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Determination of Level of Quantification (LoQ) for Measuring Chlorobenzenes in Chlorinated Solvents

Pentachlorobenzene (QCB) and tetrachlorobenzenes (TeCB) meet the criteria of persistence, bioaccumulation and primarily from anthropogenic sources. Virtual elimination from the environment of this type of substance is the main objective of the Toxic Substance Management Policy.

The Level of Quantification (LoQ) will be the benchmark for achieving virtual elimination for the contamination of chlorobenzenes in chlorinated solvents. LoQ is defined as the lowest concentration of target compounds that can be quantified confidently. It is determined by assessing the variability (standard deviation) of replicate measurements of analytes at a concentration near the detection limit.

Pentachlorobenzene and tetrachlorobenzenes in various grades of chlorinated solvents including trichloroethylene and tetrachloroethylene were analyzed using the gas chromatography - mass spectrometry (GC-MS) and internal standard quantification (isotope dilution) method. Repeated analysis of four solvent samples containing Chlorobenzenes at levels from 2.5 to 50 ng/sample was performed. Linear regression plots for the analytes (3 TeCBs and QCB) suggest that standard deviation increases with the chlorobenzene concentration. At 10DL (10 times detection limit), LoQ for Chlorobenzenes in trichloroethylene and tetrachloroethylene is estimated as 2 ng/sample or 0.02 ng/mL on a 100-mL sample size.

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