC MERCURY
N
TRUE VAL.
MEAN
MEDIAN
ACCURACY
21
0.34
0.34095
0.33000
0.28003
RANGE
VARIANCE
STD. OEV.
CONF. liM.
peT RELATIVE
0.32000 eOEF. VAR.
0.00443 SKEWNESS
0.06662 NO. OF CEllS
0.13058 (95 PCT)
ERROR, RETAINED DATA
0.19541
0.45532
4
DATA IN ASCENDING ORDER
MIDPOINT FREQ HISTOGRAM
0.2000 2 XX
0.3066 12 XXXXXXXXXXXX
0.4133 6 XXXXXX
0.5199 1 X
0.20
0.25
0.28
0.30
0.30
0.30
0.31
0.31
0.32
0.33
0.33
0.35
0.35
0.35
0.38
0.38
0.40
0.40
0.40
0.40
0.52
R REJECTED DATA
-------
METHOD & PERfORMANCE EVALUATION, AQCL
PRELIMINARY STUDY, ANALYSES fOR MERCURY IN WATER
19
ALL DATA, ALL LABORATORIES
EPA METHOD
RECOVERY OF INCREMENT FROM NATURAL WATER
AM PU L 1
INCREMENT =
0.34 ~g/1 iter, INORGANIC MERCURY
N
TRUE VAL.
MEAN
MEDIAN
ACCURACY
13
0.34
0.35076
0.34000
3.16737
RANGE
VARIANCE
STD. DEV.
CONF. LIM.
PCT RELATIVE
0.25000 CDEF. VAR.
0.00480 SKEWNESS
0.06933 NO. OF CELLS
0.13590 (95 PCT)
ERROR, RETAINED DATA
0.19761
1.92644
3
DATA IN ASCENDING ORDER
MIDPOINT
0.30
0.30
0.30
0.30
0.30
0.32
0.34
0.35
0.35
0.36
0.39
0.40
0.55
0.3000
0.4250
0.5500
FREQ
10
2
1
HISTOGKAM
xxxxxxxxxx
xx
X
R REJECTED DATA
-------
20
METHOD & PERFORMANCE EVALUATION, AQCL
PRELIMINARY STUDY, ANALYSES FOR MERCURY IN WATER
ALL DATA, ALL LABORATORIES
OTHER METHOD
RECOVERY OF INCREMENT FROM DISTILLED WATER
AM PU L 1
INCREMENT =
0.34 ~g/liter, INORGANIC MERCURY
N
TRUE VAL.
MEAN
MEDIAN
ACCURACY
24
0.34
0.40814
0.40000
20.22049
RANGE
VARIANCE
STD. oev.
CONF. LIM.
PCT RELATIVE
0.80000 COfF. VAR.
0.02619 SKEWNESS
0.16368 NO. OF CELLS
0.32082 (95 PCT)
ERROR, RETAINED DATA
0.40046
-0.01854
4
DATA IN ASCENDING ORDER
MIDPOINT FREQ HISTOGRAM
0.0000 1 X
0.2666 12 XXXXXXXXXXXX
0.5333 10 XXXXXXXXXX
0.8000 1 X
0.00
0.20
0.25
0.30
0.30
0.30
0.31
0.32
0.33
0.34
0.36
0.40
0.40
0.42
0.45
0.48
0.50
0.50
0.50
0.56
0.59
0.60
0.60
0.80R
R REJECTED DATA
-------
METHOD & PERFORMANCE EVALUATION, AQCL
PRELIMINARY STUDY, ANALYSES FOR MERCURY IN WATER
ALL DATA, ALL LABORATORIES
OTHER METHOD
RECOVERY OF INCREMENT FROM NATURAL WATER
AMPU L 1
N
TRUE VAL.
MEAN
MEDIAN
ACCURACY
INCREMENT =
8
0.34
0.36874
0.31500
8.45584
0.34 Jjgl1 iter, I NORGAN I C MERCURY
RANGE
VARIANCE
STD. DEV.
eONF. LIM.
PCT RELATIVE
DATA IN ASCENDING ORDER
0.20
0.30
0.30
0.35
0.40
0.40
0.40
0.60
R REJECTED DATA
0.39999 eOEF. VAR.
0.01352 SKEWNESS
0.11630 NO. OF CELLS
0.22795 (95 peT)
ERROR, RETAINED DATA
MIDPOINT
FREQ
HISTOGRAM
0.2000
0.6000
4
4
xxxx
xxxx
21
0.31540
0.61914
2
-------
22
METHOD & PERFORMANCE EVALUATION, AQCl
PRELIMINARY STUDY, ANALYSES FOR MERCURY IN WATER
ALL DATA, ALL LABORATORIES
EPA METHOD
RECOVERY OF INCREMENT FROM DISTILLED WATER
AM PU L 2
INCREMENT =
4.2 \Jg/l i te r, I NORGAN I C MERCURY
N
TRUE VAL.
MEAN
MEDIAN
ACCURACY
28
4.2
3.93535
4.15000
-b.30110
RANGE
VARIANCE
STD. DEV.
CONF. LIM.
PCT RELATIVE
2.50000 COEF. VAR.
0.28664 SKEWNESS
0.53539 NO. OF CELLS
1.04937 (95 PCT)
ERROR, RETAINED DATA
0.13604
-1.92003
5
DATA IN ASCENDING ORDER
MIDPOINT FREO HISTOGRAM
2.0000 1 X
2.6250 0
3.2500 4 XXXX
3.8150 9 XXXXXXXXX
4.5000 14 XXXXXXXXXXXXXX
2.0R
3.1
3.1
3.4
3.5
3.b
3.8
3.8
3.8
3.8
3.9
4.0
4.1
4.1
4.2
4.2
4.2
4.2
4.2
4.2
4.3
4.3
4.3
4.3
4.3
4.4
4.5
4.5
R REJECTED DATA
-------
METHOD & PERFORMANCe EVALUATION, AQCL
PRELIMINARY STUDY, ANALYSES FOR MERCURY IN WATER
23
All DATA, All lABORATORIES
EPA METHOD
RECOVERY OF INCREMENT FROM NATURAL WATER
AM PU l 2
INCREMENT =
4.2 ~g/liter, INORGANIC MERCURY
N
TRUE VAL.
MEAN
MEDIAN
ACCURACY
18
4.2
3.98555
4.00000
-5.10581
RANGE
VARIANCE
STD. DEV.
CONF. LIM.
PCT KELATIVE
3.30000 COEF. VAR.
0.43646 SKEWNESS
0.66065 NO. OF CELLS
1.29481 (95 PCT)
ERROR, RETAINED DATA
0.16516
-0.95181
4
DATA IN ASCENDING ORDER
MIDPOINT FREQ HISTOGRAM
2.1000 1 x
3.2000 2 XX
4.3000 14 XXXXXXXXXXXXXX
5.3999 1 X
2.1R
3.0
3.7
3.9
3.9
3.9
3.9
3.9
4.0
4.0
4.1
4.1
4.2
4.3
4.4
4.4
4.5
5.4
R ~EJECTEO DATA
-------
24
METHOD & PERFORMANCE EVALUATION, AQCl
PRELIMINARY STUDY, ANALYSES FOR MERCURY IN WATER
ALL DATA, ALL LABORATORIES
OTHER METHOD
RECOVERY OF INCREMENT FROM DISTILLED WATER
AMPUL 2
INCREMENT =
4.2 ~g/liter, INORGANIC MERCURY
N
TRUE VAL.
MEAN
MEDIAN
ACCURACY
29
4.2
3.86309
4.10000
-8.02143
RANGE
VARIANCE
STD. DEV.
CONF. lIM.
PCT RELATIVE
3.59999 COEF. VAR.
0.58928 SKEWNESS
0.76164 NO. OF CELLS
1.50459 (95 PCT)
ERROR, RfTAINED DATA
0.19811
-1.48013
5
DATA IN ASCENDING ORDER
MIDPOINT FREQ HISTOGRAM
1.5000 1 X
2.4000 2 XX
3.2999 6 XXXXXX
4.1999 19 XXXXXXXXXXXXXXX
5.0999 1 X
1.5R
2.0R
2.1
3.0
3.2
3.5
3.5
3.5
3.6
3.9
4.0
4.0
4.0
4.1
4.1
4.1
4.1
4.1
4.1
4.2
4.3
4.3
4.3
4.4
4.4
4.5
4.6
4.6
5.1
R REJECTED DATA
-------
METHOD & PERFORMANCE EVALUATION, AQCL
PRELIMINARY STUDY, ANALYSES FOR MERCURY IN WATER
All DATA, All lABORATORIES
OTHER METHOD
RECOVERY OF INCREMENT FROM NATURAL WATER
AMPUL 2
N
TRUE: VAL.
MEAN
MEDIAN
ACCURACY
INCREMENT =
10
4.2
4.33999
4.40000
3.33327
4.2 ~g/liter, INORGANIC MERCURY
RANGE
VARIANCE
STD. DEV.
CONF. LIM.
PCT RELATIVE
DATA IN ASCENDING ORDER
3.0
4.0
4.0
4.3
4.4
4.4
4.6
4.6
4.9
5.2
R REJECTED DATA
2.20000 COEF. VAR.
0.35822 SKEwNESS
0.59851 NO. OF CELLS
1.17309 (95 PCT)
ERROR, RETAINED DATA
MIDPOINT
HISTOGRAM
FREQ
3.0000
4.1000
~.1999
1
7
2
x
xxxxxxx
xx
25
0.13790
-0.89451
3
-------
26
METHOD & PERFORMANCE EVALUATION, AQCL
PRELIMINARV STUDY, ANALVS~S FOR MERCURV IN WATER
ALL DATA, ALL LABORATORIES
EPA METHOD
RECOVERY OF INCREMENT FROM DISTILLED WATER
AMPUL 3
INCREMENT.
6.3 ~g/llter, ORGANIC + INORGANIC MERCURY
oN
TRUE VAL.
MEAN
MEDIAN
ACCURACV
28
6.3
6.10499
6.10000
-3.09521
RANGE
VARIANCE
STD. DEV.
CONF. LIM.
PCT RELATIVE
4.00000 COEF. VAR.
0.46351 SKEWNESS
0.68081 NO. OF CELLS
1.33440 (95 PCT)
ERROR, RETAINED DATA
0.11151
-0.25132
~
DATA IN ASCENDING ORDER
MIDPOINT fREQ HISTOGKAM
4.0900 1 X
5.0000 2 XX
6.0000 21 XXXXXXXXXXXXXXX
1.0000 3 XXX
8.0000 1 X
4.0R
5.2
5.4
5.6
5.6
5.8
5.8
5.9
6.0
6.0
6.0
6.0
6.0
6.1
6.1
6.1
6.2
6.2
6.2
6.2
6.4
6.4
6.5
6.5
6.8
6.9
1.0
8.0
R REJECTED DATA
-------
27
METHOD & PERFORMANCE EVALUATION, AOCl
PRELIMINARY STUDY, ANALYSES FOR MERCURY IN WATER
ALL DATA, ALL LABORATORIES
EPA METHOD
RECOVERY OF INCREMENT FROM NATURAL WATER
AM PU L 3
INCREMENT =
6.3 ~g/liter, ORGANIC + INORGANIC MERCURY
N
TRUE VAL.
ME:AN
MEDIAN
ACCURACY
18
6.3
5.61055
5.85000
-10.94361
RANGE
VARIANCE
STD. DEV.
CONF. liM.
PCT RELATIVE
5.30000 COEF. VAR.
1.61873 SKEWNESS
1.21229 NO. OF CELLS
2.49369 (95 PCT)
ERROR, RETAINED DATA
0.22616
-1.62836
4
DATA IN ASCE~DING ORDER
MIDPOINT FREQ HISTOGRAM
1.1000 1 X
3.4666 1 X
5.2333 9 XXXXXXXXX
1.0000 1 XXXXXXX
1.7R
4.2
4.4
5.0
5.1
5.4
5.5
5.6
5.8
5.9
5.9
6.2
6.3
6.5
6.6
6.8
7.0
1.0
R R.t:JECTED DATA
-------
28
METHOD & PERFORMANCE EVALUATION, AQCL
PRELIMINARY STUOY, ANALYSES FOR MERCURY IN WATER
ALL DATA, ALL LABORATORIES
OTHER METHOD
RECOVERY OF INCREMENT FROM DISTILLED WATER
AMPUL 3
INCREMENT =
6.3 ~g/liter, ORGANIC + INORGANIC MERCURY
N
TRUE VAL.
MEAN
MEDIAN
ACCURACY
29
6.3
5.23102
5.40000
-16.96711
RANGE
VARIANCE
STD. DEV.
eONF. LIM.
PCT RELATIVE
7.00000 COEF. VAR.
2.11163 SKEWNESS
1.45314 NO. OF CELLS
2.84816 (95 peT)
ERROR, RETAINED DATA
0.27779
-0.14497
5
DATA IN ASCENDING ORDER
MIDPOINT FREQ HISTOGRAM
1.7000 1 X
3.4499 7 XXXXXXX
5.1999 11 xxxxxxxx,xxx
6.9499 9 XXXXXXXXX
8.6999 1 X
1.1R
3.0
3.5
3.6
3.7
3.8
4.0
4.1
4.4
4.6
4.8
4.9
5.1
5.3
5.4
5.4
5.7
5.8
5.9
6.1
6.2
6.2
6.3
6.4
6.4
6.7
6.9
7.0
8.7
R REJECTED DATA
-------
METHOD & PERFORMANCE EVALUATION, AQCL
PRELIMINARY STUDY, ANALYSES FOR MERCURY IN WATER
ALL DATA, ALL '~BORATORIES
OTHER METHOD
RECOVERY OF INCREMENT FROM NATURAL WATER
AM PU L 3
N
TRUE VAL.
MEAN
MEDIAN
ACCURACY
INCREMENT =
10
6.3
6.14999
6.00000
-2.38091
29
6.3 ~g/lfter, ORGANIC + INORGANIC MERCURY
RANGE
VARIANCE
STD. DEV.
CONF.. LIM.
PCT RELATIVE
DATA IN ASCENDING ORDER
4.8
5.4
5.4
5.6
6.0
6.0
6.3
6.4
1.0
8.6
R REJECTED DATA
3.19999 COEF. VAR.
1.12211 SKEWNESS
1.05961 NO. OF CELLS
2.01683 (95 PCT)
ERROR, RETAINED DATA
MIDPOINT
HISTOGRAM
FREQ
4.8000
6.6999
8.6000
4
5
1
XXXX
XXXXX
X
0.11229
1.16116
3
-------
30 '
METHOD & PERFORMANCE EVALUATION, AQCl
PRELIMINARY STUDY, ANALYSES FOR MERCURY IN WATER
ALL DATA, ALL LABORATORIES
EPA METHOD
RECOVERY OF INCREMENT FROM DISTILLED WATER
AM PU L 4
INCREMENT.
4.2 ~g/ltter, ORGANIC MERCURY
N
TRUE VAL.
MEAN
MEDIAN
ACCURACY
29
4.2
4.02344
4.20000
-4.20312
RANGE
VARIANCE
STD. DEV.
CONF. lIM.
PCT RELATIVE
4.50000 COEF. VAR.
0.63394 SKEWNESS
0.19620 NO. OF CEllS
1.56056 (95 PCT»
ERROR, RETAINED DATA
0.19789
-1.91521
5
DATA IN ASCENDING ORDER
MIDPOINT FREQ HISTOGRAM
1.0000 1 X
2.1250 1 X
3.2500 4 XXXX
4.3150 21 XXXXXXXXXXXXXXX
5.5000 2 XX
1.OR
2.5
3.0
3.3
3.5
3.8
4.0
4.1
4.1
4.1
4.1
4.1
4.2
4.2
4.2
4.2
4.2
4.2
4.2
4.3
4.3
4.3
4.3
4.3
4.3
4.6
4.1
5.0
5.5
R REJECTED DATA
-------
31
METHOD & PERFORMANCE EVALUATION, AQCL
PRELIMINARY STUDY, A~ALYSES FOR MERCURY IN WATER
ALL DATA, ALL LABORATORIES
EPA METHOD
RECOVERY OF INCREMENT FROM NATURAL WATER
AM PU L 4
INCREMENT =
4.2 ~g/liter, ORGANIC MERCURY
N
TRUE VAL.
MEAN
MEDIAN
ACCURACY
18
4.2
3.83388
4.00000
-8.71698
RANGE
VARIANCE
STD. DEV.
CONF. LIM.
PCT RELATIVE
5.30000 COEf. VAR.
1.140~5 SKEWNESS
1.06796 NO. OF CELLS
2.09321 (95 PCT)
ERROR, RETAINED DATA
0.27855
-2.14235
4
DATA IN ASCENDING URDER
MIDPOINT FREQ HISTOGRAM
0.2000 1 X
1.9666 0
3.7333 16 XXXXXXXXXXXXXXX
5.5000 1 X
0.2R
2.9
3.3
3.5
3.6
3.8
3.9
3.9
4.0
4.0
4.1
4.1
4.3
4.4
4.4
4.5
4.6
5.5
R REJECTED DATA
-------
32
METHOD t PERFORMANCE EVALUATION, AQCL
PRELIMINARY STUDY, ANALYSES FOR MERCURY IN WATER
All DATA, All lABORATORIES
OTHER METHOD
RECOVERY OF INCREMENT FROM DISTillED WATER
AMPU l 4
INCREMENT =
4.2 ~g/1iter, ORGANIC MERCURY
N
TRUE VAL.
MEAN
MED IAN
ACCURACY
28
4.2
3.02464
3.35000
-27.98476
RANGE
VARIANCE
STD. DEV.
CONF. LIM.
PCT RELATIVE
4.80000 COfF. VAR.
2.35456 SKEWNESS
1.53445 NO. OF CELLS
3.00753 (95 PCT)
ERROR, RETAINED DATA
0.50731
-0.46796
5
DATA IN ASCENDING ORDER
MIDPOINT FREQ HISTOGRAM
0.6000 7 XXXXXXX
1.7999 1 X
3.0000 6 XXXXXX
4.1999 13 XXXXXXXXXXXXX
5.3999 1 X
0.6
0.6
0.7
0.7
0.7
0.8
1.0
2.3
2.6
2.8
2.8
2.8
2.9
3.0
3.7
3.1
3.9
3.9
4.0
4.2
4.2
4.4
4.4
4.4
4.6
4.6
4.8
5.4
R REJECTED DATA
-------
METHOD & PERFORMANCE EVALUATION, AQCl
PRELIMINARY STUDY, ANALYSES FOR MERCURY IN WATER
ALL DATA, ALL LABORATORIES
OTHER METHOD
RECOVERY OF INCREMENT FROM NATURAL WATER
AM PU L 4
N
TRUE VAL.
MEAN
MEDIAN
ACCURACY
INCREMENT =
10
4.2
3.29999
3.85000
-21.42860
4.2 ~g/1iter, ORGANIC MERCURY
RANGE
VARIANCE
STD. DEV.
CONF. LIM.
PCT RELATIVE
DATA IN ASCENDING ORDER
0.6
0.7
3.2
3.2
3.7
4.0
4.1
4.2
4.6
4.7
R REJECTED DATA
4.10000 COEF. VAR.
2.20222 SKEWNESS
1.48398 NO. OF CELLS
2.90861 (95 PCT)
ERROR, RETAINED DATA
MIDPOINT
0.6000
2.6500
4.6999
FREe
2
2
6
HISTOGRAM
xx
xx
xxx xxx
33
0.44969
-1.09921
3
-------
34
DISCUSSION
0.34 ~g/liter, Inorganic Mercury
At the 0.34 ~g inorganic mercury/liter level, the EPA Method was more
accurate and more precise in both distilled water and natural water.
Accuracies
of 0.3% positive bias for EPA Method and 20% positive bias for the Other Method
were found in distilled water and 3% and 8.5% positive bias in the natural waters
for these two methods, respectively.
Differences in precision were similar
in distilled and natural waters with 20% and 40% relative deviation for the
EPA and Other Method in distilled water, and 20% and 32% relative deviation
in natural waters for the two methods, respectively.
4.2 ~g/liter, Inorganic Mercury
At this 4.2 ~g/liter level, the EPA and Other Method showed low bias
values of 6% and 8% in distilled water and -5% and +3% in natural waters.
The precision values were similar for the two methods with relative deviations
of 14% and 20% in distilled water for the EPA and Other Method, respectively,
and 17% and 14% in natural waters for the two methods, respectively.
6.3 ~g/liter of Organic and Inorganic Mercury
This higher level of mercury made up of equal amounts of organic and
inorganic mercury showed negative bias of 3% and 17% in distilled water for
the EPA and Other Methods, respectively.
However, in natural water, the
negative bias values were reversed with 11% for the EPA Method and 2% for
the Other Method.
Likewise, precision as relative deviation was 11% for the EPA Method
and 28% for the Other Method in distilled water.
In natural waters the
EPA Method showed a 23% deviation while the Other Method showed a 17% deviation.
4.2 ~g/liter, Organic Mercury
The presence of only organic mercury as phenyl mercuric acetate
in the
fourth sample provided a rigorous test of the oxidation step in the methods
-------
35
since no mercury was measurable without conversion.
In distilled water, the
results showed a negative bias of 4% for the EPA Method and 28% for the Other
Method, and relative deviations of 20% and 51% for the EPA and Other Methods,
respectively.
In the natural water samples the results showed negative bias of 9% for
the EPA Method and 21% for the Other Method, and relative deviations of 28%
and 45% for the EPA and Other Methods, respectively.
This study was not intended to demonstrate the superiority of the EPA
Method for total mercury over all other methods.
However, the complete
variety of methods applied in this study has forced an evaluation only of
the EPA Method and other methods as a group.
The reader is urged to compare
recoveries by each of the methods in Tables 2, 3, 4, and 5.
He will note
that almost all methods used did recover inorganic mercury rather completely.
However, there was a divergence of results from the Other Method, with
samples containing organic mercury, into those which could and those which could
not recover the added levels.
In Table 5 reporting recoveries of 4.2 ~g/liter
of organic mercury, the copper wire deposition method of laboratory 5, the
acid permanganate of laboratory 12 and the acid permanganate and persulfate
of laboratory 20 obtained very good recovery from distilled water.
Laboratories
5 and 12 repeated their good recovery of organic mercury in natural waters and
were joined by laboratories 31 and 34.
Table 5 shows examples of poor recovery from distilled water samples where
laboratories 1, 6, 10, 21, and 42 had minimal recovery with their own method
and very good recovery with the EPA Method.
-------
36
CONCLUSIONS
This preliminary study on measurement of organic and/or inorganic mercury
in distilled and natural waters showed that problems of level of mercury and
sample substrate (distilled vs. natural water) were not as significant as the
form of the mercury tested.
At the 0.34 - 4.2 ~g/liter level of inorganic mercury with one exception
the EPA and Other Method showed similar levels of accuracy and precision for
both the distilled and natural water samples containing 0.34 or 4.2 ~g of
inorganic mercury/liter.
As expected, when the mercury level was less than
1 ~g/liter, the results showed a greater imprecision than at the 4.2 ~g/liter
level.
At the 6.3 ~g/liter level of organic/inorganic mercury containing equal
amounts of organic and inorganic mercury, the two methods reversed accuracies
and precision in distilled and natural waters.
The EPA Method had better
accuracy and precision with the distilled water sample, -3% and 11% respectively
than in the natural waters where it had a -11% bias and 23% deviation respectively.
Conversely, the Other Method showed a negative 17% bias and 28% deviation in
distilled water and a negative 2% bias and 17% deviation in the natural waters.
Despite the similar accuracy and precision values shown by the two methods
with Sample 3 which contained equal amounts of organic and inorganic mercury,
the methods differed significantly with Sample 4 which contained only organic
mercury.
The EPA Method had a -4% bias in distilled water and a 9% bias in
natural water while the Other Method had a -28% bias in distilled water and
a -21% in natural water.
Likewis~the relative deviation of the EPA Method
was 20 and 28% in the distilled and natural water while the Other Method had
a relative deviation of 51 and 45% respectively for the distilled and natural
water samples.
-------
37
The performances of the EPA Method and Other Method in recovery of organic
and inorganic mercury from distilled and natural water samples have shown that:
1.
The EPA Method was more precise with three of the four inorganic
mercury samples and three of the four of the samples containing
organic mercury.
2.
Both methods showed a limited and variable bias with the two inorganic
mercury samples and a larger and consistently negative bias with the
samples containing organic mercury.
If water samples contain mercury in organic form, a method involving a
vigorous digestion step such as that in the EPA Method should be used to
insure good recovery.
-------
39
APPENDIX A
EPA Method for Mercury in Water, April 1972
(Note: Heating step~ 8.1~ ws not incZuded
in EPA Method evaZuated in this study)
-------
Apri 1, 1972
41
MERCURY IN WATER
(Cold Vapor Techniaue)
STORET NO.
Total:
Dissolved:
71900
71890
1.
Scope and Application
1.1
This method is applicable to surface waters, saline waters, waste-
waters, effluents, and domestic sewage.
1.2
In addition to inorganic forms of mercury: organic mercurials may
also be present in an effluent or surface
water sample.
These
organomercury compounds will not respond to the flameless atomic
absorption technique unless they are first broken down and converted
to mercuric ions.
Potassium permanganate oxidizes many of these
compounds but recent studies have shown that a number of organic
mercurials, including phenyl m rcuric acetate and methyl mercuric
chloride, are only partially oxidized by this reagent.
Potassium
persulfate has been found to give approximately 100% recovery when
used as the oxidant with these compounds.
Therefore, a persulfate
oxidation step following the addition of the permanganate has been
included to insure that organomercury compounds, if present, will be
oxidized to the mercuric ion before measurement.
A heat step is
required for methyl mercuric chloride when present in or spiked to a
natural system.
For distilled water the heat step is not necessary.
1.3
The range of the method may be varied through instrument and/or
recorder expansion.
Using a 100 ml sample, a detection limit of 0.2 ~g
Hg/l can be achieved; concentrations below this level should be reported
as <0.2 (see Appendix 11.2).
-------
42
2.
Summary of Method
2.1
3.
4.
The flameless AA procedure is a physical method based on the absorption
of radiation at 253.7 nm by mercury vapor.
The mercury is
reduced to the elemental state and aerated from solution in a closed
system.
The mercury vapor passes through a cell positioned in the
light path of an atomic absorption spectrophotometer.
Absorbance
(peak height) is measured as a function of mercury concentration and
recorded in the usual manner.
Sample Handling and Preservation
3.1
Until more conclusive data are obtained, samples should be preserved
by acidification with nitric acid to a pH of 2 or lower immediately
at the time of collection(l).
If only dissolved mercury is to be
determined, the sample should be filtered before the acid is added.
For total mercury the filtration is omitted.
Interference
4.1
Possible interference from sulfide is eliminated by the addition of
potassium permanganate.
Concentrations as high as 20 mgll of sulfide
as sodium sulfide do not interfere with the recovery of added in-
organic mercury from distilled water.
4.2
Copper has also been reported to interfere; however, copper concen-
trations as high as 10 mgll had no effect on the recovery of mercury
from spiked samples.
4.3
Sea waters, brines and industrial effluents high in chlorides require
additional permanganate (as much as 25 ml).
During the oxidation
step chlorides are converted to free chlorine which will also absorb
radiation at 253 nm.
Care m~st be taken to assure that free chlorine
is absent before the.mercury is reduced and swept into the cell.
may be accomplished by using an excess of hydroxylamine sulfate
This
-------
5.
43
reagent (25 ml).
In addition, the dead air space in the BOD bottle
must be purged before the addition of stannous sulfate.
Both in-
organic and organic mercury spikes have been quantitatively recovered
from sea water using this technique.
4.4
Interference from certain volatile organic materials which will
absorb at this wavelength is also possible.
A preliminary run with-
out reagents should determine if this type of interference is present
(see Appendix 11.1).
Apparatus
5.1
Atomic Absorption Spectrophotometer*:
Any atomic absorption unit
having an open sample presentation area in which to mount the
absorption cell is suitable.
Instrument settings recommended by the
particular manufacturer should be followed.
5.2
Mercury Hollow Cathode Lamp:
Westinghouse WL - 22847, argon filled,
or equivalent.
5.3
Recorder:
Any multi-range variable speed recorder that is compatible
with the UV detection system is suitable.
5.4 Absorption Cell:
Standard spectrophotometer cells 10 cm long, having
quartz end windows may be used.
Suitable cells may be constructed from
plexiglass tubing, 1" O.D. x 4-1/2".
The ends are ground perpendicular
to the longitudinal axis and quartz windows (1" diameter x 1/16"
thickness) are cemented in place.
Gas inlet and outlet ports (also
of plexiglass but 1/4" O.D.) are attached approximately 1/2" from
each end.
The cell is strapped to a burner for support and aligned
in the light beam by use of two 2" by 2" cards.
One inch diameter
*Instruments designed specifically for the measurement of mercury using
the cold vapor technique are commercially available and may be substituted
for the atomic absorption spectrophotometer.
-------
44
6.
6.2
holes are cut in the middle of each card; the cards are then placed
over each end of the cell.
The cell is then positioned and adjusted
vertically and horizontally to give the maximum transmittance.
5.5
Air Pump:
Any peristaltic pump capable of delivering 1 liter of air
per minute may be used.
A Masterflex pump with electronic speed
control has been found to be satisfactory.
5.6
Capable of measuring an air flow of 1 liter per minute.
Flowmeter:
5.1
Aeration Tubing:
A straight glass frit having a coarse porosity.
Tygon tubing is used for passage of the mercury vapor from the sample
bottle to the absorption cell and return.
5.8
6" x 3/4" diameter tube containing 20 grams of magnesium
Drying Tube:
perchlorate (see Note 1.)
The apparatus is assembled as shown in the
accompanying diagram.
NOTE 1:
In place of the magnesium perchlorate drying tube, a small
reading lamp with 60W bulb may be used to prevent condensation of
moisture inside the cell.
The lamp is positioned to shine on the
absorption cell maintaining the air temperature in the cell about
10°C above ambient.
Reagents
6.1
Sulfuric Acid, Conc:
Reagent grade
6.1.1
Sulfuric acid, 1.0 N:
Dilute 28.0 ml of conc. sulfuric acid
to 1.0 liter.
6.1.2
Sulfuric acid, 0.5 N:
Dilute 14.0 ml of conc. sulfuric acid
to 1.0 liter.
Nitric Acid, Conc:
Reagent grade of low mercury content.
NOTE 2:
If a high reagent blank is obtained, it may be necessary to
distill the nitric acid.
-------
7.
45
6.3
Add 25 g stannous sulfate to 250 ml of 0.5 N
Stannous Sulfate:
sulfuric acid.
This mixture is a suspension and should be stirred
continously during use.
NOTE 3:
Stannous chloride and hydroxylamine hydrochloride may also
be used.
6.4
Sodium Chloride-Hydroxylamine Sulfate Solution:
Dissolve 12 grams
of sodium chloride and 12 grams of hydroxylamine sulfate in distilled
water and dilute to 100.0 mI.
6.5
5% solution, w/v.
Dissolve 5 grams of
Potassium Permanganate:
potassium permanganate in 100 ml of distilled water.
6.6
5% solution, w/v.
Dissolve 5 grams of potassium
Potassium Persulfate:
persulfate in 100 ml of distilled water.
6.7
Dissolve 0.1354 grams of mercuric chloride in
Stock Mercury Solution:
75 ml of distilled water.
Add 10 ml of concentrated nitric acid and
adjust the volume to 100.0 mI.
1 ml = 1 mg Hg.
6.8 Working Mercury Solution:
Make successive dilutions of the stock
mercury solution to obtain a working standard containing 0.1 ~g per
mI.
This working standard and the dilutions of the stock mercury
solution should be prepared fresh daily.
Acidity of the working
standard should be maintained at 0.15% nitric acid.
This acid should
be added to the flask as needed before the addition of the aliquot.
Calibration
7.1
Transfer 0, 0.5, 1.0, 2.0, 5.0 and 10.0 ml aliquots of the working
mercury solution containing 0 to 1.0 ~g of mercury to a series of
300 ml BOD bottles.
Add enough distilled water to each bottle to make
a total volume of 100 mI.
Mix thoroughly and add 5 ml of concentrated
sulfuric acid and 2.5 ml of nitric acid to each bottle.
-------
%
Add 15 ml of KMn04 solution to each bottle and allow to stand at
least 15 minutes.
Add 8 ml of potassium persulfate to each bottle
and heat for 2 hours in a water bath maintained at 95°C.
Cool
and add 6 ml of sodium chloride - hydroxylamine sulfate solution
to reduce the excess permanganate.
When the solution has been
decolorized wait 30 seconds, add 5 ml of the stannous sulfate
solution and immediately attach the bottle to the aeration
apparatus forming a closed system.
At this point the sample is
allowed to stand quietly without manual agitation.
The circulating
pump, which has previously been adjusted to a rate of 1 liter per
minute, is allowed to run continuously.
NOTE 4:
An open system where the mercury vapor is passed through
the absorption cell only once may be used instead of the closed
system.
The absorbance will increase and reach maximum within 30 seconds.
As
soon as the recorder pen levels off, approximately 1 minute, open the
bypass valve and continue the aeration until the absorbance returns to
its minimum value (see Note 5).
Close the bypass valve, remove the
stopper and frit from the BOD bottle and continue the aeration.
Proceed with the standards and construct a standard curve by plotting
peak height versus micrograms of mercury.
NOTE 5:
Because of the toxic nature of mercury vapor precaution must
be taken to avoid its inhalation.
Therefore, a bypass has been
included in the system to either vent the mercury vapor into an exhaust
hood or pass the vapor through some absorbing media, such as:
a)
equal volumes of 0.1 N KMn04 and 10% H2S04
b)
0.25% iodine in a 3% KI solution
-------
8.
9.
10.
10.1
47
A specially treated charcoal that will adsorb mercury vapor is
also available from Barnebey and Cheney) E. 8th Ave. and North
Cassidy St., Columbus, Ohio 43219, Cat. #580-13 or #580-22.
Procedure
8.1
Transfer 100 ml or an aliquot diluted to 100 ml containing not more
than 1.0 ~g of mercury to a 300 ml BOD bottle.
Add 5 ml of sulfuric
acid and 2.5 ml of nitric acid mixing after each addition.
Add IS
ml of potassium permanganate solution to each sample bottle.
For
sewage samples additional permanganate may be required.
Shake and
add additional portions of potassium permanganate solution if
necessary until the purple color persists for at least IS minutes.
Add 8 ml of potassium persulfate to each bottle and heat for 2 hours
in a water bath at 95°C.
Cool and add 6 ml of sodium chloride -
hydroxylamine sulfate to reduce the excess permanganate.
After a
delay of at least 30 seconds add 5 ml of stannous sulfate and
immediately attach the bottle to the aeration apparatus.
Continue as
described under Calibration.
Calculation
9.1
Determine the peak height of the unknown from the chart and read the
mercury value from the standard curve.
9.2
Calculate the mercury concentration in the sample by the formula:
~gHg/l
~g Hg
in aliquot
x
1000
volume of a11quot
=
9.3
Report mercury concentrations as follows:
Below 0.2 ~g/l, <0.2; between 1 and 10 ~g/l, one decimal; above 10 ~g/l,
whole numbers.
Precision and Accuracy
Using an Ohio River composite sample with a background mercury con-
centration of 0.35 ~g/l, spiked with concentrations of 1, 3 and 4
-------
48
11.
11.1
11.2
~g/l, the standard deviations were fO.14, fO.lO and fO.08,
respectively.
Standard deviation at the 0.35 level was fO.16.
Percent recoveries at the three levels were 89, 87, and 87%,
respectively.
Appendix
While the possibility of absorption from certain organic substances
actually being present in the sample does exist, the AQC Laboratory
has not encountered such samples.
This is mentioned only to caution
the analyst of the possibility.
A simple correction that may be used
is as follows:
If an interference has been found to be present (4.4), the sample
should be analyzed both by using the regular procedure and again under
oxidizing conditions only, that is without the reducing reagents.
The true mercury value can then be obtained by subtracting the two
values.
If additional sensitivity is required, a 200 ml sample with recorder
expansion may be used provided the instrument does not produce
undue noise.
Using a Coleman MAS-SO with a drying tube of magnesium
perchlorate and a variable recorder, 2 mv was set to read full scale.
With these conditions, and distilled water solutions of mercuric
chloride at concentrations of 0.15, 0.10, 0.05 and 0.25 ~g/l the
standard deviations were fO.027, fO.006, fO.Ol and fO.004.
Percent
recoveries at these levels were 107, 83, 84 and 96%, respectively.
-------
49
References
1.
Wallace, R.A., Fulkerson, W., Shults, W.D., and Lyon, W.S., "Mercury
in the Environment - The Human Element", Oak Ridge National Laboratory,
ORNL - NSF - EP - 1. January, 1971, Page 31.
2.
Hatch, W.R., and Ott, W.L., "Determination of Sub-Microgram Quantities
of Mercury by Atomic Absorption Spectrophotometry", Anal. Chem. 40,
2085 (1968). -
3.
Brandenberger, H. and Bader, H.. "The Determination of Nanogram Levels of
Mercury in Solution by a Flame1ess Atomic Absorption Technique", Atomic
Absorption Newsletter, ~, 101 (1967).
4.
Brandenberger, H. and Bader, H., "The Determination of Mercury by Flame1ess
Atomic Absorption II. A Static Vapor Method", Atomic Absorption Newsletter,
7.., 53 (1968).
AIR PUMP
DESICCANT
SCRUBBER
CONTAINING
A MERCURY
ABSORBING MEDIA
BUBBLER
SAMPLE SOLUTION IN BOD BOTTLE
FIGURE I.
APPARATUS FOR FLAMELESS MERCURY
DETERMINATION.
-------
51
APPENDIX B
Details on the Other Method (non-EPA)
Used for Mercury Analyses in this Study
-------
S3
Details of the Other Method (non-EPA) Used for Mercury Analysis in this Study
Laboratory
Designation
1
Digestion Steps Used in
Other Method, Details, and Reference
Silver-Wire Method:
Fishman, J. J., AnaZ. Chern'.J
42, 1462 (1970).
2
To sample, add 25 ml 18 N sulfuric acid, 20 ml 7 N
nitric acid and 1 ml sodium molybdate solution
(2% W/V). Heat for one hour. Cool, add 20 ml (1 + 1)
nitric acid-perchloric acid. Boil vigorously till
white fumes appear. Heat for another 10 minutes,
cool, add 10 ml water, boil again for 10 minutes, cool
bring to volume.
Source:
Massachusetts Division of Fisheries and Game
Field Headquarters
Westborough, Massachusetts 01581
4
Mercury is precipitated from the sample by cadmium
sulfide followed by emission spectrographic arc
excitation of the mercury in the precipitate.
Powdered copper metal is added to samples suspected
of containing organo-mercury compounds to reduce the
mercury to the metallic form.
Source:
E. I. du Pont de Nemours & Co. (Inc.)
Savannah River Plant
Aiken, South Carolina 29801
5
Electrodeposition of mercury onto copper wire coil
as described in: Brandenberger and Bader, Atomic
Absorption N~sZettep.J ~, 101, (1967).
6
KMn04 oxidant for five minutes.
No other reference.
7
EPA method without persulfate.
To a 100 ml sample, add 10 ml 18 N sulfuric acid,
S ml 7 N nitric, 2 ml of 4% potassium permanganate.
Let stand overnight.
8
10
To a 100 ml sample, add 10 ml 18 N sulfuric acid,
5 ml 7 N nitric acid and 5 ml of 4% potassium
permanganate. Mix; then neutralize.
-------
54
Details on the Other Method (non-EPA) Used for Mercury Analysis in this Study contd.
Digestion Steps Used in
Other Method. Details. and Reference
To a 100 ml sample. add 2-1/2 ml acid-persulfate
(2: 1 V /W) . Digest on shaking water bath at 55 C
for one hour. Cool to R. T.. add 5\ W/V potassium
permanganate in 1 ml increments until color holds
for 10 minutes.
Laboratory
Designation
11
Nitric acid-permanganate digestion described in:
Rolf. A. C., Russell. F. R.. and Wilkinson. N. T..
The AnaZyst~ 80. 523. (1955).
12
15
To a 100 ml sample add 25 ml nitric acid. heat
gently for 30 minutes
Source:
18
Texas A & M University
Agricultural Analytical Services
College Station. Texas 77843
Samples digested at 50 - 60 C with sulfuric acid
and oxidize with permanganate.
Source:
20
Uthe. J. F.. Armstrong. F. A. J.. and
Stainton. M. P.. J. of the Fisheries
Researah Board of Canada.~ 27. 805. (1970).
EPA procedure modified: sulfuric acid: nitric acid
(20: 10 ml), 10 ml potassium persulfate. 15 ml
potassium permanganate. heat for four hours at 50 C.
Source:
21
Surveillance and Analysis Division. EPA
Technical Support Branch
620 Central Avenue
Alameda. California 94501
Sulfuric acid-potas~ium permanganate digestion.
No further reference.
28
To a 50 ml sample add 1 ml of 1:4 sulfuric acid
and 1 ml of 4\ potassium permanganate. Heat to
boiling for few seconds. allow to cool.
Source:
Dow Method CAS-AM-70.l3. June 22. 1970.
revised.
Chlorine Institute Pamphlet MlR-l04.
No.3, (1970).
-------
5S
Details on the Other Method (non-EPA) Used for Mercury Analysis in this Study contd.
Laboratory
Designation
Digestion Steps Used in
Other Method, Details, and Reference
30
Add 10 ml 7 N nitric acid, 25 ml 18 N sulfuric
acid and cool. Add 5% potassium perrnanganate
until pink color persists.
Source:
Hatch, W. R. and Ott, W. L., Analytiaal
Chemitttry, 40, 2085 (1968).
31
a) Dow procedure as in 28.
b) Dow procedure modified by addition of one ml
of 10% potassium bromide after the acid and
perrnanganate. Sample allowed to set fOT one
minute before boiling.
Source: Diamond Shamrock Chemical Company
Sheffield, Alabama 35660
34
To a 100 ml sample add 10 ml of 18 N sulfuric acid,
S ml of 7 N nitric acid and 5 ml of 4% W/V potassium
perrnanganate. Modification from Hatch and Ott,
reference 30.
36
To a 5.0 ml sample add 0.5 ml of 5% stannous chloride
in 1 N hydrochloric acid.
Source:
Applications Laboratory
Instrumentation Laboratory, Inc.
Lexington, Massachusetts 02173
38
a) To a 10 ml, diluted sample add 10 ml sulfuric acid
and 2 ml 5% potassium perrnanganate. Digest 15 minutes
at 90 C then cool.
b) To a 5 ml, diluted s~rnple add 10 ml nitric acid,
digest for 1-1/2 hours at 75 C and 1-1/2 hours at
90 C, cool.
Measurement using a Beckman DB-G spectrophotometer
and a 62.5 ern cell.
Source:
University of Illinois
Agronomy Department
Urbana-Champaign Campus
Urbana, Illinois 61801
-------
56
Details on the Other Method (non-EPA) Used for Mercury Analysis in this Study contd.
Laboratory
Designation
39
Digestion Steps Used in
Other Method, Details, and Reference
To a one-liter sample, add 10 ml of 1 + 1 sulfuric acid
and 5 ml of aqueous 2% W/V potassium permanganate.
Mix well and let stand 20 hours at room temperature.
Source:
Omang, S., AnaZ. Chim Acta, 53, 415 (1971).
40
Add 20-30 ml sulfuric acid to sample and reflux on a
steam bath with agitation for 30 minutes. Cool to room
temperature. Add 50% hydrogen peroxide in 1/2 - 1 ml
portions with vigorous mixing. After decomposition is
complete, add 5 ml portions of permanganate slowly until
color persists for 15 minutes.
Source:
Kimura, Y. and Miller, V., AnaZ. Chim Acta,
~, 325-331 (1962).
41
To a 100 ml sample add potassium permanganate until
a pink color is maintained. 20 ml of 2:1 sulfuric and
nitric acid added and sample digested for 24 hours.
Source:
Water Quality Control Research
Stanford University
Civil Engineering Department
Palo Alto, California 94305
Laboratory
42
Modified DON procedure.
To a 50 ml sample add 1 ml 4% KMn04, boil 2 seconds
Source:
Westvaco Corporation
Westvaco Research Center
Laurel, Maryland 20810
-------
57
GLOSSARY OF TERMS
The statistical measurements used in method study reports of the Analytical
Quali ty Control Laboratory, are defined as follows:
Accuracy as % Relative Error (Bias). The signed difference between mean
value and the true value, expressed as a percent of the true value.
x -x
R. E.. % = true
, X
true
x 100
Confidence Limit (95%). The range of values within which a single analysis
will be included, 95% of the time.
95% C. L.
= X ::!:
1.960"
Mean.
The arithmetic mean of reported values, the average.
y = EX
n
Median. Middle value of all data ranked in ascending order.
are two middle values, the mean of these values.
If there
n.
The number of sets of values or analysts reported in a study.
Range. The difference between the lowest and highest values reported
for a sample.
ReZative Deviation (Coefficient of Variation). The ratio of the standard
deviation, 0", of a set of numbers to their mean, X, expressed as percent.
It is an attempt to relate deviation (precision) of a set of data to the
size of the numbers so that deviations between levels of values can be
compared.
R. D.
=
100 ~
X
Skewness Ckl. A pure number, positive or negative, which indicates the
lack of symmetry in a distribution. For example, k is positive if the
distribution tails to the right and negative if the distribution tails
to the left.
k =
E (X. -X) 3
1
3
nO"
-------
58
StandaPd Deviation (a), (s). The most widely used measure of dispersion of a
set of data. It is equal to the square root of the variance and indicates
the deviation of 68% of the values around the mean, and 1.96a, the devia-
tion of 95\ of the values around the mean. a, the standard deviation~
is the measure of the deviation of the universe. However, in most experi-
mental work with limited sampling and in this study only an estimated
standard deviation (s) is measurable. This differs in calculation in
that n-l rather than n is used as the denominator. In this study and in
further studies, s and s2 not a and a2 will be used to measure deviation
of the data. They will be referred to as the starIdaM deviation and
variance respectively.
I X~ (I X.) 2
1 1
n
a =
n
I 2 (I X.) 2
X. -
1 1
n
s = n - I
t-test. The difference in analyzed and true value expressed as ratio over
the st~ deviation. The value obtained is compared with critical
values in a table. If the calculated t-value exceeds the theoretical
t-value, the analyzed value is probably not from the same population as
the rest of the data and can be rejected.
t-value
=
X
n - true value
Standazod Deviation ( s)
Variance (a2) , (s2). The average of the squares of the deviations of a group
of numbers from their average, X.
I X~ - (I x.)2
1 1
n
2
a
=
n
2
s
E X~ - (1: X.) 2
1 1
n
=
n - I
ft U.s._PtIINTINGOfFIC~lm- 759-551/1065
-------
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ENVIRONMENTAL PROTECTION AGENCY
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