用于微量气体定量分析的全真空FTIR光谱仪（N2气体中的H2O）

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先前已经报道了使用长路径气室分析低浓度气体，然而，当目标气体的吸收峰与大气水蒸气的峰重叠时，或者当目标气体本身是存在于大气中的H2O或CO2时，可能难以准确地定量低浓度气体。这是因为即使使用真空FTIR光谱仪，也不可能在存在长路径长度样品池的情况下排空样品室。本申请说明中介绍的FT/IR-6000系列全真空气体分析系统在样品室中集成了一个特殊的气室，使整个光路在气室就位的情况下保持在全真空下。该全真空模型使得即使在0.2ppm水平下也能够定量H2O的浓度。对于测量，有单独的真空管线用于FT/IR-6800FV和气室的排空，单独的隔间独立排空。在气室中添加真空计可以控制极低浓度的气体样品。Application Note230TR0199 Full Vacuum FTIR Spectrometer forQuantitative Trace Gas Analysis (H，O in N， Gas)2/2Application Note Full Vacuum FTIR Spectrometer for Quantitative Trace Gas Analysis (H，O in N， Gas) I n trodu c tion T h e a n a l ysis of low conc e ntratio n gas e s using long p a t h l e n gth g a s c e ll s h as b ee n r e port e d p r e viously， h owev e r， i t can b e d iff icult to accurately quan ti tat e gas e s at low conc e nt r atio n s when th e a b sorpt i on p eaks of the t arget gas ov e rlap with the peaks of a t mosph e r i c water vapor or， when t h e targe t gas itse l f i s H，O or CO，， wh i ch are present i n the a t mosph e re.T h is is because eve n wit h a vacuum FTIR spectrom e te r， i t was n ot possible to evacuate the sam pl e chambe r with the l ong p at h l e ngth ce l l pres e n t . Th e F T /IR -6000 S e r ie s ful l vacuum gas analysis syst e m i n trod u c e d i n th i s a p pl i cat i o n n ote has a special gas ce l l i ntegrated in t o t h e sample chambe r ， allowing t h e e n tir e light pa t h to remai n under full vacuum wi th the gas ce l l in p lace. T his full vacuu m model makes it possible to quant i t a t e co n cen tr ations of H，O even at th e 0.2 ppm level. Ins t rumen t and M easur e ment For t h e measurement， t h ere are s e para t e vacuum l i n es for evacuat i on of th e F T/I R-6800FV and t h e gas ce l l， with in depe n dent evac u a t io n of th e sepa r ate compartments. Add in g a vacuum gauge to t h e gas cell makes i t possible to cont r ol extremely low conce n trat i ons of the ga s samples. C el l S peci fi cation C el l ty p e： Mu l t i -pass White'cell Pathleng t h ： 10 meters Cell body： Stainless stee l Cell inne r su r face： Electrochemically pol i shed Mirror m ateria l ： Stainless stee l Mirro r surface： Gold coated O-ri ng：Wind o w： CaF. Viton H eating： Possible， max. 100°C Cell capacity： Approx.2L FT /IR-6100 Gas in /o u tput p ort 1/4 i n c h VCR Measur e m e n t E xamp le The qu a n ti tatio n of a t rac e amoun t s of water vapor (H ，0) i n CO， i n a cyl i nder was attem p ted. Water vapor with a conc e ntration of 15.0 p pm was dilut e d by monitoring the pr e ssure ga u g e dur i ng dilut i on of t h e sta n da r d samples with concentrat i ons of 1.5， 3.0， 4.5， 6.0， 7.6 a n d 9.12 ppm . Fi gure 2 s h ows t h e IR spectra of water vapor for e ach co n c e n tr atio n .The l owest detection l i mit calc u l ated f ro m t h e Signal to Noise ra ti o was approx. 0.2-0.3 ppm. Th e calibration curve i n Figure 3 was c r eated usi n g t h e a b sorpt i on p eak at 1734 cm -1. As see n ， the precise qua n titat i on of low conce n tration can be made with t h is system. Figure 2. Expa n ded region of spec t ra wit h low conce n t r ation H，O Figure 3. H ，O cali b ra t ion c u rve 28600 Mary's Co u rt ， E as t o n ， MD 21601 US A