1.1 This Recommendation provides performance requirements and testing procedures for a gas chromatograph/mass spectrometer/data (GC/MS) system when used for measurements in determining water pollutants in pollution control programs and in assessing the quality of water as may be mandated by national laws and regulations. Several types of mass spectrometers are available which employ a wide variety of techniques to achieve separation of ions according to mass-to-charge ratios; however, only low-resolution mass spectrometers are addressed. This Recommendation does not intend to exclude any other equivalent means of measurement or analysis. 1.2 The mass spectrometers addressed and coupled with appropriate gas chromatographs may be used successfully to analyze a variety of water samples, such as ground waters, surface waters, aqueous municipal and industrial effluents, and saline waters. A sample may require specific preparation techniques prior to analysis by a GC/MS system. Although important to an overall analysis, considerations of sampling, sample preparation, and pollutant measurement methods are beyond the scope of this Recommendation. 1.3 Pollutant compounds of interest in a sample may be analyzed by a GC/MS system if they are present in detectable amounts, can pass through the gas chromatographic column, and are not significantly affected by thermal or catalytic decomposition or adsorption. Some compounds that are difficult to analyze, such as those that are non-volatile or thermally unstable, can be converted to derivative compounds that then may undergo gas chromatographic separation and detection by the mass spectrometer. 1.4 Performance criteria better than those prescribed in this Recommendation for these applications of a GC/MS system may be achieved by paying careful attention to optimizing the performance of each component of the measurement system. In such cases, success depends on the knowledge, skill, and experience of the analyst.