ASTM D4059 Test Method forAnalysis of Polychlorinated Biphenyls in Insulating Liquids by Gas Chromatography
6. Interferences
6.1 Electron capture detectors respond to other chlorine containing compounds and to certain other electrophilic materials containing elements such as other halogens, nitrogen, oxygen, and sulfur. These materials may give peaks with retention times comparable to those of PCBs. Most common interferences will be removed by the simple pre-analysis treatment steps detailed within this test method. The chromatogram of each analyzed test specimen should be carefully compared with those of the standards. The results of an analysis are suspect if major extraneous or unusually large individual peaks are found.
6.1.1 Data acquisition and treatment by electronic integrators or other instrumental means easily permits the unrecognized inclusion of interferences in the quantification of results. Visual examination of chromatograms by those skilled in the method should be made to obtain maximum accuracy.
6.2 The sensitivity of EC detectors is reduced by mineral oils. The same amount of oil must pass through the detector in both calibration and analysis to ensure a meaningful comparison for quantification. Sample, standard dilutions, and injection volumes should be carefully chosen in this test method to match the interference of the oil.
6.2.1 The sensitivity of EC detectors is not significantly affected by silicone liquids. Evaluate the need for matrix matching within your analytical scheme before proceeding. Mineral oil should be absent from standards and dilution solvents used in the analysis of silicone test specimens.
6.3 Residual oxygen in the carrier gas may react with components of test specimens to give oxidation products to which EC detectors will respond. Take care to ensure the purity of the carrier gas.
6.3.1 The use of an oxygen scrubber and a moisture trap on both the carrier gas and the detector makeup gas is recommended to extend the useful column and detector life.
6.4 Trichlorobenzenes (TCBs) are often present with PCBs in insulating oils and will generate a response in the EC detector. These appear earlier than the first chlorinated biphenyl peak (i = 11) in most cases and should be neglected in this analysis. Unusually high concentrations of TCBs may be present occasionally and may obscure the lower molecular weight PCB peaks.
6.5 Components of high-molecular weight mineral oils may have longer than normal retention on the chromatography column, resulting in "ghost" peaks or excessive tailing. These conditions interfere with the data system's ability to accurately quantify material at levels approaching the method detection limit. Inject reagent grade solvent blanks until the chromatogram's baseline returns to normal before continuing with the analysis.
