EPA-600/4-75-013
December 1975
Environmental Monitoring Series
TENTATIVE REFERENCE METHOD FOR
MEASUREMENT OF TRITIUM IN
ENVIRONMENTAL WATERS
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, Nevada 89114
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development,
U.S. Environmental Protection Agency, have been grouped into
five series. These five broad categories were established to
facilitate further development and application of environmental
technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in
related fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL MONITORING
series. This series describes research conducted to develop
new or improved methods and instrumentation for the identifi-
cation and quantification of environmental pollutants at the
lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants
in the environment and/or the variance of pollutants as a
function of time or meteorological factors.
This document is available to the public through the National
Technical Information Service, Springfield, Virginia 22161.
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EPA-600/4-75-013
December 1975
TENTATIVE REFERENCE METHOD FOR MEASUREMENT OF
TRITIUM IN ENVIRONMENTAL WATERS
by
Quality Assurance Branch
Monitoring Systems Research and Development Division
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114
ROAP Number 22ACW
Program Element 1HA327
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
LAS VEGAS, NEVADA 89114
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring and Support
Laboratory-Las Vegas, U.S. Environmental Protection Agency, and approved for
publication. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
Effective June 29, 1975, the National Environmental Research Center-Las
Vegas (NERC-LV) was designated the Environmental Monitoring and Support Labo-
ratory-Las Vegas (EMSL-LV). This Laboratory is one of three Environmental
Monitoring and Support Laboratories of the Office of Monitoring and Technical
Support in the U.S. Environmental Protection Agency's Office of Research and
Development.
11
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CONTENTS
Page
1. Principle and Applicability 1
2. Range and Sensitivity 2
3. Interferences 3
4. Precision and Accuracy 4
5. Apparatus 4
6. Reagents 5
7. Procedure 7
8. Calibration 8
9. Calculations and Reporting 9
References 11
Bibliography 11
APPENDIX. Error and Statistical Calculations . 12
111
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TENTATIVE REFERENCE METHOD FOR MEASUREMENT OF
TRITIUM IN ENVIRONMENTAL WATERS
1. Principle and Applicability
The most common method used for the analysis of tritium in an
aqueous solution is liquid scintillation counting. In liquid scintilla-
tion counting, the sample material is incorporated into a liquid scin-
tillator solution and the light pulses generated by the interaction
between the nuclide and the scintillator are counted by means of a
single photomultiplier tube, or more commonly by two tubes operating
in coincidence.
For tritium analysis a fluorescent substance dissolved in a suit-
able solvent is used (called a liquid scintillator). The sample is
dissolved or suspended directly in the liquid scintillator. Beta par-
ticles, emitted as the tritium decays, interact with the liquid scin-
tillator to produce very small light pulses. The number of pulses
per unit time is proportional to the quantity of activity present.
%
In most liquid scintillation counting instruments light pulses are
detected and converted to electrical signals by two photomultiplier
tubes operated in coincidence. These electrical signals are amplified,
recorded, and the count rate determined. The pulse height is propor-
tional to the energy of the beta particle which excited the scintillator
molecule. Therefore, radionuclides which have significantly different
beta energies can be selectively counted from the same sample with
instruments that have pulse height discrimination capability. The
spectrometer is calibrated with standard solutions of tritiated water.
Background, standards, and unknown samples are counted alternately
to nullify errors'which could result from instrument drift or from
aging of the scintillator solutions.
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In the method described here, samples of potable water sources are
treated by an alkaline permanganate distillation (1) and samples of
nonpotable water sources are treated by an azeotropic-benzene, alkaline
permanganate distillation (2). For both types of samples (also stand-
ards), 100 milliliters (ml) of sample (or standard) is used, the first
10 ml of water distillate is discarded, and the next 50 ml of water
distillate is collected for analysis.
This method is applicable to the measurement of tritium activities
in potable and nonpotable water sources, and the aqueous fractions of
other types of samples such as biological and soil samples.
2. Range and Sensitivity
The minimum concentration of tritium in water to which this method
is applicable will depend on sample size, counting efficiency, and
counting time. The decay of radioactivity is random in nature rather
than uniform. Therefore, the emissions of radioactive decay (in this
case, beta particles) must be counted sufficiently long to obtain the
desired statistical reliability. It is recommended that samples be
counted long enough so that samples with tritium activity as low as
the detection limit of the method and counting instrument used will
have a counting error at the 95 percent confidence level of no more
than the sample net count rate (when counting error counts per minute
(cpm) equals net cpm, the counting error is 100 percent). For instance,
when a 10-ml sample distillate aliquot is mixed with 10 ml of liquid
scintillator solution (such as Solution G, see Section 6) in a glass
counting vial and counted in a liquid scintillation counter for 20
minutes, with a gross count rate of 18.7 cpm, a background count rate
of 16 cpm, and a counting efficiency of 15 percent, tne sample will
have a net count rate of 2.7 cpm and a counting error of plus or minus
(±) 2.6 cpm at the 95 percent confidence level. This corresponds to
a detection limit of 0.8 ± 0.8 pCi/ml. Counting error can be reduced
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by lower background, higher counting efficiency, longer counting time,
and with more sample tritium activity. See the Appendix for error and
statistical calculations.
The range of tritium concentrations which can be measured by the
method, utilizing currently available liquid scintillation instruments,
is from less than 1 pCi/ml to 15,000 pCi/ml for 10-ml sample aliquot
size. Higher tritium concentrations can be measured by diluting and/or
using smaller sample aliquots.
The method provides for the detection of tritium levels well below
the maximum allowable concentrations above natural background as indi-
cated in the Federal Register, Title 10, Part 20, Section 20.106, para-
graph (e), with reference to Appendix B, Table II (1/3 of 3000 pCi/ml
equals 1000 pCi/ml).
3. Interferences
3.1 Significant reduction in the absolute counting efficiency may
result from quenching (attenuation of pulse heights) caused by
impurities in the sample which are introduced into the scintillator
solution and which will inhibit the transfer of energy, or by color
in the sample which may absorb the emitted light. Correction must
be made for quenching or quenching materials should be removed from
the sample. Correction for quenching can be accomplished either by
the use of an internal standard (3) or by the channels ratio method
of quench correction (4). The approach in the method described here
is to eliminate quench interference materials and such volatile radio-
nuclides as radioiodine and radiocarbon. An alkaline permanganate
distillation of aqueous samples should eliminate most quench inter-
ferences as well as radioiodine and radiocarbon. Too vigorous a dis-
tillation will carry over interfering materials with the distillate,
as is easily seen with a sample treated with potassium permanganate.
(The permanganate color in the distillate does not appear to quench,
up to concentrations of 10 parts per million, but it is evidence of
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carryover of unwanted materials.) An azeotropic-benzene distillation
of aqueous samples greatly minimizes the carryover of inorganic as
well as volatile organic materials. A boiling chip must be used with
each distillation to avoid bumping, which can amount to a carryover
excursion.
3.2 Scintillator stock solutions or samples exposed to daylight must
be dark-adapted for at least 24 hours. If toluene or xylene
base scintillators are exposed to fluorescent lighting they should
be dark-adapted for a minimum of 6 hours. If dioxane base scintillators
are exposed to fluorescent lighting, 24-hour dark-adaption is necessary.
All fluors should be checked for excitation under lighting conditions
being used and if possible they should be exposed only to red light.
4. Precision and Accuracy
4.1 Samples with tritium activity above 200 pCi/ml can be analyzed
with a precision of less than ± 6 percent at the 95 percent confi-
dence level and samples with as little activity as 1 pCi/ml can be
analyzed with a precision of less than ± 10 percent.
4.2 Overall accuracy can be calculated from the accuracy of the
standard used (data furnished by the supplier) combined with
the precision and accuracy of the method. Accuracy is dependent on
the influence of interferences. Interferences are minimized in this
method.
5. Apparatus
Coincidence-type liquid scintillation spectrometer
Liquid scintillation vials, low-potassium glass is
recommended. Polyethylene vials may be used when
dioxane scintillator solution is used.
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One-liter, tight-sealing, polyethylene bottles
Labels for sample identification
Distillation apparatus:
For aqueous distillation: 250-ml round bottom
pyrex flask; connecting side arm adapter (such as
Corning part #9060), condenser, graduated cylinder,
boiling chips, and heating mantle
For azeotropic-benzene-aqueous distillations:
500-ml round bottom flask, Barrett-type distilling
receiver (such as Corning part #3622), condenser,
boiling chips, graduated cylinder, and heating mantle
6. Reagents. All chemicals should be of "reagent-grade" or equivalent
whenever they are commercially available.*
Reagents for distillation treatment: sodium hydroxide
pellets, potassium permanganate, and benzene
Background water with tritium activity below the minimum
detectable activity (most deep well waters are low in
tritium content)
Scintillator solutions:
Dioxane liquid scintillator solution: Thoroughly
mix 4 grams (g) PRO (2,5-diphenyloxazole), 0.05 g
POPOP [l,4-bis(5-phemyloxazolyl-2-ylJbenzene],
* "Reagent Chemicals, American Chemical Society Specifications,"
American Chemical Society (ACS), Washington, DC. For reagents not
listed by the ACS see "Reagent Chemicals and Standards" by Joseph
Rosin, D. Van Nostrund Company, Inc., New York, NY, or the "United
States Pharmacopeia" for purity tests.
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and 120 g of solid napthalene in 1 liter of
spectroquality 1,4-dioxane. Store the solution
in a dark (amber) bottle no longer than 2 months.
This solution can be used with glass or poly-
ethylene vials.
Solution 6 scintillator solution: Dissolve 18 g
of scintillation-grade PRO (2,5-diphenyloxazole)
and 3.6 g of scintillation-grade BIS-MSB [p-bis
(o-methylstyryl)benzene] in 2 liters of spectro-
quality p-xylene. Add 1 liter of Triton N-101
detergent (Rohm & Haas) to the p-xylene scintil-
lator solution. Dissolve 50 g of SXS (sodium
xylene sulfonate) in 100 ml of distilled water
and add this solution to the p-xylene scintillator-
Triton solution. Mix thoroughly. Store the solu-
tion in a dark (amber) bottle. This solution
should be used with glass vials since the p-xylene
solvent evaporates slowly through the wall of the
polyethylene vials.
"Handifluor1® scintillator solution (available
from Mallinkrodt Chemical Works). This solution
should be used with the glass vials for the
reason stated above.
"Insta-Gel1® scintillator solution (available
from Packard Instrument Company). This solution
should be used with glass vials for the reason
stated above.
6
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7. Procedure
7.1 Sampling
Sampling should be accomplished as described in "Environmental
Radioactivity Surveillance Guide," published by the U.S. Environmental
Protection Agency as report ORP/SID 72-2.
7.2 Analysis
7.2.1 For samples of potable water sources: Add 0.5 g of sodium
hydroxide and 0.1 g of potassium permanganate to a 100-ml ali-
quot of the sample in a 250-ml distillation flask. Add a boiling chip
to the flask. Connect a side arm adapter and a condenser to the out-
let of the flask. Place a graduated cylinder at the outlet of the con-
denser. Heat the sample to 100°-105° C to distill, discard the first
10 ml of distillate (should contain most of the ammonia from amines and
amino compounds), and then collect the next 50 ml of distillate for
tritium analysis. Thoroughly mix the distillate fraction.
7.2.2 For samples of nonpotable water sources: Add 0.5 g of sodium
hydroxide, 0.2 g of potassium permanganate, and 200 ml of ben-
zene to a 100-ml sample aliquot in a 500-ml distillation flask. Add a
boiling chip to the flask. Attach a Barrett-type distilling receiver
and condenser to the flask. Heat the flask contents to 78°-82° C to
distill and discard the first 10 ml of water distillate. Do not collect
more than 10 ml and then drain the bottom 10 ml because there is a
gradient in the tritium concentration of the distillate and it is impor-
tant that the same fractional part of samples and standards be discarded.
After discarding the first 10 ml of water distillate, collect the next
50 ml of water distillate for tritium analysis. Thoroughly mix the
distillate fraction.
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7.2.3 Thoroughly mix 4 ml of the distillate with 16 ml of the dioxane
scintillator or 10 ml of distillate with 12 ml of Insta-Gel,
Handifluor, or Solution G scintillators in a liquid scintillation vial.
Three aliquots of the sample distillate should be analyzed for tritium.
7.2.4 Prepare background and standard tritium-water solutions for
counting, using the same amount of water and the same scintil-
lator as used in the preparation of samples. Use low tritium background
distilled water for these preparations (distillate of most deep well
water sources is acceptable, but each source should be checked for
tritium activity before using).
7.2.5 Dark-adapt all samples, backgrounds, and standards. Count the
samples, backgrounds, and standards. Count samples containing
less than 200 pCi/ml for 100 minutes and samples containing more than
200 pCi/ml for 50 minutes.
8. Calibration
8.1 Determination of Recovery and Counting Efficiency Factors
8.1.1 Prepare a tritium standard solution in a 1-liter volumetric
flask containing approximately 1000 disintegrations per minute
(dpm) per ml. Use low level tritium background raw water (undistilled)
and standard tritium activity for preparing this solution. Label this
solution "Raw Water Tritium Standard Solution." Distill approximately
600 ml of water, obtained from the same source as above (without
tritium activity added). Use this distillate for background tritium
corrections. Using the distillate and standard tritium activity, pre-
pare a tritium standard solution in a 500-ml volumetric flask to con-
tain the same activity concentration as the "Raw Water Tritium Standard
Solution." Label this solution "Distilled Water Tritium Standard
Solution."
8
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8.1.2 Aqueous alkaline permanganate distillation: Place a 100-ml
aliquot of the "Raw Water Tritium Standard Solution" in a 250-ml
distillation flask. Add 0.5 g of sodium hydroxide, 0.1 g of potassium
permanganate, and a boiling chip. After discarding the first 10 ml of
distillate, collect 50 ml of distillate by the procedure described in
paragraph 7.2.1. Mix the distillate fraction. Repeat this distillation
step with two more 100-ml aliquots for triplicate analyses.
8.1.3 Azeotropic-benzene-aqueous alkaline permanganate distillation:
Place a 100-ml aliquot of the "Raw Water Tritium Standard Solu-
tion" in a 500-ml distillation flask. Add 0.5 g of sodium hydroxide,
0.2 g of potassium permanganate, 200 ml of benzene, and a boiling chip.
After discarding the first 10 ml of water distillate, collect 50 ml of
water distillate by the procedure described in paragraph 7.2.2. Mix
the distillate fraction. Repeat the distillation step with two more
100-ml aliquots for triplicate analyses.
8.1.4 Prepare for counting three aliquots of the "Raw Water Tritium
Standard Solution" distillate (from step 8.1.2 or 8.1.3),
3 aliquots of the "Distilled Water Tritium Standard Solution," and
3 aliquots of the distilled raw water (for background). Mix 4 ml of
water vith 16 ml of the dioxane scintillator solution or 10 ml of water
with 12 ml of the Instal-Gel, Handifluor, or Solution G scintillator
solutions in liquid scintillator vials (glass vials should be used
for the Insta-Gel, Handifluor, and Solution G scintillator solutions).
Dark-adapt the vials overnight and count in a liquid scintillation
counter. Count each vial for 50 minutes.
9. Calculations and Reporting
9.1 Counting Efficiency
cpm of Distilled Water Standard - cpm of background
~ dpm of Distilled Water Standard
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9.2 Recovery Correction Factor
p _ cpm of Raw Water Standard distillate - cpm of background
e x dpm of Raw Water Standard (before distillation)
9.3 Sample Tritium Activity
A (pCi/ml) = C " B
2.22 x e x V x F
where C = cpm for sample aliquot
B = cpm for background aliquot
e = counting efficiency, as determined above
V = volume of the sample aliquot in ml
F = recovery factor, as determined above
Error associated with the results of the analysis should also be re-
ported. See Appendix for error and statistical calculations.
10
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REFERENCES
1. Standard Methods for the Examination of Water and Wastewater,
13th Edition, American Public Health Association, Washington,
D.C., 1971.
2. Moghissi, A. A., E. W. Bretthauer, and E. H. Compton, "Separation
of Water from Biological and Environmental Samples for Tritium
Analysis," Anal. Chem.t 45:1565, 1973.
3. Chase, 6. D., and J. L. Rabinowitz, Principles of Eadioisotope
Methodology, Burgess Publishing Co., Minneapolis, Minnesota, 1967.
4. Bush, E. T., "General Applicability of the Channels Ratio Method
of Measuring Liquid Scintillation Counting Efficiencies," Anal.
Chem., 35:1024, 1963.
BIBLIOGRAPHY
Fried!ander, G., J. W. Kennedy, and J. Miller, Nuclear and Radio-
chemistry f John Wiley and Sons, Inc., New York, New York, 1964.
Sodd, V. J., and K. L. Scholz, "Analysis of Tritium in Water;
A Collaborative Study," J. Ass. Of fie. Anal. Chem. 52:1, 1969.
1973 Annual Book of ASTM Standards, Part 23, American Society for
Testing and Materials, Philadelphia, Pennsylvania.
Precision Measurements and Calibration, Statistical Concepts and
Procedures, U.S. Department of Commerce, NBS, Special Pub. 300,
1:349-354.
11
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APPENDIX. ERROR AND STATISTICAL CALCULATIONS
Because of the random nature of radioactive disintegrations there
is an error associated with any measured count of these disintegrations.
The variability of any measurement is indicated by the standard devia-
tion. The standard deviation in the counting rate is determined by the
following equation:
(R) Mr1
where R = gross count rate
ti = counting time for the gross count
B = background count rate
tz = counting time for the background count
The counting error for a given sample expressed in pCi/ml and at
the 95% confidence level is shown by:
2. 22 eVF
where 1.96 = 95% confidence factor
2.22 = dpm/pCi
e = efficiency factor, cpm/dpm
V = volume of the aliquot analyzed, in ml
F = recovery factor
The standard deviation of a number of experimental analyses or
observations is determined by:
B
fr, -
where n = activity (pCi/ml) of a given sample
n = mean activity (pCi/ml) of a series of analyses
m = the number replicate analyses
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TECHNICAL REPORT DATA
(Please read Instruction* on the reverse before completing)
1. REPORT NO.
EPA-600/4-75-013
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
TENTATIVE REFERENCE METHOD FOR MEASUREMENT OF
TRITIUM IN ENVIRONMENTAL WATERS
5. REPORT DATE
December 1975
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Quality Assurance Branch
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, Nevada 89114
10. PROGRAM ELEMENT NO.
1HA327
11. CONTRACT/GRANT NO.
in-house report
12. SPONSORING AGENCY NAME AND ADDRESS
Same as above
13. TYPE OF REPORT AND PERIOD COVERED
reference method
14. SPONSORING AGENCY CODE
EPA-ORD, Office of Monitor-
ing and Technical Support
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A tentative reference method for the measurement of tritium in potable and non-
potable environmental water is described. Water samples are treated with sodium
hydroxide and potassium permanganate and then a water fraction is separated from
interferences by distillation. Two distillation procedures are described, a
simple aqueous distillation for samples from potable water sources, and an aqueous-
azeotropic-benzene distillation for nonpotable water sources.
Alliquots of a designated distillate fraction are measured for tritium activity by
liquid scintillation detection. Distillation recovery and counting efficiency
factors are determined with tritium standards. Results are reported in picocuries
per milliliter.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
tritium
distillation
calibrating
standards
radioactivity
radiochemistry
quality assurance
reference method
liquid scintillation
07B
14B
18B
8. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
unclassified
21, NO. OF PAGES
20
20. SECURITY CLASS (Thispage)
unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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