APPLICATION OF A PERCHLORINATION METHOD TO ASSAY FOOD CONTAMINATION BY POLYCHLORINATED BIPHENYLS AND INSECTICIDES

Lech Rak, Eryk Adamczyk
Department of Food Hygiene and Consumer Protection, Faculty of Veterinary Medicine, Agricultural University Wrocław, Poland

ABSTRACT

Polychlorinated biphenyls (PCBs) and chloroorganic insecticides interfere with gas chromatographic analysis, thereby complicating their quantitative determination when multiple compounds are assayed. Perchlorination of the standards of the chlorinated compounds was used to simplify quantitative determination of these contaminants. Results indicate that perchlorination converts PCBs to a single compound (decachlorobiphenyl – DCB) that does not interfere with the assay for chloroorganic insecticides. These data confirm that perchlorination allows for simultaneous testing of both PCBs and chloroorganic insecticides during chromatographic analysis.

Key words: as chromatography; perchlorination, PCB, chloroorganic insecticides.

INTRODUCTION

Chlorinated compounds such as polychlorinated naphthalenes (PCN), biphenyls (PCB) and triphenyls (PTC) were widely used by industry and agriculture in the last century. These compounds possess useful features such as incombustibility, chemical resistance, lubricity, dielectricity and solubility in organic solvents. Consequently, they were used for impregnation of fabrics and wood, as additives to paints and lacquer, as insulators in the electronic industry and used instead of oil in transformers and central heating systems.

Polychlorinated compounds such as DDT, HCH and their derivatives were used by agriculture to fight pest infestation. Long-term use resulted in the development of resistance to this group of insecticides.

Unfortunately, all of the above mentioned chemicals share some negative qualities. They are all capable of permeating the environment and accumulating within it. From the soil, they penetrate the food chain and accumulate in both animal and human tissues, especially adipose tissue. At high concentrations these compounds have both teratogenic and carcinogenic properties. As a result, the amount of chlorinated compounds permitted in industry has been minimized. All such compounds have been withdrawn from agriculture – including chlorinated insecticides.

These chlorinated compounds persist in the environment in amounts sufficient to permeate to the food chain. The problem of mass pollution by chlorinated compounds has not been eliminated [5, 7, 10]. In Belgium, for example, incidents have occurred in which used transformer oil containing polychlorinated biphenyls were incorporated into animal feed. The PCBs were precursors of the dioxins, among the most toxic environmental contaminants known, indicating the importance of inspecting food for both animals and humans.

PCBs include 209 congeners that can be identified by chromatographic analysis. The number of peaks observed depends on chromatographic conditions, especially on the column quality. Separation on a short packed column gives only several peaks, whereas a capillary column is capable of separating most congeners [2,11].

Data shown in Table 1 indicate that the molecular weights of some PCBs and the chloroorganic insecticides listed are similar, implying potential difficulties in distinguishing among them during chromatographic analysis [3].

The aim of this work was to study the reduction in the number of signals on chromatogram observed when standards of PCBs and chlorinated insecticides were determined simultaneously. The results of chromatographic studies of standards of polychlorinated biphenyls as well as insecticides reveal that both groups of compounds can interfere with and cause difficulties in separation, identification and quantification.

Perchlorination of all 209 isomers and congeners of PCB should convert them into decachlorobiphenyl, which should be evident on chromatogram as one signal.

MATERIALS AND METHODS

Aroclor 1254 – Monsanto USA,
Insecticides – pure chemical standards – solution 1:10
SbCl₅ – Merck
Solvent – n-hexane Merck

Gas chromatograph Mera-Elwro 504 fitted with electron capture detector (ECD) with ⁶³Ni and glass column 4 mm x 2 m filled with 10% DC 200 on Chromosorb W/DMCS 80 – 10 mesh. Operating parameters: inlet and detector temperature 230°C, column temperature 235°C, carrier gas – nitrogen, flow 100 cm³min^-1, sample 5 µl.

Perchlorination was performed according the method by Berg and co. [4] with modification made by Ernst [6].

RESULTS AND DISCUSSION

The results of perchlorination reactions are shown in Figs. 2–5.

Fig. 2 illustrates chromatogram of a mixture of insecticides and PCBs analyzed in the same conditions. Retention times of the two groups compounds are similar, suggesting mutual interference. The peaks of insecticides are marked. For PCBs there are some isomers marked by numbers.

Perchlorination of PCB samples results in the conversion of all PCB compounds into decachlorobiphenyl (DCB). Retention time of DCB is 19.0 min (see Fig. 3). This peak is beyond the other peaks of PCB isomers (upper part of figure). As can be seen in Fig. 3, there is no other peak except for DCB.

Fig. 4 shows comparison chromatograms of PCBs after perchlorination and insecticides that have not been perchlorinated. The peak of pp-DDD has a shorter retention time (14.0) than DCB (19.0). These data indicate that perchlorination of PCB with insecticides should not result in chromatogram peaks that interfere, as shown in Fig. 5. Perchlorinated insecticides are slightly modified by extra chlorine atoms, but peaks do not interfere [1].

The colorimetric Schechter-Haller’s method modified by Maier-Bode [8] and Mattson [9] was attempted to use for the quantification PCB and chloroorganic insecticides. The results shown in Table 2 confirm that this method is suitable only for analyses of insecticides. PCBs do not give colored reactions under any conditions, so these compounds are not detectable by this method. Therefore, Schechter-Haller’s method could be applied for the analysis PCBs and chloroorganic insecticides containing food sample only as an auxiliary method.

CONCLUSION

1. It is possible to carry out quantitative measurements for some isomers occurred in DDT and DDE using colorimetric methods and Mattson’s formula.

2. Perchlorination gives facilities for determining PCB congeners through conversion to DCB.

3. It is possible to carry out studies on PCB and chlorinated insecticides in any laboratory in which a gas chromatograph with an electron capture detector is available.

REFERENCES

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2. Ballschmiter K., Zell M. 1980 Analysis of Polychlorinated Biphenyls (PCB) by Glass Capillary Gas Chromatography. Fresenius Zeitschrift für Analytik Chemie Band 302, 20-31.

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