EPA 680/4 73 002
February 1974
Environmental Monitoring Series
Simplified Atomic Absorption
Determination of Stable
Strontium in Milk and Hay
National Environmental Research Center
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 Develop-
ment, Environmental Protection Agency, have been grouped
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plication of environmental technology. Elimination of
traditional grouping was consciously planned to foster
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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 MON-
ITORING series. This series describes research conducted
to develop new or improved methods and instrumentation
for the identification and quantification of environ-
mental pollutants at the lowest conceivably significant
concentrations. It also includes studies to determine
the ambient concentrations of pollutants in the environ-
ment and/or the variance of pollutants as a function of
time or meteorological factors.
EPA REVIEW NOTICE
This report has been reviewed by the Office of Research
and Development, EPA, and approved for publication. Ap-
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dation for use.
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EPA-680/4-73-002
February 1974
SIMPLIFIED ATOMIC ABSORPTION DETERMINATION
OF STABLE STRONTIUM IN MILK AND HAY:
A Comparison of Methods and Stepwise Procedure
by
Julius Barth
Benjamin H. Bruckner*
Monitoring Systems Research and Development Laboratory
National Environmental Research Center
Las Vegas, Nevada
*now with
National Institute for Occupational Safety and Health
Center for Disease Control
U.S. Department of Health, Education and Welfare
5600 Fishers Lane, Rockville, Maryland 20852
Prepared for
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
LAS VEGAS, NEVADA 89114
For sale by the Superintendent oE Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price 70 cents
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ABSTRACT
A highly simplified atomic absorption procedure for the deter-
mination of stable strontium in fluid milk, milk powder, and alfalfa
is evaluated. A comparison is made between the atomic absorption
method of additions and the standard curve method. A suggested step-
wise procedure is given.
ii
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CONTENTS
Page
Abstract ii
List of Tables iv
Acknowledgements v
Introduction 1
Milk Analysis 2
Alfalfa Pellets Analysis 10
Discussion 15
References 16
Appendix. Suggested Stepwise Procedure 17
111
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TABLES
No. Page
1 Stable Strontium in Milk Powder by Atomic 5
Absorption Using a Standard Curve
2 Stable Strontium in Milk Powder by Atomic 6
Absorption Using the Method of Additions
3 Stable Strontium in Reconstituted Powdered 7
Milk by Atomic Absorption Using a Standard
Curve
4 Stable Strontium in Reconstituted Powdered 8
Milk by Atomic Absorption Using the Method
of Additions
5a Stable Strontium in Untreated Alfalfa 12
Pellets by Atomic Absorption Using a
Standard Curve
5b Stable Strontium in Alfalfa Pellets with 12
Added Strontium by Atomic Absorption Using
a Standard Curve
6a Stable Strontium in Untreated Alfalfa 13
Pellets by Atomic Absorption Using Method
of Additions
6b Stable Strontium in Alfalfa Pellets with 13
Added Strontium by Atomic Absorption
Using Method of Additions .
iv
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ACKNOWLEDGMENTS
The suggestions we received from Anthony Lamanna were most help-
ful and are greatly appreciated. We also appreciate the assistance
of Dr. Gordon Jessup, National Center for Radiological Health, and
Gaynell Jayson, formerly of the National Center for Radiological
Health who analyzed the data statistically. The technical assistance
of Katherine M. Selby is gratefully acknowledged. We wish to extend
our appreciation to Ruth DePrenda for typing this and related papers.
The helpful review of this manuscript by Sabina Slavin,
Walter Slavin, and other members of the staff of Perkin-Elmer
Corporation, Norwalk, Connecticut, is appreciated.
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INTRODUCTION
Flame emission spectrophotometry and atomic absorption spectro-
photometry procedures are currently used for the determination of
stable strontium in biological materials. Flame emission spectropho-
tometry involves the separation and removal of interfering ions by
precipitation and ion exchange procedures (1-, 2). Atomic absorption
procedures usually involve the removal of phosphate by anion exchange
resin. Calcium and phosphate together in solution seriously depress
o
absorption of the»4607 A strontium resonance line, but neither calcium
nor phosphate alone produces serious depression (3).
This report describes in detail a very rapid and simplified pro-
cedure for determining stable strontium in milk* and livestock feed.
Precipitation or ion exchange procedures are unnecessary. The step-
wise procedure described here and in the Appendix was developed from
principles and information reported by Trent and Slavin (4). The ash
solutions are analyzed directly in the atomic absorption spectropho-
tometer without ion exchange resin treatment of any kind. The pro-
cedure is adaptable to the routine analysis of large numbers of
samples.
To evaluate the procedure, two atomic absorption methods were
compared: the standard curve procedure and the method of additions.
The method of additions is described both by David (3) and
Perkin-Elmer Analytical Methods for Atomic Absorption Spectropho-
tometry (5) .
*The powdered and reconstituted milk samples were prepared and sup-
plied by the Analytical Quality Control Service, Northeast Radio-
logical Health Laboratory, U.S.P.H.S., Winchester, Massachusetts, as
part of their program.
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MILK ANALYSIS
SAMPLE PREPARATION
A batch of whole, dry, powdered milk used in ice cream manufacture
was purchased by the Analytical Quality Control Service. The milk pow-
der with nothing added provided one sample for analysis. A second milk
sample was prepared by reconstituting the milk powder with distilled
water so that 6.06 ml of reconstituted milk contained one gram of milk
powder. Strontium nitrate was added to the reconstituted milk at a
level of 0.0040 mg strontium per gram of milk powder.
PREPARATION OF ASH SOLUTION
Fifteen grams of milk powder was added to each of three porcelain
crucibles. The samples were placed into a muffle furnace and the tem-
perature was raised about 40° C each hour until 450° C was reached.
The samples were then ashed for 18 hours. The ashes were transferred
to small beakers and the crucibles washed with 5 ml of 6 N HC1. The
crucibles were washed twice more with small amounts of 6 N HCl and all
washings were added to the beakers. The beakers were evaporated to dry-
ness on a steam bath and the residue redissolved. in 6 N HCl. The beak-
ers were again evaporated to dryness. The residues were dissolved in 10
ml of 1.0 N HCl and filtered warm through Whatman No. 42 filter paper
into 100 ml volumetric flasks. The filter paper was washed with small
volumes of hot water, until the flasks were not quite full. The flasks
were allowed to cool and diluted to the mark.
In the case of reconstituted milk, 115 ml of milk was pipetted in-
to each of three porcelain crucibles, then five milliliters of glacial
acetic acid was added to each. The crucibles were placed in a drying
oven set at about 80° C for about three days. Then the temperature was
gradually raised to about 115° C and the milk held until as dry as
possible. The crucibles were then placed in a cold muffle furnace and
the temperature was brought up to about 150° C. The temperature was
then raised about 40° C each hour until about 450° C was reached. The
ash solutions were prepared in the same way as 'described previously for
,
the milk powder. It was found that the ashing procedure described was
-------
not entirely satisfactory since there was a small amount of carbona-
ceous material remaining. This procedure was therefore modified when
the alfalfa pellets were ashed and is described in that section.
ATOMIC ABSORPTION ANALYSIS
Two methods of atomic absorption analysis were used for each ash
solution. In the first procedure, standard solutions were prepared and
analyzed on the atomic absorption spectrophotometer, their absorbances
plotted, and a working curve was drawn. The second procedure employed
the method of additions. Both analyses were done on the same day and
the analyses of the ash solutions were repeated on another day.
Standard Curve Procedure
A blank and standards were made up in 25 ml volumetric flasks as
follows: solutions were made up containing 0.00, 0.10, 0.15, 0.20,
0.25, 0.30, 0.35, and 0.40 ppm strontium. To each'flask was added 5 ml
of 5.0% lanthanum solution as lanthanum oxide, 2.5 ml of a solution of
NaCl containing 5 mg Na per ml, and 5 ml of 0.1 N HC1 solution.
Each ash solution was run in triplicate each day. Two milliliters
of ash solution was pipetted into a 10 ml volumetric flask. Two milli-
liters of 5% lanthanum stock solution was added and the flasks filled
to the mark. These samples were ready for atomic absorption analysis.
Method of Additions
For a single determination using the method of additions, two mil-
liliters of ash solution was pipetted into each of five 10 ml volumet-
ric flasks. Additions of strontium were made to the flasks as follows:
zero, 0.05, 0.10, 0.15, and 0.20 ppm. Two milliliters of 5 per cent
lanthanum stock solution was added and the flasks filled to the mark.
These solutions were then ready for atomic absorption analysis.
ATOMIC ABSORPTION INSTRUMENTATION
The samples were analyzed in a Perkin-Elmer Atomic Absorption
Spectrophotometer Model-303 equipped with a three-slot Boling burner
head.
The instrument- settings described in the Perkin-Elmer Instrument
-------
Manual (5) were used with one exception. The range was set at visible,
o '
the slit at 4, and the wavelength at 4607 A with the instrument scale
setting at about 230. As described by Trent and Slavin (4) the hollow
cathode lamp was set at 16 ma instead of 10 ma. A scale expansion set-
ting of ten was used for all the milk analyses. It was necessary to
use the time response control at all times.
The lamp current setting was higher than that usually recommended
for the strontium hollow cathode tube. This allowed a minimum gain
setting which resulted in minimum noise. The gain was set at approxi-
mately 5 scale divisions to the left of center, or the needle of the-
energy meter was just within the left hand portion of the black region*
of the scale.
The same blank was used to zero the instrument in both methods.
The instrument absorption readings were converted to absorbance. The
results of the milk analyses are shown in Tables 1, 2, 3, and 4.
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TABLE 1. STABLE STRONTIUM IN MILK POWDER BY ATOMIC ABSORPTION USING A
STANDARD CURVE*
Ash Solution
Sub Sample
Powder
10"3 mg/g
10
Ash
~2 mg/g
First Trail
1
2
3
Average
1
2
3
Average
.2
3
Average
First Trial Average
4.97
4.84
4.97
4.93
5.47
4'. 95
5.19
5.21
5.20
5.20
5.48
5.29
5.14
6.0S5
5.915
6.065
6.015
6.680
6.045
6.344
6.356
6.344
6.344
6.680
6.456
6.276
Second Trial
1
1 2
3
Average
1
2 2
3
Average
1
3 2
3
Average
Second Trial Average
5.00
5.00
5.03
5.01
4.89
4.89
4.92
4.90
4.87
4.84
4.89
4.86
4.92
6.102
6.102
6.140
6.113
5.971
5.971
6.008
5.983
5.934
5.896
5.964
5.931
6.009
*Final average of milk powder determined by standard curve method,.
5.033 x 10~3 mg/g powder
Standard deviation + 0.198 X 10"3
Coefficient of variation 3.9340
6.1428 X 10"2 mg/g ash
Standard deviation + 0.241 X 10
-2
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TABLE 2. STABLE STRONTIUM IN MILK POWDER BY ATOMIC ABSORPTION USING
THE METHOD OF ADDITIONS*
Ash Solution Sub Sample
First Trial
1
1 2
3
Average
1
2 2
3
Average
1
.3 2
3
Average
First Trial Average
Second Trial
1
1 2
3
Average
1
2 2
3
Average
1
3 2
3
Average
Second Trial Average
Powder
10" 3 ms/R
4.78
4.78
5.37
4.98
5.53
5.07
5.20
5.19
5.57
5.45
4.87
5. .29
5.16
4.81
4.97
5.03
4.94
5.41
5.53
5.35
5.43
4.99
5.42
5.45
5.28
5.22
Ash
10" 2 mg/g
5.850
5.840
6.551
6.073
6.754
6.194
6.344
6.431
6.792
6.643
5.934
6.456
6.321
5.878
6.065
6.140
6.028
6.605
6.754
6.530
6.630
6.084
6.605
6.643
6.444
6.367
*Final average of milk powder determined by method of additions:
5.198 X 10"3 mg/g powder
Standard deviation + 0.284 X 10
Coefficient of variation 5.4636
6.3442 X 10"2 mg/g ash
Standard deviation + 0.346 X 10
-3
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TABLE 3. STABLE STRONTIUM IN RECONSTITUTED POWDERED MILK BY ATOMIC
ABSORPTION USING A STANDARD CURVE*
MilkAsh .
Ash Solution Sub Sample 10"3 mg/ml IP"-2 mg/g
First Trial
1 1.56 10.14
1 2 1.54 10.03
3 1.54 10.06
Average 1.55 10.07
1 1.52 9.909
2 2 1.52 . 9.909
3 1,51 9.880
Average 1.52 9.90
1 1.48 9.425
3 2 1.48 9.425
3 1.54 9.796
Average 1.50 9.55
First Trial Average 1.52 9.84
Second Trial
1
1 2
3
Average
1
2 2
3
Average
1
3 2
3
Average
Second Trial Average
1.51
1.51
1.55
1.53
1.55
1.55
1.54
1.55
1.49
1.49
1.51
1.52
1.52
9.86
9.86
10.09
9.94
10.14
10.11
10.09
10.11
9.51
9.48
9.65
9.55
9.87
*Final average of reconstituted milk powder using the standard curve
method: 1.5214 X.10~3 mg/ml of reconstituted milk
Standard deviation + 0.025709 X 10"3
Coefficient of variation 1.6898
9.8536 X 10~2 mg/g ash
Standard deviation + 0.253446 X 10'2
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TABLE 4. STABLE STRONTIUM IN RECONSTITUTED POWDERED MILK BY ATOMIC
ABSORPTION USING THE METHOD OF ADDITIONS*
Ash Solution Sub Sample
First Trial
1
1 2
3
Average
1
2 2
3'
Average
1
3 2
3
Average
First Trial Average
Second Trial
1
1 2
3
Average
1
2 2
3
Average
1
3 2
3
Average
Second Trial Average
Milk
10" 3 mg/ml
1.66
1.55
1.61
1.60
1.68
1.54
1.60
1.61
1.61
1.57
1.54
1.57
1.60
1.50
1.52
1.60
1.54
1.60
1.60
1.61
1.60
1.63
1.67
1.62
1.64
1.59
Ash
KT2 mg/8
10.82
10.12
10.46
10.47
10.99
10.05
10.45
10.50
10.28
10.01
9.84
10.04
10.34
9.75
9.92
10.46
10.04
10.48
10.45
10.53
10.49
10.32
10.90
10.53
10.60
10.38
*Final averages of reconstituted milk powder using method of additions;
1.5954 X 10" 3 mg/ml reconstituted milk
Standard deviation + 0.050497 X 10'3
Coefficient.of variation 3.1652
10.3533 X 10~2 mg/g ash
Standard deviation + 0.353802 X 10'2
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Accuracy
Strontium content of reconstituted milk is higher than that of
milk powder by 0.0040 mg/g of powder as supplied by the Analytical
Quality Control Service. The reconstituted milk was made up so that
6.06 ml of milk was equivalent to one gram of powder and one ml of milk
was equivalent to 0.16501 gram of powder.
Standard curve method
5.033 X 10~3 mg Sr/g powder
1.5214 X 10~3 mg Sr/ml of reconstituted milk
9.2196 X 10"3 mg Sr/g powder of the reconstituted milk
9.220 X 10"3 minus 5.033 X 10~3 = 4.187 X 10~3 mg Sr/g
4.187 X 10~3 minus 4.0 X 10"3 = 0.187 X 10"3 mg/g high
Method of additions
5.198 X 10"3 mg Sr/g powder
1.5954 X 10"3 mg Sr/ml reconstituted milk
9.668 X 10~3 mg Sr/g powder of the reconstituted milk
9.668 X 10"3 minus 5.198 X 10"3 = 4.470 X 10'3
4.470 X 10"3 minus 4.0 X 10"3 = 0.470 X 10~3 mg/g high
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ALFALFA PELLETS ANALYSIS
PREPARATION OF SAMPLES AND ASH SOLUTIONS
Twelve grams of alfalfa pellets was weighed into each of six por-
celain crucibles. Into three of the crucibles, 0.60 mg of strontium as
strontium carbonate solution was pipetted directly onto the pellets.
The crucibles were placed in a drying oven to evaporate the added stron-
tium carbonate solution.
The six samples were placed in a cold muffle furnace and ashed for
about 18 hours at about 450° C. The crucibles were allowed to cool and
the ash moistened with distilled H20. Ten milliliters of 6.0 N HN03
was added to each sample and the contents stirred carefully. The cruci-
bles were then taken to dryness on a steam bath, returned to a cold muf-
fle furnace and ashed overnight at about 450° C. They were cooled and
weighed.
Five milliliters of 6.0 N HC1 was added to each crucible and the
contents were evaporated to dryness on a steam bath. Five milliliters
of 6.0 N HC1 was added to each crucible and evaporated on a steam bath
a second time. Ten milliliters of 1.0 N HC1 was added and the crucibles
heated on a steam bath. The contents of each crucible were filtered
while hot through Whatman No. 42 filter paper into 250 ml volumetric
flasks. A Pasteur pipette was used to transfer the contents from the
crucibles to the filter paper. The crucibles and filter paper were
washed well with hot water with the aid of a Pasteur pipette.
Fifty milliliters of 5 per cent lanthanum solution was added to
each flask. The flasks were allowed to cool and made up to the mark
with distilled water.
ATOMIC ABSORPTION ANALYSIS AND INSTRUMENTATION
As in the case of milk, the alfalfa ash solutions were analyzed
by the standard curve method and by the method of additions. One de-
termination of each ash solution was made by each method on each of
three different days.
Standard Curve Procedure
Since there was a 0.60 mg difference between the ash solutions
10
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containing alfalfa only and those containing added strontium, separate
standard curves had to be run for each.
For the analysis of alfalfa only, standards were made up in 25 ml
volumetric flasks containing 0.0, 0.5, 1.0, 1.5, 2.0, and 2.5 ppm stron-
tium. For the analysis of alfalfa with added strontium, the standards
were made up to contain 1.0, 2.0, 3.0, 4.0, and 5.0 ppm strontium. To
each flask was added 5 ml of 5 per cent lanthanum solution, 2.5 ml of a
solution of NaCl containing 5.0 mg sodium per ml, and 1.0 ml of
1.0 N HC1.
The ash solutions were analyzed directly as prepared in the 250 ml
volumetric flasks with no further preparation. The instrument settings
were similar to those described in the milk analysis except that the
scale expansion was set at "five" for the untreated alfalfa pellets and
"two" for the alfalfa pellets with added strontium.
Method of Additions
It was necessary to use a separate series of additions for the
alfalfa pellets alone and the alfalfa pellets with added strontium-
In either case, 5.0 ml of ash solution was pipetted into five 10 ml
volumetric flasks, then 0.00, 0.2, 0.4, 0.6 and 0.8 ppm of strontium
was added to the flasks containing untreated alfalfa ash solution. The
flasks containing alfalfa with added strontium ash solution had 0.00,
0.5, 1.0, 1.5, and 2.0 ppm of strontium added. One milliliter of 5 per
cent lanthanum solution was added to all volumetric flasks and then
made to volume with distilled water.
The standard curve method blank was used to zero the instrument.
The atomic-absorption spectrophotometer scale expansion was set at
"five" for the untreated alfalfa and "two" for the alfalfa with added
strontium. The time response control was used at all times. The re-
sults are shown in Tables 5a, 5b, 6a, and 6b.
11
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TABLE 5a. STABLE STRONTIUM IN UNTREATED ALFALFA PELLETS BY ATOMIC
ABSORPTION' USING A STANDARD CURVE
Ash Solution
1
2
3
Day
1
2
3
Average
1
2
3
Average
1
2
3
Average
Final average
Standard deviation
Coefficient of variation
Alfalfa
ing/ 12 g
.2475
.2500
.2400
.2458
.2750
.2500
. 2425
.2558
.2500
.2525
.2425
.2483
.2500
.01031
4.1240
Ash
mg/g
.2150
.2172
.2085
.2136
.2428
.2207
.2141
.2259
.2194
.2216
.2128
.2179
.2191
.009798
TABLE 5b. STABLE STRONTIUM IN ALFALFA PELLETS WITH ADDED STRONTIUM
BY ATOMIC ABSORPTION USING A STANDARD CURVE
Ash Solution
1
2
*
3
Final average
Day
1
2
3
Average
1
2
3
Average
1
2
3
Average
Standard Deviation
Coefficient of
variation
Alfalfa
rag/ 12 g
. 8500
.8475
.8375
.8450
.8475
.8425
. 8300
.8400
.8225
.8125
.7975
.8108
.8319
.01806
2.1709
Ash
mg/g
.7408
.7386
.7299
.7364
.7480
.7436
.7326
.7414
.7130
.7044
.6914
.7031
.7270
.01954
12
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TABLE 6a. STABLE STRONTIUM IN UNTREATED ALFALFA PELLETS BY ATOMIC
ABSORPTION USING METHOD OF ADDITIONS
Ash Solution Day
1
1 2
3
Average
1
2 2
3
Average
1
3 2
3
Average
Final Average
Standard Deviation
Coefficient of variation
Alfalfa
mg/12 R
.2495
.2550
.2600
. 2548
'. 2400
.2500
.2585
.2495
.2500
.2590
.2515
.2535
.2526
.006317
2.5008
TABLE 6b. STABLE STRONTIUM IN ALFALFA PELLETS WITH ADDED
BY ATOMIC ABSORPTION USING METHOD OF ADDITIONS
Ash Solution Day
1
1 2
3
Average
1
2 2
3
Average
1
3 §
Average
Final Average
Standard Deviation
Coefficient of variation
Alfalfa
mg/12 K
.8600
.9000
.8950
.8850
.9000
.8650
.8900
.8850
.8550
. 8450
.8450
.8483
.8728
.02333
2.6730
Ash
mg/g
.2168
.2215
.2259
.2214
.2119
.2207
.2282
.2203
.2194
.2273
.2221
.2229
.2215
.005214
STRONTIUM
Ash
mg/g
.7495
.7844
.7800
.7713
.7944
.7635
.7855
.7811
.7412
.7326
.7326
.7355
.7626
.02435
13
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Accuracy
Six crucibles contained 12 g of alfalfa pellets. Into three of the
crucibles 0.60 mg of strontium was added.
Standard Curve Method
0.8319 mg Sr/12 g pellets with added strontium
0.2500 mg Sr/12 g untreated pellets
0.5819 mg Sr Recovered
Method of Additions
0.8728 mg Sr/12 g pellets with added strontium
0.2526 mg Sr/12 g untreated pellets
0.6202 mg Sr Recovered
14
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DISCUSSION
This simplified stable strontium procedure, employing either the
standard curve method or method of additions, facilitates the analysis
of large numbers of samples. However, to obtain satisfactory results
with this procedure, strict adherence to details is essential. Since
low levels of strontium are present in both the ash and standard solu-
tions, it is important that the standards and final sample solutions
be carefully prepared. It is also important that the null meter needle
be set at mid-position accurately and frequently with the zero control.
Difficulty was experienced "zeroing-in" the null meter when the milk
was analyzed due to the scale expansion of ten. Following the milk
analysis and preceeding the alfalfa analysis, the instrument was up-
dated and the 3-turn zero control was replaced by a 10-turn zero con-
trol. This alleviated the difficulty considerably.
The three-slot "Doling" burner head provided a wider flame which
improved absorbance and increased detection limits considerably. This
greatly facilitated the detection of strontium in biological materials
at trace levels.
A statistical comparison was made between the standard curve meth-
od and the method of additions. An "F" test for differences between
two variances showed a significant difference between the two methods
in the case of the reconstituted milk only, at 1.0% (p<0.01) (6).
Hence for practical purposes, experimental evidence indicates that a
difference was not detected between methods.
15
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REFERENCES
1. Krieger, Herman L., Velten, Richard J., Burmann, Franz J.,
Radionuclide Analysis of Environmental Samples. A Laboratory
Manual of Methodology. Robert A. Taft Sanitary Engineering
Center Technical Report R59-6. Revised 1966.
2. Porter, C. H., Augustine, R. J., Matusek, J. M. and Carter, M. W.,
Procedures for Determination of Stable Elements and Radionuclides
i
in Environmental Samples. Environmental Health Series,
U. S. Public Health Service Publication No. 999-RH-10, January 1965.
3. David, J., Determination of Strontium in Biological Materials and
Exchangeable Strontium in Soils by Atomic-Absorption Spectropho-
tometry. Analyst 87:576-85, 1962.
4. Trent, Dorothy and Slavin, Walter, Factors in the Determination of
Strontium by Atomic Absorption Spectrophotometry with Particular
Reference to Ashed Biological Samples. Atomic Absorption
Newsletter No. 22, July 1964. Perkin-Elmer Corporation,
Norwalk, Connecticut.
5. Analytical Methods for Atomic Absorption Spectrophotometry.
Perkin-Elmer Corporation, Norwalk, Connecticut.
6. Pearson, E. S. and Hartley, H. 0., Biometrika Tables for
Statisticians. Vol. 1, Third Edition, Cambridge University Press,
London, 1966, Pages 66-67, 202.
16
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APPENDIX
Suggested Stepwise Procedure
Page
I. Preparation of Ash Solution 18
II. Standard and Atomic Absorption Solutions 19
Milk Analysis
III. Standard and Atomic Absorption Solutions 20
Hay Analysis
IV. Atomic Absorption Spectrophotometry 22
V. Calculations 23
VI. Reagents 2*
17
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APPENDIX
SUGGESTED STEPWISE PROCEDURE
I. PREPARATION OF ASH SOLUTION
1. Weigh or pipette a sample into suitable .porcelain, crucibles.
Do not use crucibles in which the porcelain glaze is worn. The
sample should yield about one gram of ash. Fifteen grams of milk
powder, 150 milliliters of fluid milk, or 12 g of alfalfa are suf-
ficient. Add 5 ml of glacial acetic acid to the fluid milk. Pro-
ceed to step 1-3, except for fluid milk. If fluid milk is used
proceed to step 1-2.
2. (Fluid Milk Only)
Place crucibles in drying oven set at about 80° C for about three
or four days. Then raise the temperature gradually until about
115° C is reached. Hold milk in drying oven until as dry as
possible. Proceed to step 1-3.
3. Place milk samples in a cold muffle furnace with the tempera-
o o
ture set at 150 C. After 150 C is reached, raise the temperature
about 40 C each hour until 450 C is attained. The crucibles are
held at 450 C for 18 hours. Crucibles containing hay samples may
be placed in a cold muffle furnace and the temperature brought di-
rectly up to 450 C and held for 18 hours.
4. The crucibles are allowed to cool and the ash is moistened with
distilled water. Pipette 10 milliliters of 6.0 N HNO- slowly and
carefully into each crucible and mix gently.
5. Place crucibles on a steam bath and evaporate to dryness.
6. Return crucibles to a cold muffle furnace and ash at 450 C
overnight.
7. Cool and weigh.
8. Add 5 ml of 6.0 N HC1 to each crucible and evaporate to dry-
ness on a steam bath.
9. Repeat step 8.
10. Take up residues in 10 ml of 1.0 N HC1 and heat crucibles on
steam bath.
Ha. (Milk only) Filter contents of crucibles while warm through
Whatman No. 42 filter paper into 100-ml volumetric flasks. Use
18
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a Pasteur pipette to transfer the crucible contents to the filter
paper. Rinse crucibles several times with small quantities of hot
water and transfer the rinsings to filter paper. Wash filter paper
with small volumes of hot water until the flasks are not quite full.
Cool and dilute to mark.
lib. (Hay only) Treat the crucibles containing hay ash the s.ame as
milk ash with the following exceptions: Filter the contents of
each crucible while hot into 250-ml volumetric flasks. Wash the
crucibles and filter paper with hot water until flasks are about
one-half full. Add 50 ml of 5.0% lanthanum solution' to each flask.
Allow to cool and dilute to mark. The hay ash solutions are ready
for atomic absorption analysis by the standard curve method without
further treatment.
II. STANDARD AND ATOMIC ABSORPTION SOLUTIONS. MILK ANALYSIS
Standard Curve Method
Prepare 25-ml standard solutions containing 0.0 (blank), 0.1, 0.15,
0.20, 0.25, 0.30, 0.35, and 0.40 ppm strontium as follows:
.1. To each of eight 25-ml volumetric flasks add the following vol-
umes of strontium solution containing 0.01 mg strontium per milli-
liter.
PPM ml of Std. Soln.
00.0 (Blank)
0.1
0.15
0.20
0.25
0.30
0.35
0.40
0.000
0.250
0.375
0.500
0.625
0,750
0,875 -
1.00
2. Add 5 ml of 5.0 per cent lanthanum solution.
3. Add 2.5 ml of sodium chloride solution containing 5.0 fflg
sodium per milliliter.
19
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4. Add 5.0 ml of 0.1 N HC1 solution.
5. Dilute to volume.
Prepare final sample solutions from ash solutions for atomic ab-
sorption analysis as follows:
1. Pipette two milliliters of ash solution into a 10 ml volumet-
ric flask.
2. Pipette two milliliters of 5.0% lanthanum solution into each
flask.
3. Dilute to mark with distilled water.
Method of Additions
Each sample determination requires the preparation and atomic ab-
sorption readings of five solutions. Ten-milliliter solutions are pre-
pared containing an aliquot of ash solution and strontium additions of
zero, 0.05, 0.10, 0.15 and 0.20 ppm as follows:
1. To each of five 10-ml volumetric flasks add the following vol-
umes of strontium solution containing 0.01 mg strontium per milli-
liter.
PPM
0.00
0.05
0.10
»
0.15
0.20
ml of Std. Soln.
0.00
0.05
0.10
0.15
0.20
2. Add a two milliliter aliquot of ash solution.
3. Add 2 ml of 5.070 lanthanum solution.
4. Dilute to mark.
(A blank is made up as described in the standard curve method)
III. STANDARDS AND ATOMIC ABSORPTION SOLUTIONS. HAY ANALYSIS
Stable strontium levels in the various hays and forages vary over
a considerable range. Hence it will be necessary to establish stron-
tium levels for standards according to the levels of strontium present
in the samples analyzed. It is suggested that before a large number
of samples are prepared for atomic absorption analysis, either by the
20
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standard curve method or method of additions, a preliminary analysis
be made on a few ash solutions to obtain an approximation "of the range
of strontium levels which are present. The standard curve method
should be used for this. The strontium levels for standards and addi-
tions given below are intended as an example only.
Standard Curve Method
Prepare 25-ml standard solutions containing 00.0 (blank), 0.5,
1.0, 1.5,«2t.O, and 2.5 ppm strontium as follows:
1. To each of six 25-ml volumetric flasks add the following vol-
umes of strontium solution containing 0.01 mg strontium per milli-
liter.
PPM ' ml of Std. Soln.
0.0 (Blank) 0.00
0.5 1.25
1.0 2.5
1.5 3.75
2.0 5.00
2.5 6/25
2. Add 5.0 ml of 5.0% lanthanum solution.
3. Add 2.5 ml of a sodium chloride solution containing 5.0 mg of
sodium per milliliter.
4. A'dd 1 ml of 1.0 N HC1.
5. Dilute to mark.
Final sample solution;
1. Ash solutions as prepared in the 250 ml volumetric flasks are
ready for analysis without further treatment.
Method of Additions
As in the case of the milk strontium determinations, each sample
requires the preparation and instrument reading of five solutions.
Ten milliliter solutions are prepared containing an aliquot of ash
solution and strontium additions of zero, 0.2, 0.4, 0.6, and 0.8 ppm
as follows:
21
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1. To each of five 10-ml volumetric flasks add the following
volumes of strontium solution containing 0.01 mg strontium per
milliliter.
PPM
0.00
0.20
0..4
0.6
0.8
ml of Std. Soln.
0.00
0.20
0.40
0.60
0.80
2. Add a five milliliter aliquot of ash solution.
3. Add one milliliter of 5.0% lanthanum solution.
4. Dilute to mark.
(A blank is made up as described in the standard curve method)
IV. ATOMIC ABSORPTION SPECTROPHOTOMETRY
The procedure and instrument settings given are for the
Perkin-Elmer Atomic Absorption Spectrophotometer Model-303. The in-
strument should be equipped with a 10-turn zero control and a time
response control. The instrument settings are the same as those given
in the Perkin-Elmer instrument manual (5) with some modifications.
Refer to the standard conditions for strontium in the instrument man-
ual for general operating conditions and information not given here.
1. Burner head: Equip instrument with a three-slot Boling burn-
er head.
2. Range: Visible
3. Slit: Four
o
4. Wavelength: 4607 A with the instrument scale setting at
approximately 230.
5. Source: Hollow cathode lamp set at 16 ma lamp current.
6. Scale expansion: It will be necessary to use a setting of
"ten" for the milk analysis. For hay analysis use either "five
or two" depending on the strontium levels present.
7. Time response control: It is suggested that this control be
used. The instrument operator should pick the setting which works
best for each scale expansion.
22
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8. Gain setting: The gain setting should be minimum. Set the
gain so that the needle of the energy is about five scale divisions
to the left of center or just within the left hand portion of the
black region of the scale.
9. The blank or zero strontium standard made up for the standard
curve method is used to zero the instrument for both the standard
curve method and method of additions. The null meter needle should
be set at mid-position accurately and frequently.
V. CALCULATIONS
Divide the average instrument reading by the scale expansion set-
ting to obtain absorption. Convert absorption to absorbance. The
absorption should be read on the table, two places beyond the decimal,
and the corresponding absorbance determined by interpolation.
Standard Curve Method
Plot a working curve relating absorbance to concentration and deter-
mine the concentration of strontium in the final sample solution.
1. Milk
ppm in final sample soln. = mg in 10 ml final solution or
100 2.0 ml aliquot
mg Sr in aliquot x 50 = mg Sr in 100 ml ash soln. or total
sample
mg Sr in sample = mg per g powder
sample weight
mg Sr in sample = mg per ml milk
sample vol.
mg Sr in sample *= mg per g ash
ash weight
2, Alfalfa
ppm in 250 ml ash soln. = mg Sr in ash soln. or total sample
4
Method of Additions
An example of a method of additions working curve for an alfalfa
determination is shown in Figure 1. Plot absorbance against concen-
trations of strontium added as shown. As described in the instrument
manual (5), extrapolate the resulting straight line through zero
23
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absorbance. The intercept on the concentration axis gives the concen-
tration of strontium in the original sample. The working curve should
be a straight line.
1. Milk
Determine concentration of strontium in final sample solution and
proceed with calculations given for standard curve procedure.
2. Alfalfa
ppm in atomic absorption soln. x 2.0 = ppm in ash solution
ppm in ash solution = mg Sr in 250 ml ash solution or total
4.0 sample
VI. REAGENTS
Glacial acetic acid (fluid milk analysis)
Nitric acid: 6 N
Hydro-chloric acid: 6 N, IN, 0.1 N
Lanthanum oxide solution, La_0 : 5.0% lanthanum. As described in the
the instrument manual (5.), dissolve 58.65 g of La£03 in 250 ml of
concentrated HC1. Add the acid very slowly using extreme care
(REACTION IS VIOLENT) until the material is dissolved (hood is re-
commended) . Dilute to 1000 ml with distilled water.
Stock strontium standard solution: 1000 ppm strontium as strontium
carbonate. Dissolve in minimum HC1 and dilute to volume.
Strontium standard solution: 0.01 milligram strontium per milli-
liter.
Sodium chloride solution: 5.0 milliligrams sodium per milliliter.
24
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SAMPLE 1
TRIAL IE
UNTREATED ALFALFA PELLETS
0.04
0.03
UJ
u
z
g 0.02
o
uo
CO
0.01
0.8
0.52 ppm
0.6'
0.4
0.2 0.0 0.2
STRONTIUM ADDITIONS ppm
0.4
0.6
Figure 1. Working curve for an alfalfa determination by the method of additions
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-680/4-73-002
3. RECIPIENT'S ACCESSION-NO.
TITLE ANDSUBTITLE
AMPLIFIED ATOMIC ABSORPTION DETERMINATION OF STABLE
STRONTIUM IN MILK AND HAY: A comparison of methods
and stepwise procedure
5. REPORT DATE
December 1973 (preparation)
6. PERFORMING ORGANIZATION CODE
'. AUTHOR(S)
Julius Barth, NERC-Las Vegas, EPA
Benjamin H. Bruckner, Center for Disease Control, NIOSh
8. PERFORMING ORGANIZATION REPORT NO.
n/a
9. PERFORMING ORGANIZATION NAME AND ADDRESS
National Environmental Research Center
U.S. Environmental Protection Agency
P. 0. Box 15027
Las Vegas, NV 89114
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
n/a
12 SPONSORING AGENCY NAME AND ADDRESS
Office of Research and Development
U.S. Environmental Protection Agency
Washington, DC 20460
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
This work was performed at the Rockville Radiological Health Laboratory when it was a
part of the National Center for Radiological Health, DHEW, under a program later in-
cor.poratod into the EPA. - - - -
. ABSTRACT
A highly simplified atomic absorption procedure for the determination of stable
strontium in fluid milk, milk powder, and alfalfa is evaluated/ A comparison i
made between the atomic absorption method of additions and the standard curve
method. A suggested stepwise procedure is given.
7.
KEY WORDS AND DOCUMENT ANALYSIS
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b.lDENTIFIERS/OPEN ENDED TERMS
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chemical analysis
hay
milk
quantitative analysis
strontium
07 02 / 02 01
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