A Improved Method on Determination of Trace Organic Vapors in Ambient Air

Abstract

A improved gas chromatographic determination of trace organic vapors such as esters, ketones, alchols and aromatic hydrocarbons in ambient air has been reported. The analytical system consists of a stainless steel sampling tubing (10 cm×3 mm i.d.) packed with 60-80 mesh Tenax GC (7 cm×3 mm i.d.), a sample concentration unit with a 120 ml sampling loop and a gas chromatograph with a flame ionization detector (FID). The sampling tubing is silver-welded on a modified stem assembly of Swagelok Quick-Connects so that the tubing can be instantly installed on or off the concentration unit or the injection port of the gas chromatograph.
Ambient air is sampled by a diaphram pump into a polyester bag (Flek Sampler) at 200-500 ml/min for 5-30 min. Using the concentration unit, 120 ml of the sample are taken into the sampling loop, and the trace organics contained in the sample are then trapped into the sampling tubing by passing helium gas at 120 ml/min for 4 min. After the tubing is transfered to the injection port of the gas chromatograph, the concentrated organics are thermally desorbed for 30 seconds, and introduced into the analytical column by backflushing the carrier gas through the tubing for 30 seconds. The operation conditions of the gas chromatograph are as follows: column-3 m×2 mm i.d. stainless steel tube packed with 20 % PEG 20M on 80-100 mesh Celite 545, injection port temperature-140°C, column temperature-90-120°C, FID temperature-140°C, carrier gas-40 ml/min nitrogen. Advantages of the technique
Advantages of the technique are low ppb sensitivity, excellent quantitative accuracy and rapid analysis time. Relative standard deviations of measured values for a number of organic vapors are 1.8-14.2 % in the range of 2-200 ppb, and analysis time can be 7-12 min per a sample.