Polychlorinated Biphenyl Compounds (PCBs) Determination from Water by Gas Chromatography Coupled with Mass Spectrometry (GC-MS)

摘要

Because they are not biodegradable, PCBs contribute to irreversible environmental pollution, and by ingestion, accumulate in adipose tissue, contributing to endocrine disrupters. By reason of these problems, it is necessary to improve the sensitivity and speed of PCB monitoring technology. In general, PCB is analyzed by gas chromatography with electron capture detector (GC-ECD) using classical columns with packed or capillary columns. These conventional analytical techniques, however, have accuracy problems in PCB detection that can occur due to interference owing to the matrix. The detection method by mass spectrometry, in the variant Selected Ion Monitoring contributes to the elimination of some interference between PCBs and some chemical compounds from the matrix, remained after the separation step. It chased the development of an analytical method for PCBs determination in water matrix by gas chromatography on fussed capillary column coupled with quadrupole mass spectrometry. As the method has been developed in laboratory, the method validation has been necessary studying the following performance parameters: specificity, selectivity, repeatability, intermediary precision, recovery, detection limit and robustness. The development of GC-MS method for PCBs determination in water consisted in establishing of the separation conditions of the analyzed components from water matrix (at an adequate recovery), by liquid-liquid extraction, the establishing of the optimal GC-MS parameters and the validation of this method. In the step of the analytes-matrix separation, PCBs from water samples prepared for analysis was extracted with hexane, carbon disulfide and chloroform through stirring at an appropriate speed followed by separating funnel separation. The organic fractions were concentrated to a final volume of 10 mL at a constant vacuum, with a Kuderna-Denish evaporator for GC-MS analysis. In the step II were established the optimal GC-MS separation parameters. The detection and quantitative determination by mass spectrometry, in the variant Selected Ion Monitoring"(MS-SIR) was used. In order to determine the PCBs recovery of the samples, three series of standards of the PCBs 28, 52, 101, 138, 153, 180 of 10 ppb in the solution to be analyzed using as extraction solvent hexane, carbon disulfide and chloroform were used. Recovery levels obtained were between 50% and 117% for hexane, 37-127 % for carbon disulfide and 65-111 % for chloroform. The selectivity determined as lack of interferences with the compounds of interest, was achieved through the repeatability of the gas chromatographic retention times and by quantification ion and qualifying ions from MS-SIR method. This improved selectivity eliminates interferences between PCBs and some chemical compounds in water matrix remaining after liquid-liquid extraction step and incomplete gas chromatographic separation. The GC-MS-SIR method performs an adequate separation of PCBs from the water matrix and eliminates some extractible interfering elements with a recovery of 50-120 % and determines the PCBs in the concentration range of 1-100 pg/mL PCB in water (1-100 ng/mL in the solution to be analyzed