氣相層析-哨式偵測器的開發與研究

Abstract

本研究開發了應用於氣相層析儀(gas chromatography)的哨式偵測器。哨式偵測器比熱傳導偵測器高出一個數量級的靈敏度。哨式偵測器可以直接與氣相層析儀的毛細管柱結合。管柱氣體以及外加的鞘流氣體通過哨式偵測器後會產生聲音，此聲音可以簡單的由麥克風接收再由LabVIEW的內建程式做傅立葉轉換(Fourier transform)後，可得到非常尖銳的頻率訊號(半高寬約為1.6 Hz)。分析氣體可經由滯留時間進行定性，並由哨式偵測器產生頻率訊號的變化量，對分析氣體進行定量的分析。當管柱氣體以及鞘流氣體使用氮氣的情況下，對各種不同氣體進行偵測，包括氫氣、氦氣、氬氣、二氧化碳、二氧化硫以及氙氣，各氣體偵測極限約在3 μL，並且發現單位體積頻率變化量與分子量具有線性關係。在偵測液體部分，包括甲醇，環己烷，四氫呋喃，正己烷和丙酮，各液體偵測極限約在10 μg。將管柱氣體以及鞘流氣體改為氫氣的情況之下，可以改善哨式偵測器的偵測極限。以偵測丙酮為例，線性範圍在0.2~200 μg。此外，本實驗也嘗試利用阿達瑪進樣器，使待分析的氣體依據阿達瑪序列注射至氣相層析-哨式偵測器進行偵測，阿達瑪轉換技術最大的特點是能將低於偵測極限的訊號提升，利用255次、511次、1023次以及2047次的阿達瑪序列成功的提升二氧化硫的偵測極限的訊號峰7.4倍、9.7倍、15.2倍以及21.1倍。A simple milli-whistle was developed for the use in GC (gas chromatography) detection, in which compared to a thermal conductivity detector (TCD) one order of magnitude superior sensitivity can be obtained.The milli-whistle can be directly connected to the outlet of a GC capillary. The gas and make-up gas passing through the capillary produces a sound as it passes through the milli-whistle (i.e. the gas of the GC-eluate). The sound can easily be detected by a microphone, which, after a Fourier transform (FT) by means of a LabVIEW (Laboratory Virtual Instrumentation Engineering Workbench) built-in program, a very sharp frequency peak (full width at half maximum, ~ 1.6 Hz) can be simultaneously observed. As a result, GC-elutes can be qualitatively determined based on their retention times, and a quantitative analysis can be achieved based on the frequency-shifts. When the make-up and carrier gases used were nitrogen, in the case of gas samples, including hydrogen, helium, argon, carbon dioxide, sulfur dioxide and xenon, the limits of detection were found to be ~ 3 µL/each injection and found the linear correlation between frequency shift per µL and molecular weight ; in the case of liquid samples, including methanol, cyclohexane, tetrahydrofuran, hexane and acetone, the limits of detection were determined to be ~ 10 µg/each injection, respectively. When the background gases were shifted to hydrogen, the limits of detection can be further improved. In this case, when acetone was selected as the model sample, a linear relationship was found in the range of 0.2 ~ 200 µg/injection.In addition, a novel Hadamard-injector was successfully designed and used in the Hadamard transform-gas chromatography (HT-GC) method.When SO2 gas was selected as model compound, thesignal-to-noise (S/N) ratio was substantially improved after inverse Hadamard transformation of the encoded chromatogram. Under optimized conditions, when Hadamard matrix of 255 ,511 ,1023 and 2047 was used, the S/N ratio of the signal for SO2 was significantly improved to 7.4 ,9.7 ,15.2 and 21.1 fold.