EPA/600/4-90/024
October 1990
MODIFICATION OF METHODS 9030 AND 9031 FOR THE
ANALYSIS OF SULFIDE BY SPECIFIC ION ELECTRODE
by
Daniel C. Hillman and Piotr Nowinski
Lockheed Engineering and Sciences Company
1050 E. Flamingo Rd., Suite 120
Las Vegas, NV 89119
Contract Number 68-03-3249
Project Officer
Steven M. Pyle
Quality Assurance and Methods Development Division
Environmental Monitoring Systems Laboratory
Las Vegas, Nevada 89193-3478
ENVIRONMENTAL MONITORING SYSTEMS LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
LAS VEGAS, NEVADA 89193-3478
-------
NOTICE
The information in this document has been funded wholly by the United States
Environmental Protection Agency. It has been subject to the Agency's peer and administration
review, and it has been approved for publication as an EPA document. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.
ii
-------
ABSTRACT
Two OSW SW-846 methods (Method 9030 and 9031) used for the determination of sulfide
have been modified to include the use of sulfide specific ion electrodes (SIE). Currently in both
methods sulfide is converted to hydrogen sulfide and distilled into a scrubber solution for
subsequent determination by iodometric titration. In the modified methods, the hydrogen sulfide
in the scrubber is determined by sulfide SIE. A single-lab evaluation was performed to determine
the operating characteristics. The sulfide SIE is linear over the range 0.25-6000 mg/L sulfide
with a detection limit is about 0.2 mg/L sulfide. Over the range 5-6000 mg/L, the relative
precision of the SIE is 2-4 percent. The accuracy (expressed as percent recovery) over the range
0.25-6000 mg/L varies from 75-103 percent. The response time for the electrode was less than a
minute over the entire linear concentration range. The sulfide SIE is very selective for the sulfide
dianion, and in the scrubber solution, there are no interferences. If the sulfide SIE is used to
measure sulfide directly in samples (i.e., no distillation), mercury and silver ions may interfere.
However, under the conditions of analysis (pH>12), neither ion is present at interfering
concentrations. Another factor is important if the SIE is used to determine sulfide directly; it only
responds to free sulfide dianion and will not detect sulfide tied up in complexes. Recoveries in
real samples spiked with 17.5 mg/L sulfide varied from 68-77 percent before distillation and 93-
98 percent after distillation. The results from the evaluation indicate that the sulfide SIE provides
an alternate technique to determine sulfide in environmental samples after distillation.
iii
-------
CONTENTS
ABSTRACT iii
FIGURES vii
TABLES viii
INTRODUCTION 1
EXPERIMENTAL DESIGN 2
EXPERIMENT 1 (LINEARITY) 2
EXPERIMENT 2 (PRECISION AND ACCURACY) 2
EXPERIMENT 3 (INTERFERENCES) 2
EXPERIMENT 4 (DIRECT MEASUREMENT IN REAL SAMPLES) 2
EXPERIMENT 5 (RECOVERY OF DISTILLED HYDROGEN SULFIDE IN THE
SAOBSCRUBBER) 3
PROCEDURE 4
APPARATUS 4
Orion Silver/Sulfide Electrode, Model 94-16 4
Orion Double Junction Reference Electrode, Model 90-20-00 4
Orion Ion Analyzer 940 4
REAGENTS .. 4
Sulfide Stock Solution (10,000 mg/L) 4
Sulfide Stock Solution (1,000 mg/L) 4
Dilute Sulfide Solutions- 4
Zinc Acetate Solution (2 N) 5
Starch Indicator Solution 5
Iodine Solution (0.025 N) 5
Thiosulfate Solution (0.025 N) 5
Potassium Iodate Solution (0.0490 N) 5
Sodium Hydroxide Solution (6 N) 5
Sulfide Anti-Oxidant Buffer (SAOB) 6
Reagent Water 6
REAGENT STANDARDIZATION 6
Stock Sulfide Solutions 6
Thiosulfate Solution 6
Iodine Solution 6
SULFIDE ELECTRODE ANALYSIS 7
Calibration of the Ion meter 7
Sample Analysis 7
RESULTS AND DISCUSSION 8
EXPERIMENT 1 (LINEARITY) 8
EXPERIMENT 2 (PRECISION AND ACCURACY) 9
V
-------
EXPERIMENT 3 (INTERFERENCES) 9
SULFIDE SIE OPERATING CHARACTERISTICS 11
SULFIDE STANDARDS II
DIRECT MEASUREMENT IN REAL SAMPLES 11
RECOVERY OF DISTILLED HYDROGEN SULFIDE IN THE SAOB SCRUBBER 12
DISCUSSION AND CONCLUSIONS 13
APPENDIX A 14
APPENDIX B 33
vi
-------
FIGURES
Number Pase
Figure 1. Plot of Sulfide SIE response vs. log (sulfide concentration, mg/L) 10
vii
-------
TABLES
Number Page
TABLE 1. SULFIDE SIE RESPONSE VS. SULFIDE CONCENTRATION 8
TABLE 2. COMPARISON OF TRUE SULFIDE CONCENTRATION VS.
CONCENTRATION MEASURED BY SULFIDE SIE 9
TABLE 3. PRECISION AND ACCURACY DATA FOR THE SULFIDE SIE 9
TABLE 4. INTERFERENCE STUDY RESULTS 10
TABLE 5. RESULTS FOR THE DIRECT COMPARISON OF SULFIDE BY SIE AND
COMPARISON TO METHOD 9030 12
TABLE 6. RECOVERY OF HYDROGEN SULFIDE IN SAOB SOLUTION 13
viii
-------
INTRODUCTION
Currently two methods for determining sulfide exist in OSW SW-846 "Test Methods for
Evaluating Solid Waste", Method 9030 and Method 9031. Method 9030 is useful for determining
acid-soluble and acid-insoluble sulfide in aqueous and solid waste materials and effluents except
those which contain oil, are multiphasic, or are not amenable to distillation. Method 9031 is
useful for determining extractable sulfide and essentially is applicable to all samples which can't
be analyzed by Method 9030.
In Method 9030, samples are acidified to convert all free sulfide and acid-soluble sulfides to
H2S, which is distilled into a zinc acetate scrubber solution. Sulfide in the scrubber is then
determined by iodometric titration. Acid-insoluble sulfide is determined similarly except that the
acidification/ distillation step is more severe. In Method 9031, sulfides are extracted from oily or
non-aqueous phases into a basic aqueous phase. Any original aqueous phase and the basic extract
are then combined, acidified, and the sulfide distilled into a zinc acetate scrubber solution.
Sulfide in the scrubber is then determined by iodometric titration.
In both Method 9030 and 9031, the distillation step is inherent in the method. However,
once distilled, methods other than iodometric titration exist for the determination of sulfide in the
scrubber. One alternative method is the sulfide SIE. The sulfide SIE in general is very sensitive
and interference-free. The most common interfering ions are silver and mercury, neither of
which will be present in the distillate scrubber. This is an advantage over the titrimetric method,
which suffers from interferences due to other sulfur compounds (sulfite, thiosulfate, sulfur
dioxide) which can distill over into the scrubber.
The purpose of this study was to evaluate the use of the sulfide SIE to measure sulfide in
the distillate scrubber. The distillate scrubber in Methods 9030 and 9031 is a zinc acetate solution
in which the distilled sulfide is precipitated as zinc sulfide. To use the SIE, the scrubber is
changed to sulfide anti-oxidant buffer (SAOB, a sodium hydroxide solution (pH>12) with ascorbic
and salicylic acids added as an oxygen scavengers). The precision, accuracy, and linearity of the
sulfide SIE were determined in the scrubber matrix as well as the response time of the electrode
and its ease of operation.
Effects of known interferences (silver ion and mercuric ion) in undistilled samples were
evaluated. Also the use of the SIE for the direct measurement of sulfide in environmental samples
was demonstrated. Beth spiked and unspiked samples were measured. The direct measurements
were compared to results obtained by Method 9030. Based on this evaluation, protocols for
Method 9030 and Method 9031 were modified to include the use of the sulfide SIE. The modified
protocols are attached as Appendix A and B, respectively.
1
-------
EXPERIMENTAL DESIGN
EXPERIMENT 1 (LINEARITY)
The sulfide SIE was calibrated with 100 and 1000 mg/L standards. Twelve sulfide samples
were prepared (0.1, 0.25, 0.5, 1, 5, 25, 50, 100, 500, 1,000, 5,000, 10,000 mg/L sulfide). The
samples were analyzed in a random order (25, 1,000, 0.5, 10,000, 500, 0.25, 1, 100, 0.1, 5, 50,
5,000). The three low and three high samples were analyzed in triplicate. The measured
concentration was plotted vs. true concentration and a linear regression was calculated.
EXPERIMENT 2 (PRECISION AND ACCURACY)
Three sulfide samples were prepared (low, medium, and high; 25, 100, and 1000 mg/L).
Triplicate measurements of each were performed in the following order; medium, low, high, high,
low, medium. Precision estimates were calculated from the average percent RSD taken within
each block of triplicate measurements. Accuracy estimates were calculated from average percent
recovery.
EXPERIMENT 3 (INTERFERENCES)
No interferences were expected in the scrubber solution. However the compounds that
interfere with the titration analysis were tested for interference with the sulfide electrode analysis.
Portions of a 100 mg/L sulfide sample were spiked TO contain 100 mg/L sodium sulfite and 100
mg/L sodium thiosulfate. An unspiked sample and the two spiked samples were analyzed to check
for any interference.
In environmental samples (undistilled), there are few substances which can interfere with
the chemistry of the sulfide SIE. The two major interferences are silver ion and mercuric ion.
Organic species will not interfere chemically with the electrode, though they can cause physical
interferences (i.e., by coating the electrode). An experiment was performed to test the effect of
silver and mercury on the sulfide SIE. Silver was also tested with the addition of ammonia, which
prevents silver precipitation in the basic measuring solution. Additionally, the effect of humic
acid, a common natural organic compound, was also studied. In this experiment, two matrices
were studied; deionized water and tap water. The experimental procedure entailed the following
steps: Mix 8 mL of the SAOB and 25 mL of the matrix containing the interferent, filter the
solution, measure sulfide by SIE.
EXPERIMENT 4 (DIRECT MEASUREMENT IN REAL SAMPLES)
The sulfide SIE responds only to dissolved sulfide ion. Any sulfide present as a solid or
complex was not detected by the sulfide SIE. Four samples (described below) were prepared by
slurrying the sample with SAOB and measuring sulfide with the SIE. The experiment was
repeated after spiking the sample with sulfide. The experiment was repeated for the spiked
samples using Method 9030 to determine sulfide.
2
-------
Sample
Description
Sand
100% silica sand
Soil 1
soil contaminated
with heavy metals
Soil 2
soil contaminated
with heavy metals
Oil
NIST base oil 1083
EXPERIMENT 5 (RECOVERY OF DISTILLED HYDROGEN SULFIDE IN THE SAOB
SCRUBBER)
As part of Methods 9030 and 9031, hydrogen sulfide gas was distilled from a sample and
absorbed into a zinc acetate scrubber solution. For the modified protocols using the sulfide SIE,
the hydrogen sulfide gas was distilled from a sample and absorbed into a SAOB scrubber solution.
To test the efficiency of the SAOB as a scrubber solution, three standards (1, 10, and 40 mg/L
sulfide) were distilled into SAOB scrubber and the resulting sulfide concentration measured.
3
-------
PROCEDURE
APPARATUS
Orion Silver/Sulfide Electrode. Model 94-16
Orion Double Junction Reference Electrode. Model 90-20-00
Orion Ion Analyzer 940
REAGENTS
Sulfide Stock Solution (10.000 me/L)
Dissolve 24.3 g anhydrous Na2S (or 74.7 g Na2S-9H20) and 10 g NaOH in 1 L reagent
water. Keep tightly closed and store at 4#C. Standardize weekly by iodometric titration.
Sulfide Stock Solution (1.000 mg/L)
Dissolve 2.4 g anhydrous Na2S (or 7.5 g Na2S-9H20) and 10 g NaOH in 1 L reagent water.
Keep tightly closed and store at 4°C. Standardize weekly by iodometric titration.
Dilute Sulfide Solutions
The following dilute sulfide solutions must be prepared daily as required.
5,000 mg/L - Pipet 20.00 mL scrubber solution and 50.00 mL 10,000 mg/L sulfide stock
solution into a 100 mL volumetric flask and dilute to the mark with reagent
water.
500 mg/L - Pipet 20.00 mL scrubber solution and 50.00 mL 1,000 mg/L sulfide stock
solution into a 100 mL volumetric flask and dilute to the mark with reagent
water.
100 mg/L - Pipet 20.00 mL scrubber solution and 10.00 mL 1,000 mg/L sulfide stock
solution into a 100 mL volumetric flask and dilute to the mark with reagent
water.
50 mg/L - Pipet 20.00 mL scrubber solution and 5.00 mL 1,000 mg/L sulfide stock
solution into a 100 mL volumetric flask and dilute to the mark with reagent
water.
25 mg/L - Pipet 20.00 mL scrubber solution and 2.50 mL 1,000 mg/L sulfide stock
solution into a 100 mL volumetric flask and dilute to the mark with reagent
water.
4
-------
5 mg/L - Pipet 20.00 mL scrubber solution and 0.500 mL 1,000 mg/L sulfide stock
solution into a 100 mL volumetric flask and dilute to the mark with reagent
water.
1 mg/L - Pipet 20.00 mL scrubber solution and 0.100 mL 1,000 mg/L sulfide stock
solution into a 100 mL volumetric flask and dilute to the mark with reagent
water.
0.5 mg/L - Pipet 20.00 mL scrubber solution and 0.0500 mL 1,000 mg/L sulfide stock
solution into a 100 mL volumetric flask and dilute to the mark with reagent
water.
0.25 mg/L - Pipet 20.00 mL scrubber solution and 0.0250 mL 1,000 mg/L sulfide stock
solution into a 100 mL volumetric flask and dilute to the mark with reagent
water.
0.1 mg/L - Pipet 20.00 mL scrubber solution and 0.0100 mL 1,000 mg/L sulfide stock
solution into a 100 mL volumetric flask and dilute to the mark with reagent
water.
Zinc Acetate Solution (2 N~)
Dissolve 220 g zinc acetate dihydrate Zn(CH3C00)2-2H20 in 500 mL reagent water then
dilute to 1,000 mL.
Starch Indicator Solution
Dissolve 2 g laboratory grade soluble starch and 0.2 g salicylic acid (as a preservative) in 100
mL hot reagent water.
Iodine Solution (0.025 N)
Dissolve 20-25 g KI in 200 mL reagent water. Add 3.2 g iodine then dilute to 1,000 mL.
Standardize with 0.025 N Na2S2Os using a starch indicator.
Thiosulfate Solution (0.025 N)
Dissolve 6.205 g Na2S203-5H20 in reagent water. Add 1.5 mL 6 N NaOH (or 0.4 g solid
NaOH) and dilute to 1,000 mL. Standardize with potassium iodate solution.
Potassium Iodate Solution (0.0490 N)
Dissolve 0.1748 g primary standard grade KIOs (dried at 105°C for 1 hour) in reagent
water and dilute to 100 mL in a volumetric flask.
Sodium Hydroxide Solution (6 N)
Dissolve 240 g NaOH in 1,000 mL reagent water. Keep tightly closed.
5
-------
Sulfide Anti-Oxidant Buffer (SAOB)
Dissolve 80 g NaOH, 320 g sodium salicylate, and 72 g ascorbic acid in 1 L reagent water.
Prepare fresh weekly.
Reagent Water
Water used to prepare reagents and standards must conform to ASTM specifications for
Type II water (ASTM, 1984, Vol.11.01, D1193-77).
REAGENT STANDARDIZATION
Stock Sulfide Solutions
Dilute 5.00 mL standard sulfide solution to 100 mL with reagent water. Add 5.00 mL 0.025
N iodine solution and 2.0 mL 6 N HCI. Back titrate with 0.025 N Na2S203 solution, adding a few
drops of starch indicator as end point is approached. Continue titration until blue color
disappears. The concentration is calculated as follows;
Sulfide img/L) = [(AxB)-(Cx0)1xl6000
E
A = volume of iodine solution (5.00 mL)
B = normality of iodine
C = volume of Na2S203 solution (mL)
D = normality of Na2S203 solution (eq/L)
E = volume of sulfide standard (5.00 mL)
Thiosulfate Solution
Dissolve 2 g KI (free from iodate) in 100 mL reagent water. Add 2 mL
6 N HCI and 5.00 mL iodate solution. Dilute to 200 mL and titrate the liberated iodine with the
thiosulfate solution, adding starch indicator as the endpoint is approached (pale straw color). The
endpoint is reached when the solution changes from dark blue to colorless. Calculate the
thiosulfate concentration as follows;
Ax R
Thiosulfate conc. (eq/L) = ——
A » volume of iodate solution (5.00 mL)
B = normality of iodate solution (eq/L)
V = volume of tniosulfate solution (mL)
6
-------
Iodine Solution
Dilute 5.00 mL of iodine solution to 100 mL with reagent water. Titrate with the
standardized thiosulfate solution, add 2 mL of starch indicator as the endpoint is approached.
Continue titration to the endpoint. Calculate the iodine solution concentration as follows;
Iodine conc. (ea/L) = VxC
A
V = volume of thiosulfate solution (mL)
A = volume of iodine solution (5.00 mL)
C = thiosulfate normality (eq/L)
SULFIDE ELECTRODE ANALYSIS
Calibration of the Ion meter
The ion meter was calibrated following the manufacturer's directions using 1,000 and 100
mg/L sulfide standards.
Sample Analysis
The following procedure was used to analyze samples using the sulfide electrode.
1) Rinse the electrodes thoroughly with reagent water.
2) Add 60 mL sample and 20 mL SAOB to a disposable beaker and cover with a
polyethylene lid.
3) Place on insulated stir plate and begin stirring.
4) Insert the electrodes. Record the sulfide concentration and analysis time when a stable
reading is obtained.
7
-------
RESULTS AND DISCUSSION
EXPERIMENT 1 (LINEARITY)
The sulfide SIE was connected to a ion meter and a series of sulfide standards analyzed
(Table 1). The electrode response vs. the log of the sulfide concentration is plotted in Figure 1.
The curve is linear over the range 1-12,000 mg/L. For practical routine analysis, the sulfide SIE
is calibrated using a 2-point calibration. To evaluate practical analyses, the sulfide SIE was
calibrated with 100 and 1000 mg/L standards, the a series of standards analyzed as unknowns.
The results are listed in Table 2. Recoveries ranged from 76-124% over the range 0.25-12,000
mg/L sulfide. This indicates that there is no practical difference between the true and observed
values for sulfide over this concentration range. The detection limit is estimated to be about 0.2
mg/L sulfide (from the precision at the 0.5 mg/L level).
TABLE 1. SULFIDE SIE RESPONSE
VS. SULFIDE CONCENTRATION
SULFIDE (mg/L)
RESPONSE
(mV)
0.100
-767.8
0.250
-769.1
0.500
-770.7
0.500
-771.1
1.000
-774.1
1.09
-774.6
5.00
-786.2
27.4
-805.5
55.0
-813.7
110
-821.8
591
-843.7
1183
-852.3
6000
-873.8
12000
-885.6
8
-------
TABLE 2. COMPARISON OF TRUE SULFIDE CONCENTRATION VS.
CONCENTRATION MEASURED BY SULFIDE SIE
True (mg/L)
Measured
(mg/L)
Std. Dev
(mg/L)
RSD (%)
Recovery (%)
0
-0.2
0.10
0 01
10
0.25
0.19
76
0.50
0.47
0.059
12.7
94
1.00
0.99
0.092
9.3
99
1.09
1.10
101
5.00
4.94
0.17
3.4
99
27.4
26.8
98
55.0
52.3
95
110
109
99
591
607
103
1183
1157
5.2
0.4
98
6000
6028
123
2.0
100
12000
14850
332
2.2
124
n = 3 for samples with standard deviation
EXPERIMENT 2 (PRECISION AND ACCURACY)
After calibration, the sulfide SIE was used to measure the concentration of three standards six
times each. The data is listed in Table 3. Upon examination of the data in Tables 2 and 3, it is
apparent that for sulfide concentrations greater than 10 times the detection limit (estimated at
0.2 mg/L), the relative precision ranges from 2-4 percent. Over the entire range, 0.25-12,000
mg/L, the percent recovery ranges from 75-124 percent.
TABLE 3. PRECISION AND ACCURACY DATA FOR THE SULFIDE
SIE
True
(mg/L)
Measured
(mg/L)
Std. Dev.
(mg/L)
RSD (%)
Recovery
(%)
23.6
19.2
0.81
4.2
82.5
118.1
114.8
2.2
1.9
97.2
1503
1455
26
1.8
96.8
n = 6 for all samples
EXPERIMENT 3 (INTERFERENCES)
The effect of sulfur compounds (with sulfur in the +4 oxidation state) on the sulfide SIE in the
absorbing solution (which interfere with the titrimetric method) was tested (e.g., sulfite or
9
-------
LLI
m
z
0
CL
1 r
LU
cr
LLi
C/j
1JJ
c
-700
-750
-800
•850
-900
950
1000
* *
SLOPE = -27.20
Y-INT = -769.6
R =0.996
*
LINEAR RANGE = 1-12,000
J_ i i i i
'
0.01
0.1 1 10 100 1000
SULFIDE CONCENTRATION CMG/IO
Figure 1. Plot of Sulfide SIE response vs. log (sulfide
concentration, mg/L)
thiosulfate). The electrode did not respond to either compound. A 110 mg/L sulfide solution was
spiked with 100 mg/L sulfite and 100 mg/L thiosulfate. The measured concentrations for the
unspiked and spiked samples were identical (114 mg/L).
The effects of silver, mercury, and humic acid on the sulfide SIE are presented in Table 4.
TABLE 4. INTERFERENCE STUDY RESULTS
Interferent
Sulfide Concentration (mg/L)
DI matrix
Tap water matrix
Ag+ (20 mg/L)
<1
<1
Ag+ + NH4+ (20 mg/L each)
<1
<1
Hg+ (20 mg/L)
<1
<1
Humic acid (100 mg/L)
2.1
1.6
Humic acid + sulfide
(100 mg/L each)
114
87.8
* The humic acid contains 2-3 mg/L sulfide as determined by Method 9030.
10
-------
The data indicates that neither silver, mercury, nor humic acid interfere with the electrode. An
interference would be indicated by a positive response. This is not surprising for the conditions
of analysis, which are at pH>12. At this pH, both silver and mercury precipitate and do not effect
the electrode. If ammonia is present, silver still does not interfere. Apparently the silver-
ammonia complex prevents any silver present from interfering with the electrode. Silver and
mercury are listed as interferents (by the electrode manufacturers) for the sulfide electrode for
analyses performed under different conditions (i.e. those in which the ions are in solution).
SULFIDE SIE OPERATING CHARACTERISTICS
The response time of the electrode was less than 1 minute across the entire concentration range
investigated. The stability of the electrode is affected by the solution temperature. A change in
temperature of 1°C results in a 4% error (Orion Model 94-16 Silver/Sulfide Electrode Manual).
Most ion meters have the capability of empirically correcting for temperature drift throughout the
course of a day. However, for the most accurate and precise work, samples and standards should
all be equilibrated to the same temperature.
SULFIDE STANDARDS
Sulfide standards are subject to degradation due to oxidation by dissolved oxygen. However,
when prepared fresh daily in SAOB, the sulfide standards are stable throughout a working day
(less than 10% degradation over 6-8 hours). Standardization of the sulfide standards is a critical
step in calibrating the sulfide SIE. The calibration standards must be independently standardized
daily. Standardization is normally performed by iodometric titration. The iodometric titration is
tedious and labor intensive; a solution of thiosulfate is standardized against a standard iodate
solution, an iodine solution is standardized against the thiosulfate solution, and the sulfide
standard is standardized against the iodine solution/thiosulfate solution. Also the iodine solution
requires daily calibration itself. An alternate procedure for standardizing the sulfide calibration
standards is by a potentiometric titration with standardized silver nitrate using the sulfide SIE as
the working electrode. Silver nitrate solutions are stable when stored properly and are easily
standardized against sodium chloride.
DIRECT MEASUREMENT IN REAL SAMPLES
The sulfide SIE responds only to dissolved sulfide ion. Any sulfide present as a solid or complex
will not be detected by the sulfide SIE. Four samples were prepared by slurring the sample with
SAOB and measuring sulfide with the SIE. The experiment was repeated after spiking the sample
with 17.5 mg/L sulfide. The experiment was repeated for the spiked samples using Method 9030
to determine sulfide. The results are presented in Table 5.
The spike recovery varies from 68-77 percent for the SIE results and from 93-98 percent for the
Method 9030 results. This indicates that some of the added sulfide is tied up and not
11
-------
TABLE 5. RESULTS FOR THE DIRECT COMPARISON OF SULFIDE BY SIE AND
COMPARISON TO METHOD 9030
Sample
Spike added
(mg/L)
Results
SIE
Method 9030
(mg/L)
% Recovery
(mg/L)
% Recovery
Sand
0
<3
17.5
12.5
71.4
16.6
94.9
Soil 1
0
<3
17.5
13.4
76.6
17.1
97.7
Soil 2
0
<3
17.5
11.7
66.9
16.3
93.1
Oil
0
<3
17.5
12.5
71.4
16.6
94.9
detected by the SIE, which is expected. Recoveries are better for Method 9030 because hydrogen
sulfide gas is liberated from any complexed or solid sulfide during the distillation step.
RECOVERY OF DISTILLED HYDROGEN SULFIDE IN THE SAOB SCRUBBER
As part of Methods 9030 and 9031, hydrogen sulfide gas is distilled from a sample and
absorbed into a zinc acetate scrubber solution. For the modified protocols using the sulfide SIE,
the hydrogen sulfide gas is distilled from a sample and absorbed into a SAOB scrubber solution.
To test the efficiency of the SAOB as a scrubber solution, three standards (1, 10, and 40 mg/L
sulfide) were distilled into SAOB scrubber and the resulting sulfide concentration measured. The
results are listed in Table 6. As seen in the table, excellent recoveries are obtained using the
SAOB scrubber solution. The one low recovery for the 40 mg/L standard is most likely due to
incomplete sparging of oxygen from the system prior to distillation. The key to acceptable recov-
eries is the use of the proper apparatus and careful assembly of the distillation apparatus to
prevent leaks in the flow path. Additionally it is important to sparge oxygen from the apparatus
prior to distillation. If these steps are not taken, low recoveries will result, as seen in the initial
trials performed to test the recovery in SAOB, in which results ranged from 20-95 percent.
12
-------
TABLE 6. RECOVERY OF HYDROGEN
SULFIDE IN SAOB SOLUTION
Sulfide (mg/L)
% Recovery
1
91.0
89.8
86.7
10
96.6
100
96.0
40
69.3
98.9
89.2
DISCUSSION AND CONCLUSIONS
The sulfide SIE can be used to quantitatively detect soluble, uncomplexed sulfides in both
liquid and solid samples (after slurring with SAOB). However results may not be comparable to
those obtained by Methods 9030 or 9031, which measure total sulfide. If solid or complexed
sulfides are present, SEE results may be biased low. In such instances, the bias can be minimized
by performing the distillation step in Method 9030 prior to analysis. Once distilled, sulfide can be
analyzed acceptably by either titration or SIE. If measured by SIE, the distillation scrubber
solution is replaced by SAOB.
The use of a sulfide SIE is a simple procedure to measure sulfide ion in distillates obtained
from environmental samples. Distillation separates sulfide (as hydrogen sulfide gas) from any
significant matrix interferences present in environmental matrices (water, soil, and oil sample
matrices have been tested). Of course (as with all electrodes), if the electrode membrane becomes
fouled or scratched, its performance will be affected and it will have to be cleaned or polished.
The primary drawback with sulfide SIEs is the stability of calibration standards, which can
degrade by more than 10% from day-to-day. Standards have to be standardized daily before use
(by titration) and checked throughout the day if used as QC samples. For the determination of
total sulfide, the sulfide SIE offers no marked advantages over the typical titration, as the
distillation step is rate-limiting. If a better distillation procedure is developed (e.g., using the
Lachat micro-block distillation apparatus), the ease of automating the measurement step will be a
factor in determining which technique is better.
This evaluation has demonstrated that the sulfide SIE provides an alternate technique for
quantifying sulfide in distillate absorbing solutions. The precision and accuracy of the sulfide SIE
are adequate for sulfide determinations (2-4 percent RSD, 75-105 percent recoveries). Using the
sulfide SIE should increase throughput by a factor of two when compared to the iodometric
titration. Also, if the sulfide SIE is used, it is simpler to standardize the calibration standards with
a potentiometric titration rather than the iodometric titration.
13
-------
APPENDIX A
MODIFIED METHOD 9030
ACID-SOLUBLE AND ACID-INSOLUBLE SULFIDES
1.0 SCOPE AND APPLICATION
1:1 The distillation procedure described in this method is designed for the determination of
sulfides in aqueous and solid waste materials and effluent.
1.2 This method provides only a semi-quantitative determination of sulfide compounds
considered acid-insoluble (e.g. CuS and SnS2) in solid samples. Recovery has been shown
to be 20 to 40 percent for CuS, one of the most stable and insoluble compounds, and 40
to 60 percent for SnS2 which is slightly more soluble.
1.3 This method is not applicable to oil or multiphasic samples or samples not amenable to
the distillation procedure. These samples can be analyzed by Method 9031.
1.4 Method 9030 is suitable for measuring sulfide concentrations in samples which contain
between 0.2 and 50 mg/kg of sulfide.
1.5 This method is not applicable for reactive sulfide. Refer to Chapter Seven, Step 7.3.4.1
for the determination of reactive sulfide.
1.6 This method measures total sulfide which is usually defined as the acid-soluble fraction
of waste. If, however, one has previous knowledge of the waste and is concerned about
both soluble sulfides such as H2S, and metal sulfides, such as CuS and SnS2, then total
sulfide is defined as the combination of both acid-soluble and acid-insoluble fractions.
For wastes where only metal sulfides are suspected to be present, only the acid-insoluble
fraction needs to be measured.
2.0 SUMMARY OF METHOD
2.1 For acid-soluble samples, separation of sulfide from the sample matrix is accomplished
by the addition of sulfuric acid to the sample. The sample is heated to 70° C and the
hydrogen sulfide (H2S) which is formed is distilled under acidic conditions and carried
by a nitrogen stream into gas scrubbing bottles. If the sulfide is to be determined by
titration, the gas scrubbers contain zinc acetate where sulfide is precipitated as zinc
sulfide. If the sulfide is determined by sulfide ion specific electrode (SIE), the gas ¦
scrubbers contain sulfide anti-oxidant buffer (SAOB, a sodium hydroxide solution
containing salicylic and ascorbic acids at a pH>12) where it is trapped as sulfide ion.
2.2 For acid-insoluble sulfide samples, separation from the sample matrix is accomplished by
suspending the sample in concentrated hydrochloric acid by vigorous agitation. Tin(ll)
chloride is present to prevent oxidation of sulfide to sulfur by metal ions (e.g.,
14
-------
copper(II)), by the matrix, or by dissolved oxygen in the reagents. The prepared sample
is distilled under acidic conditions at 100°C under a stream of nitrogen. Hydrogen
sulfide gas is released from the sample and collected in gas scrubbing bottles containing
either a zinc acetate buffer or SAOB.
2.3 If determined by titration, the sulfide in the zinc sulfide precipitate is oxidized to sulfur
with a known excess amount of iodine. The excess iodine is determined by titration with
a standard solution of phenyl arsine oxide (PAO) or sodium thiosulfate until the blue
iodine starch complex disappears. As the use of standard sulfide solutions is difficult
because of oxidative degradation, quantitation is based on the PAO or sodium thiosulfate.
2.4 If determined by sulfide SIE, the sulfide in the SAOB is determined directly with a
calibrated sulfide SIE. The sulfide SIE is calibrated using freshly standardized sulfide
standards in a SAOB matrix (to minimize degradation prior to calibration). The sulfide
• standards are standardized by either a thiosulfate or silver nitrate titration.
3.0 INTERFERENCES
3.1 Aqueous samples must be taken with a minimum of aeration to avoid volatilization of
sulfide or reaction with oxygen, which oxidizes sulfide to sulfur compounds that are not
detected.
3.2 Reduced sulfur compounds, such as sulfite and hydrosulfite, decompose in acid, and may
form sulfur dioxide. This gas may be carried over to the zinc acetate gas scrubbing
bottles and subsequently react with the iodine solution yielding false high value. The
addition of formaldehyde into the zinc acetate gas scrubbing bottles removes this
interference. Any sulfur dioxide entering the scrubber will form an addition compound
with the formaldehyde which is unreactive towards the iodine in the acidified mixture.
This methods shows no sensitivity to sulfite or hydrosulfite at concentrations up to 10
mg/kg of the interferant. Sulfur dioxide will not interfere with the SIE determination.
3.3 Interferences for acid-insoluble sulfides have not been fully investigated. However,
sodium sulfite and sodium thiosulfate are known to interfere in the procedure for soluble
sulfides. Sulfur also interferes because it may be reduced to sulfide by tin(II) chloride in
this procedure.
3.4 The iodometric method suffers interference from reducing substances that react with
iodine, including thiosulfate, sulfite, and various organic compounds. The SIE method is
free from interferences.
3.5 The insoluble method should not be used for the determination of soluble sulfides
because it can reduce sulfur to sulfide, thus creating a positive interference.
4.0 APPARATUS AND MATERIALS
4.1 Distillation apparatus as shown in Figure 1.
4.1.1 Three Neck Flask—500 mL, 24/40 standard taper joints.
4.1.2 Dropping Funnel—100 mL, 24/40 outlet joint.
4.1.3 Purge Gas Inlet Tube—24/40 joint, with coarse frit.
15
-------
4.1.4 Purge Gas Inlet Tube—24/40 joint, with coarse frit.
4.1.5 Gas Scrubbing Bottles--125 mL, with ± in. o.d. inlet and outlet tubes. Impinger
tube must be fritted.
4.1.6 Tubing—± in. o.d. Teflon or polypropylene. Do not use rubber.
4.2 Sulfide SIE
4.3 Double Junction reference electrode
4.4 pH/mV/Ion meter capable of reading to 0.1 mV
REAGENTS
5.1 Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is
intended that all reagents shall conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society, where such specifications are
available. Other grades may be used, provided it is first ascertained that the reagent is of
sufficiently high purity to permit its use without lessening the accuracy of the
determination.
5.2 ASTM Type II Water (ASTM D-l 193-77 (1983)) -- All water used in this method will be
Type II unless otherwise specified.
5.3 Zinc Acetate Solution for Sample Preservation (2N) — Dissolve 220 g of zinc acetate
dihydrate in 500 mL of water.
5.4 Sodium Hydroxide (IN), NaOH -- Dissolve 40 g of NaOH in water and dilute to 1 liter.
5.5 Formaldehyde (37 percent solution) — This solution is commercially available.
5.6 Zinc Acetate for the Scrubber
5.6.1 For Acid-Soluble Sulfides Zinc Acetate Solution (approximately 0.5M)--Dissolve
about 110 g zinc acetate dihydrate in 200 mL of water. Add 1 mL hydrochloric
acid (concentrated), HC1, to prevent precipitation of zinc hydroxide. Dilute to 1
liter.
5.6.2 For Acid-Insoluble Sulfides Zinc Acetate/Sodium Acetate Buffer — Dissolve 100
g sodium acetate, and 11 g zinc acetate dihydrate in 800 mL of water. Add 1 mL
concentrated hydrochloric acid and dilute to 1 liter. The resulting pH should be
6.8.
5.7 Acid to Acidify the Sample
5.7.1 For Acid-Soluble Sulfides -- Sulfuric acid (concentrated)
5.7.2 For Acid-Insoluble Sulfides — Hydrochloric acid (9.8N). Place 200 mL of water
in 1 liter beaker. Slowly add concentrated HC1 to bring the total volume to 1 liter.
16
-------
5.8 Starch Solution — Use either an aqueous solution or soluble starch powder mixtures.
Prepare an aqueous solution as follows. Dissolve 2 g soluble starch and 2 g salicylic acid,
as a preservative, in 100 mL hot water.
5.9 Nitrogen gas
5.10 Iodine Solution (approximately 0.025N)—Dissolve 25 g potassium iodide, KI, in 700 mL
of water in a 1 liter volumetric flask. Add 3.2 g iodine. Allow to dissolve. Dilute to 1
liter and standardize as follows. Dissolve approximately 2 g KI in 150 mL of water.
Pipet exactly 20 mL of the iodine solution to be titrated and dilute to 300 mL with water,
Titrate with 0.025N standardized phenylarsine oxide or 0.025N sodium thiosulfate until
the amber color fades to yellow. Add starch indicator solution. Continue titration drop
by drop until the blue color disappears. Run in replicate. Calculate the normality as
follows:
Iodine concentration (eq/L) = VxN
V = volume of titrant (mL)
N = normality of titrant (eq/L)
S = volume of iodine solution (mL)
5.11 Sodium Sulfide Nonahydrate, Na2S • 9H20 — For the preparation of standard solution
to be used for calibration curves. Standards must be prepared at pH >9 or <11. Protect
standard from exposure to oxygen by preparing it without headspace. If standards are
for use with the SIE, prepare in 20 percent SAOB. These standards are unstable and
must be standardized immediately before use by either an iodometric titration or
potentiometric titration.
5.12Tin(II) chloride, SnCl2, granular.
5.13 Titrants.
5.13.1 Standard phenylarsine oxide (PAO) solution (0.025N), — This solution is
commercially available.
CAUTION: PAO is toxic.
5.13.2 Standard Sodium Thiosulfate Solution (0.025N) — Dissolve 6.205 ± 0.005 g
Na2S2Os • 5H20 in 500 mL water. Add 9 mL IN NaOH and dilute to 1 liter.
5.13.3 Standard Silver Nitrate Solution (0.10N) — Dissolve 16.989 g of AgNOs (dried for
2 hours at 150°C) in water and dilute to 1 L. Store in a brown bottle. Standardize
weekly against standard sodium chloride solution.
5.14 Sodium Hydroxide (6N), NaOH — Dissolve 240 g of sodium hydroxide in 1 liter of
water.
5.15 Sulfide Anti-Oxidant Buffer (SAOB) — Dissolve 80 g NaOH, 320 g sodium salicylate
and 72 g ascorbic acid in 1 L water. Prepare fresh weekly.
17
-------
5.16 Standard Sodium Chloride Solution (0.100N) — Dissolve 5.84 g NaCl (dried for 2 hours
at 140°C) in water and dilute to 1 L.
5.17 Potassium Chromate Indicator Solution — Dissolve 50 g K2Cr04 in a little water. Add
AgNOj solution until a definite red precipitate is formed. Let stand 12 hours, filter, and
dilute to 1 L.
6.0 SAMPLE COLLECTION, PRESERVATION, AND HANDLING
6.1 All samples must have been collected using a sampling plan that addresses the
considerations discussed in Chapter Nine of the EPA test methods for evaluating solid
waste (SW-846).
6.2 All aqueous and effluents must be preserved with zinc acetate and sodium hydroxide.
Use four drops of 2N zinc acetate solution per 100 mL of sample. Adjust the pH to
greater than 9 with 6N sodium hydroxide solution. Fill the sample bottle completely and
stopper with a minimum of aeration. The treated sample is relatively stable and can be
held for up to 7 days. If high concentrations of sulfide are expected to be in the sample,
continue adding zinc acetate until all the sulfide has precipitated. For solid samples, fill
the surface of the solid with 2N zinc acetate until moistened. Samples must be cooled to
4°C and stored headspace free.
6.3 Sample Preparation
6.3.1 For an efficient distillation, the mixture in the distillation flask must be of such a
consistency that the motion of the stirring bar is sufficient to keep the solids from
settling. The mixture must be free of solid objects that could disrupt the stirring
bar. Prepare the sample using one of the procedures in this section then proceed
with the distillation step (Section 7.0).
6.3.2 If the sample is aqueous, shake the sample container to suspend any solids, then
quickly decant the appropriate volume (up to 250 mL) of the sample to a
graduated cylinder, weigh the cylinder, transfer to the distillation flask and
reweigh the cylinder to the nearest milligram. Be sure that a representative aliquot
is used, or use the entire sample.
6.3.3 If the sample is aqueous but contains soft clumps of solid, it may be possible to
break the clumps and homogenize the sample by placing the sample container on a
jar mill and tumble or roll the sample for a few hours. The slurry may then be
aliquoted and weighed as above to the nearest milligram then diluted with water
up to a total volume of 250 mL to produce a mixture that is completely suspended
by the stirring bar.
6.3.4 If the sample is primarily aqueous, but contains a large proportion of solid, the
sample may be roughly separated by phase and the amount of each phase measured
and weighed to the nearest milligram into the distillation flask in proportion to
their abundance in the sample. Water may be added up to a total volume of 250
mL. As a guideline, no more than 25 g dry weight or 50 g of sludge can be
adequately suspended in the apparatus.
6.3.5 If the sample contains solid objects that can not be reduced in size by tumbling,
the solids must be broken manually. Clay-like solids should be cut with a spatula
18
-------
or scalpel in a crystallizing dish. If the solids can be reduced to a size that they
can be suspended by the stirring bar, the solid and liquid can be proportionately
weighed.
6.3.6 Non-porous harder objects, for example stones or pieces of metal, may be weighed
and discarded. The percent weight of non-porous objects should be used in the
calculation of sulfide concentration if it has a significant effect on the reported
result.
7.0 PROCEDURE
For acid-soluble sulfide samples, go to 7.1.
For acid-insoluble sulfide samples, to 7.2.
7.1 Acid-Soluble Sulfide
7.1.1 In a preliminary experiment, determine the approximate amount of sulfuric acid
required to adjust a measured amount of the sample to pH less than or equal to 1.
The sample size should be chosen so that it contains between 0.2 and 50 mg of sul-
fide. Place a known amount of sample or sample slurry in a beaker. Add water
until the total volume is 200 mL. Stir the mixture and determine the pH. Slowly
add sulfuric acid until the pH is less than or equal to 1.
CAUTION: Toxic hydrogen sulfide may be generated from the acidified sample.
This operation must be performed in the hood and the sample left in
the hood until the sample has been made alkaline or the sulfide has
been destroyed. From the amount of sulfuric acid required to acidify
the sample and the mass or volume of the sample acidified, calculate
the amount of acid required to acidify the sample to be placed in the
distillation flask.
7.1.2 Prepare the gas evolution apparatus as shown in Figure 1 in a fume hood.
7.1.3 Prepare a hot water bath at 70°C by filling a crystallizing dish or other suitable
container with water and place it on a hot plate stirrer. Place a thermometer in the
bath and monitor the temperature to maintain the bath at 70° C.
7.1.4 Assemble the three neck 500 mL flask, fritted gas inlet tube, and exhaust tube.
Use Teflon sleeves to seal the ground glass joints. Place a Teflon coated stirring
bar into the flask.
7.1.5 If determining sulfide by titration, place into each gas scrubbing bottle 10 ± 0.5
mL of the 0.5M zinc acetate solution, 5.0 ± 0.1 mL of 37 percent formaldehyde
and 100 ± 5.0 mL water.
7.1.6 If determining sulfide by SIE, place into each gas scrubbing bottle 10.0 mL SAOB
solution and 40.0 mL water.
7.1.7 Connect the gas evolution flask and gas scrubbing bottles as shown in Figure 1.
Secure all fittings and joints.
19
-------
7.1.8 Carefully place an accurately-weighed sample which contains 0.2 to 50 mg of
sulfide into the flask. If necessary, dilute to approximately 200 mL with water.
7.1.9 Place the dropping funnel onto the flask making sure its stopcock is closed. Add
the volume of sulfuric acid calculated in Step 7.7.1 plus an additional 50 mL into
the dropping funnel. The bottom stopcock must be closed.
7.1.10 Attach the nitrogen inlet to the top of the dropping funnel gas shut-off valve.
Turn on the nitrogen purge gas and adjust the flow through the sample flask to 25
mL/min. The nitrogen in the gas scrubbing bottles should bubble at about five
bubbles per second. Nitrogen pressure should be limited to approximately 10 psi
to prevent excess stress on the glass system and fittings. Verify that there are not
leak in the system. Open the nitrogen shut-off valve leading to the dropping
funnel. Observe that the gas flow into the sample vessel will stop for a short
period while the pressure throughout the system equalizes. If the gas flow through
the sample flask does not return within a minute, check for leaks around the
dropping funnel. Once flow has stabilized, turn on magnetic stirrer. Purge system
for 15 minutes with nitrogen to remove oxygen.
7.1.11 Heat sample to 70°C. Open dropping funnel to a position that will allow a flow of
sulfuric acid of approximately 5 mL/min. Monitor the system until most of the
sulfuric acid within the dropping funnel has entered the sample flask. Solids
which absorb water and swell will restrict fluid motion and, therefore, lower
recovery will be obtained. Such samples should be limited to 25 g dry weight.
7.1.12 Purge, stir, and maintain a temperature of 70#C for a total of 90 minutes from
start to finish. Shut off nitrogen supply. Turn off heat.
7.1.13 Proceed to Step 7.3 for the analysis of the zinc sulfide by titration and to Step 7.4
for the analysis of sulfide by SIE.
Acid-Insoluble Sulfide
7.2.1 As the concentration of HC1 during distillation must be within a narrow range for
successful distillation of H2S, the water content must be controlled. It is
imperative that the final concentration of HC1 in the distillation flask be about
6.5N and that the sample is mostly suspended in the fluid by the action of the
stirring bar. This is achieved by adding 50 mL of water, including water in the
sample, 100 mL of 9.8N HC1, and the sample to the distillation flask. Solids which
absorb water and swell will restrict fluid motion and, therefore, lower recovery
will be obtained. Such sample should be limited to 25 g dry weight.
7.2.2 If the matrix is a dry solid, weigh a portion of the sample such that it contains 0.2
to 50 mg of sulfide. The solid should be crushed to reduce particle size to 1 mm or
less. Add 50 mL of water.
7.2.3 If the matrix is aqueous, then a maximum of 50 g of the sample may be used. No
additional water may be added. As none of the target compounds are volatile,
drying the sample may be preferable to enhance the sensitivity by concentrating
the sample. If less than 50 g of the sample is required to achieve the 0.2 to 50 mg
of sulfide range for the test, then add water to a total volume of 50 mL.
-------
7.2.4 If the matrix is a moist solid, the water content of the sample must be determined
(Karl Fischer titration, loss on drying, or other suitable means) and the water in
the sample included in the total 50 mL of water needed for the correct HC1
concentration. For example, if a 20 g sample weight is needed to achieve the
desired sulfide level of 0.2 to 50 mg and the sample is 50 percent water then 40
mL rather than 50 mL of water is added along with the sample and 100 mL of
9.8N HC1 to the distillation flask.
7.2.5 Weigh the sample and 5 g SnCl2 into the distillation flask. Use up to 50 mL of
water, was calculated above, to rinse any glassware.
7.2.6 Assemble the distillation apparatus as in Figure 1. If the sulfide is determined by
titration, place 100 ± 2.0 mL of zinc acetate/sodium acetate buffer solution and 5.0
± 0.1 mL of 37 percent formaldehyde in each gas scrubbing bottle. Tighten the
pinch clamps on the distillation flask joints.
7.2.7 If determining sulfide by SIE, place into each gas scrubbing bottle 10.0 mL SAOB
solution and 40.0 mL water.
7.2.8 Make sure the stopcock is closed and then add 100 ±1.0 mL of 9.8N HC1 to the
dropping funnel. Connect the nitrogen line to the top of the funnel and turn the
nitrogen on to pressurize the dropping funnel headspace.
7.2.9 Set the nitrogen flow at 25 mL/min. The nitrogen in the gas scrubbing bottles
should bubble at about five bubbles per second. Purge the oxygen from the system
for about 15 minutes.
7.2.10 Turn on the magnetic stirrer. Set the stirring bar to spin as fast as possible. The
fluid should form a vortex. If not, the distillation will exhibit poor recovery. Add
all of the HC1 from the dropping funnel to the flask.
7.2.11 Heat the water bath to the boiling point (100°C). The sample may or may not be
boiling. Allow the purged distillation to proceed for 90 minutes at 100°C. Shut
off nitrogen supply. Turn off heat.
7.3 Titration of Distillate
7.3.1 Pipet a known amount of standardized 0.025N iodine solution (See Step 5.10.3) in a
500 mL flask, adding an amount in excess of that needed to oxidize the sulfide.
Add enough water to bring the volume to 100 mL. The volume of standardized
iodine solution should be about 65 mL for samples with 50 mg of sulfide.
7.3.2 If the distillation for acid-soluble sulfide is being used, add 2 mL of 6N HCl. If
the distillation for acid-insoluble sulfides is performed, 10 mL of 6 N HCl should
be added to the iodine.
7.3.3 Pipet both of the gas scrubbing bottle solutions to the flask, keeping the end of the
pipet below the surface of the iodine solution. If at any point in transferring the
zinc acetate solution or rinsing the bottles, the amber color of the iodine disappears
or fades to yellow, more 0.025N iodine must be added. This additional amount
must be added to the amount from Step 7.3.1 for calculations. Record the total
volume of standardized 0.025N iodine solution used.
21
-------
7.3.4 Prepare a rinse solution of a known amount of standardized 0.025N iodine
solution, 1 mL of 6N HC1, and water to rinse the remaining white precipitate (zinc
sulfide) from the gas scrubbing bottles into the flask. There should be no visible
traces of precipitate after rinsing.
7.3.5 Rinse any remaining traces of iodine from the gas scrubbing bottles with water,
and transfer the rinses to the flask.
7.3.6 Titrate the solution in the flask with standard 0.025N phenylarsine oxide or 0.025N
sodium thiosulfate solution until the amber color fades to yellow. Add enough
starch indicator for the solution to turn dark blue and titrate until the blue color
disappears. Record the volume of titrant added. Calculate the sulfide
concentration as follows;
Sulfide (mg/L) = - (V2x«2) xJf
s
VI = volume of iodine solution (mL)
N1 = normality of iodine solution (eq/L)
V2 = volume of titrant added (mL)
N2 = normality of titrant (mL)
S » sample weight (kg)
K. = 16.03 mg sulfide/meq sulfide
7.4 Sulfide SIE Measurement of Distillate
7.4.1 Standardization of Silver Nitrate -- Add 10.00 mL of 0.100N NaCl and 40 mL
water to a 125 mL flask. Adjust pH to 7-10 with 6N NaOH solution. Add 1.0 mL
potassium chromate indicator. Titrate with silver nitrate solution to a pinkish
yellow end point. Be consistent with end point recognition. Repeat with a reagent
blank (water and indicator). Calculate the normality of the silver nitrate as
follows:
Silver nitrate conc. {eq/L) = (VI-Vb) xN
VI » volume of silver nitrate added for NaCl sample (mL)
Vb ¦ volume of silver nitrate added for blank sample (mL)
N - normality of NaCl (eq/L)
V2 * volume of NaCl (10.00 mL)
7.4.2 Standardization of Sulfide Standards — From the sodium sulfide salt, prepare
standards with nominal concentrations of 10, 100, and 1,000 mg/L sulfide in a
matrix of 20 percent SAOB. Standardize each solution immediately prior to
calibrating the SIE. The standards may be calibrated by iodometric titration
(described in section 7.3) or by potentiometric titration as described below.
The titration is monitored with a combination silver electrode (silver-coated
platinum ring sensing electrode with a silver/silver chloride reference electrode).
22
-------
Prior to use the electrode is conditioned by soaking in 2 percent sodium sulfide for
5 minutes, soaking in 10 percent sodium sulfide until the brownish layer becomes
black, rinsing with water, and cleaning with a soft cloth. After conditioning, the
electrode is connected to the pH/mV meter. 20 mL of a sulfide standard (or
suitable quantity to get accurate titration) and 1 mL concentrated ammonia are
pipetted into a titration vessel. The electrode is inserted and the potential
recorded. The sample is titrated with the standardized silver nitrate until a
potential of 100 mV is attained. The potential is recorded after each titrant
addition. The equivalence point is determined from the first derivative of the
titration curve. The sulfide concentration is then calculated as follows:
Sulfide conc. (rng/L) -
A = volume of silver nitrate (mL)
B = normality of silver nitrate (eq/L)
K = 16,000 mg/meq
C = volume of sulfide standard (mL)
7.4.3 Calibration of Sulfide SIE and Meter — Following the meter operating
instructions, calibrate the meter directly in terms of concentration using the 10,
100, and 1,000 mg/L sulfide standards. The standards must be freshly
standardized.
7.4.3.1 For meters which cannot be calibrated in terms of concentration, measure
the mV reading for each of the standards. Prepare a calibration curve by
plotting the mV vs. concentration on semi-log paper.
7.4.3.2 The measurement of the standards is performed by pouring 25 mL
standard into a 50 mL beaker, adding a stir bar and gently stirring, and
placing the sulfide SIE and reference electrode into the solution. The
reading is recorded when stable.
7.4.4 Measurement of Sulfide in Unknown Samples — Sulfide in unknown samples is
determined with the SIE as follows:
Rinse the electrodes with water, blot dry, pour 25 mL sample from the scrubber
bottle into a 50 mL beaker, add a stir bar and stir gently, insert the electrodes,
record the sulfide concentration (or mV reading) when a stable reading is obtained.
If mV is recorded, calculate the sulfide concentration from the calibration curve.
8.0 QUALITY CONTROL
8.1 All quality control data must be maintained and available for reference or inspection for
a period of 3 years. This method is restricted to use by or under supervision of
experienced analysts. Refer to the appropriate section of Chapter One for additional
quality control requirements.
8.2 A reagent blank should be run once in 20 analyses or per analytical batch, whichever is
more frequent.
23
-------
8.3 Check standards are prepared from water and a known amount of sodium sulfide. A
check standard should be run with each analytical batch of samples, or once in 20
samples. Acceptable recovery will depend on the level.
8.4 A matrix spike sample should be run for each analytical batch or every 20 samples,
whichever is more frequent, to determine matrix effects. If recovery is low, acid-
insoluble sulfides are indicated. A matrix spike sample is a sample brought through the
whole sample preparation and analytical process.
8.5 A laboratory control sample (LCS) must be analyzed with each batch of samples. An
LCS is a sulfide standard which is processed exactly like a sample, including distillation.
An LCS may be prepared in a sodium hydroxide matrix and precipitated with zinc
acetate prior to distillation. The SAOB matrix may precipitate upon acidification and
cause problems with the distillation. The acceptance criterion for percent recovery is 80-
120 percent.
METHOD PERFORMANCE
9.1 Accuracy -- Accuracy for this method was determined by three independent laboratories
by measuring percent recoveries of spikes for both clean matrices (water) and actual
waste samples. The results are summarized below.
9.1.1 For Acid-Soluble Sulfide (Spiking levels ranged from 0.4 to 8 mg/L)
Accuracy of Titration Step Only -- Lab A 84-100 percent recovery, Lab B 110-
122 percent recovery.
Accuracy of Sulfide SIE Step Only -- Lab D 75-105 percent recovery.
Accuracy for Entire Method for Clean Matrices (water) — Lab 94-106 percent
recovery.
Accuracy of Entire Method for Actual Waste Samples -- Lab C 77-92 percent
recovery.
9.1.2 For Acid-Insoluble Sulfide (Spiking levels ranged from 2.2 to 22 mg/kg)
The percent recovery was not as thoroughly studied for acid-insoluble sulfide as it
was for acid-soluble sulfide.
Accuracy of Entire Method for Synthetic Waste Samples — Lab C 21-81 percent
recovery.
9.2 Precision
9.2.1 For Acid-Soluble Sulfide
Precision of Titration Step Only -- Lab A Coefficient of Variation (CV) percent
2.0 to 37, Lab B CV percent 1.1 to 3.8.
Precision of Sulfide SIE Step Only — Lab D CV percent 2.0 to 10.
24
-------
Precision of Entire Method for Clean Matrices (water) — Lab C CV percent 3.0 to
12.
Precision of Entire Method for Actual Waste Samples — Lab C CV percent 0.86 to
45.
9.2.1 For Acid-Insoluble Sulfide
Precision of Entire Method with Synthetic Wastes — Lab C CV percent 1.2 to 42.
9.3 Detection Limit
9.3.1 For the titration procedure, the detection limit was determined by analyzing seven
replicates at 0.45 and 4.5 mg/L. The detection limit was calculated from the
standard deviation times the student's t-value for one-tailed test with n-1 degrees
of freedom at 99 percent confidence level. The detection limit for a clean matrix
(water) was found to be between 0.2 and 0.4 mg/L.
9.3.2 For the sulfide SIE, the practical detection limit is about 1 mg/L. It is possible to
detect lower quantities, however the electrode has a sluggish response below 1
mg/L.
10.0 REFERENCES
1. Test Methods for Evaluating Solid Waste, Physical/Chemical Methods, 3rd ed.;
Emergency Response. U.S. Government Printing Office: Washington, D.C., SW-846,
955-001-00000-1, 1987.
2. Methods for Chemical Analysis of Waster and Wastes; EPA-600\4-79-020, Method 376.1.
U.S. Environmental Protection Agency. Office of Research and Development.
Environmental Monitoring and Support Laboratory. ORD Publication Office. Center
for Environmental Research Information, Cincinnati, Ohio, 1979.
3. CRC: CDC Handbook of Chemistry and Physics. 66th ed. Weast, R., Ed,; Boca Raton,
FL, 1985.
4. Standard Methods for the Examination of Water and Wastewater, 16th ed.; Greenberg, A.
E.; Trussell, R. R.; Clesceri, L. S., Eds.; American Water Works Association, Water
Pollution Control Federation, American Public Health Association: Washington, D.C.,
1985; Methods 427, 427A, 427B, and 427D.
5. Andreae, M. O., Banard, W. R. Anal. Chem. 55, 608-612, 1983.
6. Barclay, H. Adv. Instrum. 35(2): 59-61, 1980.
7. Bateson, S. W., Moody, G. J., Thomas, J.P.R. Analyst, 111: 3-9, 1986.
8. Berthage, P. O. Anal. Chim. Acta 10: 310-311,1954.
9. Craig, P. J.; Moreton, P. A. Environ. Technol. Lett., 3:
511-520, 1982.
25
-------
10. Franklin, G. O.; Fitchett, W. W. Pulp & Paper Canada. 83(10):
40-44, 1982.
11. Fuller, W. In: Cyandie in the Environment; Van Zyl, D., Ed.; Proceedings of
Symposium; December, 1984.
12. Gottfried, G. J. "Precision, Accuracy, and MDL Statements for EPA Methods 9010,
9030, 9060, 7520, 7521, 7550, 7551, 7910, and 7911"; final report to the U.S.
Environmental Protection Agency (EMSL-CI); Biopheric.
13. Kilroy, W. P. Talanta 30(6): 419-422,1983.
14. Kurtenacher, V. A., Wallak, R. Z. Anorg. U. Allg. Chem. 161:
202-209, 1927.
15. Landers, D. H., David, M. B., Mitchell, M. J. Int. J. Anal. Chem. 14: 245-256, 1983.
16. Opekar, F., Brukenstein, S. Anal. Chem. 56: 1206-1209, 1984.
17. Ricklin R. D., Johnson, E. L. Anal. Chem. 55: 4, 1983.
18. American Chemical Society. Rohrbough, W. G., et al. Reagent Chemicals, American
Chemical Society Specification, 7th ed.; Washington, D.C., 1986.
19. Iowa State University. Snedecor, G. W., Ghran, W. G. Statistical Methods; Ames, Iowa,
1980.
20. Umana, M., Beach, J., Sheldon, L. Revisions to Method 9010; final report, Contract No.
68-01-7266, U.S. Environmental Protection Agency, Research Triangle Institute.
Research Triangle Park, North Carolina, 1986; Work Assignment No. 1.
21. Umana, M., Sheldon, L. Interim Report: Literature Review, interim report, Contract
No. 68-01-7266, U.S. Environmental Protection Agency Research Triangle Institute.
Research Triangle Park, North Carolina, 1986; Work Assignment No. 3.
22. Wang, W., Barcelona, M. J. Environ. Inter. 9: 129-133, 1983.
23. Wronski, M. Talanta, 28: 173-176 1981.
24. Princeton Applied Research Corp. Applications Note 156. Princeton, New Jersery.
25. Guidelines for Assessing and Reporting Data Quality for Environmental Measurements;
U.S. Environmental Protection Agency. Office of Research and Development. U.S.
Government Printing Office: Washington, D.C., 1983.
26. Fed. Regist. 45(98): 33122,1980.
27. The Analytical Chemistry of Sulfur and Its Compounds, Part I; Karchmer, J. H., Ed.,
Wiley-Interscience, New York, 1970.
28. Methods for the Examination of Water and Associated Materials; Department of the
Environment: England, 1983.
26
-------
29. EAL. Development and Evaluation of a Test Procedure for Reactivity Criteria for
Hazardous Waste; final report, Contract 68-03-2961,
U.S. Environmental Protection Agency, Richmond, California.
30. 1985 Annual Book of ASTM Standards, Vol. 11.01; Standards Specification for Reagent
Water; ASTM; Philadelphia, Pennsylvania, D1193-77, 1985.
31. Single Laboratory Evaluation of the Sulfide SIE; report, Contract 68-32-3249, U.S.
Environmental Protection Agency, EMSL-Las Vegas, Nevada.
32. Test Method to Determine Hydrogen Sulfide Released from Wastes; U.S. Environmental
Protection Agency. Office of Solid Waste. Preliminary unpublished protocol, 1985.
27
-------
Gas Evolution Apparatus
H2S04 (HCI for acid insoluble sulfides)
Zinc Acetate &
Formaldehyde
Scrubbing
Botftes
Hot Water Bath
with Magnetic Stirrer
Stirring Bar
Figure 1.
28
-------
ACID
ACID
SOLUBLE
INSOLUBLE
CHOOSE SAM
iS i ZE(.2-50HG
SULFIDE). PUT IN
BEAKER. ADO H20,
ADO H2S04 UNTIL
.7.0 PREDICT ACID
SOLUBILITY y
CALCULATE AMOUNT
OF H2S04 NEC. TO
AC 10 I FY SAMPLE
!for purge
NO
/7.2.1 SAMPLE\
EASILY SUSPENDED
YES
DRY
SOLID
MOIST
SOLID
IPREPARE HOT
UATcR BATH
7.2.2-7.2.4
MATRIX TYPE
AQUEOUS
YES
7.2.3 IS<50G\
SAMPLE NEC ?/*
NO
START
7.2.3
ADD H20 TO
SAMPLE FOR TOTAL
VOLUME OF 50 mL
H20 CONTENT MUST
BE CONTROLLED.
HCl SHOULD BE
6.5N
SAMPLE SIZE HAY
BE 25-50 G
ASSEHBLE 3-HEDC
FLASK
LIMIT SAMPLE
SIZE TO 25 G DRY
WEIGHT
PREPARE GAS
EVOLUTION
APPARATUS
7.2.4
DETERMINE H20
CONTENT. INCL.
7.H20 IN CALC FOR
HCl CONC
7.2.2
WEIGH SAMPLE
(.2-50MG
SULFIDE) CRUSH
IF NEC, ADD 50mL
H20
29
-------
7.1.2.3
PLACE SCRUBBING
SOLN IN GAS
SCRUBBING
BOTTLES
±
7.1.2.4
CONNECT FLASK
A MO SCRUBBING
BOTTLES, SECUTE
JOINTS
A
7.1.3
PLACE WEIGHED
SAMPLE IN FLASK.
DILUTE WITH H20
IF NEC.
V
7.1.4
PLACE DROPPING
FUNNEL ONTO
FLASK, ADO H2S04
\/
7.1.5
AOJUST N2 FLO <.
CHECK FOR LEAKi.
TURN ON STIRRER.
PURGE SYSTEM OF
02 FOR 15 HIM.
7.2.6
ASSEMBLE 01 ST
PLACE SCRUBBING
SOLN IN
SCRUBBING
7.2.7
ADO 100 mL 9.8N
"CI TO DROPPING
FUNNEL
PLACE SAMOLE IN
CLASK. ADO SnCl2
7.2.3
USE 50G SAMPLE
SET N2 FLOW.
PURGE SYSTEM OF
02 FOR 15 MIN.
30
-------
NO
7.3.2 \
ACIO SOL. OIST ?
YES
STOP
7.2.9
TURN OH'STIRRER
ADD HCl TO DIST
FLASK
HEAT TO 70C. ADO
H2S04, CLOSE
FUNNEL
7.3.2
ADD 10 mL 6N HCl
PI PET KNOUN mL
12 SOLN INTO
FLASK. DILUTE TO
VOL WITH H20.
7.2.11
ANALYZE 8Y TITR
(STEP 7.3.1) OR
SIE (STEP 7.4.1)
7.3.2
ADD 2 mL 6N HCl
ANALYZE er
TITR(STEP 7.3.1)
OR BY SIE (STEP
7.4.1 - 7.4.2
STANDARDIZE
AgN03 AND
SULFIDE STDS
7.4.3 - 7.4.4
CALIB. SIE
METER, DETH
SULFIDE IN
SCRUBBER 8Y SIE
7.2.10
HEAT H20 BATH TO
BOIL. OIST. FOR
90 MIN AT 100C.
TURH OFF HEAT
PURGE, STIR,
HEAT FOR 90 HIH
SHUT OFF N2,
TURN OFF HEAT
31
-------
7.7.3 AMBER
12 COLOR
Disappears ?'
STOP
CALCULATE THE
SULFIDE CONC.
THE SAMPLE
ADO HOSE 12
SOLUTION
7.3.3
RECORO TOTAL 12
VOLUME ADDED
7.7.3
PI PET SCRUB8ER
SOLM INTO FLASK
7.3.4
PREPARE RINSE
SOLN FROM 12, &N
MCI, AND H20
7.3.5
RINSE 12 TRACES
FROM SCRUBBER
BOTTLE INTO
FLASK
7.3.6
TITR. SOLN WITH PAO OR
Na2S203 UNTIL 12 COLOR
FADES. ADD STARCH. TITR.
TILL BLUE DISAPP. RECORD
TITR. VOL.
32
-------
APPENDIX B
MODIFIED METHOD 9031
EXTRACTABLE INSOLUBLE SULFIDES
1.0 SCOPE AND APPLICATION
1.1 The extraction procedure described in this method is designed for the extraction of
sulfides from matrices that are not directly amenable to the distillation procedure Method
9030. This method is also not applicable for reactive sulfide. Refer to Chapter Seven,
Step 7.3.4.1 for the determination of reactive sulfide. This method is applicable to oil,
soil, multiphasic, and all other matrices not amenable to analysis by Method 9030.
1.2 Method 9031 is suitable for measuring sulfide in solid samples at concentrations above 1
mg/kg.
2.0 SUMMARY OF METHOD
2.1 If the sample contains solids that will interfere with agitation and homogenization of the
sample mixture, or so much oil or grease as to interfere with the formation of a
homogeneous emulsion in the distillation procedure, the sample must be filtered and the
solids extracted with water at pH>9 or <11. The extract is then combined with the
filtrate and analyzed by the distillation procedure. Separation of sulfide from the sample
matrix is accomplished by the addition of sulfuric acid to the sample. The sample is
heated to 70°C and the hydrogen sulfide (H2S) which is formed is distilled under acidic
conditions and carried by a nitrogen stream into gas scrubbing bottles. If the sulfide is to
be determined by titration, the gas scrubbers contain zinc acetate where it is precipitated
as zinc sulfide. If the sulfide is determined by sulfide ion specific electrode (SIE), the
gas scrubbers contain sulfide anti-oxidant buffer (SAOB, a sodium hydroxide solution
containing salicylic and ascorbic acids at a pH>I2) where it is trapped as sulfide ion.
2.2 If determined by titration the sulfide in the zinc sulfide precipitate is oxidized to sulfur
with a known amount of excess iodine. Then the excess iodine is determine by titration
with a standard solution of phenylarsine oxide (PAO) or sodium thiosulfate until the blue
iodine starch complex disappears. The use of standard sulfide solutions is not possible
because of their instability to oxidative degradation. Therefore quantitation is based on
the PAO or sodium thiosulfate.
If determined by sulfide SIE, the sulfide in the SAOB is determined directly with a
calibrated sulfide SIE. The sulfide SIE is calibrated using freshly standardized sulfide
standards in a SAOB matrix (to minimize degradation prior to calibration). The sulfide
standards are standardized by either a thiosulfate or silver nitrate titration.
3.0 INTERFERENCES
33
-------
3.1 Samples with aqueous samples must be taken with a minimum of aeration to avoid
volatilization of sulfide or reaction with oxygen, which oxidizes sulfide to sulfur
compounds that are not detected.
3.2 Sulfur compounds, such as sulfite and hydrosulfite, decompose in acid, and may form
sulfur dioxide. This gas may be carried over to the zinc acetate gas scrubbing bottles and
subsequently react with the iodine solution yielding false high value. The addition of
formaldehyde into the zinc acetate gas scrubbing bottles removes this interference. Any
sulfur dioxide entering the scrubber will form an addition compound with the
formaldehyde which is unreactive towards the iodine in the acidified mixture. This
methods shows no sensitivity to sulfite or hydrosulfite at concentrations up to 10 mg/kg
of the interferant.
3.3 The iodometric method suffers interference from reducing substances that react with
iodine, including thiosulfate, sulfite, and various organic compounds. The SIE method is
free from interferences.
3.4 Interferences have been observed when analyzing samples with high metal content such
as electroplating waste and chromium containing tannery waste, and interference.
APPARATUS AND MATERIALS
4.1 Extractor - Any suitable device that sufficiently agitates a sealed container of 1 liter
volume or greater. For the purpose of this analysis, agitation is sufficient when all
sample surfaces are continuously brought into contact with extraction fluid, and the
agitation prevents stratification of the sample and fluid. Examples of suitable extractors
are shown in Figures 2 and 3. The tumble-extractors turn the extraction bottles end-
over-end at a •.•ate of about 30 rpm. The apparatus in Figure 2 may be easily fabricated
from plywood. The jar compartments must be padded with polyurethane foam to absorb
shock. The drive apparatus is a Norton jar mill.
4.2 Buchner funnel apparatus
4.2.1 Buchner Funnel—500 mL capacity, with 1 liter vacuum filtration flask.
4.2.2 Glass Wool--Suitable for filtering, 0.8 um diameter such as Corning Pyrex 3950.
4.2.3 Vacuum Source—Preferably a water driven aspirator. A valve or stopcock
to release vacuum is required.
4.3 Distillation apparatus as shown in Figure 1.
4.3.1 Three Neck Flask -- 500 mL, 24/40 standard tapered joints.
4.3.2 Dropping Funnel — 100 mL, 24/40 outlet joint.
4.3.3 Purge Gas Inlet Tube — 24/40 joint, with coarse frit.
4.3.4 Purge Gas Inlet Tube — 24/40 joint, with coarse frit.
4.3.5 Gas Scrubbing Bottles — 125 mL, with i in. o.d. inlet and outlet tubes. Impinger
tub must be fritted.
34
-------
4.3.6 Tubing — { in. o.d. Teflon or polypropylene. Do not use rubber.
4.4 Hot plate stirrer
4.5 pH/mV/ion meter capable of reading to 0.1 mV
4.6 Nitrogen regulator
4.7 Flowmeter
4.8 Separatory Funnels — 500 mL.
4.9 Tumbler — See Figures 2 and 3.
4.10 Sulfide SIE
4.11 Double-junction reference electrode (silver/silver chloride)
REAGENTS
5.1 Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is
intended that all reagents shall conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society, where such specifications are
available. Other grades may be used, provided it is first ascertained that the reagent is
sufficiently high purity to permit its use without lessening the accuracy of the
determination.
5.2 ASTM Type II Water (ASTM D-l 193-77 (1983)) — All waster used in this method will
be Type II unless otherwise specified.
5.3 Zinc Acetate Solution for Sample Preservation (2N) — Dissolve 220 g of zinc acetate
dihydrate in 500 mL of water.
5.4 Sodium Hydroxide (50 percent w/v in water), NaOH — Commercially available.
5.5 Tin (II) Chloride, SnCl2 • 2HzO, granular.
5.6 n-Hexane
5.7 Nitrogen gas
5.8 Sulfuric Acid (concentrated), H2S04.
5.9 Zinc Acetate for the Scrubber (approximately 0.5M)
Dissolve about 110 g zinc acetate dihydrate in 200 mL of water. Add 1 mL hydrochlor
acid (concentrated), HC1, to prevent precipitation of zinc hydroxide. Dilute to 1 liter.
5.10 Formaldehyde (37 percent solution).
35
-------
5.11 Starch Solution — Use either an aqueous solution or a soluble starch powder mixture.
Prepare an aqueous solution as follows; Dissolve 2 g soluble starch and 2 g salicylic acid
(as a preservative) in 100 mL hot water.
5.12 Iodine Solution (approximately 0.025N) — Dissolve 25 g potassium iodide, K.I, in 700 mL
of water in a 1 liter volumetric flask. Add 3.2 g iodine and allow to dissolve. Dilute to 1
liter and standardize as follows. Dissolve approximately 2 g KI in 150 mL of water.
Pipet exactly 20 mL of the iodine solution to be titrated and dilute to 300 mL with water.
Titrate with 0.025N standardized phenylarsine oxide or 0.025N sodium thiosulfate until
the amber color fades to yellow. Add starch indicator solution. The solution will turn
deep blue. Continue titration drop by drop until the blue color disappears. Run in
replicate. Calculate the normality as follows:
Iodine conc. (eq/L) =
Vt = volume of titrant (mL)
Nt = normality of titrant (eq/L)
Vi = volume of iodine solution (20.00 mL)
5.13 Sodium Sulfide Nonahydrate, Na2S -9H20 — For the preparation of standard solution
to be used for calibration curves. Standards must be prepared at pH >9 or <11. Protect
standard from exposure to oxygen by preparing it without headspace. If standards are
for use with the SIE, prepare in 20 percent SAOB. These standards are unstable and
must be standardized immediately before use by either an iodometric titration or
potentiometric titration.
5.14Titrants.
5.14.1 Standard phenylarsine oxide solution (PAO) (0.025N) — This solution is
commercially available.
CAUTION: PAO is toxic.
5.14.2 Standard Sodium Thiosulfate Solution (0.025N) — Dissolve 6.205 ± 0.005 g
Na2S2Os • 5H20 in 500 mL water. Add 9 mL IN NaOH and dilute to 1 liter.
5.14.3 Standard Silver Nitrate Solution (0.10N). Dissolve 16.989 g of AgN03 (dried for 2
hours at 150°C) in water and dilute to 1,000 L. Store in a brown bottle.
Standardize weekly against standard sodium chloride solution.
5.15 Sulfide Anti-Oxidant Buffer (SAOB) — Dissolve 80 g NaOH, 320 g sodium salicylate
and 72 g ascorbic acid in 1 L water. Prepare fresh weekly.
5.16Standard Sodium Chloride Solution (O.rOON) — Dissolve 5.84 g NaCl (dried for 2 hours
at 140°C) in water and dilute to 1,000 L.
5.17 Potassium Chromate Indicator Solution -- Dissolve 50 g K2Cr04 in a little water. Add
AgNOs solution until a definite red precipitate is formed. Let stand 12 hours, filter, and
dilute to 1 L.
36
-------
6.0 SAMPLE COLLECTION, PRESERVATION, AND HANDLING
6.1 All samples must have been collected using a sampling plan that addresses the
considerations discussed in Chapter Nine of the EPA test methods for evaluating solid
waste (SW-846).
6.2 All samples must be preserved with zinc acetate and sodium hydroxide. Use four drops
of 2N zinc acetate solution per 100 mL of sample. Adjust the pH to greater than 9 with
50 percent NaOH. Fill the sample bottle completely and stopper with a minimum of
aeration. For solid samples, fill the surface of the solid with 2N zinc acetate until
moistened. Samples must be cooled to 4CC during storage.
7.0 PROCEDURE
7.1 Assemble the Buchner funnel apparatus. Unroll the glass wool and fold the fiber over
itself several times to make a pad about 1 cm thick when lightly compressed. Cut the
pad to fit the Buchner funnel. Dry and weigh the pad, then place it in the funnel. Turn
on the aspirator and wet the pad with a known amount of water.
7.2 Transfer a sample that contains between 1 and 50 mg of sulfide to the Buchner funnel.
Rinse the sample container with known amounts of water and add the rinses to the
Buchner funnel. When no free water remains in the funnel, slowly open the stopcock to
allow air to enter the vacuum flask. A small amount of sediment may have passed
through the glass fiber pad. This will not interfere with the analysis.
7.3 Transfer the solid and the glass fiber pad to a dried tared weighing dish. Since most
greases and oils will not pass through the fiber pad, solids, oils, and greases will be
extracted together. If the filtrate includes an oil phase, transfer the filtrate to a
separatory funnel. Collect and measure the volume of the aqueous phase. Transfer the
oil phase to the weighing dish with the solid and glass fiber pad.
7.4 Weight the dish containing solid, oil (if any) and glass fiber pad. Subtract the weight of
the dry glass fiber pad. Calculate the volume of water present in the original sample by
subtracting the total volume of rinses from the measured volume of the filtrate.
7.5 Place the following in a 1 liter wide-mouth bottle:
500 mL water
5 mL 50 percent w/v NaOH
1 g SnCl2 • 2H20
50 mL n-hexane (if an oil or grease is present).
Cap the bottle with a Teflon- or polyethylene-lined cap and shake vigorously to saturate
the solution with stannous chloride. Direct a stream of nitrogen gas at about 10 mL/min
into the bottle for about 1 minute to purge the headspace of oxygen. If the weight of the
solids (Step 7.4) is greater than 25 g, weigh out a representative aliquot of 25 g and add it
to the bottle while still purging with nitrogen. Otherwise, add all of the solids. Cap the
bottle; avoid the influx of air.
7.6 The pH of the extract must be maintained at >9 or <11 throughout the extraction step
and subsequent filtration. Since some samples may release acid, the pH must be
monitored as follows. Shake the extraction bottle and wait 1 minute. Open the bottle
37
-------
under a stream of nitrogen and check the pH. If the pH is below 9, add 50 percent
NaOH in 5-mL increments until it is at least 9. Recap the bottle, and repeat the
procedure until the pH does not drop. The bottle must be thoroughly purged of oxygen
before each recapping. Oxygen will oxidize sulfide to elemental sulfur or other sulfur
containing compounds that will not be detected.
7.7 Place the bottle in the tumbler, making sure there is enough foam insulation to cushion
the bottle. Turn the tumbler on and allow the extraction to run for about 18 hours.
7.8 Prepare a Buchner funnel apparatus as in Step 7.1 with glass fiber pad filter.
7.9 Decant the extract to the Buchner funnel.
7.10 If the extract contains an oil phase, separate the aqueous phase using a separatory funnel.
Neither the separation nor the filtration are critical, but are necessary to be able to
measure the volume of the aqueous extract analyzed. Small amounts of suspended solids
and oil emulsions will not interfere with the extraction.
7.11 At this point, an aliquot of the filtrate of the original sample may be combined with an
aliquot of the extract in a proportion representative of the sample. Calculate the
proportions as follows:
Af _ Sey Vs
Ae St Vt
Af ¦ aliquot volume of the filtrate (mL)
Ae = aliquot volume of the extract (mL)
Se = mass (g) of solid extracted from step 7.5
St = total mass (g) of solid from step 7.4. Includes only weight of solids and oil.
Vs = total volume (mL) of sample filtrate from steps 7.1 and 7.2. Includes volume of all
rinses.
Vt = total volume (mL) of extraction fluid from steps 7.5 and 7.6. Does not include
hexane, which is later removed.
Alternatively, the samples may be analyzed separately, concentrations for each phase
reported separately, and the amounts of each phase present in the sample reported
separately.
7.12 Distillation of Sulfide
7.12.1 In a preliminary experiment, determine the approximate amount of sulfuric acid
required to adjust a measured amount of the sample to pH less than or equal to 1.
The sample size should be chosen so that it contains between 0.2 and 50 mg of
sulfide. Place a known amount of sample or sample slurry in a beaker. Add water
until the total volume is 200 mL. Stir the mixture and determine the pH. Slowly
add sulfuric acid until the pH is less than or equal to 1.
CAUTION: Toxic hydrogen sulfide may be generated from the acidified sample.
This operation must be performed in the hood and the sample left in
the hood until the sample has been made alkaline or the sulfide has
been destroyed.
38
-------
From the amount of sulfuric acid required to acidify the sample and the mass or
volume of the sample acidified, calculate the amount of acid required to acidify
the sample to be placed in the distillation flask.
7.12.2 Prepare the gas evolution apparatus as shown in Figure 1 in a fume hood.
7.12.2.1 Prepare a hot water bath at 70°C by filling a crystallizing dish or other
suitable container with water and place it on a hot plate stirrer. Place a
thermometer in the bath and monitor the temperature to maintain the bath
at 70° C.
7.12.2.2 Assemble the three neck 500 mL flask, fritted gas inlet tube, and exhaust
tube. Use Teflon sleeves to seal the ground glass joints. Place a Teflon
coated stirring bar into the flask.
7.12.2.3 If the sulfide is determined by titration, place into each gas scrubbing
bottle 10 ± 0.5 mL of the 0.5M zinc acetate solution, 5.0 ± 0.1 mL of 37
percent formaldehyde and 100 ± 5.0 mL water.
If the sulfide is determined by SIE, place into each gas scrubbing bottle
10.0 mL SAOB solution and 40.0 mL water.
7.12.2.4 Connect the gas evolution flask and gas scrubbing bottles as shown in
Figure 1. Secure all fittings and joints.
7.12.3 Carefully place an accurately weighed sample which contains 0.2 to 50 mg of
sulfide into the flask. If necessary, dilute to approximately 200 mL with water.
7.12.4 Place the dropping funnel onto the flask making sure its stopcock is closed. Add
the volume of sulfuric acid calculated in Step 7.7.1 plus an additional 50 mL into
the dropping funnel. The bottom stopcock must be closed.
7.12.5 Attach the nitrogen inlet to the top of the dropping funnel gas shut-off valve.
Turn on the nitrogen purge gas and adjust the how through the sample flask to 25
mL/min. The nitrogen in the gas scrubbing bottles should bubble at about five
bubbles per second. Nitrogen pressure should be limited to approximately 10 psi
to prevent excess stress on the glass system and fittings. Verify that there are no
leaks in the system. Open the nitrogen shut-off valve leading to the dropping
funnel. Observe that the gas flow into the sample vessel will stop for a short
period while the pressure throughout the system equalizes. If the gas flow through
the sample flask does not return within a minute, check for leaks around the
dropping funnel. Once flow has stabilized, turn on magnetic stirrer. Purge
system for 15 minutes with nitrogen to remove oxygen.
7.12.6 Heat sample to 70°C. Open dropping funnel to a position that will allow a flow of
sulfuric acid of approximately 5 "mL/min. Monitor the system until most of the
sulfuric acid within the dropping funnel has entered the sample flask. Close the
dropping funnel while a small amount of acid remains. Immediately close the gas
shut-off valve to the dropping funnel.
7.12.7 Purge, stir, and maintain a temperature of 70°C for a total of 90 minutes from
start to finish. Shut off nitrogen supply. Turn off heat.
39
-------
7.13 Titration of Distillate
7.13.1 Pipet a known amount of standardized 0.025N iodine solution (See Step 5.10.3) in a
500 mL flask, adding an amount in excess of that needed to oxidize the sulfide.
Add enough water to bring the volume to 100 mL. The volume of standardized
iodine solution should be about 65 mL for samples with 50 mg of sulfide.
7.13.2 Add 2 mL of 6N HC1.
7.13.3 Pipet both of the gas scrubbing bottle solutions to the flask, keeping the end of the
pipet below the surface of the iodine solution. If at any point in transferring the
zinc acetate solution or rinsing the bottles, the amber color of the iodine disappears
or fades to yellow, more 0.025N iodine must be added. This additional amount
must be added to the amount from Step 7.3.1 for calculations. Record the total
volume of standardized 0.025N iodine solution used.
7.13.4 Prepare a rinse solution of a known amount of standardized 0.025N iodine
solution, 1 mL of 6N HC1, and water to rinse the remaining white precipitate (zinc
sulfide) from the gas scrubbing bottles into the flask. There should be no visible
traces of precipitate after rinsing.
7.13.5 Rinse any remaining traces of iodine from the gas scrubbing bottles with water,
and transfer the rinses to the flask.
7.13.6 Titrate the solution in the flask with standard 0.025N phenylarsine oxide or 0.025N
sodium thiosulfate solution until the amber color fades to yellow. Add enough
starch indicator for the solution to turn dark blue and titrate until the blue
disappears. Record the volume of titrant used.
Sulfide conc. img/L) =
s
Vi = volume of iodine solution (mL)
Ni = normality of iodine solution (eq/L)
Vt = volume of titrant (mL)
Nt = normality of titrant (eq/L)
K » 16.03 mg sulfide/meq sulfide
7.14 Sulfide SIE Measurement of Distillate
7.14.1 Standardization of Silver Nitrate -- Add 10.00 mL of 0.100N NaCl and 40 mL
water to a 125 mL flask. Adjust pH to 7-10 with dilute NaOH solution. Add 1.0
mL potassium chromate indicator. Titrate with silver nitrate solution to a pinkish
yellow end point. Be consistent with end point recognition. Repeat with a reagent
blank (water and indicator). Calculate the normality of the silver nitrate as
follows;
Silver nitrate conc. (eq/L) = xN
40
-------
VI = volume of silver nitrate added for NaCl sample (mL)
Vb = volume of silver nitrate added for blank sample (mL)
N = normality of NaCl (eq/L)
V2 = volume of NaCl (10.00 mL)
7.14.2 Standardization of Sulfide Standards — From the sodium sulfide salt, prepare
standards with nominal concentrations of 10, 100, and 1,000 mg/L sulfide in a
matrix of 20 percent SAOB. Standardize each solution immediately prior to cali-
brating the SIE. The standards may be calibrated by iodometric titration
(described in section 7.3) or by potentiometric titration as described below.
The titration is monitored with a combination silver electrode (silver-coated
platinum ring sensing electrode with a silver/ silver chloride reference electrode).
Prior to use the electrode is conditioned by soaking in 2 percent sodium sulfide for
5 minutes, soaking in 10 percent sodium sulfide until the brownish layer becomes
black, rinsing with water, and cleaning with a soft cloth. After conditioning, the
electrode is connected to the pH/mV meter. 20 mL of a sulfide standard (or
suitable quantity to get accurate titration) and 1 mL concentrated ammonia are
pipetted into a titration vessel. The electrode is inserted and the potential
recorded. The sample is titrated with the standardized silver nitrate until a
potential of 100 mV is attained. The potential is recorded after each titrant
addition. The equivalence point is determined from the first derivative of the
titration curve. The sulfide concentration is then calculated as follows:
Sulfide conc. (mg/L) =
A = volume (mL) of silver nitrate
B = normality of silver nitrate (eq/L)
C = volume (mL) of sulfide standard
K = 16,000 mg/meq
7.14.3 Calibration of Sulfide SIE and Meter — Following the meter operating
instructions, calibrate the meter directly in terms of concentration using the 10,
100, and 1,000 mg/L sulfide standards. The standards must be freshly
standardized.
For meters which cannot be calibrated in terms of concentration, measure the mV
reading for each of the standards. Prepare a calibration curve by plotting the mV
vs. concentration on semi-log paper.
The measurement of the standards is performed by pouring 25 mL standard into a
50 mL beaker, adding a stir bar and gently stirring, and placing the sulfide SIE
and reference electrode into the solution. The reading is recorded when stable.
7.14.4 Measurement of Sulfide in Unknown Samples — Sulfide in unknown samples is
determined with the SIE as follows:
Rinse the electrodes with water, blot dry, pour 25 mL sample from the scrubber
bottle into a 50 mL beaker, add a stir bar and stir gently, insert the electrodes,
41
-------
record the sulfide concentration (or mV reading) when a stable reading is obtained.
If mV is recorded, calculate the sulfide concentration from the calibration curve.
8.0 QUALITY CONTROL
8.1 All quality control data must be maintained and available for reference or inspection for
a period of 3 years. This method is restricted to use by or under supervision of
experienced analysts. Refer to the appropriate section of Chapter One for additional
quality control requirements.
8.2 A reagent blank should be run once in 20 analyses or per analytical batch, whichever is
more frequent.
8.3 Check standards are prepared from water and a known amount of sodium sulfide. A
check standard should be run with each analytical batch of samples, or once in 20
samples. Acceptable recovery is 80-120 percent.
8.4 A matrix spike sample should be run for each analytical batch or every 20 samples,
whichever is more frequent, to determine matrix effects. If recovery is low, acid-
insoluble sulfides are indicated. A matrix spike sample is a sample brought through the
whole sample preparation and analytical process.
8.5 Verify the calibration with an independently prepared QC reference sample every 20
samples or once per analytical batch, whichever is more frequent.
8.6 A laboratory control sample (LCS) must be analyzed with each batch of samples. An
LCS is a sulfide standard which is processed exactly like a sample, including distillation.
An LCS may be prepared in a sodium hydroxide matrix and precipitated with zinc
acetate prior to distillation. The SAOB matrix may precipitate upon acidification and
cause problems with the distillation. Acceptable recovery for the LCS is 80-120 percent.
9.0 METHOD PERFORMANCE
9.1 Accuracy — Accuracy for this method was determine by three independent laboratories
by measuring percent recoveries of spikes for both clean matrices (water) and actual
waste samples. The results are summarized below.
Accuracy of entire method for four synthetic waste samples 70-104 percent recovery.
9.2 Precision — Precision of entire method for four synthetic wastes. Percent coefficient of
variation 1.0-3.4.
10.0 REFERENCES
1. Test Methods for Evaluating Solid Waste, Physical/Chemical Methods, 3rd ed.;
Emergency Response. U.S. Government Printing Office: Washington, D.C., SW-846,
955-001-00000-1, 1987.
2. Methods for Chemical Analysis of Waster and Wastes; EPA-600\4-79-020, Method 376.1.
U.S. Environmental Protection Agency. Office of Research and Development.
Environmental Monitoring and Support Laboratory. ORD Publication Office. Center
for Environmental Research Information, Cincinnati, Ohio, 1979.
42
-------
3. CRC: CDC Handbook of Chemistry and Physics. 66th ed. Weast, R., Ed,; Boca Raton,
FL, 1985.
4. Standard Methods for the Examination of Water and Wastewater, 16th ed.; Greenberg, A.
E.; Trussell, R. R.; Clesceri, L. S., Eds.; American Water Works Association, Water
Pollution Control Federation, American Public Health Association: Washington, D.C.,
1985; Methods 427, 427A, 427B, and 427D.
5. Andreae, M. O., Banard, W. R. Anal. Chem. 55, 608-612, 1983.
6. Barclay, H. Adv. Instrum. 35(2): 59-61, 1980.
7. Bateson, S. W., Moody, G. J., Thomas, J.P.R. Analyst, 111: 3-9, 1986.
8. Berthage, P. O., Anal. Chim. Acta 10: 310-311,1954.
9. Craig, P. J.; Moreton, P. A. Environ. Technol. Lett., 3:
511-520,1982.
10. Franklin, G. O.; Fitchett, W. W. Pulp & Paper Canada. 83(10):
40-44, 1982.
11. Fuller, W. In: Cyandie in the Environment; Van Zyl, D., Ed.; Proceedings of
Symposium; December, 1984.
12. Gottfried, G. J. "Precision, Accuracy, and MDL Statements for EPA Methods 9010,
9030, 9060, 7520, 7521, 7550, 7551, 7910, and 7911"; final report to the U.S.
Environmental Protection Agency (EMSL-CI); Biopheric.
13. Kilroy, W. P. Talanta 30(6): 419-422,1983.
14. Kurtenacher, V. A., Wallak, R. Z. Anorg. U. Allg. Chem. 161:
202-209, 1927.
15. Landers, D. H., David, M. B., Mitchell, M. J. Int. J. Anal. Chem. 14: 245-256, 1983.
16. Opekar, F., Brukenstein, S. Anal. Chem. 56: 1206-1209,1984.
17. Ricklin R. D., Johnson, E. L. Anal. Chem. 55: 4, 1983.
18. American Chemical Society. Rohrbough, W. G., et al. Reagent Chemicals, American
Chemical Society Specification, 7th ed.; Washington, D.C., 1986.
19. Iowa State University. Snedecor, G. W., Ghran, W. G. Statistical Methods; Ames, Iowa,
1980.
20. Umana, M., Beach, J., Sheldon, L. Revisions to Method 9010; final report, Contract No.
68-01-7266, U.S. Environmental Protection Agency, Research Triangle Institute.
Research Triangle Park, North Carolina, 1986; Work Assignment No. 1.
43
-------
21. Umana, M., Sheldon, L. Interim Report: Literature Review, interim report, Contract
No. 68-01-7266, U.S. Environmental Protection Agency Research Triangle Institute.
Research Triangle Park, North Carolina, 1986; Work Assignment No. 3.
22. Wang, W., Barcelona, M. J. Environ. Inter. 9: 129-133, 1983.
23. Wronski, M. Talanta, 28: 173-176 1981.
24. Princeton Applied Research Corp. Applications Note 156. Princeton, New Jersery.
25. Guidelines for Assessing and Reporting Data Quality for Environmental Measurements;
U.S. Environmental Protection Agency. Office of Research and Development. U.S.
Government Printing Office: Washington, D.C., 1983.
26. Fed. Regist. 45(98): 33122,1980.
27. The Analytical Chemistry of Sulfur and Its Compounds, Part I; Karchmer, J. H., Ed.,
Wiley-Interscience, New York, 1970.
28. Methods for the Examination of Water and Associated Materials; Department of the
Environment: England, 1983.
29. EAL. Development and Evaluation of a Test Procedure for Reactivity Criteria for
Hazardous Waste; final report, Contract 68-03-2961,
U.S. Environmental Protection Agency, Richmond, California.
30. 1985 Annual Book of ASTM Standards, Vol. 11.01; Standards Specification for Reagent
Water; ASTM: Philadelphia, Pennsylvania, D1193-77, 1985.
31. Single Laboratory Evaluation of the Sulfide SIE; report, Contract 68-32-3249, U.S.
Environmental Protection Agency, EMSL-Las Vegas, Nevada.
44
-------
Gas Evolution Apparatus
H2S04 (HCi for acid insoluble sulfides)
N, in
Zinc Acetate &
Formaldehyde
Scrubbing
Bottles
Hot Water Bath
with Magnetic Stirrer
Stirring Bar
Figure 1.
45
-------
Tumbler-Extractor
Foam Lined
1-L Bottle
with Cap
Jar Mill Drive
Box Wheels Plywood
Figure 2.
46
-------
Extractor
Hinged Cover
1 - Gallon Plastic
or Glass Bottle
Foam Bonded to Cover
Box Assembly
Plywood
Construction
Totally Enclosed
Fan Cooled Motor
40 rpm. 1/8 HP
Foam Inner Liner
3 position Toggle
Switch
Fuse
12 In.
Figure 3.
-------
START
/ 7.3 \
OIL PHASE IH
\FILTRATE
PLACE IN 1L BOTTLE:
500mL H20,5mL SOXNaOH
1G SnCl2, 50ml HEXANE
(IF OIL OR GREASE
PRESENT)
ASSEMBLE FUNNEL APP,
INS. GLASS WOOL, WET
WITH MEAS. VOL H20
WEIGH OUT 25G, ADO TO
BOTTLE WHILE PURGING
CAP BOTTLE AND SHAKE,
SPARGE BOTTLE WITH NZ TO
PURGE 02
7.6
pH OF EXTRACT MUST BE >9
<11. SHAKE BOTTLE 1
MIN, OPEN UNDER N2,
CHECK pH
ADD ALL SOLIDS, CAP
BOTTLE
773
TRANSFER SOLID AND GLASS
WOOL TO DRIED TARED
WEIGHING DISH
TRANSFER SAMPLE (1-50MG
SULFIDE) TO FUNNEL,
FILTER UNTIL NO FREE
WATER REMAINS IN FUNNEL.
7.3
TRANSFER FILTRATE TO
SEP. FUNNEL, COLLECT
AOUEOUS PHASE, MEAS.
VOL., TRANSFER OIL PHASE
TO WEIGHING DISH
WEIGH DISH AND CONTENTS
SUB. GLASS F'lBER (IF
ANY), SU. TOTAL RINSE
VOL. FROM FILTRATE VOL.
48
-------
7.6
ADO 5mL ALIQUOT 50X NaOH
UNTIL pH>9, PURGE 02,
jRECAP BOTTLES, REPEAT IF
NECESSARY
YES
NO
YES
/ 7.10 \
'OIL PHASE IN"
v EXTRACT
NO
7.9
DECANT EXTRACT INTO
FUNNEL
7.8
PREPARE FUNNEL AS IN
STEP 7.1
7.10
PLACE EXTRACT IN SEP.
FUNNEL, COLLECT AND
HEASURE VOLUME OF
AQUEOUS PHASE
PLACE BOTTLE IN TUH8LER
TURN ON AND RUN FOR 18
HOURS.
49
7.12.2
PREPARE GAS EVOLUTION
APPARATUS (SEE FIGURE 1)
COMBINE AQUEOUS EXTRACT
AND SAMPLE FILTRATE IN
ALIQUOTS PROPORTIONAL TO
THE ORIGINAL SAMPLE
CALCULATE mL H2S04
REQUIRED TO ACIDIFY
SAMPLE
7.12.2.1
PREPARE HOT UATER BATH
CHOOSE SAMPLE SIZE
(1-50MG SULFIDE), PLACE
IN BEAKER, ADD H20, ADD
H2S04 UNTIL pH<=1
-------
7.12.2.3
PLACE SCRUBBER SOLUTION
INTO SCRUBBING BOTTLES
(7.12.2.4
CONNECT FLASK AND
SCRUBBING BOTTLES.
SECURE JOINTS.
7.12.4
PLACE DROPPING FUNNEL
ONTO FLASK, ADD H2S04
FROM STEi> 7.12 INTO
DROPPING'FUNNEL.
7.12.3
PLACE WEIGHED SAMPLE IN
FLASK. DILUTE WITH H20
IF NECESSARY.
7.12.2.2
ASSEMBLE 3-NECK FLASK
7.14
7.13
HEAT TO 70C, ADD H2S04
TO FLASK. CLOSE DROPPING
FUNNEL VHEII ACID 'DDED.
7.12.5
AOJUST N2 FLOW,'CHECK
FOR LEAKS, TURN ON
STIRRER, PURGE FOR 15
MINUTES
7.12.7
PURGE, STIR, ANO HEAT
FOR 90 MINUTES. SHUT OFF
N2 ANO HEAT.
ANALYZE BY TITRATION
(STEP 7.13) OR SIE (STEP
7.14)
50
-------
!PIPET KNOW Hi 12 IHTO
'flask, dilute to volume,
[ado 2mL 6N HCl
YES
^ 7.13.3 x
12 COLOR
¦DISAPPEARS.
RECORD TOTAL VOLUME OF
12 SOLUTION ADDED.
STOP
STOP
RINSE 12 TRACES FROM
SCRUBBING BOTTLE.
TRANSFER RINSES TO
FLASK.
7.14.4
MEASURE THE SULFIDE IN
THE SCRUBBER WITH THE
7.14.1
STANDARDIZE THE AaN03
TITRANT.
7.13.7
CALCULATE THE SULFIDE
CONCENTRATION IN THE
SAMPLE.
7.14.3
CALIBRATE THE SIE AND
METER
7.14.2
STANDARDIZE THE SULFIOE
STANOARDS.
7.13.3
ADO MORE 12 SOLUTION
7.13.6
TITRATE SOLN WITH PAO OR
Na2S203 UNTIL 12 COLOR
FADES. ADO STARCH, TITR
UNTIL BLUE COLOR DISAPS.
REC TITRANT VOLUME.
PI PET SCRU8EING SOLUTION
INTO FLASK
PREPARE RINSE SOLUTION
FROM 12, 6H HCl, AND H20
51
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completi
1. REPORT NO. 2.
EPA/600/4-90/024
3.
4. TITLE AND SUBTITLE
MODIFICATION OF METHODS 9030 AND 9031 FOR THE ANALYSIS
OF SULFIDE BY SPECIFIC ION ELECTRODE
5. REPORT DATE
October 1990
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
D.C. Hillman and P. Nowinski
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME ANO AOORESS
Lockheed Engineering and Sciences Company
1050 E. Flamingo Road, Suite 120
Las Vegas, NV 89119
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
Contract No. 68-03-3249
12. SPONSORING AGENCY NAME ANO ADDRESS
Environmental Monitoring Systems Laboratory - Las Vegas
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, NV 89193-3478
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Two C)SW SW-846 methods (Method 9030 and 9031) used for the
determination of sulfide have been modified to include the use of
sulfide specific ion electrodes (SIE). Currently in both methods
sulfide is converted to hydrogen sulfide and distilled into a scrubber
solution for subsequent determination by iodometric titration. In the
modified methods, the hydrogen sulfide in the scrubber is determined
by sulfide SIE. A single lab evaluation was performed to determine
the operating characteristics. The sulfide SIE is linear over the
range 0.25-6000 mg/L sulfide with a detection limit.is about 0.2 mg/L
sulfide. Over the range 5-6000 mg/L, the relative precision of the
SIE is 2-4 percent. The accuracy (expressed as percent recovery) over
the range 0.25-6000 mg/L varies from 75-103 percent. The sulfide SIE
is very selective for the sulfide dianion and in the scrubber
solution, there are no interferences. Recoveries in real samples
spiked with 17.5 mg/L sulfide varied from 68-77 percent before
distillation and 93-98 percent after distillation. The results from
the evaluation indicate that the sulfide SIE provides an alternate
technique to determine sulfide in environmental samples after
distillation.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATi Field/Group
18. DISTRIBUTION STATEMENT
RELEASE TO PUPLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21 . NO. OF PAGES
fin
20. SECURITY CLASS (This page;
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (Re*. 4-77) previous edition is obsolete
------- |