1.1 This Recommendation provides requirements for defining, testing, and verifying the performance of high performance liquid chromatographic (HPLC) systems when used for measurement of pesticides and toxic substances in carrying out pollution control programs and in assessing the quality of food products as mandated by national laws and regulations. It does not intend to exclude any other equivalent means of measurement and analysis. An HPLC system can be applied successfully in the analysis of a variety of sample types including ground and surface water, municipal and industrial effluents, workplace air, soils and sediments, plant and animal tissue, and food products [1, 2, and 3]. Sample collection and extraction techniques, which depend on the sample type, are required prior to analysis. Sampling techniques and measurement methods are beyond the scope of this Recommendation; however, some relevant measurement methods may be found in references listed in Annex A. Note: High performance liquid chromatography is synonymous with high pressure liquid chromatography. 1.2 Metrological and technical requirements are provided for the major components of an HPLC system including the pump(s), injector(s), column(s), detector(s), and temperature control and data handling systems. The conditions of operation of a single instrument, or one combined from separate components, are intended to cover the application for trace analysis. 1.3 Four principles of separation in liquid chromatography exist: partition, adsorption, ion exchange, and gel permeation. Other terms are used to refer to each type. For many separations, however, the actual mechanism may not clearly be defined and may involve adsorption, partition, or a combination of both. Furthermore, the polarity of the stationary phase can be greater or less than the mobile phase. The separation method is called normal-phase HPLC when the stationary phase is more polar than the mobile phase, and the separation method is called reversed-phase HPLC when the reverse condition exists. The reversed-phase HPLC system has become the more frequently used technique for separation and analysis of organic compounds. It can separate a broad spectrum of non-ionic, ionizable, and ionic compounds. Reverse phase columns are usually stable and separations may be performed with good repeatability since the stationary phases are chemically bonded. Therefore, this Recommendation is intended to cover requirements of reversed-phase HPLC systems. Microbore-column, ion-exchange-column, and gel-permeation-column HPLC systems are not covered in this Recommendation. 1.4 The detector type selected for use with an HPLC system depends generally on the concentration and chemical and physical properties of the sample component to be measured and its matrix. The following detectors are covered in this Recommendation: UV/visible spectrophotometric, fluorescence, and electrochemical. Note: The mass spectrometer is a highly specific and sensitive detector appropriate for application. It is normally coupled to the system through an appropriate interface and is to be covered by a separate Recommendation because of its specialized nature. 1.5 The following are examples of compound classes that may be measured by an HPLC system: carbamates, pyrethroids, organophosphates, polynuclear aromatics, phenolics, isocyanates, aflatoxins, chlorophenoxy-acid herbicides, triazine herbicides, and amines. Some sample components may have to be converted to derivatives before measurement; however, an advantage of an HPLC system is that it may be used for the direct measurement of thermolabile compounds, compounds of low volatility, and strongly polar compounds without conversion to derivatives. 1.6 Instrument performance better than the criteria prescribed for these applications may be achieved by optimizing the performance of each major component of the measuring system. In such cases, success may depend on the knowledge, skill, and experience of the analyst.