Internal standards: A source of analytical bias for volatile organic analyte determinations

Analytes were grouped by how similar their boiling points and natural log of their relative volatilities (ln RVs) were to their Method 8260C recommended ISTDs. For the most similar analytes, the Method 8260C determinations yielded an average bias less than 10% and a failure to meet calibration criteria less than 7%. However, as the difference between analyte and ISTD became greater the bias increased to over 40% (matrix dependent) and its calibration failure rate approached 70%. In comparison, when the Method 8260C data were reprocessed as Method 8261A determinations, this trend for groupings was minimized with biases increasing from 6% to only 20% and the calibration failure rate went from 0% to 15%.