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A coated piezoelectric crystal detector for the selective detection and determination of hydrogen sulfide in the atmosphere
Anglytica Chimica -4cta. 97 (1978) 29-36 @ELsevier Scientific Publishing Company, Amsterdam -
Printed in The Netherlands
A COATED PIEZOELECTRIC CRYSTAL DETECTOR FOR THE SELECTIVE DETECTION AN7D DETERMKNATION OF HYDROGEN SULFIDE IN THE ATlMOSPHERE
L. M. WEBBER, K. H. KARiiARKAR Department (U.S.A.)
of Chemisfry.
and G. G. GUILB_4ULT*
Uniuersity of New Orleans, New Orleans. Louisana 70122
(Received 12th September 1977)
SUMMARY A method for the selective detection and determination of hydrogen sulfide in the atmosphere is presented. This method utilizes the reversible adsorption of H,S on a piezoelectric quartz crystal coated with an acetone extract of soots resulting from the burning of organochlorine compounds. The extract of a soot prepared from chlorobenzoic acid provided the best substrate. ‘I?le method is useful in the concentration range l-60 ppm.
It is now recognized that even trace amounts of noxious gases have an adverse effect on ecological systems. Such recognition has dramatized the need to develop increasingly -more sensitive devices to measure such low concentrations_ Piezoelectric crystals, with active coatings which will electively adsorb gaseous pollutants, have been shown to be useful in the detection of trace pollutants [l-3]. Many coatings are not selective, so that a method to separate individual components is necessary. A gas chromatographic method has been developed for this purpose [4,5]. A piezoelectric device is most useful when it can be used to detect a specific component only. A number of methods for the selective detection of specific gases have been developed. The detection of SO, has received the most attention and a number of selective coatings have been found [6]. The detection of SO, under various conditions has been investigated [7-9], as has the use of a coated piezoelectric crystal for the continuous monitoring of SO* [IO, 111. The specific detection of ammonia has also received some attention, and a method for the detection of this gas, using a dry nitrogen carrier gas, has been developed. A similar method was developed for NO2 1121. A method for the detection of ammonia in air has also been developed 1131. Hydrogen sulfide is a toxic gas which has caused atmospheric pollution problems and is detrimental to industrial health and safety. Various methods for the detection of H,S in low concentrations have been developed 114, i5], but most of these are time-consuming or require bulky instrumentation.
30
A piezoelectric device can be quite portable and takes little time for a measurement. This paper reports the development of a new coating for a piezoelectric crystal which is sensitive toward H,S in the concentration range l-60 ppm.
The apparatus and instrumentation were identical with those reported previously [ 131, except for the oscillator. An OT-03 oscillator circuit from International Crystal Mfg. Co. was used. The crystal was a general-purpose crystal with silver electrodes (Jan Crystals, Fort Myers, Fla.). Some particular experiments, which will be discussed later, used a gold electrode crystal (International Crystal Mfg. Co.). All crystals were of the smaller size, HC25fU, and hsd a resonant frequency of 9 MHz. Briefly, the procedure was as follows. A &ml sample of test gas containing Ii2S diluted by air was injected into a stream of air, the carrier gas, at a flow rate of 30 rd min-‘; nitrogen was not used as carrier gas. When the H,S strikes the coated piezoelectric crystal surface, it is adsorbed and the weight change caused by that adsorption is observed as a change in frequency of the crystal, This change is related to the concentration of H2S in the test sample. The change in frequency was measured by a frequency counter which was adapted for use with a chart recorder. The coating for the crystal was prepared by burning several substances in air over a bunsen flame and collecting the soot residue. The compounds burned to obtain soots are listed in Table 1, Soots were obtained by repeatedly dipping a spatula into the particular compound, placing the spatula near the bunsen flame to ignite it and collecting the black residue. The soot residue was then placed in acetone, the extract was placed onto the crystal, and the acetone was allowed to evaporate leaving a film residue. The extract solution was applied to the electrode of the piezoelectric device {see Fig. I). Care was taken to ensure that carbon particles were not applied to the crystal at the same time as the extracts since particles can stop the resonance of the crystal. TABLE
1
Frequency Soot
changes
produced
extract
by H$
Frequency
in reaction change
with Soot
various
soot extracts
extract
Benzene Toluene Xylene
0 0 0
Chiorobenzoic acid Benzyl chloride Chloroaniline
Carbon tetrachloride Chloroform Chloroform extract Acetone extract
0
Benzoyi chloride Chloroacetic acid
10 30
Frequency 85 8 24 0 70
change
31
Test gas solutions were prepared by the syringe dilution method [5]. Chemically pure anhydrous HIS was diluted with room air to the desired concentration by successive dilutions in a 10 ml syringe. RESULTS
Choice of soot Acetone extracts of certain soots showed a strong reaction with H2S when applied to the quartz piezoelectric crystal. This reaction was indicated by the decrease in resonant frequency of the crystal; the amount of decrease was related to the concentration of H,S in a mixture with air (Fig 2). The acetone extracts of soots prepared from various compounds were tested as coatings. About lO,OOO-Hz change in frequency was observed for each coating substrate. In this coating procedure, the observation of change in frequency is the only way to know the quantity of the coating material_ The compounds tested are listed in Table 1, along with the resultant frequency change observed for a lo-ppm sample. The soots of the first four compounds were extracted by the parent compound rather than acetone. Chloroform soot was extracted by chloroform as well as acetone, and the frequency changes exhibited by both extracts as a coating are shown for comparison. Table 1 shows that the acetone extract of chlorobenzoic
acid made the
best coating. Chloroacetic acid coatings produced a frequency change that was almost as high, but those coatings saturated easily and were useful for 6OOi
CONCENTRATION
Fig. 1. Typical
piezoelectric
Fig. 2. Concentration
IPPM)
crystal.
vs. frequency
change
plot for chlorobenzoic
acid soot extract.
32
only two or three days. The chloroform soot acetone extract was useful as a coating but its response to H2S was much less than the chlorobenzoic acid soot extract; the same is true of other chlorine-containing compounds_ Organic compounds without chlorine substituents proved inactive. Linear range and psecision The usefulness of the acetone extract of the chlorobenzoic acid soot as a coating for a piezoelectric crystal for the determination of H,S is demonstrated by Fig. 2, which shows a typical concentration vs. frequency change calibration plot. The plot is linear from 1 to 50 ppm with a correlation coefficient of 0.993. After 50 ppm the curve levels off, probably because of saturation of the coating by H2S. The lower concentrations were the first measxed, so that by the time the higher concentrations were determined the coating had been exposed to a number of samples. When the higher concentrations were measured first, a linear relationship was observed up to concentrations over 100 ppm. However, under such conditions of measurement, the recovery time was so slow that the coating was not as useful. Fi,we 3 illustrates the effect of recovery time. When the injected H,S test sample strikes the crystal surface and is adsorbed, the frequency change reaches a.peak in less than 1 min. However, desorption is slower, and the time ne YLCUY for the frequency to regain a constant level is the recovery time. L’igure 3 shows the relationship between the recovery time and the concentration tested. At low concentrations, the recovery time is reasonable being about 15 min for 10 ppm. At higher concentrations, recovery is much slower (about 30 min at 60 ppm). This should not be a problem in atmospheric
0
20 TIME
40 (MIN)
60
Fig. 3. Recovery time experiments. Time is that required for the crystal to return to its original base line.
33
measurements, however, because the higher concentrations should be found only in extreme cases. Pure chlorobenzoic acid was also tried as a coating to ensure that the parent compound was not the active component of the coating. A coating made from that compound was inactive toward H$, and rapidly evaporated from the crystal surface. The precision of the experimental data was demonstrated by a series of 10 consecutive measurements at 10 ppm. Of the 10, two measurements were significantly low and were eliminated. The mean reading for the remaining 8 was 64.13 with a standard deviation of 2.36 (r.s.d. = 3.6%). In another series of 6 consecutive measurements, the standard deviation was 3.97 (r.s.d. = 6.1%). Precisions of this order are adequate for measurements in this low range. Errors can be caused by not waiting long enough for recovery; this was the cause of the two low measurements mentioned above. The syringe dilution method for the preparation of the test gases also gives rise to measurement errors (ca. 3% uncertainty). However, this type of error should not be a factor in the measurement of unknown atmospheric samples, and an accurate assay should result. Day-to-day precision was not as good, and daily calibration would probably be necessary in the utilization of this method. All of the many calibration curves measured were linear in the same concentration range as reported above, and thus only one or two calibration points would be necessary_ Least-squares correlation coefficients of 0.996,0.993,0.973 and 0.989 were obtained on four different days. Sensitivity also varied from day to day, being especially good mmediateIy after preparation of a fresh coating. For example, a frequency change of around 900 Hz was obtained for a concentration of 100 ppm on the day of preparation. Concentrations as low as 0.1 ppm could be detected within 3 days of Thitialcrystal preparation. A more realistically useful range (after a few days of use) is, however, l-60 ppm. The useful lifetime of a single crystal preparation was not established. However, one crystal was still sensitive in the useful concentration range after 3 months of constant use. Atmospheric humidity had negligible effects. Frequency changes caused by the injection of room air (blank measurement) was approximately 6 or 7 Hz, and were important only at very low concentrations of H,S. Studies of the reaction mechanism Some attempts were made to characterize the reaction of H,S with the chlorobenzoic acid soot coating. Gas chromatographic measurements with a flame ionization detector showed that the soot extract was composed of 3 or 4 major components and lo-15 minor ones. The last observed:major component emerged from the column only when the column temperature reached 200°C. This peak was reduced in size by the addition of H,S to the extract solution. Three to four major peaks were also observed when an electron capture detector was employed, indicating that chlorine (or perhaps
34
oxygen) was present in the compound. Elemental analysis of the chloroform soot showed 24.54% chlorine and 46.26% oxygen. Infrared spectra of the soot extracts were not changed by H,S adsorption, aud there were no dominant peaks which could help characterize the soot extract. The results reported above were performed with soot extracts coated on a crystal which had silver electrodes_ A crystal with gold electrodes was also coated with the cblorobenzoic acid soot extract; no reaction with H,S was observed. However, there was a reaction when silver nitrate was applied along with the soot extract. A nickel-plated gold electrode was also tried with some success, but the activity masnot as high as with the silver electrode. Crystals without coatings were not active. Since the metal of the electrode is involved in the reaction of H,S with the soot extract coating as is the chlorine of the organic molecule, perhaps some type of Ag (or Ni)-RCl--&S complex is the reactive intermediate. Since the complex is readily reversible, it is not likely that a direct sulfide of silver or nickel is formed. Clearly, there is not sufficient information to determine a reaction mechanism or to characterize the soot extract coating. It is believed that the coating provides a medium where the l&S gas & adsorbed and reacts with the metal electrode to form a sulfide on the electrode surface. This reaction is completely reversible. Further research is necessary to determine a more lucid mechanism and to characterize the coating. Some gases other than H2S were injected into the system to test the selectivity of the chlorobenzoic acid soot coating. Carbon monoxide, chloroform, benzene, toluene and hexane ail produced peaks that were nearly the same as the blank, and thus would not interfere with l&S measurements. The signals produced by 1000 ppm of SOZ and NH3 were equivalent to 10 ppm I&S; thus these gases would interfere when present at very high concentrations not normally present in air. NO, at 1000 ppm showed a very strong irreversiblereaction. Since 33,s reacts with SOZ, NH3 and NC& mixtures of these gases were not tested. Because of the reaction between those gases and i&S, it is doubtful that condensations in atmospheric samples would be sufficiently high to cause an interference when atmospheric H,S is measured.
The co&ted piezoelecfrie quartz crystals can be used to determine I&S at cdncentrations up to 60 ppm. Since the Occupational Safety and He&h Administration (0SH.A) lists 20 ppm as a ceiling vaiue for HZS, this type of coated crystal provides a measurement within the range of interest. A piezoelectric detection system has as its greatest advantages simplicity and compactness. Most accepted methods [ 14,151 for the determination of HIS tend to be time-consuming or costly, or both. Even some recently reported methods fall into one of these categories f IS-IS], “Pm commercial devices are available which measure and monitor H2S concentrations within the range of interest; although they are reasonably simple in design [X9,20], they lack the simplicity and po~ab~ty of the piezoeleetric crystal device.
35 The financial
assistance
of the Army
Research
Office,
Grant
No. DAAG29-
76-G-0215, is gratefully acknowledged. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
W. H. King, Jr., Anal. Chem., 36 (1964) 1735. W. H. King, Jr. and L. W. Corbett, Anal. Chem., 41 (1969) 580. W. H. King, Jr., Environ. Sci. Technol., 4 (1970) 1136. F. W. Karasek and K. R. Gibbins, J. Chromatogr. Sci., 9 (1971) 535. F. W. Karasek and J. M. Tiemay, J. Chromatogr., 89 (1974) 31. M. W. Frechette and J. L. Fasching, Environ. Sci. Technol., 7 (1973) 1135. K. H. Karmarkar and G. G. Guilbault, Anal. Chim. Acta, 71 (1974) 419. K. H. Karmarkar, L. M. Webber and G. G. Guilbault, Environ. I.&t., 8 (1975) 345. K. H. Karmarkar, L. M. Webber and G. G. Guilbault, Anal. Chim. Acta, 81 (1976) 265. J. L. Cheney and J. B. Homolya, Anal. L&t., 8 (1976) 175. J. L. Cheney, T. Nor-wood and J. Homolya, Anal. Lett., 9 (1976) 361. K. H. Karmarkar and G. G. Guilbault, Anal. Chim. Acta, 75 (1976) 111. L. RI. Webber and G. G. Guilbault, Anal. Chem., 48 (1976) 2244. W. E. Ruth, The Andysis of Gaseous Pollutants, Ann Arbor-Humphrey, Ann Arbor, Michigan, 1970, p_ 131. M. B. Jacobs, The Analytical Toxicology of Industrial Inorganic Poisons, Interscience, New York, 1967, p. 540. T. L. C. De Souza and S. P. Bhatia, Anal. Chem., 48 (1976) 2234. D. L. Ehman, Anal. Chem., 48 (1976) 918. A. R. Blanchette and A. D. Cooper, Anal. Chem., 48 (1976) 729. Technical Bulletin, General Monitors, Inc., Costa Mesa, Calif. Technical Bulletin, Energetics Science, Inc., Elmsford, N.Y.
Printed in The Netherlands
A COATED PIEZOELECTRIC CRYSTAL DETECTOR FOR THE SELECTIVE DETECTION AN7D DETERMKNATION OF HYDROGEN SULFIDE IN THE ATlMOSPHERE
L. M. WEBBER, K. H. KARiiARKAR Department (U.S.A.)
of Chemisfry.
and G. G. GUILB_4ULT*
Uniuersity of New Orleans, New Orleans. Louisana 70122
(Received 12th September 1977)
SUMMARY A method for the selective detection and determination of hydrogen sulfide in the atmosphere is presented. This method utilizes the reversible adsorption of H,S on a piezoelectric quartz crystal coated with an acetone extract of soots resulting from the burning of organochlorine compounds. The extract of a soot prepared from chlorobenzoic acid provided the best substrate. ‘I?le method is useful in the concentration range l-60 ppm.
It is now recognized that even trace amounts of noxious gases have an adverse effect on ecological systems. Such recognition has dramatized the need to develop increasingly -more sensitive devices to measure such low concentrations_ Piezoelectric crystals, with active coatings which will electively adsorb gaseous pollutants, have been shown to be useful in the detection of trace pollutants [l-3]. Many coatings are not selective, so that a method to separate individual components is necessary. A gas chromatographic method has been developed for this purpose [4,5]. A piezoelectric device is most useful when it can be used to detect a specific component only. A number of methods for the selective detection of specific gases have been developed. The detection of SO, has received the most attention and a number of selective coatings have been found [6]. The detection of SO, under various conditions has been investigated [7-9], as has the use of a coated piezoelectric crystal for the continuous monitoring of SO* [IO, 111. The specific detection of ammonia has also received some attention, and a method for the detection of this gas, using a dry nitrogen carrier gas, has been developed. A similar method was developed for NO2 1121. A method for the detection of ammonia in air has also been developed 1131. Hydrogen sulfide is a toxic gas which has caused atmospheric pollution problems and is detrimental to industrial health and safety. Various methods for the detection of H,S in low concentrations have been developed 114, i5], but most of these are time-consuming or require bulky instrumentation.
30
A piezoelectric device can be quite portable and takes little time for a measurement. This paper reports the development of a new coating for a piezoelectric crystal which is sensitive toward H,S in the concentration range l-60 ppm.
The apparatus and instrumentation were identical with those reported previously [ 131, except for the oscillator. An OT-03 oscillator circuit from International Crystal Mfg. Co. was used. The crystal was a general-purpose crystal with silver electrodes (Jan Crystals, Fort Myers, Fla.). Some particular experiments, which will be discussed later, used a gold electrode crystal (International Crystal Mfg. Co.). All crystals were of the smaller size, HC25fU, and hsd a resonant frequency of 9 MHz. Briefly, the procedure was as follows. A &ml sample of test gas containing Ii2S diluted by air was injected into a stream of air, the carrier gas, at a flow rate of 30 rd min-‘; nitrogen was not used as carrier gas. When the H,S strikes the coated piezoelectric crystal surface, it is adsorbed and the weight change caused by that adsorption is observed as a change in frequency of the crystal, This change is related to the concentration of H2S in the test sample. The change in frequency was measured by a frequency counter which was adapted for use with a chart recorder. The coating for the crystal was prepared by burning several substances in air over a bunsen flame and collecting the soot residue. The compounds burned to obtain soots are listed in Table 1, Soots were obtained by repeatedly dipping a spatula into the particular compound, placing the spatula near the bunsen flame to ignite it and collecting the black residue. The soot residue was then placed in acetone, the extract was placed onto the crystal, and the acetone was allowed to evaporate leaving a film residue. The extract solution was applied to the electrode of the piezoelectric device {see Fig. I). Care was taken to ensure that carbon particles were not applied to the crystal at the same time as the extracts since particles can stop the resonance of the crystal. TABLE
1
Frequency Soot
changes
produced
extract
by H$
Frequency
in reaction change
with Soot
various
soot extracts
extract
Benzene Toluene Xylene
0 0 0
Chiorobenzoic acid Benzyl chloride Chloroaniline
Carbon tetrachloride Chloroform Chloroform extract Acetone extract
0
Benzoyi chloride Chloroacetic acid
10 30
Frequency 85 8 24 0 70
change
31
Test gas solutions were prepared by the syringe dilution method [5]. Chemically pure anhydrous HIS was diluted with room air to the desired concentration by successive dilutions in a 10 ml syringe. RESULTS
Choice of soot Acetone extracts of certain soots showed a strong reaction with H2S when applied to the quartz piezoelectric crystal. This reaction was indicated by the decrease in resonant frequency of the crystal; the amount of decrease was related to the concentration of H,S in a mixture with air (Fig 2). The acetone extracts of soots prepared from various compounds were tested as coatings. About lO,OOO-Hz change in frequency was observed for each coating substrate. In this coating procedure, the observation of change in frequency is the only way to know the quantity of the coating material_ The compounds tested are listed in Table 1, along with the resultant frequency change observed for a lo-ppm sample. The soots of the first four compounds were extracted by the parent compound rather than acetone. Chloroform soot was extracted by chloroform as well as acetone, and the frequency changes exhibited by both extracts as a coating are shown for comparison. Table 1 shows that the acetone extract of chlorobenzoic
acid made the
best coating. Chloroacetic acid coatings produced a frequency change that was almost as high, but those coatings saturated easily and were useful for 6OOi
CONCENTRATION
Fig. 1. Typical
piezoelectric
Fig. 2. Concentration
IPPM)
crystal.
vs. frequency
change
plot for chlorobenzoic
acid soot extract.
32
only two or three days. The chloroform soot acetone extract was useful as a coating but its response to H2S was much less than the chlorobenzoic acid soot extract; the same is true of other chlorine-containing compounds_ Organic compounds without chlorine substituents proved inactive. Linear range and psecision The usefulness of the acetone extract of the chlorobenzoic acid soot as a coating for a piezoelectric crystal for the determination of H,S is demonstrated by Fig. 2, which shows a typical concentration vs. frequency change calibration plot. The plot is linear from 1 to 50 ppm with a correlation coefficient of 0.993. After 50 ppm the curve levels off, probably because of saturation of the coating by H2S. The lower concentrations were the first measxed, so that by the time the higher concentrations were determined the coating had been exposed to a number of samples. When the higher concentrations were measured first, a linear relationship was observed up to concentrations over 100 ppm. However, under such conditions of measurement, the recovery time was so slow that the coating was not as useful. Fi,we 3 illustrates the effect of recovery time. When the injected H,S test sample strikes the crystal surface and is adsorbed, the frequency change reaches a.peak in less than 1 min. However, desorption is slower, and the time ne YLCUY for the frequency to regain a constant level is the recovery time. L’igure 3 shows the relationship between the recovery time and the concentration tested. At low concentrations, the recovery time is reasonable being about 15 min for 10 ppm. At higher concentrations, recovery is much slower (about 30 min at 60 ppm). This should not be a problem in atmospheric
0
20 TIME
40 (MIN)
60
Fig. 3. Recovery time experiments. Time is that required for the crystal to return to its original base line.
33
measurements, however, because the higher concentrations should be found only in extreme cases. Pure chlorobenzoic acid was also tried as a coating to ensure that the parent compound was not the active component of the coating. A coating made from that compound was inactive toward H$, and rapidly evaporated from the crystal surface. The precision of the experimental data was demonstrated by a series of 10 consecutive measurements at 10 ppm. Of the 10, two measurements were significantly low and were eliminated. The mean reading for the remaining 8 was 64.13 with a standard deviation of 2.36 (r.s.d. = 3.6%). In another series of 6 consecutive measurements, the standard deviation was 3.97 (r.s.d. = 6.1%). Precisions of this order are adequate for measurements in this low range. Errors can be caused by not waiting long enough for recovery; this was the cause of the two low measurements mentioned above. The syringe dilution method for the preparation of the test gases also gives rise to measurement errors (ca. 3% uncertainty). However, this type of error should not be a factor in the measurement of unknown atmospheric samples, and an accurate assay should result. Day-to-day precision was not as good, and daily calibration would probably be necessary in the utilization of this method. All of the many calibration curves measured were linear in the same concentration range as reported above, and thus only one or two calibration points would be necessary_ Least-squares correlation coefficients of 0.996,0.993,0.973 and 0.989 were obtained on four different days. Sensitivity also varied from day to day, being especially good mmediateIy after preparation of a fresh coating. For example, a frequency change of around 900 Hz was obtained for a concentration of 100 ppm on the day of preparation. Concentrations as low as 0.1 ppm could be detected within 3 days of Thitialcrystal preparation. A more realistically useful range (after a few days of use) is, however, l-60 ppm. The useful lifetime of a single crystal preparation was not established. However, one crystal was still sensitive in the useful concentration range after 3 months of constant use. Atmospheric humidity had negligible effects. Frequency changes caused by the injection of room air (blank measurement) was approximately 6 or 7 Hz, and were important only at very low concentrations of H,S. Studies of the reaction mechanism Some attempts were made to characterize the reaction of H,S with the chlorobenzoic acid soot coating. Gas chromatographic measurements with a flame ionization detector showed that the soot extract was composed of 3 or 4 major components and lo-15 minor ones. The last observed:major component emerged from the column only when the column temperature reached 200°C. This peak was reduced in size by the addition of H,S to the extract solution. Three to four major peaks were also observed when an electron capture detector was employed, indicating that chlorine (or perhaps
34
oxygen) was present in the compound. Elemental analysis of the chloroform soot showed 24.54% chlorine and 46.26% oxygen. Infrared spectra of the soot extracts were not changed by H,S adsorption, aud there were no dominant peaks which could help characterize the soot extract. The results reported above were performed with soot extracts coated on a crystal which had silver electrodes_ A crystal with gold electrodes was also coated with the cblorobenzoic acid soot extract; no reaction with H,S was observed. However, there was a reaction when silver nitrate was applied along with the soot extract. A nickel-plated gold electrode was also tried with some success, but the activity masnot as high as with the silver electrode. Crystals without coatings were not active. Since the metal of the electrode is involved in the reaction of H,S with the soot extract coating as is the chlorine of the organic molecule, perhaps some type of Ag (or Ni)-RCl--&S complex is the reactive intermediate. Since the complex is readily reversible, it is not likely that a direct sulfide of silver or nickel is formed. Clearly, there is not sufficient information to determine a reaction mechanism or to characterize the soot extract coating. It is believed that the coating provides a medium where the l&S gas & adsorbed and reacts with the metal electrode to form a sulfide on the electrode surface. This reaction is completely reversible. Further research is necessary to determine a more lucid mechanism and to characterize the coating. Some gases other than H2S were injected into the system to test the selectivity of the chlorobenzoic acid soot coating. Carbon monoxide, chloroform, benzene, toluene and hexane ail produced peaks that were nearly the same as the blank, and thus would not interfere with l&S measurements. The signals produced by 1000 ppm of SOZ and NH3 were equivalent to 10 ppm I&S; thus these gases would interfere when present at very high concentrations not normally present in air. NO, at 1000 ppm showed a very strong irreversiblereaction. Since 33,s reacts with SOZ, NH3 and NC& mixtures of these gases were not tested. Because of the reaction between those gases and i&S, it is doubtful that condensations in atmospheric samples would be sufficiently high to cause an interference when atmospheric H,S is measured.
The co&ted piezoelecfrie quartz crystals can be used to determine I&S at cdncentrations up to 60 ppm. Since the Occupational Safety and He&h Administration (0SH.A) lists 20 ppm as a ceiling vaiue for HZS, this type of coated crystal provides a measurement within the range of interest. A piezoelectric detection system has as its greatest advantages simplicity and compactness. Most accepted methods [ 14,151 for the determination of HIS tend to be time-consuming or costly, or both. Even some recently reported methods fall into one of these categories f IS-IS], “Pm commercial devices are available which measure and monitor H2S concentrations within the range of interest; although they are reasonably simple in design [X9,20], they lack the simplicity and po~ab~ty of the piezoeleetric crystal device.
35 The financial
assistance
of the Army
Research
Office,
Grant
No. DAAG29-
76-G-0215, is gratefully acknowledged. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
W. H. King, Jr., Anal. Chem., 36 (1964) 1735. W. H. King, Jr. and L. W. Corbett, Anal. Chem., 41 (1969) 580. W. H. King, Jr., Environ. Sci. Technol., 4 (1970) 1136. F. W. Karasek and K. R. Gibbins, J. Chromatogr. Sci., 9 (1971) 535. F. W. Karasek and J. M. Tiemay, J. Chromatogr., 89 (1974) 31. M. W. Frechette and J. L. Fasching, Environ. Sci. Technol., 7 (1973) 1135. K. H. Karmarkar and G. G. Guilbault, Anal. Chim. Acta, 71 (1974) 419. K. H. Karmarkar, L. M. Webber and G. G. Guilbault, Environ. I.&t., 8 (1975) 345. K. H. Karmarkar, L. M. Webber and G. G. Guilbault, Anal. Chim. Acta, 81 (1976) 265. J. L. Cheney and J. B. Homolya, Anal. L&t., 8 (1976) 175. J. L. Cheney, T. Nor-wood and J. Homolya, Anal. Lett., 9 (1976) 361. K. H. Karmarkar and G. G. Guilbault, Anal. Chim. Acta, 75 (1976) 111. L. RI. Webber and G. G. Guilbault, Anal. Chem., 48 (1976) 2244. W. E. Ruth, The Andysis of Gaseous Pollutants, Ann Arbor-Humphrey, Ann Arbor, Michigan, 1970, p_ 131. M. B. Jacobs, The Analytical Toxicology of Industrial Inorganic Poisons, Interscience, New York, 1967, p. 540. T. L. C. De Souza and S. P. Bhatia, Anal. Chem., 48 (1976) 2234. D. L. Ehman, Anal. Chem., 48 (1976) 918. A. R. Blanchette and A. D. Cooper, Anal. Chem., 48 (1976) 729. Technical Bulletin, General Monitors, Inc., Costa Mesa, Calif. Technical Bulletin, Energetics Science, Inc., Elmsford, N.Y.