Figure 1C shows the extracted ion chromatograms of BPA from QCBs with BPA interference obtained when using contaminated water in both SPE and HPLC mobile phases, but adding guard cartridges after the SPE and HPLC pumps.
We followed strict QC protocols, namely having at least two QCBs, two low-concentration QCs, and two highconcentration QCs in each analytical batch with 50 study samples, and including replicate analysis of at least 10% of study samples.
In a similar situation, we detected random contamination of triclosan in the QCBs and QCs while analyzing urine (Ye et al.
If replicate analysis is not possible (e.g, limited sample volume), another alternative is including additional QCBs and QCs within the analytical batch.
In another example, we noticed random, yet often repeated contamination with triclosan in some QCBs and QCs included in the batches prepared by one analyst, but not others.
* Prepare the QCBs using the same procedure and apparatus as the unknown study samples to avoid missing labware and apparatus potential contamination.
Furthermore, it is well recognized that reagent or quality control blank (QCB) and quality control (QC) samples, when used and evaluated properly, are invaluable to monitoring potential contamination during analysis and the accuracy/precision of the measurements (Taylor 1987).
During analysis, contamination from solvents (including water) or reagents is monitored through the scalculated concentration and the signal/noise (S/N) ratio of the reagent blank or QCB peak (Taylor 1987).