An Analysis of Pesticides and Polychlorinated Biphenyls in Biological Samples and Foods

Extraction and clean-up methods for organochlorine pesticides determination in milk

Organochlorine pesticides (OCPs) can cause environmental damage and human health risks since they are lipophilic compounds with high resistance to degradation and long half-lives in humans. As most persistent OCPs have been banned years ago, it is expected to find these compounds at trace levels in environment. Therefore, increasingly sensitive and reliable analytical techniques are required to ensure effective monitoring of these compounds. The aim of this review is to discuss extraction and clean-up methods used to monitor OCP residues in milk, reported in the last 20 years. To carry out this review, an exhaustive bibliographic review was conducted. Despite the disadvantages of conventional extraction and clean-up methods, such as liquid-liquid, solid-phase or Soxhlet extractions, these procedures are still used due to their reliability. New extraction methods, like solid-phase microextraction, matrix solid-phase dispersion or QuEChERS, have not been thoroughly evaluated for OCP determination in milk. Almost all the methodologies analyzed in this review presented good performance characteristics according to the performance acceptability criteria set in SANCO's procedure. Comparison between limits of quantification (LOQ) and detection (LOD), for the reported methodologies, is not always possible due to the heterogeneity of the units. Thus, researchers should take into account an homogenization of LOD and LOQ units, according to the international regulations and MRLs established. Finally, more research is necessary to obtain the ideal methodology for OCPs determination in milk, which comprises the environmentally friendly characteristics of the new techniques and the reliability of the traditional methodologies.

Methods for determining pesticides and polychlorinated biphenyls in food samples--problems and challenges

Determination of residual amounts of pesticides and polychlorinated biphenyls (PCBs) in food samples requires the use of specific techniques regarding sample preparation as well as instrumental analysis which should be characterized by a very low detection limit. A problem associated with the use of pesticides and PCBs is the need for controlling their residues in the environment, particularly in food, as these chemicals show a propensity to accumulate. The analysis of food samples for the presence of pesticides and PCBs brings on many difficulties because of the specificity of sample preparation consisting of multistep purification procedures of samples that contain trace amounts of an analyte. Concentration determinations of pollutants that easily dissolve in complex matrices, particularly in the presence of a large apportionment of interfering substances, pose a big challenge. Therefore, the basic step in food analysis for the presence of pesticides and PCBs is sample preparation which mainly consists of analyte enrichment and the removal of interfering substances. But all steps of the analytical procedure that include sample collection and preparation, extraction of analytes from matrix, extract purification, and final determination, are very significant; their precision and correct application have a decisive effect on the final result.

Challenges in the application of conventional PCB quantitation methods to studies of "invasive" freshwater organisms

We describe significant and unexpected errors in application of a conventional method for the quantitative determination of polychlorinated biphenyls (PCBs) in unusual biological tissue samples. A standard method based upon microwave-assisted extraction (MAE) and gas chromatography tandem mass spectrometry (GC-MS/MS) was applied to a variety of "invasive" freshwater organisms, representing a variety of genera. The 12 "co-planar" PCBs (co-PCBs) were determined at ng g(-1) levels in small samples (ca. 750-1000 mg) of eight freshwater species (n = 172). We found that the conventional method could lead to random and relatively large changes in retention times. A nearly five-fold increase in retention variability was observed for "lower" organisms compared to that observed in the analysis of predatory fish tissue. These unexpected retention time changes would result in misidentifications, and become problematic not only for non-selective detectors such as electron capture but also for MS-based approaches. That is, for electron impact (EI) ionization methods, molecular ions (M(+)) are produced by loss of Cl not only for congeners in the same homolog class but also for fragments of higher homologs (e.g. M - 35 and M - 37), thereby yielding false positive measurement of the target congener when the retention time windows overlap.