Friday, October 10, 2014

A New Method for ppb Analysis of H2S in Air and Water

Accepted for presentation at Pittcon 2015
March 8 - 12, 2015
New Orleans, LA
Abstract Number: 770 - 3
Session 770 - Environmental - LC/GC Techniques
Day and Time: Monday, March 09, 2015, 02:10 PMRoom 257
Authors: Jack Driscoll and Jennifer Maclachlan, PID Analyzers, LLC

Methodology:Gas ChromatographyApplication: EnvironmentalPrimary Focus: ApplicationTitle: A New Method for ppb Analysis of H2S in Air and WaterKeywords:
Environmental Analysis
Gas Chromatography
GC Detectors
Specialty Gas Analysis

The photoionization detector (PID) is a very sensitive GC detector for sulfur compounds with pg detection limits for hydrogen sulfide. This compound can be efficiently collected in the field in an impinger with a basic solution (0.01M NaOH) at a known period of time and flow rate. The solution should be kept out of sunlight. Back in the lab, since the pKa for H2S is 6.9, the addition of 0.1 M acid will convert the sulfide (collected) to H2S which can be swept out of a vessel with an inlet, exhaust and septum (for addition of acid {H+}). Once the H+ is added, the solution is stirred for several minutes, then the nitrogen is turned on at 15 cc/min/ and the H2S is swept into the sample loop of the six port GC injection valve. The H2S is separated on a porous polymer column and detected by the PID. A 10ng/L sample (permeation tube) of H2S collected for 10 minutes indicated a detection limit (3 sigma) of 0.9 ppb. The coefficient of variation at 25 ppb was 16.3% for 5 successive runs. The PID has a dynamic range > 107 so a high level stack sample (200 ppm) would still be in the linear range with a slightly shorter sampling time.

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