United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Las Vegas NV 89114
Research and Development
EPA-600/S4-84-090 Jan. 1985
<§EPA Project Summary
Interlaboratory Evaluation of
Measurements for HCN and H2S
Released from Wastes
Thomas A. Hinners, Robert W. Handy, Doris J. Smith, and Edo D. Pellizzari
The objective of this project was to
assess a proposed method for deter-
mining whether a waste is hazardous on
the basis of its release of hydrogen
cyanide or hydrogen sulfide upon
contact with an acidic medium. This
was accomplished by performing a
single-laboratory evaluation of the
method and by conducting an interlab-
oratory study to estimate method
precision. The test method, proposed
by the Environmental Protection Agen-
cy's Office of Solid Waste, involves
acidifying a waste material to pH 2 and
measuring the gaseous hydrogen cya-
nide (HCN) or hydrogen sulfide (H2S)
evolved by means of stain tubes. This
report contains a description of the
interlaboratory study and an assess-
ment of the proposed method for
measuring HCN and H2S evolved from
waste materials.
In the interlaboratory study, twelve
laboratories analyzed eight cyanide-
containing and eight sulfide-containing
waste samples for the gaseous HCN or
H2S evolved upon acidification. The
twelve laboratories performed triplicate
analyses of the test samples following a
detailed set of instructions. Estimates
of within-day and across-day repeat-
ability with reproducibility were deter-
mined for the measurements.
Based on the interlaboratory results,
the proposed method was shown to be
potentially useful for measuring HzS
evolved from waste materials. However,
the measurements for HCN released
from waste samples were not reliable
because of an interfering stain on the
detector tubes. Carbon dioxide can pro-
duce an interfering color change on
HCN stain tubes. Mass spectrometric
measurements confirmed that the
major gas evolved from the cyanide-
containing waste samples was carbon
dioxide.
This Project Summary was developed
by EPA's Environmental Monitoring
Systems 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).
Introduction
The United States Environmental
Protection Agency (EPA) has specified in
the Federal Register (Vol. 45, No. 98, May
19, 1980, p. 33122) that a solid waste
exhibits the characteristic of reactivity if
"it is a cyanide- or sulfide-bearing waste
which, when exposed to pH conditions
between 2 and 12.5, can generate toxic
gases, vapors or fumes in a quantity
sufficient to present a danger to human
health or the environment." Presently,
there are no suitable, validated methods
for determining HCN or H2S evolved from
waste maferials.
The EAL Corporation, Richmond,
California, has developed (under EPA
Contract No. 68-03-2961 with the
Environmental Monitoring Systems
Laboratory-Las Vegas) a stain-tube
method proposed by the EPA Office of
Solid Waste. The method involved
acidifying the waste material to pH 2 and
measuring the gaseous hydrogen cyanide
or hydrogen sulfide evolved by means of
stain tubes. Gas detector tubes are
available commercially that were designed
to develop stains when exposed to
specific gases. The length of the stain
developed in a gas detector tube reflects
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the amount of the specific gas sampled
(when no other gas present causes a
color change). Stain tubes with calibrated
scales are available. Use of stain tubes to
detect and measure toxic gases is rapid
and requires no special instrumentation
or extensive training. The present study
was designed to further evaluate this
method.
Procedure
The interlaboratory study consisted of
the analysis of eight sulfide-bearing and
eight cyanide-bearing waste samples for
the H2S or HCN evolved upon acidification.
The cyanide-containing waste samples
were obtained from metal processing
operations, and the sulfide-containing
waste samples were obtained from a
paper mill, a tannery, a calcium sulfide
plant, and a coal plant. Twelve laboratories
participated in this study. They performed
triplicate analyses of the test samples
following a detailed set of instructions. In
every case, two determinations were
carried out on the same day and the third
on a different day. In this way, estimates of
within-day and across-day repeatability
and reproducibility were obtained for the
sample measurements. Before any test
samples were analyzed, a quality control
(QC) check solution was used to verify
that the system was operating properly.
The test samples included performance
evaluation (PE) solutions containing
concentrations of cyanide and sulfide
unknown to the participating laboratories.
Results
The results reported for the QC system
checks and the quality assurance (QA)
performance evaluation samples are
summarized in Tables 1 and 2. Table 1
shows a 17-percent relative standard
deviation for the HCN system check
solution, which coincides with the 17-
percent figure reported by the EAL
Corporation for HCN. The QA performance
evaluation results gave similar precision
estimates. Table 2 shows interlaboratory
precision estimates for the H2S quality
assurance/quality control samples. The
68-percent average recovery in the gas
phase for the generated H2S is in the
range reported by the EAL Corporation
and also found in preliminary work at the
Research Triangle Institute, Research
Triangle Park, North Carolina. It is
noteworthy that the recovery in the gas
phase for the generated HCN is between
5 and 6 percent, which is in the range
reported by the EAL Corporation and
confirmed by the Research Triangle
Institute. When HCN and H2S are gen-
erated by acidifying salt solutions,
Table 1. Hydrogen Cyanide QA/QC Results
Lab No. "
01
02
04
05
07
08
09
10
11
12
14
Mean
Std. Dev.
% RSDf
HCN Added
Mean Recovery
QC System Check
Mean Tube
Reading, pL
31
25
28
23
24
22
32
22
33
* *
* *
26.7
4.4
17
454 pL
5.9%
QA Samples Mean Cone., pg/mL
PE-1
8.4
6.6
8.0
7.1
6.8
6.8
7.5
6.5
10.5
* *
* *
7.6
1.3
17
150 pg/mL
5.1%
PE-2
2.5
3.2
2.8
2.3
2.6
2.4
2.7
2.4
3.4
* *
* *
2.7
0.38
14
50 pg/mL
5.4%
"Laboratories 03, 06 and 13 did not report data.
"The PE and QC samples appear to have been interchanged.
f/o RSD = percent relative standard deviation.
Table 2. Hydrogen Sulfide QA/QC Results
Lab No. *
01
02
04
05
06
07
08
09
10
11
12
14
QC System Check
Mean Tube
Reading, pL
21
22
16
37
31
18
24
22
24
26
21
24
QA Samples
PE-1
0.0
0.2
0.0
0.0
0.1
0.3
0.0
0.0
0.0
0.0
1.5
1.2
Mean Cone., fjg/mL
PE-2
3.8
2.2
4.1
3.0
4.5
2.2
4.3
3.9
2.8
4.4
2.4
4.4
Mean
Std. Dev.
% RSDf
H2S Added
Recovery
23.8
5.6
24
37 pL
66%
0.06"
0.06"
700**
0.0 pg/mL
3.5
0.92
26
5.0 /jg/mL
70%
'Laboratories 03 and 13 did not report data.
**Outlier values from two laboratories have been excluded.
f/o RSD = percent relative standard deviation.
recovery of these compounds in the gas
phase is less than 100 percent because of
the solubilities of these gases in aqueous
media. The much lower recovery for HCN
than for H2S is a reflection of the much
larger partition coefficient between liquid
and vapor phase for HCN than for H2S (238
versus 2.76 at 20°C).
The interlaboratory precision values for
the HCN and H2S measurements are
shown in Tables 3 and 4. The repeatability
and reproducibility coefficients for the
waste samples are listed and summarized
in Tables 5 and 6. As defined in Standard
E 173 of the American Society for Testing
and Materials (ASTM), the repeatability
coefficient represents the 95-percent
confidence limit for the difference
between two determinations by a typical
single laboratory expressed as a percent-
age of the average concentration for a
sample and the reproducibility coefficient
represents the 95-percent confidence
limit for the difference between two
determinations by two typical laboratories
(one determination by each) expressed as
a percentage of the average concentration
for the sample. The repeatability and
reproducibility values for the sulfide
measurements are clearly superior to
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Table 3. Hydrogen Cyanide Precision
A verage
Number of Concentration RSD*
Waste Samplef Measurements (/jg/mL) (%)
HCN -A** 24 0.26 32
HCN-B 33 5.6 91
HCN-D 32 2.2 WO
HCN-E 30 1.4 62
HCN-F 30 0.14 150
HCN-G 31 2.9 130
HCN-H 30 1.3 75
"Relative standard deviation of individual measurements by all contributing laboratories.
**0ut/ier values from one laboratory have been excluded.
fNo measurable response was obtained for sample HCN-C.
Table 4. Hydrogen Sulfide Precision
Average
Number of Concentration RSD*
Waste Samplef Measurements {ug/mL) (%)
H2S-A 36 0.48 140
H2S-B 36 2.4 140
H2S-D 36 415 27
H2S-£ 36 3.8 27
H2S-F 33 862 64
H2S-G 35 367 56
H2S-H"" 25 420 47
"Relative standard deviation of individual measurements by all contributing laboratories.
""Outlier values from one laboratory have been excluded.
fNo measurable response was obtained for sample H2S-C.
Table 5. Hydrogen Cyanide Repeatability and Reproducibility
Waste • Repeatability Reproducibility
Samplef Parameter Coefficient (%) Coefficient (%)
A* within day 92 120
across days 79; 64 140:140
B within day 130 250
across days 180:100 260; 280
D within day 90 280
across days 120:170 320:320
E within day 73 220
across days 81;140 200; 200
F within day 230 510
across days 440; 370 450; 480
G within day 350 410
across days 260; 210 370; 330
H within day 57 250
across days 85; 1 10 190; 220
Average" within day 150 290
across days 1 70 280
"Outlier values from one laboratory have been excluded.
fNo data are shown for sample C because no measurable HCN was reported.
Carbon dioxide (C02) is known to react
with HCN stain tubes to give a mottled
orange-to-pink appearance. This coloring
was reported by nearly all the participating
laboratories. In the presence of a limited
amount of carbon dioxide, the mottled
pink color fades, and observation of a
normal cyanide stain front is possible.
With wastes conlaining more carbonate,
an obscuring stain front, which develops
on the detector tube, remains even after a
prolonged gas sampling period. The
outlier values cited in Tables 3 and 5
probably reflect the misreading of the
interference stains for HCN stains.
Analysis of headspace gas after acidi-
fication of a cyanide waste confirmed that
C02 was the major gas evolved. An
attempt to trap the evolved carbon dioxide
from this waste using a CCb stain tube
placed in front of the hydrogen cyanide
tube was not successful because of the
large volume of C02 released. When C02
was purged from one problem waste (by
adding water, adjusting the pH to 8 and
stirring) before applying the test method,
a readable HCN stain was obtained
Although there is a potential for loss of
HCN at pH values below 12, ASTM
Standard D2777 includes a pretreatment
at pH 6 for some cyanide samples.
Since the coloring of HCN stain tubes
by C02 appeared to be reversible to some
extent, a gas sampling time in excess of
the 30-minute period in the test method
was investigated. The success of in-
creasing the sampling time by an addi-
tional 30 minutes depended upon the
amount of carbonate present in the
sample. Samples with relatively low
amounts of carbonate benefited most
from this extra sampling time. In this
situation, the diffuse coloration caused by
carbon dioxide faded to give a readable
hydrogen cyanide stain front. Samples
with large quantities of carbonate
benefited little if at all from this extra
sampling time.
Conclusions
The suitability of this stain-tube
method for measuring the gaseous HCN
and H2S released from some waste
materials has been investigated and the
following conclusions are presented:
those for the cyanide measurements.
Except for the repeatability of the H2S
results, there are no appreciable dif-
ferences for within-day and across-day
measurements shown in Tables 5 and 6.
In nearly every case, the precision
between laboratories was poorer than
within laboratories.
Interference Study
Some cyanide waste samples caused
difficulties during the interlaboratory
study, as evidenced by the comments
from the participating laboratories. The
remarks indicated the presence of a
common interferent in all of the samples.
Based mainly on the likelihood of
C02 interference from cyanide-
containing wastes, the use of this
stain-tube method (in its present
form) for measuring HCN evolved
from waste materials is not recom-
mended.
The partial-acidification purge tech-
nique to reduce the effect of carbon
dioxide on HCN measurements
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shows promise but caused as much
as a 25-percent loss of HCN from
standards.
3. Based mainly on the absence of
interferences and the reasonable
analytical precision noted in this
study, this stain-tube method rep-
resents a potentially useful tech-
nique for measuring HaS evolved
from waste materials. Optimizing
certain test parameters (stirring,
acidification, sampling time) could
improve the precision of the FUS
measurements.
Recommendations
1. When C02 interference is en-
countered in HCN measurements,
one could acidify another portion of
the sample to a pH of 8 and stir the
mixture (in a hood) until the evolution
of gas has ceased before conducting
the analysis according to the test
method. However, some HCN, to-
gether with C02, will be evolved by
this procedure. For samples which
still give an unreadable stain front,
some improvement may be realized
by extending the gas sampling time
past 30 minutes.
2. Future work should include an
investigation of the advantages and
disadvantages of performing the
COa purge for cyanide wastes at
various pH levels with the pump on
(but without the HCN detector tube
in place). Loss of HCN during any
COa-purge procedure should be
evaluated.
3. Carbon dioxide interference with
HCN measurements might prove
avoidable by trapping water before it
reaches the stain tube (to prevent
carbonic acid formation) or by
developing an HCN detector tube
that involves a different stain
reaction.
Table 6. Hydrogen Sullide Repeatability and Reproducibility
Waste
Sample f
A
B
D
E
F
G
H*
Average"
Parameter
within day
across days
within day
across days
within day
across days
within day
across days
within day
across days
within day
across days
within day
across days
within day
across days
Repeatability
Coefficient (%)
58
340; 280
20
270; 240
22
65; 82
21
86; 76
78
140; 150
55
72; 79
84
120; 160
48
150
Reproducibility
Coefficient (%)
460
450; 430
460
480; 470
90
71; 81
57
93; 76
180
230; 200
160
190; 220
120
110; 150
220
230
"Outlier values from one laboratory have been excluded.
fNo data are shown for sample C because no measurable H2S was reported.
The EPA author Thomas A. Hinners is with the Environmental Monitoring
Systems Laboratory, Las Vegas, NV 89114; Robert W. Handy, Doris J. Smith.
and Edo D. Pellizzari are with Research Triangle Institute, Research Triangle
Park. NC 27709.
Werner F. Beckert and Thomas A. Hinners are the EPA Project Officers (see
below).
The complete report, entitled "Interlaboratory Evaluation of Measurements for
HCN and HzS Released from Wastes," (Order No. PB 85-138 659; Cost; $11.50,
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 Officers can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
P.O. Box 15027
Las Vegas, NV 89114
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use S300
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