MARLAP_12 - 12 LABORATORY SAMPLE PREPARATION 12.1...

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12 LABORATORY SAMPLE PREPARATION 12.1 Introduction On first impression, sample preparation may seem the most routine aspect of an analytical protocol. However, it is critical that analysts realize and remember that a measurement is only as good as the sample preparation that has preceded it. If an aliquant taken for analysis does not represent the original sample accurately, the results of this analysis are questionable. As a general rule, the error in sampling and the sample preparation portion of an analytical procedure is considerably higher than that in the methodology itself, as illustrated in Figure 12.1. Sampling Concentration, Separation, Isolation, etc. Steps Sample Preparation Measurement (After Scwedt, 1997) FIGURE 12.1–Degree of error in laboratory sample preparation relative to other activities One goal of laboratory sample preparation is to provide, without sample loss, representative aliquants that are free of laboratory contamination that will be used in the next steps of the protocol. Samples are prepared in accordance with applicable standard operating procedures (SOPs) and laboratory SOPs using information provided by field sample preparation (Chapter 10, Field and Sampling Issues that Affect Laboratory Measurements ), sample screening activities, and objectives given in the appropriate planning documents. The laboratory sample preparation techniques presented in this chapter include the physical manipulation of the sample (heating, screening, grinding, mixing, etc.) up to the point of dissolution. Steps such as adding carriers and tracers, followed by wet ashing or fusion, are discussed in Chapter 13 ( Sample Dissolution ) and Chapter 14 ( Separation Techniques ). Contents 12.1 Introduction. ......................... 12-1 12.2 General Guidance for Sample Preparation . . 12-2 12.3 Solid Samples . ...................... 12-12 12.4 Filters . ............................ 12-30 12.5 Wipe Samples . ...................... 12-31 12.6 Liquid Samples . ..................... 12-32 12.7 Gases . ............................. 12-36 12.8 Bioassay . .......................... 12-36 12.9 References. ......................... 12-37 This chapter presents some general guidance JULY 2004 12-1 MARLAP
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Laboratory Sample Preparation for sample preparation to avoid sample loss and sample contamination. Due to the physical nature of the matrix, sample preparation for solids requires the most attention, and therefore is discussed at great length (Section 12.3). General procedures for preparing solid samples (such as drying, obtaining a constant weight, grinding, sieving, mixing, and subsampling) are discussed. Some sample preparation procedures then are presented for typical types of solid samples (e.g.,
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MARLAP_12 - 12 LABORATORY SAMPLE PREPARATION 12.1...

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