William E. Brewer

Disposable pipette extraction for the analysis of pesticides in fruit and vegetables using gas chromatography/mass spectrometry

Organochlorine, organophosphate pesticides and fungicides in fruits and vegetables were analyzed using disposable pipette extraction (DPX) followed by gas chromatography-mass spectrometry-selective ion monitoring (GC/MS-SIM). The intrinsic rapid mixing capabilities of DPX result in fast and efficient extractions, and eluates are concentrated by using minimal elution solvent volumes rather than solvent evaporation methods. Matrix-matched calibrations were performed with reversed phase mechanisms (DPX-RP), and the limits of detection (LOD) were determined to be lower than 0.1 microg/mL for all targeted pesticides in carrot and orange sample matrices. Coefficients of determination (r(2)) were greater than 0.995 for most studied pesticides. DPX-RP exhibited recoveries between 72 and 116% for nonpolar and slightly polar pesticides (logP>2) with most of the recoveries over 88%. Only very polar pesticides (e.g., acephate, mathamidophos) were not extracted well using DPX-RP.

Raman Spectroscopy for the in Situ Identification of Cocaine and Selected Adulterants

We demonstrate the in situ identification of crack cocaine and cocaine·HCl by using a fiber-optic Raman probe and a portable Raman spectrograph. The Raman spectrum of freebase cocaine (crack) is obtained in just seconds without any sample preparation, and differs significantly from that of cocaine·HCl. We also show that the Raman spectra of these drugs are easily distinguishable from common cutting agents and impurities such as benzocaine and lidocaine. Another advantage of using Raman spectroscopy is that the drugs can be identified while contained in transparent containers, such as clear plastic evidence containers that are used to store drug evidence and to maintain chain of custody. We also demonstrate the in situ Raman identification of drugs separated by thin-layer chromatography. We discuss the utility of surface-enhanced Raman spectroscopy (SERS) in toxicological drug screening and present preliminary SERS data for cocaine in solution using colloidal silver. We believe this to be the first published SERS spectrum of freebase cocaine.

Measurement of Carboxyhemoglobin in Forensic Blood Samples Using UV-Visible Spectrometry and Improved Principal Component Regression

The forensic determination of carboxyhemoglobin (COHb) in blood was performed by using an improved principal component regression (PCR) technique applied to UV-visible spectra. Calibration data were decomposed into principal components, and the principal components useful for prediction were selected by their correlation with calibration spectra. Cross-validation of prediction results was done by leverage-corrected residuals. Confidence and prediction intervals derived from classical regression theory were found to be reasonable in size. The results compared favorably to a comparison study conducted by using a CO Oximeter method. In analysis of forensic case study samples, the improved PCR method allowed detection of abnormal samples and successfully predicted percentages of COHb and methemoglobin (MetHb), and provided error estimates for those predictions.

New Approach to Multiresidue Pesticide Determination in Foods with High Fat Content Using Disposable Pipette Extraction (DPX) and Gas Chromatography−Mass spectrometry (GC-MS)

Organochlorine and organophosphate pesticides in corn muffin mix and cocoa beans were analyzed using disposable pipette extraction (DPX) for rapid cleanup followed by gas chromatography-mass spectrometry (GC-MS). The DPX method in this study used weak anion exchange (WAX) mechanisms to remove the major sample matrix interferences, fatty acids, from the chromatographic analyses. The limits of detection (LOD) were determined to be <10 ppb for all studied pesticides in corn muffin. DPX-WAX exhibited average recoveries reaching 100% for most targeted pesticides, with relative standard deviations below 10%. These results indicate that DPX with weak anion exchange sorbent is effective at eliminating fatty acid interferences in foods of high fat content prior to multiresidue pesticide analysis. Furthermore, the DPX cleanup method takes approximately 2 min to perform. In addition, removal of fatty acids from cocoa beans demonstrates the high capacity of this extraction method for samples containing up to 50% fat.

Multiresidue analysis of pesticides in fruits and vegetables using disposable pipette extraction (DPX) and micro-luke method.

Simple and rapid methods for the analysis of pesticides in produce samples have been developed. The current study involves analysis of nonpolar and polar pesticides using GC-ECD and GC-NPD, respectively. The nonpolar pesticides were extracted using disposable pipette extraction (DPX) following a preliminary acetone extraction based on the Luke method. Recoveries of the fortified pesticides ranged between 70.5 and 110.0%, with relative standard deviations (% RSD) below 10% for most target analytes. From calibration plots, the limits of detection (LOD) were determined to be <0.05 ppm for most studied pesticides with coefficients of determination (r(2)) >0.99. A micro-Luke method was adapted and used for the analysis of polar pesticides, which greatly reduces the volumes of solvent and time for sample preparation. This new method of analysis, combining DPX and micro-Luke, was compared directly with the modified Luke method for analysis of pesticides in produce samples over a 9 week period. This study validates the suitability for routine analysis of pesticides in acetone extract of fruits and vegetables using the proposed DPX and micro-Luke method.

Temperature-dependent study of the ground-state reverse proton transfer of 3-hydroxyflavone

Abstract Temperature-dependent studies of the rate of the ground-state reverse proton transfer of 3-hydroxyflavone have been performed. At room temperature, the rate of the reverse proton transfer is 6.9×10 4 s −1 in n -heptane. However, the reverse proton-transfer rate is 6.3×10 4 s −1 in a 77 K n -heptane Shpolskii matrix, which does not conform to predictions based on extrapolation of the liquid phase kinetic data. In the course of this study we have found that, unlike the steady-state tautomer emission, the tautomer emission measured by the two-step laser excitation experiment is not obscured by contributions due to hydrogen-bonding impurities in n -heptane Shpolskii matrices. An infrared spectrum of 3-HF in a 12 K argon matrix is presented for the first time. Photolysis of matrix-isolated 3-HF monitored by infrared spectroscopy fails to afford the ground-state tautomer.

Analysis of 10 β-agonists in pork meat using automated dispersive pipette extraction and LC-MS/MS

An analytical procedure for the analysis of 10 β-adrenergic agonists (cimaterol, terbutaline, salbutamol, isoxsuprine, ractopamine, cimbuterol, clenbuterol, brombuterol, mabuterol and mapenterol) in pork meat was developed and validated using LC-MS/MS. An automated dispersive pipette extraction (DPX) was employed on a Hamilton Microlab® NIMBUS96® platform to extract the analytes of interest prior to LC-MS/MS analysis. The extraction time was <20 min with a total LC-MS/MS run time of 9.6 min. The method was fully validated in accordance with the international guidelines (European Commission Decision 2002/657/EC and National Standards of Peoples Republic of China, GB/T 22286-2008) for limit of detection, limit of quantitation, carryover, extraction efficiency, matrix effects, linearity, and within and between-run precision. The proposed method can be successfully used in the routine determination of 10 β-adrenergic agonists in pork and as a potential solution for compliance monitoring in regulatory laboratories.