用于分析低浓度气体的具有长路径长度池的真空FTIR

低浓度气体或蒸气化合物的FTIR分析通常需要高S/N测量。然而，由于仪器的光路中存在大气水蒸气和二氧化碳，即使使用氮气吹扫，一些气体的测量也可能很困难。分析NO特别困难，因为吸收带与水蒸气在同一光谱区域，测量NO2、CO2和CO气体也很困难，它们的吸收带与CO2吸收在同一区域。使用全真空光谱仪，可以完全消除光路中的水蒸气和二氧化碳，并且可以在低得多的浓度下进行测量。Figure 1 Spectrum of a 2 ppm CO sample in a 20 m gas cell, with a S/N approx. 200:1. Figure 2 The noise level of a  spectrum measured with the same conditions is ~4 x 10-5 Abs. At this noise level, measurement of CO gas can be easily  made with concentrations as low as 20-50 ppb.‍Application Note230TR0165-E Vacuum FTIR with Long Path Length Cell for theAnalysis of Low Concentration Gases2/2Application Note Vacuum FTIR with Long Path Length Cell for the Analysis of Low Concentration Gases Introdu c tio n A high S/N measureme n t is generally required for FT I R ana l ysis of low concentrat i ons of gas or vapor com p o u nds.Howeve r the measurement of so m e gases can be di f ficult due to the presence of atmospheric water vapor and ca r bon d i ox i de present in the optical path of the instrument ， even wit h n itrogen purging. It is especial l y d if ficul t to analyze NO because the absorption ba n d i s in the same spectra l region a s water vapor， it is also d if ficul t to measure NO，，CO，and CO gases， whose absorption bands are i n the same region as CO， absorpt i on. Usi n g a full-vacuum spectrometer， water vapor a n d carbon dioxide i n the light path can be completely el im inated and the measurement can be made at mu c h l ower concentr a tions. Figure 1 Spect r um of a 2 ppm CO sample in a 20 m gas cel l ， wit h a S/N approx. 200：1. Figu r e 2 The n oise level of a spectrum measured with the same condit i ons is ~4x 10-5 Abs. At t h is noise level ， measurement of CO gas can be easily made with concentrations as low as 20-50 ppb. Keywo r ds Vacu u m FTIR long path gas cell， gas analysis， ca r bon monoxide Nitrogen d i ox i de， nitr i c ox i de carbo n dioxide CO， NO，NO，CO. Condition R e so lu ti o n ： 4c m -1 Sca n s ： 500 Detector ： MC T C ell： 2800 2600 Wavenumber[cm-11