Automated sample clean‐up and fractionation of organochlorine pesticides and polychlorinated biphenyls in human milk using NP‐HPLC with column‐switching

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Abstract
A method has been developed for the automated sample pretreatment of organochlorine pesticides (OCP's) and polychlorinated biphenyls (PCB's) in extracts of human milk. This work was part of a regular monitoring program presently carried out at our institute. In this program several hundreds of human milk samples have to be analyzed for the occurrence of PCB's and OCP's.With a normal bore straight phase HPLC system, utilizing column switching we are able to separate the fat from the compounds of interest and, moreover, complete separation of the PCB fraction from the OCP's can be achieved. Under the conditions used to separate the PCB fraction from intefering OCP's column‐switching is essential since the retention times for the OCP's vary from 4 minutes for hexachlorobenzene (HCB) to more than 2 hours for dieldrin.1 ml of an extract containing 45 mg of fat is injected on the first (pre)column, the fat is retained on this column and the early eluting HCB, the PCB fraction, and the DDT complex are transferred to the second (analytical) column. Compounds eluting later than p,p′‐DDT are collected directly from the precolumn. Meanwhile, the PCB fraction is separated from the rest of the OCP's on the analytical column.Contrary to conventional gravity‐controlled chromatography or solid phase extraction the clean‐up process can be monitored on‐line by UV‐detection, thus rendering a fast and reliable optimization of the system. The OCP‐fractions collected from the LC are pooled before they are transferred to a high resolution gas chromatograph equipped with a large volume option. The PCB‐fraction is injected directly in a HRGC equipped with a concurrent solvent evaporation injection device.The limits of detection for the OCP's (HCB, α‐,β‐ and γ‐HCH, β‐Hepo (heptachlorepoxide), dieldrin, p,p′‐DDE, o,p′‐DDT p,p′‐DDT and TDE) and the PCB's investigated are at sub‐ppb level (fat basis); the recoveries vary from 80 to 100%.