直接大容量样品注射和窄孔径柱接合及信号平均化分析水样中有机物

ANALYSIS OF ORGANICS IN AQUEOUS SAMPLES BY INTERFACING THE DIRECT LARGE VOLUME SAMPLE INJECTION WITH NARROW BORE COLUMN AND SIGNAL AVERAGING

将大容量水样（５００μＬ至５ｍＬ）注射到并保持在Ｎａｆｉｏｎ管内，用逆流氮气将扩散穿过Ｎａｆｉｏｎ管的水蒸气带走。将所得的样品气流引到５０μｍ内径的开口管毛细管柱内。柱头热解吸调制器对所接受的样品的均匀调制得到浓度脉冲，一个脉冲产生一组色谱图，通过对这样一系列的快速色谱图的信号平均比能得到特殊的多重气相色谱图─—整体样品色谱图。热解吸调制器是通过将导电涂料涂到５０μｍ的分析柱的前端５．０ｃｍ一段而制得的。施加到导电薄膜上的电流脉冲将调制器段及其内部的固定相加热，释放出作为浓度脉冲的保留物质。对于连续不断流动的样品气流，调制器的功能就像一个自动的、高重复性的小容量注射器。用于水蒸气扩散的Ｎａｆｉｏｎ管和用于信号平均化的热调制器可将传统的样品注射和窄孔径柱接合起来，并充分利用窄孔径柱的分离性能。用氢焰电离检测器能得到１×１０－９（Ｖ／Ｖ）以下的检测限。该方法相当简单，重复性高。由该技术得到的相对标准偏差小于３％，不需要像冷阱那样的样品预处理或预浓缩。

A large volume of aqueous sample (500 μL to 5mL) is injected and held inside a Nafion tubing throughout which the water vapor is diffused by a counter-current sweeping nitrogen gas. The resulting sample flow is adopted into a 50 μm diameter open tubular capillary column. A specifc multiplex gas chromatogramthe total sample chromatogram can be generated by signal averaging of a series of fast chromatograms, each of which is resulted from one of the concentration pulses which are obtained from the adopted sample even chopping or modulating by an on-column thermal desorption modulator (TDM). The modulator is prepared by applying an electrically conductive paint to a 5. 0cm section at the head of the 50μm column. An electrical current pulse applied to a thin conductive film heats the modulator section and the stationary phase within it,releasing a certain number of retained substances as concentration pulses. The modulator functions like an automatic and highly reproducible small-volume injector for a continuously flowing sample stream. It is possible to get detection limits below 1 × 10-9(V/V) using a flame ionization detector. This method is rather simple and highly reproducible and the relative standard deviations obtained by this technique are less than 3% and no sample pretreatment or preconcentration such as cold trap is required. Nafion tubing for water vapor diffusion and TDM for signal averaging make it possible to interface the traditional sample injection with narrow bore capillary column and to make full use of the narrow bore column separation ability.