Flame Photometric Detector: The Application of a Specific Detector for Phosphorus and for Sulfur Compounds -- Sensitive to Subnanogram Quantities

Abstract

The principle revealed by Draegerwerk for the detection of phosphorus and sulfur compounds has been applied to produce a detector for gas chromatography which is compact, sensitive and specific. This detector is sensitive to parts per billion (p.p.b.) of the phosphorus compounds and less than parts per million (p.p.m.) for the sulfur compounds. The response to phosphorus compounds is linear over a range of at least four decades of concentration. The response to sulfur compounds varies exponentially (approximately 2) in the range of 1 to 100 p.p.m. concentration. The principle upon which the detector is based is the photometric detection of flame emission of phosphorus and sulfur compounds in a hydrogenair flame. The unit described here uses narrow bandpass interference filters for spectral isolation of the phosphorus emission at 526 mµ and sulfur emission at 394 mµ. Interferences from the flame emission produced by other elements is eliminated by an optical arrangement whereby only the portion above the tip of a normal flame envelope is viewed by the photomultiplier tube. Specificity is demonstrated in the utilization of the detector in conjunction with a gas chromatograph by the full scale response obtained for 0.25 p.p.m. triethyl phosphate while a mixture of other organic compounds containing chlorine, nitrogen and oxygen were barely detectable at 250 p.p.m. The detector is sensitive to 0.25 nanograms of malathion and parathion using the 526 mµ filter; the response (peak height) is linear from 6 parts per billion to 60 parts per million. An example of the utility of the detector in the sulfur mode in conjunction with gas chromatograph is demonstrated by comparison of high test and regular grades of four brands of gasoline. Significant differences in concentrations of the sulfur compounds were detected.