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appropriate hand-held instrument(e.g., LTX-31 0 calibrated for <br /> hydrogen sulfide or Jerome 6314). <br /> 1. Detection Limit: The DL should be equal to or less than 0.5 <br /> ppmv or be sensitive enough to allow for a modeled ambient air <br /> concentration (at least one microgram per cubic meter) at the <br /> soil surface. <br /> 2. Holding Time: Hydrogen sulfide samples should be extracted <br /> directly into a hand-held analyzer within 30 minutes of <br /> collection to minimize the risk of losing the hydrogen sulfide <br /> due to reaction with active surfaces. If a hand-held instrument <br /> is not used, hydrogen sulfide samples should be analyzed as <br /> below: <br /> a. Within 30 minutes of collection, using the GC procedures; <br /> or <br /> b. Within 24 hours of collection, if a surrogate is added to the <br /> samples, or 100 percent duplicate samples are collected. <br /> 3. Sample Containers: The following sample containers are <br /> recommended: <br /> a. Minimum one (1) liter black Tedlar m bag fitted with <br /> polypropylene valves or the equivalent; <br /> b. 100-ml gas-tight syringe fitted with an inert valve and <br /> wrapped in aluminum foil; <br /> c. Gas-tight glass bulb wrapped in aluminum foil; or <br /> d. Glass-lined or silicon coated Summalm canister. <br /> 4. Precautions <br /> a. Since hydrogen sulfide is extremely unstable in the <br /> presence of oxygen and moisture, contact of hydrogen <br /> sulfide samples with them should be avoided. <br /> b. Due to the high reactivity of hydrogen sulfide gas, contact of <br /> hydrogen sulfide samples with metallic or other non-passive <br /> surfaces should be avoided during sample collection, <br /> storage and analysis. <br /> c. Care must be taken so that GC components do not react <br /> with the sample. Typically glass-lined injection ports and <br /> Teflon TM tube packed columns are used to avoid loss of <br /> hydrogen sulfide due to reaction with active surfaces. <br /> 01/28/2003 - 20- <br />