Current Analytical Chemistry - Volume 7, Issue 4, 2011

Human biomonitoring results can be used to evaluate prior metals' exposures but the data production must adhere to rigorous scientific standards including validation of the analytical method and calculation of the method's uncertainty. The whole procedure is often perceived as a difficult and time-consuming task. The aim of this paper was to in house validate a sector field inductively coupled plasma mass spectrometry-based method and to speed up the calculation of measurement's uncertainty in the monitoring of As, Be, Cd, Co, Cr, Hg, Ir, Mn, Mo, Ni, Pb, Pd, Pt, Rh, Sb, Sn, Tl, U, V and W in human blood. The laboratory validation was organized so as to vary the most representative factors (operators, time, materials, instrumental settings, calibrations) that could affect the analytical data. Then, only those sources that significantly affected the final result were considered in the uncertainty estimate, simplifying so the process. Validation data in blood were: linearity, R2 > 0.9992 over two orders of concentration; detection limits between 0.0015 μg L-1 - 1.03 μg L-1; mean trueness on certified reference materials between 91.2%-109.6%; mean recovery on spikes ranging 92%-105%; repeatability from 3.0% to 6.3% and reproducibility from 3.8% to 9.2%. The expanded uncertainty budget derived from two sources (reproducibility and trueness/recovery) was between 11% and 26%. Applying the proposed procedure in future biomonitoring studies for metals' exposure will allow the production of analytical data of high quality and reliability. This is also crucial to correctly interpret the biomonitoring data with respect to statutory limits, reference limits and measures produced by other laboratories.

The present experimental work concerns the analytical determination of gold in jewellery alloys by means of potentiometric titration. In this contribution we focus on the practical aspects of this topic, in order to define a suitable procedure to be applied on real business applications. Therefore, instead of house-built electrodes as investigated before, the use of commercially available ones (Mettler-Toledo DS500 and DS800) is preferred. After a careful evaluation of experimental parameters such as pH, temperature, chloride and nitrate content, solution concentration, cleaning procedure, an optimised operating procedure has been developed, assuring the reproducibility of the method as well as the optimal electrode working-life. Finally, the efficacy and suitability of the method to cope with a plethora of different types of jewellery alloys and items have been tested comparing the results of the potentiometric titration carried out in three separate laboratories with the data obtained from fire assay. The consistency of these results supports the capability of the present method to constitute a robust and affordable alternative method to the classical fire assay.

In this study, Remazol Black B-containing sulfonamide resin was synthesized, characterized and used as a new sorption material in solid phase extraction for the determination of lead and nickel in water samples. The optimization of the parameters including pH, preconcentration period and the volumes of initial and elution solutions was performed. The optimum pH, preconcentration period and eluate volume were found to be 2.8, 30 min and 3.0 mL, respectively. In the measurement step, atomic absorption spectrometry was used. An enhancement of 350-fold in the sensitivity of Pb was achieved by combination of the slotted tube atom trap-atomic absorption spectrometry together with the optimized preconcentration method. The limits of detection were found to be 0.15 ng mL-1 for Pb and 0.75 ng mL-1 for Ni. The Pb and Ni concentrations in the natural water samples were found to be in the ranges of 0.9-8.0 ng mL-1 and <3.0-50.0 ng mL-1, respectively. It was concluded that the developed procedure can be used as removing method because the high adsorption capacity was obtained by the optimized conditions.

Electrochemical DNA biosensor was fabricated using the ZnO nanoparticles/chitosan (CHIT) nanocomposite membrane on modified gold electrode (AuE) as the working electrode. The ZnO/CHIT was used as a modified-AuE for the immobilization of the single-stranded DNA probe. This particular DNA biosensor provided some advantages such as the biocompatibility of the ZnO nanoparticles, good film forming ability of CHIT, and the high conductivity of AuE. Methylene blue was used as the electrochemical indicator for monitoring the hybridization reaction following the hybridization of the target DNA sequence. Differential pulse voltammetry was used for recording the electrochemical response of MB. The specific target DNA sequence could be detected in the concentration range of 1.0 X 10-14 to 1.82 X 10-4 mol L-1, with the detection limit at 1.0 X 10-15 mol L-1. This novel approach of constructing an electrochemical biosensor allowed the hybridization of synthetic target DNA. In addition, it also facilitated hybridization with template- DNA taken from real samples. The results proved that the ZnO/CHIT/AuE electrode has the potential for the sensitive detection of specific sequence related to a Trichoderma harzianum gene.

A very selective, reliable and precise method for rapid separation of the trace amounts of copper in aqueous samples using octadecyl silica bonded phase membrane disks modified by N,N'-ethylene-bis-(3-formyl-5-methyl salicyl aldymine) combined with flame atomic absorption spectrometric determination has been established. All the affecting experimental variables such as pH, amount of modifier, eluent type, sample and eluent flow-rate, foreign ions and disk capacity were also investigated. The target analyte (trace copper) was quantitatively retained at pH=4, and eluted with 8 mL of HCl (1M) and HNO3 0.5 M each containing 2.0% (v/v) methanol applying flow rates of 50 mL min-1 and 15 mL min-1 for sample introduction and elution steps, respectively. The proposed method exhibits a wide linear dynamic range over 5- 150 ng mL-1 and reproducibility at the most 3%. It also permits an enrichment factor of about 400 or higher and a detection limit of 0.005 ng mL-1. The method has been successfully applied for isolation and determination of copper in different aqueous, real samples, peppers and standard alloys.

A new, simple and fast automatic spectrophotometric flow injection (FI) method to determine glucosamine in dietary supplements has been developed and compared against a batch method, both based on the same reaction: “Schiff's base” formation as a result of the reaction between ninhydrin and glucosamine. Temperature and flow-rate were the main parameters to optimize the FI method because the reaction kinetic is slow. With the optimized flow-rate and temperature (0.8 ml min-1 flow-rate and 75 °C), the complex was measured in less than three minutes. By the batch method, 30 min of reaction, 20 min for a cooling step and 92.5 °C to measure the complex were needed. The sensitivity of the FI method was much lower than that of the batch method but the linear range was longer: for the FI method was from 0.3-% to 1-%; and for the batch method from 0.01-% to 0.04-%. The FI method allowed a throughput of 24 h-1 with a precision of 1.0-% for repeatability and of 3.5-% for reproducibility. The batch method had a repeatability of 2.1-% and a reproducibility of 4.1- %. The proposed method allowed an on-line determination with a very little human intervention and can be used in routine analysis laboratory. With this method the analysis time decreased 20 times with respect to the batch method demonstrating that the flow methods can be used in slow kinetic reactions improving also the precision.

A sensitive method for the simultaneous determination of azithromycin (AZI), tilmicosin (TIL), acetylspiramycin (ACE), and roxithromycin (ROX) has been established using capillary electrophoresis (CE) coupled with electrochemiluminescence (ECL) detection. The use of ionic liquid (IL) significantly improved separation efficiency and detection sensitivity. The conditions for CE separation and ECL detection were investigated in detail. Under the optimal conditions, the four macrolides were well separated and detected within 7 min. The limits of detection (LOD, S/N = 3) of AZI, TIL, ACE, and ROX were 1.3 x 10-9, 2.5 x 10-9, 2.3 x 10-8, and 7.0 x 10-8 mol L-1, respectively. The precisions of the peak area and migration times were from 1.1 to 4.9% and from 1.3 to 2.4% within a day and from 3.3 to 6.0% and from 2.4 to 4.8% in three days. The limits of quantitation (LOQ, S/N = 10) in human urine for AZI, TIL, ACE, and ROX were 9.3 x 10-8, 1.2 x 10-7, 7.6 x 10-7, and 2.1 x 10-6 mol L-1, respectively. The recoveries of the four analytes at different concentration levels, found in human urine, drug, pig fodder, and egg samples were between 87.4 - 107.9% with relative standard deviations (RSDs) ranging from 1.0 to 7.2%. The developed method has been successfully applied to the determination of AZI, TIL, ACE, and ROX in human urine, tablets, pig fodder, and egg samples.

In this study a square - wave voltammetric method was developed and validated for the direct determination of glimepiride in bulk form and pharmaceutical formulations. The best results were obtained for the quantitative determination of glimepiride in 0.04 M Britton - Robinson buffer at pH 9.0 at -1160 mV vs. Ag/AgCl reference electrode. The experimental and instrumental parameters affecting the peak current of glimepiride were investigated and optimized. The electrochemical behavior of glimepiride was also investigated by cyclic voltammetry. The monitored peak current was directly proportional to the concentration of glimepiride and it shows a linear response in the range from 0.25 - 7.81 μg mL-1 (r = 0.9998). The accuracy of the proposed method was indicated via the mean recovery of 100.95 ± 0.61 % with RSD of 1.48 % at a concentration level of 4.89 μg mL-1. After validation of the proposed method, the applicability of this voltammetric method was carried out by the determination of glimepiride in its pharmaceutical formulations. Possible interferences by several substances usually present in the pharmaceutical formulations have been also evaluated. No interferences were observed. The results obtained from the developed voltammetric method were compared with those obtained by the reported analytical method in the literature.

A novel poly (1-hexadecene-co-trimethylolpropane trimethacrylate) coating was prepared and applied as solidphase microextraction (SPME) for analysis of pesticides in tea samples. This SPME coating was fabricated on the surface of fiber by in-situ copolymerization of 1-hexadecene and trimethylolpropane trimethacrylate, in the presence of the ternary porogen (cyclohexanol/1, 4-butanediol/water). Both the effects of porogen ratio and porogen composition on the SPME performance during the polymerization process were investigated. The application of the as-prepared coating was evaluated by extracting residual pesticides in tea samples. Some parameters affecting SPME efficiency such as extraction time, temperature, pH, ionic strength and desorption conditions were examined. Good linearity of the calibration curve was obtained in the range of 1.7-500 ng ml-1 with correlation coefficient (r) better than 0.9957. The detection limits (S/N = 3) for six pesticides were 0.5-5.0 ng ml-1 and the relative standard deviations (RSDs) of precision for one fiber, fiber-tofiber, and day-to-day were 7.0-10.8 %, 4.9-13.3 % and 5.5-12.6 %, respectively (n = 5). Recoveries obtained at spiked tea samples were 80.8-108.8 % for different analytes. The results validated the as-prepared coating had high extraction efficiency toward pesticides as well as good solvent resistant.

Food allergy has become a serious human health concern. With more than 160 kinds of food allergens have been identified to date, allergen detection has become challenging. Most current allergen detection methods are capable of detecting only a few allergens at a time. The objective of this work was to develop a sensitive method for the detection of fish parvalbumin in food matrices employing a 3D aldehyde protein chip, which has the capacity to detect several allergens simultaneously. Upon testing, the protein chip was found to be highly specific in allergen detection but was found to cross-react to some extent with the allergens from some closely related fish species. The allergen recoveries ranged from 72.1% to 95.2%. The inter- and intra- assay coefficients of variation were <18% and <12% respectively. The LOD (limit of detection) and LOQ (limit of quantitation) of the protein chip of 0.048 and 0.087 mg parvalbumin/kg food, respectively, was sensitive enough given the threshold limit for the fish allergen. The newly developed assay seems reliable enough in detecting fish parvalbumin from various foods, food products and thus could prove useful in detecting and minimizing the instances of fish allergy.

An ionic-liquid ultrasound-assisted dispersive liquid-liquid microextraction method (IL-USA-DLLME) was introduced to determine four phenylurea herbicides (i.e., isoproturon, monolinuron, linuron, and diuron) in water samples with high performance liquid chromatography (HPLC). The ionic liquid of 1-hexyl-3-methylimidazolium hexafluorophosphate [HMIMPF6] was dispersed into the aqueous sample solution in fine droplets by ultrasound and was used as the extraction solvent; the phenylurea herbicides were concentrated into the ionic liquid phase. The extraction conditions, such as the volume of the extraction solvent, sonication and centrifugation time, ionic strength, and the emulsification-extraction temperature, were optimized. Under the optimized conditions, the linear correlation coefficient ranged from 0.9954 to 0.9969 for concentration levels of 2-100 μgL-1. The good recovery (68-100%) of target analytes was obtained from the water samples. The relative standard deviations (RSDs, n=6) ranged from 2.3-9.5%, and the limits of detection (LODs) for the herbicides were between 0.10 μgL-1 and 0.24 μgL-1. The applicability of the proposed method was evaluated by the extraction and determination of phenylurea herbicides from several natural water samples.