Potential of receptor-ligand interactions for sample handling in liquid and gas chromatography

Trace analysis of estrogenic chemicals in sewage effluent using liquid chromatography combined with tandem mass spectrometry

A rapid, selective, sensitive, and reproducible method for the analysis of environmental estrogens, either natural or synthetic, present in samples from sewage treatment works (STW) has been developed. Isolation of these compounds from STWs was performed by applying a simple extraction procedure using an ENVI-CARB cartridge (a graphitized non porous carbon black) as the solid-phase extraction (SPE) system. Liquid chromatography coupled with atmospheric pressure chemical ionization (APCI) and tandem mass spectrometry was used for detection. For the multiple reaction monitoring (MRM) mode, the [M + H](+) ion of estrone and the [M + H-H(2)O](+) ions of 17beta-estradiol, estriol and 17alpha-ethynylestradiol were selected as the precursors for collisionally induced dissociation (CID). The average recoveries from sewage final effluent samples ranged from 84 to 93% for low levels, and from 89 to 95% for high levels. The precision of the method ranged from 11 to 8% for low level and from 9 to 7% for high level samples. The lower level of quantitation for these estrogens in STW samples was determined at 0.5 ng/L for 17beta-estradiol and 17alpha-ethynylestradiol, and 1 ng/L for estrone and estriol, based on 1-L aliquots of sewage treatment works water, using the optimum tuning parameters for each individual selected precursor ion/product ion transition. Compared to a previous gas chromatography/mass spectrometry (GC/MS) method for the analysis of ten STW samples, this method was shown to provide higher sensitivity and lower time consumption.

Rapid alcohol determination in plasma and urine by column liquid chromatography with biosensor detection

An enzyme based amperometric biosensor used as a selective and sensitive detection unit in column liquid chromatography for the determination of ethanol and methanol in biological fluids such as plasma and urine is described. The reagentless enzyme electrode is based on the co-immobilisation of alcohol oxidase and horseradish peroxidase in carbon paste. The selectivity of the biosensor was found to vary when four various alcohol oxidase enzyme preparations from Candida boidinii, Pichia pastoris, and Hansenula polymorpha were used in the biosensors described. High sensitivity could be obtained for a number of alcohols, organic acids, and aldehydes. Optimisation regarding the sensitivity and selectivity of the four alcohol oxidase co-immobilised biosensors are outlined. A fast and reliable liquid chromatographic separation system with a PLRP-S polymer based separation column used with a phosphate buffer as the mobile phase was optimised using the best biosensor which was based on alcohol oxidase from P. pastoris and which showed the highest turnover rate for alcohols, as the detector for the determination of ethanol and methanol in human urine and plasma samples. The selectivity and stability of the biosensor were retained by working at an applied potential of -50 mV versus Ag/AgCl, the optimal operational potential, and by the casting of a protective membrane on the electrode surface. High selectivity of the enzyme electrode was also found towards other easily oxidisable interfering species normally present in biological fluids. It was found that stable and reliable determinations of ethanol and methanol in plasma and urine could be performed with only a simple dilution and centrifugation step prior to injection into the liquid chromatographic system. An analysis time of 4 min was required for the assay, with a sample throughput of 13 samples h(-1).

Reversed-phase liquid chromatography coupled on-line to receptor affinity detection based on the human estrogen receptor

On-line coupling of reversed-phase liquid chromatography to a biochemical detection system based on receptor-ligand interactions is described. The receptor affinity detection is performed using a postcolumn reaction detection system with open-tubular reaction coils. In the first step, a solution containing the steroid binding domain of the human estrogen receptor is added to the LC effluent via a mixing union, and the mixture is allowed to react. In the second step, a fluorescent estrogenic ligand, coumestrol, is added to saturate the remaining free binding sites of the estrogen receptor. Both heterogeneous and homogeneous detection systems have been developed. In the former case, free and receptor-bound coumestrol were separated prior to detection by means of a short column containing a restricted-access reversed-phase support. Since free and receptor-bound coumestrol differ significantly in fluorescence intensity, the system can also be operated in the homogeneous mode without requiring a separation step. Using 5 nmol/L of human estrogen receptor, a detection limit of 5 nmol/L was obtained for compounds possessing a high affinity for the estrogen receptor, such as 17 beta-estradiol and diethylstilbestrol. Detection limits for weaker ligands amount to 20 nmol/L. Non-estrogenic steroids such as methyltestosterone or progesterone are not detected at all. The selectivity of the present method is demonstrated for the analysis of urine samples.