Determination of the rodenticide difenacoum in biological materials by high-pressure liquid chromatography with confirmation of identity by mass spectrometry

Separation and Quantification of Superwarfarin Rodenticide Diastereomers-Bromadiolone, Difenacoum, Flocoumafen, Brodifacoum, and Difethialone-in Human Plasma

BACKGROUND

Superwarfarins, second-generation long-acting anticoagulant rodenticides, are 4-hydroxycoumarin analogues of warfarin that contain a large hydrophobic side chain. These compounds contain two chiral centers and are synthesized for commercial use as two pairs of diastereomer.

OBJECTIVE

To support studies of superwarfarin pharmacokinetics and other efforts to improve clinical care for poisoning victims, a quantitative assay was developed for the measurement of diastereomer of bromadiolone, difenacoum, flocoumafen, brodifacoum, and difethialone in human plasma.

METHOD

Based on ultrahigh-pressure liquid chromatography-tandem mass-spectrometry (UHPLC-MS/MS), this method was validated according to U.S. Food and Drug Administration (FDA) guidelines. Sample preparation involved simple protein precipitation followed by reversed phase UHPLC, which resolved all five pairs of cis/trans diastereomer in less than 10 min. Superwarfarins were measured using negative ion electrospray followed by selected-reaction monitoring on a triple quadrupole mass spectrometer.

RESULTS

Calibration curves covered 3-4 orders of magnitude with linear regression coefficients of >0.999. The lower limits of quantitation were from 0.013 to 2.41 ng/mL, and intra-day and inter-day accuracy and precision coefficients of variation were <12%.

CONCLUSIONS

A 10-min UHPLC-MS/MS assay was developed and validated for the separation and quantitative analysis of the pairs of diastereomer of five superwarfarins in human plasma.

HIGHLIGHTS

This method was used to identify and measure superwarfarins and their cis/trans diastereomers in plasma obtained from patients treated for coagulopathy following consumption of contaminated synthetic cannabinoid products.

The emerging threat of superwarfarins: history, detection, mechanisms, and countermeasures

Superwarfarins were developed following the emergence of warfarin resistance in rodents. Compared to warfarin, superwarfarins have much longer half-lives and stronger affinity to vitamin K epoxide reductase and therefore can cause death in warfarin-resistant rodents. By the mid-1970s, the superwarfarins brodifacoum and difenacoum were the most widely used rodenticides throughout the world. Unfortunately, increased use was accompanied by a rise in accidental poisonings, reaching >16,000 per year in the United States. Risk of exposure has become a concern since large quantities, up to hundreds of kilograms of rodent bait, are applied by aerial dispersion over regions with rodent infestations. Reports of intentional use of superwarfarins in civilian and military scenarios raise the specter of larger incidents or mass casualties. Unlike warfarin overdose, for which 1-2 days of treatment with vitamin K is effective, treatment of superwarfarin poisoning with vitamin K is limited by extremely high cost and can require daily treatment for a year or longer. Furthermore, superwarfarins have actions that are independent of their anticoagulant effects, including both vitamin K-dependent and -independent effects, which are not mitigated by vitamin K therapy. In this review, we summarize superwarfarin development, biology and pathophysiology, their threat as weapons, and possible therapeutic approaches.

Reversed-Phase Ion-Pair High-Performance Liquid Chromatographic Quantitation of Difethialone Residues in Whole-Body Rodents with Solid-Phase Extraction Cleanup

A reversed-phase ion-pair high-performance liquid chromatographic method was developed for the determination of difethialone residues in laboratory rats (Rattus norvegicus). Difethialone was extracted from rat tissue with chloroform/acetone/formic acid. The extracts were cleaned up by a solid-phase extraction (SPE) procedure using both silica and aminopropyl SPE sorbents, concentrated, and analyzed by reversed-phase ion-pair high-performance liquid chromatography. Difethialone was quantitated via ultraviolet absorbance at 262 nm. A surrogate compound, brodifacoum, was used to correct for method performance. The mean surrogate-corrected recoveries for whole ground rodent fortified at 0.2, 1.0, and 20 µg/g difethialone were 92.3 +/- 7.7, 84.8 +/- 6.6, and 90.2 +/- 3.1%, respectively. The method limit of detection was 0.054 µg/g.

High-performance liquid chromatographic strategies for the determination and confirmation of anticoagulant rodenticide residues in animal tissues

A comprehensive approach to the analysis of anticoagulant rodenticide residues in animal tissues based on high-performance liquid chromatography (HPLC) has been developed. Residues of warfarin, coumatetralyl, difenacoum, brodifacoum, bromadiolone, diphacinone and chlorophacinone were extracted with chloroformacetone (1:1, v/v). Extracts were cleaned-up by an integrated gel permeation and adsorption chromatographic procedure which divided the rodenticides into two groups. Residues were then determined and confirmed using normal-phase, ion-pair and weak ion-exchange HPLC techniques. Ion-pair gradient separation resolved all seven rodenticides in a single chromatographic analysis. UV detection methods were employed for all seven rodenticides. Use of a diode array detection system permitted additional confirmation of residues down to 0.1 mg kg-1 by matching UV spectra and derivatives of spectra. Sensitive fluorescence detection was possible for the coumarin-based rodenticides but not for diphacinone and chlorophacinone. Post-column pH-switching fluorescence detection methods were shown to be superior to other methods of fluorescence detection of coumarin-based rodenticides. Recoveries from spiked liver tissue were around 90% at levels from 0.05 to 1 mg kg-1. Detection limits of around 0.002 mg kg-1 for most rodenticides and of 0.01 mg kg-1 for warfarin could be achieved with animal tissue extracts.

Determination of coumarin anticoagulant rodenticide residues in animal tissue by high-performance liquid chromatography. I. Fluorescence detection using post-column techniques

A multi-residue method was developed for the determination of the rodenticides warfarin, coumatetralyl, bromadiolone, difenacoum and brodifacoum in animal tissues by high-performance liquid chromatography with fluorescence detection. Extracts were cleaned-up by gel permeation chromatography on Bio-Beads SX-3 and residues determined by normal and reversed-phase high-performance liquid chromatography using post-column pH-switching, with chloroform -sec.-butylamine and borate buffer (pH 10.4) respectively, to maximise the native fluorimetric responses. Confirmation of identification was possible by re-chromatographing extracts in the absence of the post-column reagent. Chloroform-acetone (1:1) was significantly better than chloroform for the extraction of residues of these rodenticides from liver tissues. Recoveries from spiked liver tissue were generally greater than 90% at levels of 0.05-1 mg kg-1. Detection limits in animal tissues of 0.002 mg kg-1 for coumatetratyl, difenacoum and brodifacoum, 0.01 mg kg-1 for bromadiolone and 0.02 mg kg-1 for warfarin and could be routinely achieved.

Determination of coumarin anticoagulant rodenticide residues in animal tissue by high-performance liquid chromatography. II. fluorescence detection using ion-pair chromatography

A high-performance liquid chromatographic method was developed for the determination of warfarin, coumatetralyl, bromadiolone, difenacoum and brodifacoum in animal tissues using fluorescence detection. Ion-pair chromatography, with the tetrabutylammmonium ion as counter-ion, was used to take full advantage of their native fluorescence. Detection limits in liver tissue after gel permeation clean-up were 0.002 mg kg-1 for coumatetralyl, difenacoum and bromdifacoum, 0.008 mg kg-1 for bromadiolone, and 0.01 mg kg-1 for warfarin.

The multi-residue determination of coumarin-based anticoagulant rodenticides in animal materials by high-performance liquid chromatography

The rodenticides brodifacoum, difenacoum, coumatetralyl and warfarin are determined in animal relicta by high-performance exclusion chromatography on porous silica. The first three compounds are not separated, but are subsequently differentiated by adsorption or reversed-phase high-performance liquid chromatography of the appropriate eluate fraction collected from the exclusion column. The method is rapid, and clean-up (on Sep-Pak silica cartridges) is simple. Mean recoveries from spiked substrates were generally above 80% at levels of 0.1-1.0 mg/kg. Routine limits of determination are about 0.05-0.1 mg/kg for warfarin and about 0.02 mg/kg for the other compounds. If analysis for warfarin is not required, the latter limit can be lowered to about 1 microgram/kg by a slight modification to the clean-up step.

Determination of pentachlorophenol and related compounds in animal materials by high-performance liquid chromatography and gas chromatography

The rapid determination of pentachlorophenol and tetrachlorophenols in animal materials by high-performance liquid chromatography (HPLC) on porous silica is described. Non-fatty substrates are digested in alkali and the chlorophenols extracted as ion pairs. Fatty materials are extracted with ethyl acetate-hexane after acidification. Extracts are cleaned up on "Sep-Pak" silica or Florisil cartridges. Penta- and tetrachloroanisoles are recovered by the extraction procedures and can be determined by gas chromatography if required. Mean recoveries of the chlorophenols were 73-108% at fortification levels of 0.1-10 mg/kg. A concentration of 0.1 mg/kg can readily be determined and the method can be adapted to reach about 1 microgram/kg. Identities can be confirmed by ion-pair HPLC on a reversed-phase column.

Automated on-line multi-dimensional high-performance liquid chromatographic techniques for the clean-up and analysis of water-soluble samples

The application of an automated on-line multi-dimensional liquid-liquid chromatographic technique for the clean-up and analysis of water-soluble samples was investigated. The use of microparticulate aqueous-compatible steric exclusion columns as the primary separation step coupled to either reversed-phase, normal-phase or ion-exchange columns as the secondary step allowed the direct injection of complex samples without prior clean-up. The entire operation was automatically controlled by a microprocessor-based liquid chromatograph with time-programmable events which allowed precise switching of high-pressure pneumatically operated valves. Both heart-cutting and on-column concentration methods were used. The heart-cutting technique had the advantage of selectivity but lacked sensitivity; more successful was the on-column concentration technique, which, by the concentration of the solute from a larger volume of exclusion column effluent on to the secondary column, gave better sensitivity. The technique was applied to the analysis of theophylline and caffeine in biological fluids, catecholamines in urine, vitamins in a protein food supplement and sugars in molasses and candy bars.