Anthony Gachanja

Determination of mercury species in sea-water by liquid chromatography with inductively coupled plasma mass spectrometric detection

A liquid chromatographic method coupled with inductively coupled plasma mass spectrometry for the speciation of methylmercury chloride, mercury(II) chloride and ethylmercury chloride in sea-water is described. The three species were eluted from a C18 column (150 × 3.2 mm id) at 260, 340 and 750 s, respectively, with a mobile phase of 1% v/v acetonitrile and 0.005% 2-mercaptoethanol in 0.06 mol l–1 ammonium acetate pumped at 1.0 ml min–1. The total mercury determined in TORT-1 Lobster Hepatopancreas (350 ± 62 µg l–1) was in good agreement with the certified value (330 ± 60 µg l–1). The detection limits (3s) in artificial sea-water were 0.25 µg l–1 for methylmercury chloride and mercury(II) chloride and 0.75 µg l–1 for ethylmercury chloride. Off-line preconcentration using a dithiocarbamate (Dithiochel) resin gave detection limits (signal-to-noise ration = 2) of 16 ng l–1 for methylmercury chloride and 17 ng l–1 for mercury(II) chloride using a 50-fold preconcentration factor for a 1 I sample of synthetic sea-water.

Procedures for the enhancement of selectivity in liquid phase chemiluminescence detection

Abstract An overview of liquid phase chemiluminescence (CL) processes is presented and the potential for CL detection in liquid chromatography (LC) is discussed, with particular reference to the luminol and peroxyoxalate reactions. Post column ion displacement from a solid phase reagent [a cation exchange resin in the copper(II) form] followed by catalysis of the luminol reaction is used for the quantification of mixtures of weak acids after separation by ion-exclusion chromatography. Polyaromatic hydrocarbons (PAHs) released during the combustion of biomass fuels are separated by reversed-phase chromatography and quantified by their sensitizing effect on the peroxyoxalate reaction. This procedure is also used for the determination of carboxylic acids in non-aqueous media after selective pre-column derivatization with a fluorescent label (9-anthracenemethanol).

Occurrence of selected antibiotics and antiretroviral drugs in Nairobi River Basin, Kenya

In this paper, we investigated the occurrence of three antibiotics (sulfamethoxazole, trimethoprim and ciprofloxacin) and three antiretroviral (lamivudine, nevirapine and zidovudine) drugs in the Nairobi River Basin, Kenya. The analytical procedure involved extraction using solid phase extraction followed by liquid chromatography-electrospray ionization tandem mass spectrometry (SPE-LC-ESI-MS/MS). In this study, 40 sites were selected for sampling, including 38 sites along the rivers and 2 wastewater treatment effluent sites. All the studied compounds were detected with sulfamethoxazole having the highest detection frequency of 97.5% and ciprofloxacin had the lowest at 60%. The results showed that the concentration of the drugs increased in highly populated regions especially within the informal settlements. The maximum (median) concentrations in the river waters for sulfamethoxazole, trimethoprim, ciprofloxacin, lamivudine, nevirapine and zidovudine in ng/L were 13,800 (1800), 2650 (327), 509 (129), 5430 (1000), 4860 (769), and 7680 (660), respectively. The maximum concentrations in the river waters were generally higher than those of the wastewater treatment plant effluents signifying that the rivers are substantially contaminated by domestic wastewater. The environmental risk was evaluated by calculating the risk quotients (RQs) for algae, daphnia and fish based on the maximum and median concentrations of the analytes in the river basin and was expressed as the ratios of measured environmental concentrations (MEC) to predicted no effect concentrations (PNEC). The RQs ranged from 0 to 507.8 and apart from lamivudine that had a low RQ, all the other analytes had RQ>1 at maximum and median measured concentrations for at least one taxonomic group. The high RQs are indicative of possible adverse ecological effects and calls for corrective and mitigation strategies.

Monitoring of polycyclic aromatic hydrocarbon emissions from biomass combustion in Kenya using liquid chromatography with fluorescence detection

Sampling and reversed-phase liquid chromatographic analysis with fluorescence detection of polycyclic aromatic hydrocarbons (PAHs) released from biomass combustion sources is presented. PAH emissions from charcoal obtained from Acacia mearnsii and Newtonia buchananii trees, combusted in two charcoal burning stoves commonly used in Kenya (traditional metal and ceramic-lined) are compared. Particulate bound and gaseous PAH were sampled onto a glass microfibre filter and an XAD-2 resin cartridge, respectively. PAH results from samples collected in kitchens in the Kenyan Highlands are also presented and discussed in relation to indoor air pollution in developing countries.

Determination of aliphatic carboxylic acids in non-aqueous matrices by liquid chromatography with peroxyoxalate chemiluminescence detection

Abstract A peroxyoxalate chemiluminescence (CL) method for the qualitative and quantitative analysis of used engine oils for aliphatic carboxylic acids (C6-C20) is presented. The carboxylic acids were coupled to a fluorescent label, 9-anthracenemethanol, and separated using reversed-phase liquid chromatography (LC). CL reagents (bis(2,4-dinitrophenyl)oxalate and hydrogen peroxide) were mixed with the LC eluent and the CL emission detected using a solid state photodiode-based detector. Detection limits (3 × blank signal) for aliphatic carboxylic acids (C6-C20) were in the range 1.8–4.5 pmol on-column (5 μl injection). A comparison between fluorescence and photodiode and photomultiplier-based CL detection of 9-anthracenemethyl esters of C6-C20 aliphatic carboxylic acids in a flow injection manifold is also presented.

A multiresidue analytical method for trace level determination of antibiotics and antiretroviral drugs in wastewater and surface water using SPE-LC-MS/MS and matrix-matched standards

An analytical method for simultaneous determination of seven commonly used antibiotics and three antiretrovirals in surface water and urban wastewater at the ng L−1 level has been developed. The method involves concentration and clean-up by solid phase extraction (SPE) followed by identification and quantification by liquid chromatography tandem mass spectrometry (LC-ESI-MS/MS). The use of matrix-matched calibration curves constructed by spiking surface water was evaluated for quantification and compared with the internal standard method using isotopically labelled compounds. The method gave absolute recoveries of 41–116% with most of the compounds having recoveries >50%. The LOQs ranged from 5 to 63 ng L−1 allowing for the determination of the analytes at trace levels in the environmental samples considered. The difference in the quantification results obtained using surface water matrix-matched standards and internal standards was within a ±20% margin. The method provides an affordable and relatively fast alternative with acceptable accuracy and precision. The method was applied to study the occurrence of the target analytes in the surface water of Lake Paijanne and wastewater from the Jyvaskyla wastewater treatment plant (WWTP) in Central Finland. All target compounds were detected in the WWTP streams with concentrations ranging between 10 and 570 ng L−1 while low ng L−1 levels were measured for some of the analytes in surface waters. The results institute the need for further monitoring in other WWTP streams and receiving waters as well as improvements of the wastewater treatment process with the aim of minimizing the pharmaceutical load in the effluents.

Determination of aldehydes in used engine oils by liquid chromatography with chemiluminescence detection

Straight-chain aliphatic aldehydes (C6C14) were selectively derivatised in oxidised engine-oil dialysates with the fluorophore 3-aminofluoranthene. The derivatives were separated by reversed-phase liquid chromatography on a mid-bore (3.2 mm I.D.) column and detected by monitoring the chemiluminescence emission from a post-column reaction with bis-(2,4,6-trichlorophenyl)oxalate and hydrogen peroxide. Calibrations for the aldehydes in an oil matrix (0–5.0·10−4 mol 1−1) were linear (0.9980 < r2 < 0.9997) with limits of detection (S/N = 3) in the range 3.0·10−7−3.4·10−6 mol 1−1 (0.7–75 fmol on-column). Analysis of oil samples taken from an engine test at different times (0, 16, 24 and 32 h) showed that the concentration of aldehydes increased throughout the duration of the test.