减少水蒸气和二氧化碳产生的噪音

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大气水蒸气和二氧化碳（CO2）在红外区域具有强吸收，由于光谱中存在额外的峰，会干扰弱样品峰的分析和检测。为了减少与H20和CO2相关的背景峰的影响，在测量背景和样品时，保持水蒸气和二氧化碳的浓度在相同的水平是很重要的。Application Note280-SO-0006 Minimizing the Effects of Water Vaporand Carbon Dioxide in IR Spectra2/2Application Note Minimizing the Effects of Water Vapor and Carbon Dioxide in IR Spectra Intro d uc t ion Atmospheric water vapor and ca r bo n diox i de (CO，) strong l y absorb in the infra r ed reg i on and can interfere wit h the analysis a n d detection of wea k sample peaks due to the additional peaks i n t he spec t rum. In o r der to reduce the effect of the background peaks associated with H，0 a n d CO， i t is importan t to ma i ntain the concentration o f water vapor and CO， at the same level when measur i ng both the background and sample. In thi s applicat i on note， we wou l d like to introduce a cou p le meas ur ement opt i ons to minimize t h e effects of CO， and wate r vapor，including “Shuttle Measu r ement"and"Pu r ge and Vacu u m”. Measurem e n t M ethod ATR PRO ONE Spec t rometer s 1. Shuttle Measurement In t h is method th e sample i s placed in a sample sh utt le (wi th b ackground a n d sample positions) i n the sam p le compartm en t ， th is al l ows background a n d sampl e measu r em e nts to b e mad e wi th out opening t h e sample compartment lid. Using a samp l e shu tt le al l ows measureme n ts t o b e m ade wi t hou t t h e eff e ct of c h a n ges i n t h e atmosphere. I mproved spectra are obtain e d wit h reduc e d background peaks fr om wat e r vapor and CO， b y mak i n g the measureme n ts one afte r anot h er i n short time. T h is is an easy to use and effect i ve method for transmission measurement. 2. Purge and Vacuum +Interva l Measurement Program This is useful for tr ansmission measurement or for use with sampling accessor i es suc h as ATR or DRIFTS. Both purge and vacu u m reduce the amount of water va p or and CO， i n the instrume n t by removing them from t he optical path. When using this met h od， the level of p urge or evacu a t i on has to be constan tl y maintained between background and sample measurements.Purge o r vacuum are usefu l whe n usi n g the Inte r va l Measuremen t Program to provide continuous me a surement of a p rocess wit h o u t t h e effects o f cha n gi n g wa t er vapor or CO， levels. The data obtained using purge or vacuu m u nder co n stan t condit i ons allows much e a sier acqu i sition of spectra wit h out the effects of vapor and CO，. E xamp l es of M e a s urement Measu r eme n t examples obtained wit h methods 1 a n d 2 a bove a r e i n troduced be l ow. Method 1 was used to measure a thin film of calc i um stearate on the surface of a CaF， pla t e. F i gure 1 shows the r esults of measurement wi t h and without us in g the s h u ttl e. When mea su r i ng peaks with low absorption suc h as in thin f i lms， water vapo r and CO， grea t l y inf lu ence the a c q ui r ed spect r um. Whe n us in g the shu t t l e， it can b e observed tha t t h e effects of water vapor and ca r bon dioxide are signi f icant l y decreased. Method 2 was used to measu r e a vinyl chlor i de f i lm us i ng a full vacuum system with a n ATR accessory. The results of i n terval measurement are displayed in Figu r e 2. It can be observed that the data whe r e the level of vacuum was not maintained shows the effects of wa t er vapor and CO，. In this case， measureme n t usually has to be repeated after releasing t he vacuum. During i n terval measuremen t ， it i s easy to continuously measu r e spect r a without the ef f ects of vapo r and CO， using a full vacuu m FTIR spectrometer. JASCO USA 28600 Mary's Cour t ， E a s to n ， M D 21601US A T el ： (800) 333-5272， Fa x ： (410) 822-7526A ppl ic a tio n Lib r ary： ja s c o i n c.com /appli c a t i o ns