Effect of ammonia on the response of the nitrogen phosphorus detector (NPD)

Abstract The effect of ammonia as a carrier gas and as a make‐up gas on the response of the nitrogen phosphorus detector (NPD) was investigated. This study showed that the response of the NPD increased 2.2 to 10.3 fold for all studied aliphatic amines when 5% ammonia in nitrogen was used as a make‐up gas. This increase was about 5.3 to 22.8 fold when ammonia was used as a carrier gas. The response of the NPD for nitro‐aromatic compounds increased 1.8 to 3.1 fold using 5% ammonia as a make‐up gas and 4.2 fold when ammonia was used as a carrier gas. The higher response obtained using ammonia as the carrier gas is related to improvements in the chromatographic performance (reduced tailing). The response of the NPD to phosphorus compounds was about 1.5 times higher using ammonia either as a carrier gas or as a make‐up gas compared to nitrogen. Although the noise of the NPD increased, the signal‐to‐noise ratios for both amines and phosphorus compounds improved with the use of ammonia.