Hydrogen sulfide In air sorbs onto Zeolite AAA molecular sieves in the Cd(I1) (white) form to give CdS (yellow) in the concentration range required for the determination of H,S for personnel monitoring and excursion samples as well as highlevel (ppb) air samples. The immoblilzed sulfide Is determined by spectrophotometry after conversion to methylene blue wHh a spectrophotometric detection limit of 0.25 pg of sulfide. Linear calibration curves cover the range of 0.25-35 pg of H2S. Factors affecting collection characteristics of the solid sorbent such as breakthrough, humidity, storage time, and interference by other atmospheric constituents were studied. Actual monitoring data are presented.One of the most commonly accepted methods for the determination of H2S in the air utilizes a liquid sorbent impinger containing a Cd(OH)2 suspension (1,2) which immobilizes S2-in the form of CdS. Other metal salt solutions as well as solutions of caustic soda have been used as liquid sorbents for the entrapment and determination of this pollutant (3-9). In terms of personnel monitoring, liquid sorbents are cumbersome and somewhat restrictive, hence the recent emphasis in pollutant monitoring has been toward the use of solid sorbents for the preconcentration of gaseous air pollutants.A small tube containing <1 g of a solid sorbent is easy to handle and convenient for storage. Sampling can be accomplished with a portable, battery-operated constant flow pump, and in cases where recovery is an equilibrium process, it is best to keep the quantity of the sorbent material minimal.The use of Ag(I), Hg(II), and Pb(I1) salts impregnated on paper tapes represents the first approaches of immobilization and determination of H2S on solid sorbents (10-16). None of these methods are suitable for sub-parts-per-billion H2S determinations. The Pb(I1) method has fallen into disfavor because of reports that the brown stain decomposes in the presence of light, SO2, or even air passing through the tape. Although the Hg(I1) tapes give a more stable product, this method is still not very sensitive to low background levels. Furthermore, the Ag(1) method is reported to be very sensitive to ozone, and mercaptans are reported interferents.Various other solid sorbents have been reported (17-20) for the preconcentration of H2S. However, few of these solid sorbents are specific, leave the immobilized pollutant in an inert form, and meet the criteria (e.g., high recovery, lack of interferences, and suitable storage times) for successful validation of a solid sorbent preconcentration method (21,22). Various chromatographic materials have been evaluated for use as preconcentrators. One should bear in mind that lowtemperature gas chromatography is functioning whereby pollutant molecules can migrate from one sorption site to the next and that the correct sorption-desorption properties for efficient collection and recovery are the two most self-conflicting properties of these systems. With this in view this research has developed a solid sorbent in the form (11)-e...

Instrumental techniques are compared for usage in the determination of atmospheric H2S which has been preconcentrated on Cd(II)-exchanged zeolite. The study covers the range of 0.01 to 100 μg of immobilized sulfide. For high concentrations (2–100 μg), combustion analysis followed by nondispersive IR is the simplest and most precise technique, and results with the use of this method are accurate to ±3% relative. In the range of 0.25–40 μg, the sulfide, after conversion to methylene blue, may be determined by conventional spectrophotometry, with a relative precision of ±13%. For the lowest concentration range investigated (0.01–2.0 μg), photoacoustic spectroscopy gave the only quantitative results after the H2S was converted to methylene blue.