United States
Environmental Protection
Agency
Environmental Monitoring Systems
Laboratory
Las Vegas, NV 89193-3478
Research and Development
EPA/600/S4-90/024 Dec. 1990
EPA Project Summary
Modification of Methods 9030
and 9031 for the Analysis of
Sulfide by Specific Ion Electrode
Daniel C. Hillman and Piotr Nowinski
Two OSW SW-846 methods (Method
9030 and 9031) used for the determina-
tion of sulfide have been modified to
include the use of sulfide specific ion
electrodes (SIE). Currently in both
methods sulfide is converted to hydro-
gen 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 sing le 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 of 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 in-
terferences. 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 tech-
nique to determine sulfide in environ-
mental samples after distillation.
This Project Summary was devel-
oped by EPA's Environmental Monitor-
Ing Sytems Laboratory, Las Vegas, NV,
to announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Modifications to Methods 9030 and
9031 from "Test Methods for Evaluating
Solid Waste (SW-846)" currently specified
for the determination of sulfide have been
developed that allow the use of sulfide spe-
cific ion electrodes (SIE). Currently, both
methods require that sulfide be converted
to hydrogen sulfide and distilled into a
scrubber solution for subsequent determi-
nation by iodometric titration. In these pro-
posed modifications, the hydrogen sulfide
in the scrubber is determ ined by sulfide SIE.
A single-lab evaluation was performed to
determine the operating characteristics aod
performance of the draft methods. Data
were collected on electrode linearity, preci-
siorr, and accuracy. The effect of interfer-
ences and the possibility of direct measure-
ment of sulfide without distillation were in-
vestigated. Finally, the recovery of hydro-
gen sulfide in the system was measured as
a means to establish method accurracy.
Electrode linearity was determined by mea-
suring the sulfide concentration in 12
samples (ranging from 0.1 to 10,000 mg/L
sulfide) and by comparing those values with
values obtained using iodometric titration.
Linear regression analysis indicates a lin-
ear range of 1 mg/L to 12,000 ,rng/L. The
electrode response time was less than one
minute over the linear concentration range;
the detection limit was 0.2 mg/L.
Precision and accuracy were deter-
mined by measurement of three' sulfide
solutions that contained sulfide at a concen-
tration greater than 10 times the detection'
limit. The relative precision was 2-4 percent
and the accuracy (expressed as percent
recovery) over the same range varied from
75 to 103 percent.
Printed on Recycled Paper
-------
Compounds that interfere with the titra-
tion analysis of sulfide were tested as po-
tential interference with the sulfide elec-
trode analysis. Sodium sulfite and sodium
thiosulfate, each at the 100 mg/L level,
gave no significant SIE response.
There may be substances that can
interfere with the chemistry of the sulfide
SIE in undistilled environmental samples.
According to the manufacturer, two poten-
tial interferences are silver ion and mercu-
ric ion. Organic matter should not interfere
with the electrode chemically, although there
may be a physical effect due to coating of
the electrode membrane. Humic acid (100
mg/L), mercuric ion (10 jxg/L), and silver ion
(20 mg/L) solutions were analyzed using
the sulfide SIE, and each gave less than a
1 mg/L response for sulfide.
The direct measurement of sulfide in
environmental samples was attempted by
sulfide SIE. Four environmental samples
(three soils and one waste oil) were mixed
with a sulfide anti-oxidant buffer (SAOB)
and the free sulfide levels were determined
, by SIE; those results were compared with
results obtained using Method 9030. The
spike recoveries varied from 68 to 77 per-
cent for the SIE method as compared to 93
to 98 percent using Method 9030. This
suggests that some of the sulfide was com-
plexed and was not detected by the SIE.
Therefore, sulfide SIE should be used in
conjunction with distillation to ensure that
hydrogen sulfide gas is liberated from any
complexes or solid sulfides in the sample.
Priortothetitration procedure of Method
9030 and 9031, hydrogen sulfide gas is
-distilled into-a zinc acetate_scrubber=solu=
tion. The modified SIE protocols specify
that hydrogen sulfide gas be distilled into a
SAOB scrubber solution. To test the effi-
ciency of the SAOB as a scrubber solution,
three standards (1,10, and 40 mg/L sulfide)
were distilled into SAOB and the resulting
sulfide concentrations were measured. The
results are listed in Table 1. The one low
recovery for the 40 mg/L standard is most
likely due to incomplete sparging of oxygen
fromthesystem priortodistillation. Oxygen
oxidizes sulfide and will cause low recover-
ies.
This single lab evaluation has demon-
strationed that the sulfide SIE is a suitable
alternative technique for measuring sulfide
in distillate absorbing solutions. Use of the
sulfide SIE could double the capacity of
labo ratories that currently use th e iodometric
»titcation,to measure^sulfide...—,™-.~
Table 1. Recovery of Hydrogen Sulfide Gas at Different Concentrations in SAOB' Scrubber Solution
Concentration of Sulfide fma/U
1
10
40
% Recovery
91.0
89.8
86.7
96.6
100
96.0
69.3
98.9
89.2
Daniel C. Hillman and Piotr Nowinski are with Lockheed Engineering and Sciences
Company, Las Vegas, NV89119.
Steven M. Pyle is the EPA Project Officer (see below).
The complete report, entitled ""Modification of Method 9030 and 9031 for the Analysis
ofSulfida by Specific Ion Electrode," (Order No. PB90-274 235/AS; Cost: $17.00,
cost subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650 __
The EPA Project Officer can be contacted af:"""~""^'"""""•"
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Las Vegas, NV 89193-3478
United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/S4-90/024
------- |