Checking the Laboratory

Only in rare cases do field hydrochemists themselves measure all the parameters required. In most cases samples are sent to laboratories for part, 

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Each batch of samples sent to the lab should include duplicates of one sample, sent with different names and sample numbers. The results from the duplicate sample give a picture of the quality of the data. If the duplicates fall in the range of the quoted analytical error, the data for the whole batch of samples are acceptable. If, however, the duplicate values differ by more than the stated analytical error, the results should be discussed with the laboratory personnel and the data for the whole sample batch should be regarded as questionable. The differences observed between duplicate samples of several sample batches establish the analytical error of the specific laboratory for each parameter. 

Samples should be diluted with measured amounts of distilled water. The results of the diluted sample are acceptable if they agree with the calculated diluted value within the stated analytical error. 

Example A water sample has been diluted with 1 volume of distilled water. The laboratory results for magnesium were 105mg/l for the nondiluted sample and 52.9 mg/1 for the diluted sample the analytical error was 0.8 mg/1. Thus the reported diluted value, 52.9 + 0.8 mg/1, included in its range the calculated value for a 1 1 diluted sample, 52.5 mg/1, and the magnesium data from the laboratory may be accepted for the whole batch. 

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