Application of Normal Distribution Test in Quality Control for Analytical Data of Groundwater Samples

The surrogates for the determination of 37 organic compounds in groundwater samples have been screened out and D'Agostino method has been applied to the normal distribution test for the determination results. Based on the "3σ-principle"of normal distribution theory, the effective ranges of the quality control indexes for each surrogate were fixed. And calculating using mathematical expectation and variance for the random variable of normal distribution functions, the normal distribution probability for analytical data of all surrogates is greater than 97% within effective ranges. The calculated process capability indexes of the surrogates for the volatile organic compounds (VOCs) of dibromofluoromethane, toluene-d₈, 4-bromofluorobenzene, 1,2-dichlorobenzene-d₄, fluorobenzene were between 1.00 and 1.33, indicating the effective monitoring for the analytical process. However, the process capability indexes of the surrogates for the semi-VOCs of 2,4,5,6-tetrachloro-m-xylene, dibutyl chlorendate, p-Terphenyl, decachlorobiphenyl were between 0.67 and 1.00, indicating lack capacity for monitoring the analytical process. Consulting the related regulations of EPA method, authors suggested that the quality control criteria for surrogates of 12 semi-VOCs in groundwater analysis should be handled flexibly. The quality control method has been successfully applied to the analysis of organic compounds in groundwater.