Fluorometric Field Instrument for Continuous Measurement of Atmospheric Hydrogen Sulfide

A sensitive (limit of detection ~<100 pptv at S/N = 3), fully automated, portable (32 × 25 × 38 cm, 4.5 kg) instrument has been designed for continuous field measurement of atmospheric hydrogen sulfide. Air is sampled by a PTFE membrane-based diffusion scrubber and collected into an alkaline fluorescein mercuric acetate (FMA) solution flowing under a controlled and constant pneumatic pressure. The collected sulfide quenches the fluorescence that is measured with a miniature blue LED photodiode-based fluorescence detector. Acquisition and interpretation of signal and all flow control are carried out via a mininotebook personal computer (PC) using custom software written in HP-VEE. The instrument provides for self-calibration and zero functions using an on-board permeation tube enclosed in a thermostated block, at any preprogrammed desired interval. During sampling, the computed H2S concentration is stored every 2 min. The complete system, including the PC, is operated in the field by a 12-V marine battery. The system was field tested near oil field operations in West Texas and showed good correlations with a concurrently operated lead acetate tapebased commercial sampler, with a response speed and time resolution much better than that of the latter instrument.