EPA Method 18 Measurement Of Gaseous Organic Compound Emissions By Gas Chromatography
|
ID： |
43B8E96E922B4F67AD28E7D35FDF3F8F |
|
文件大小(MB)： |
0.4 |
|
页数： |
71 |
|
文件格式： |
|
|
日期： |
2011-5-20 |
|
购买： |
文本摘录（文本识别可能有误，但文件阅览显示及打印正常，pdf文件可进行文字搜索定位）：
1048,METHOD 18 - MEASUREMENT OF GASEOUS ORGANIC COMPOUND,EMISSIONS BY GAS CHROMATOGRAPHY,NOTE: This method is not inclusive with respect to,specifications (e.g., equipment and supplies) and procedures,(e.g., sampling and analytical) essential to its,performance. Some material is incorporated by reference,from other methods in this part. Therefore, to obtain,reliable results, persons using this method should have a,thorough knowledge of at least the following additional test,methods: Method 1, Method 2, Method 3.,NOTE: This method should not be attempted by persons,unfamiliar with the performance characteristics of gas,chromatography, nor by those persons who are unfamiliar with,source sampling. Particular care should be exercised in the,area of safety concerning choice of equipment and operation,in potentially explosive atmospheres.,1.0 Scope and Application.,1.1 Analyte. Total gaseous organic compounds.,1.2 Applicability.,1.2.1 This method is designed to measure gaseous,organics emitted from an industrial source. While designed,for ppm level sources, some detectors are quite capable of,detecting compounds at ambient levels, e.g., ECD, ELCD, and,helium ionization detectors. Some other types of detectors,1049,are evolving such that the sensitivity and applicability may,well be in the ppb range in only a few years.,1.2.2 This method will not determine compounds that,(1) are polymeric (high molecular weight), (2) can,polymerize before analysis, or (3) have very low vapor,pressures at stack or instrument conditions.,1.3 Range. The lower range of this method is,determined by the sampling system; adsorbents may be used to,concentrate the sample, thus lowering the limit of detection,below the 1 part per million (ppm) typically achievable with,direct interface or bag sampling. The upper limit is,governed by GC detector saturation or column overloading;,the upper range can be extended by dilution of sample with,an inert gas or by using smaller volume gas sampling loops.,The upper limit can also be governed by condensation of,higher boiling compounds.,1.4 Sensitivity. The sensitivity limit for a,compound is defined as the minimum detectable concentration,of that compound, or the concentration that produces a,signal-to-noise ratio of three to one. The minimum,detectable concentration is determined during the presurvey,calibration for each compound.,2.0 Summary of Method.,1050,The major organic components of a gas mixture are,separated by gas chromatography (GC) and individually,quantified by flame ionization, photoionization, electron,capture, or other appropriate detection principles. The,retention times of each separated component are compared,with those of known compounds under identical conditions.,Therefore, the analyst confirms the identity and approximate,concentrations of the organic emission components,beforehand. With this information, the analyst then,prepares or purchases commercially available standard,mixtures to calibrate the GC under conditions identical to,those of the samples. The analyst also determines the need,for sample dilution to avoid detector saturation, gas stream,filtration to eliminate particulate matter, and prevention,of moisture condensation.,3.0 Definitions. [Reserved],4.0 Interferences.,4.1 Resolution interferences that may occur can be,eliminated by appropriate GC column and detector choice or,by shifting the retention times through changes in the,column flow rate and the use of temperature programming.,4.2 The analytical system is demonstrated to be,essentially free from contaminants by periodically analyzing,blanks that consist of hydrocarbon-free air or nitrogen.,1051,4.3 Sample cross-contamination that occurs when,high-level and low-level samples or standards are analyzed,alternately is best dealt with by thorough purging of the GC,sample loop between samples.,4.4 To assure consistent detector response,calibration gases are contained in dry air. To adjust,gaseous organic concentrations when water vapor is present,in the sample, water vapor concentrations are determined for,those samples, and a correction factor is applied.,4.5 The gas chromatograph run time must be sufficient,to clear all eluting peaks from the column before proceeding,to the next run (in order to prevent sample carryover).,5.0 Safety.,5.1 Disclaimer. This method may involve hazardous,materials, operations, and equipment. This test method may,not address all of the safety problems associated with its,use. It is the responsibility of the user of this test,method to establish appropriate safety and health practices,and determine the applicability of regulatory limitations,prior to ……
……