Reference method for dibenzofuran and dibenzo-p-dioxin in defoamers: section 4

Section 4: Calculations

1. From the integrated ion chromatograms for the calibration runs, calculate the relative response factors for tire native DBD and DBF relative to the corresponding perdeuterated DBD and DBF internal standards (=RRF_x) according to the following equation:

   RRF_x = (A_ix/A_x)(C_x/C_ix)

   where:

   A_ix

   peak area of the quantitation ion for the appropriate labelled internal standard (m/z 176 for DBF-d ₈ and m/z 192 for DBD-d ₈)

   A_x

   peak area of the quantitation ion for the native analyze "x" (m/z 168 for DBF and m/z 184 for DBD)

   C_x

   concentration of native analyte "x" pg/μL

   C_ix

   concentration of appropriate internal standard "x", pg/μL

   
   
2. If the RRF for DBD and DBF are constant (relative standard deviation < 10%) over the working range, it can be assumed that the RRF is invariant and the average RRF can be used. Alternatively, the results can be used to plot a calibration curve of response ratios, A_ix/A_x vs RRF.
   
3. Calculate the concentration of the native DBD and DBF in the sample, C_sx, as follows:

   C_sx = (RRF_x)(A_x/A_ix)(Q_ix/W)

   where:

   C_sx

   concentration of native parameter "x" in the sample, ng/g

   RRF_x

   response factor of native parameter "x" relative to its perdeuterated internal standard

   A_x

   peak area of the quantitation ion for native parameter "x" in the sample (m/z 168 for DBF and m/z 184 for DBD)

   A_ix

   peak area of the quantitation ion for appropriate labeled internal standard "x" in the sample (m/z 176 for DBF-d ₈ and m/z 192 for DBD-d ₈)

   Q_ix

   amount in ng (i.e., 250 ng) of the appropriate labeled internal standard "x" added to the sample before extraction

   W

   weight of defoamer sample in grams

   
   
4. Calculate the percent recovery of the perdeuterated internal standards, % R_ix, measured in the sample extract using the formula:

   % R_ix = [(A_ix/A_r)_sample][(A_r/A_ix)_standard](100)

   where:

   A_r

   peak area of the quantitation ion (m/z 147) for haxamethylbenzene recovery standard

   A_ix

   peak area of the quantitation ion for the appropriate labelled internal standard "x" (m/z 176 for DBF-d ₈ and m/z 192 for DBD-d ₈)