Determination of Chlorpyrifos, Chlorpyrifos Oxon, and 3,5,6-Trichloro-2-Pyridinol in Rat and Human Blood

Abstract

I Abstract IAnalytical methods to quantitate chlorpyrifos and two potential metabolites, chlorpyrlfos oxon (oxon) and 3,5,6-trichloro-2-pyridinol (TCP), in human and rat blood are described. Chlorpyrifos and the oxon were extracted simultaneously with a methanol/hexane mixture from 0.5 mL blood that was deactivated with an acidic salt solution. The extract was then concentrated and analyzed by negative-ion chemical ionization gas chromatography.-mass spectrometry (NCI-GC-/VlS). TCP was extracted from a separate 0.1-mL aliquot of blood, also deactivated by the addition of acid. The t-butyldimethylsilyl derivative of TCP was formed using MTBSTFA, and the analysis was performed by NCI-GC-MS. Stable isotope analogues of chlorpyrifos (-13C2-tSN), oxon (-13C2-tSN), and TCP (-t3C z) were used as internal standards. Oxon was observed to partially degrade to TCP during the sample analysis. Accurate oxon and TCP measurements were obtained with the use of oxon-t3Cz-tSN, TCp-t3C2, and TCp-t3C2-tSN internal standards, which compensated for both the degradation of oxon and the formation of artifactual TCP during analysis. The limits of quantitation were 1 n&/mL blood for both chlorpyrifos and oxon and 10 n&/ml, for TCP. Calibration curves were linear over the concentration range of 2.5-2500 n&/ml, solvent for chlorpyrifos and oxon and between 5 and 1060 nE/mL solvent for TCP. Taking concentration factors and extraction efficiencies into account, these linear ranges represent blood concentrations of approximately 0.3-300 ng/mL blood for chlorpyrifos and the oxon and 6-1300 ng/mL blood for TCP. The lowest spike level for chlorpyrifos and the oxon was 1 ng/mL blood, and the lowest spike level for TCP was 10 ng/ml. blood. Recoveries from rat blood were as follows: 106-119% for chlorpyrifos, 94-104% for oxon, and 85-102 % for TCP. In addition, chlorpyrifos and oxon were incubated with rat and human blood for various time intervals before deactivation to determine precautions that needed to he taken when collecting and handling specimens. No change in chlorpyrifos concentration was observed in rat blood up to 180 rain at 37~ In contrast, the oxon was rapidly hydrolyzed to TCP in both rat (t1/2 = 10 s) and human (tt/2 = 55 s) blood held at 37~ The hydrolysis rate for the oxon was independent of whether a rat had been administered chlorpyrifos previously, the initial oxon concentration, the presence of chlorpyrifos, and the age or gender of the human volunteers. These results suggest rapid sample preparation is critical for accurate determinations of the oxon metabolite of chlorpyrifos. These methods provide excellent tools for use in chlorpyrifos pharmacokinetic modeling studies.

In Vitro Age-Dependent Enzymatic Metabolism of Chlorpyrifos and Chlorpyrifos-Oxon in Human Hepatic Microsomes and Chlorpyrifos-Oxon in Plasma

“…Analytical Methods. Analytes were quantified using a method similar to that of Brzak et al (1998). Stable isotopes of CPF-oxon and TCPy were added after incubation as internal standards.…”

“…Ions selected for monitoring included 161 and 166 m/z for the MTBSTFA-TCPy derivative and the MTBSTFA-TCPy internal standard derivative, respectively, as well as 297 and 302 m/z for CPF-oxon and CPF-oxon internal standard, respectively. Contributions to a primary ion monitored for quantification of the analyte from the respective isotopic internal standard and vice versa were corrected using ratios of each compounds' contribution determined by analyzing individually (Brzak et al, 1998). The entire method allowed quantification of at least 12 ng/ml for both TCPy and CPF-oxon.…”

Determination of 3,5,6-trichloro-2-pyridinol (TCP) in water by a continuous competitive immunoassay system based on the streptavidin-biotin interaction

“…The current routine method, which is applied by the environmental regulatory agencies for measurement of other pesticides, is not suitable for the determination of TCP due to the physico-chemical properties of this compound. The determination of TCP has been carried out using GC with FID [12,13] or MS detection [14,15] which involves high cost and time consuming preparative steps such as extraction, cleanup, and derivatization. Recently, two methods based on immunoassay have been proposed as alternatives to the use of separation techniques.…”

Use of SPE‐GC/EIMS for residue analysis in wine elaborated from musts spiked with formulations of chlorpyriphos‐methyl, methiocarb, dicofol, and cyproconazol

“…It seems that its concentration in final wines is low [1 -3]. On the other hand, the decay of chlorpyriphos in leachates [4], soils [5], and water [6] has been studied, the known degradation product 3,5,6-trichloro-2-pyridinol has been determined by spectrophotometry in formulations [7], and in addition, chlorpyrifos-oxon and 3,5,6-trichloro-2-pyridinol have been determined in rat and human blood [8]. The degradation pathways of chlorpyrifos in water have also been elucidated [9].…”