ASTM D4281 Standard Test Method for Oil and Grease (Fluorocarbon Extractable Substances) by Gravimetric Determination
24. Quality Assurance/Quality Control
24.1 Minimum quality control requirements are an initial demonstration of proficiency, plus analysis of method blanks and quality control samples. Recovery spikes and duplicates may be required for specific programs. For a general discussion of quality control and good laboratory practices, see Practice D5789, Guide D3856, and Practice D4210.
24.2 Method Blank - Before processing any samples, the analyst shall demonstrate that all glassware and reagent interferences are under control. Each time a set of samples is extracted or reagents are changed, analyze a method blank. The blank result shall be low enough that it will not unduly influence the date (that is, <5 mg/L).
24.3 Initial Demonstration ofProficiency:
24.3.1 Select a representative spike concentration; a level used in the interlaboratory study is recommended (Method A - 21.9 mg/L; Method B - 20.7 mg/L). Use a spike material that is a sample of the same oil and grease that is expected to be present in actual samples. Add spike concentrate to at least seven 1-L aliquots of water, and analyze each aliquot according to the procedures in Section 12 (Method A) or Section 20 (Method B). Calculate the mean and standard deviation of these values and compare to the acceptable range of precision and bias found in Table 3.
24.3.2 This study should be repeated until the single operator precision and the mean value are within acceptable limits. Refer to Practice D5789 to develop limits for spikes at other concentrations.
24.3.3 The analyst is permitted to modify the procedure, use alternate solvents, or alternate extraction procedures, such as solid phase extraction, or both, to improve the procedure or lower analytical costs. Hexane has been recommended as an alternative solvent; analysts should note that hexane is lighter than water, and the water phase must be drained to collect the hexane layer. Any time such modifications are made, the initial demonstration of proficiency shall be successfully repeated.
24.4 Ongoing Quality Control Sample - To ensure that the test method is in control, analyze a single quality control sample (prepared as in 24.3.1) containing 21.9 mg/L (or selected level) of oil and grease daily or with each batch of up to 20 samples. The value obtained should be within the range listed in Table 3 if the test in control.
24.5 Duplicates and Matrix Spikes - Due to the inherent variability of oil and grease sampling and samples, results from duplicates and matrix spikes may be inconsistent or inconclusive. However, some programs may require analysis of these QC samples. Collect additional 1-L sample bottles for each duplicate and matrix spike sample to be analyzed should they be desired. Refer to Practice D5789 for guidelines on reporting and evaluating these results.
25. Keywords
25.1 gravimetric determination; oil and grease
