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Analytical and Bioanalytical Chemistry (v.380, #5-6)

Dealing with those on “the dark side”—difficult and worse people by John Fetzer (pp. 727-728).

Spectroscopy Challenge 8 by Reinhard Meusinger (pp. 729-733).

Solution to Spectroscopy Challenge 7 by Silvia Paasch; Reiner Salzer (pp. 734-735).

Scanning electrochemical microscopy (SECM) of nanolitre droplets using an integrated working/reference electrode assembly by Florin Turcu; Albert Schulte; Wolfgang Schuhmann (pp. 736-741).

Scanning electrochemical microscopy (SECM) has been performed in the restricted space of nanolitre droplets with a robust and easy-to-handle coaxial electrode assembly centring a Pt microdisk in a circular Ag electrode. Straightforward and reproducible fabrication of the specially designed probe tips was achieved by using Tollens’ reaction to chemically deposit a uniform and well-adhering layer of silver on the body of a glass-insulated Pt microdisk electrode. The suitability of the novel dual-electrode SECM tip for measurement in small volumes was evaluated by imaging an array of four Pt band microelectrodes in 500 nL electrolyte.

Keywords: Scanning electrochemical microscopy (SECM); Microelectrodes; Chemical silver deposition; Tollens reaction; Small volume electrochemistry; Microtitre plate

Determination of thiol compounds in rat striatum microdialysate by HPLC with a nanosized CoHCF-modified electrode by Meichuan Liu; Ping Li; Yuxiao Cheng; Yuezhong Xian; Chenglin Zhang; Litong Jin (pp. 742-750).

A cobalt hexacyanoferrate (CoHCF) nanoparticle (size ca. 60 nm) chemically modified electrode (CME) was fabricated and the electrochemical behavior of thiols at this nanosized CoHCF CME was studied. In comparison with a bare glassy carbon (GC) electrode and with a general CoHCF CME which was electrodeposited in the traditional manner, the present nanosized CoHCF CME efficiently performed electrocatalytic oxidation for glutathione (GSH) and L-Cysteine (L-Cys) with relatively high sensitivity, outstanding stability, and long-life. Combined with high-performance liquid chromatography (HPLC), the nanosized CoHCF CME was used for electrochemical determination (ECD) of GSH and L-Cys. The peak currents were a linear function of concentrations in the range 2.0×10⁻⁷ to 2.0×10⁻⁴ mol L⁻¹ for both GSH and L-Cys, with detection limits of 1.2×10⁻⁷ and 1.0×10⁻⁷ mol L⁻¹, respectively. Coupled with microdialysis sampling, the HPLC–ECD system has been successfully used to assess the GSH and L-Cys content of rat striatum.

Keywords: Nanosized CoHCF CME; Thiol compounds; HPLC–ECD; Microdialysis; Rat striatum; In vivo

Signals ratio method combined with wavelet transform: application to resolution of overlapped electrochemical signals by Xiuqi Zhang; Yasuaki Fuchigami; Jiye Jin (pp. 751-756).

A signals ratio method combined with wavelet transform was proposed for the resolution of a weak voltammetric signal overlapped by other components. The signals ratio method usually suffers from interference from noise and baseline contained in the original signals because these factors cause distortion of the signals ratio. The multiresolution capability of the wavelet transform method was exploited here to simultaneously remove or reduce the noise and background. As a result, a deformation-free signals ratio with good signal-to-noise ratio (SNR) was obtained even for very noisy signals. The properties of the proposed method were compared to other resolution methods. It was demonstrated that the combined signals ratio wavelet transform method was particularly applicable to resolve a minor component in the presence of large amount of other components, suggesting that it can provide improved detection limits and quantified results for minor components. The method was employed for the voltammetric determination of residual chlorine in the presence of N,N-diethyl-p-phenylenediamine (DPD).

Keywords: Signals ratio; Wavelet transform; Resolution of overlapped signals; Electrochemical signals; Square-wave voltammetry; Residual chlorine

Cytochrome c–dimyristoylphosphatidylglycerol interactions studied by asymmetrical flow field-flow fractionation by Gebrenegus Yohannes; Susanne K. Wiedmer; Esa K. J. Tuominen; Paavo K. J. Kinnunen; Marja-Liisa Riekkola (pp. 757-766).

Lipid membranes are well recognized ligands that bind peripheral and integral proteins in a specific manner and regulate their function. Cytochrome c (cyt c) is one of the partner peripheral protein that binds to the lipid membranes via electrostatic and hydrophobic interactions. In this study, asymmetrical flow field-flow fractionation (AsFlFFF) was used to compare the interactions of cyt c with the acidic phospholipid 1,2-dimyristoyl-sn-glycero-3-phospho-rac-glycerol (DMPG), oleic acid (OA), and sodium dodecyl sulfate (SDS). The influence of pH and the cyt c–lipid molar mass ratios were evaluated by monitoring the diffusion coefficients and particle diameter distributions obtained for the free and lipid-bound protein. The hydrodynamic particle diameter of cyt c (pI 10) was 4.1 nm at pH 11.4 and around 4.2 nm at pH 7.0 and 8.0. Standard molar mass marker proteins were used for calibration to obtain the molar masses of free cyt c and its complexes with lipids. AsFlFFF revealed the binding of cyt c to DMPG and to OA to be mainly electrostatic. In the absence of electrostatic interactions, minor complex formation occurred, possibly due to the extended lipid anchorage involving the hydrophobic cavity of cyt c and the hydrocarbon chains of DMPG or SDS. The possibility of the formation of the molten globule state of cyt c, induced by the interaction between cyt c and lipids, is discussed.

Keywords: Asymmetrical flow field-flow fractionation; Cytochrome c; 1,2-Dimyristoyl-sn-glycero-3-phospho-rac-glycerol; Oleic acid; Sodium dodecyl sulfate; Protein lipid complexes

Development of an HPLC method for the identification and dosage of non-allowed substances in cosmetic products. Part I: local anaesthetics and antihistaminics by Rita Porrà; Simona Berri; Luigi Gagliardi; Paola Chimenti; Arianna Granese; Daniela De Orsi; Irene Carpani; Domenica Tonelli (pp. 767-772).

An HPLC method with ultraviolet detection coupled with a solid-phase extraction sample clean up was developed for the analysis of five local anaesthetics and four antihistaminics in cosmetic products. The presence of these compounds in commercial cosmetic samples is fordbidden. Extracts from real samples were applied to a solid-phase extraction C₁₈ cartridge, and the analytes were eluted with 8:2 (v/v) acetonitrile/water containing 1‰ trifluoroacetic acid. HPLC separation was then performed for the identification and determination of the analytes using a Purospher RP-18 column, two gradient eluting systems and a photodiode-array detector. The accuracy of the method was verified by spiking experiments on home-made cosmetic samples. The analytical recoveries were satisfactory.

Keywords: HPLC; Local anaesthetics; Antihistaminics; Cosmetic products

Element content and element correlations in Chinese human liver by Peiqun Zhang; Chunying Chen; Milena Horvat; Radojko Jaćimović; Ingrid Falnoga; Martina Logar; Bai Li; Jiujiang Zhao; Zhifang Chai (pp. 773-781).

The amounts of the 19 elements As, Br, Ca, Cd, Ce, Co, Cr, Cs, Fe, K, La, Mo, Na, Rb, Sb, Sc, Se, Sm, and Zn in 92 lyophilized autopsy human liver samples from normal subjects have been analyzed by instrumental neutron-activation analysis (INAA). For intercomparison and quality control ten samples were independently analyzed in two institutes, the Institute of High Energy Physics in China and the “Jožef Stefan” Institute in Slovenia. Most of the element contents determined by the two institutes were in quite good agreement, even though different experimental conditions were applied, indicating the reliability of the analytical results. Analysis of the chemical species of mercury present in the ten liver samples was also performed in Slovenia. Possible differences between the element content of male and female liver samples were studied by means of Student’s t-test, but significant differences were found only for Ce, Co, Fe, La, Mo, and Zn. The results obtained were also compared with those reported from other areas of the world; no appreciable differences were observed. Correlation among the various elements in the human liver samples was studied using multivariate statistics. It was found that there was relatively close correlation between some elements, for example As–Fe, Ca–Fe, Cd–Co, Cd–Zn, Mo–Zn, Co–Se, Cs–Rb, Br–Rb, Sc–Sm, La–Sm, La–Ce, etc.; these correlations could be rationally explained by the similarity of the electronic structures of the elements and/or their physiological functions in the human body.

Keywords: Human liver; Element content; Correlation analysis; Neutron-activation analysis (NAA)

Determination of serum cortisol using isotope dilution–liquid chromatography–mass spectrometry as a candidate reference method by Pyong Gil Jung; Byungjoo Kim; Sang-Ryoul Park; Hun-Young So; Lian Hua Shi; Yongseong Kim (pp. 782-788).

We propose isotope-dilution mass spectrometry as a candidate reference method for determination of serum cortisol. The method uses liquid chromatography–mass spectrometry (LC–MS), interfaced with electrospray ionization, and selective monitoring of the [M+H]⁺ ions of cortisol and isotopically labeled cortisol. The isotope-dilution–liquid chromatography–mass spectrometry (ID–LC–MS) method simplifies sample-preparation, because samples are processed by simple solvent extraction without further clean-up and derivatization. We studied the time required for complete equilibration of endogenous cortisol and labeled cortisol spiked into serum and found it to be less than 1 h. The repeatability and the reproducibility of the method were evaluated and found to be 0.55% of the measurement value. CRM 192 and 193 from the Bureau Communautaire de Reference were analyzed for verification of the method. The results obtained from the ID–LC–MS method agreed with the certified values. The relative uncertainty of measurement results for samples in the range of a few tens of micrograms per kilogram to several hundred micrograms per kilogram was evaluated and found to be 0.56%. Immunoassay carried out by three independent clinical laboratories produced results more than 15% higher than this ID–LC–MS method, suggesting the presence of bias in the immunoassay methods.

Keywords: Cortisol; Serum; ID–LC–MS; Method validation; Reference method

Measurement of labile Cu in soil using stable isotope dilution and isotope ratio analysis by ICP-MS by Annette L. Nolan; Yibing Ma; Enzo Lombi; Mike J. McLaughlin (pp. 789-797).

Isotope dilution is a useful technique to measure the labile metal pool, which is the amount of metal in soil in rapid equilibrium (<7 days) with the soil solution. This is normally performed by equilibrating soil with a metal isotope, and sampling the labile metal pool by using an extraction (E value), or by growing plants (L value). For Cu, this procedure is problematic for E values, and impossible for L values, due to the short half-life of the ⁶⁴Cu radioisotope (12.4 h), which makes access and handling very difficult. We therefore developed a technique using enriched ⁶⁵Cu stable isotope and measurement of ⁶³Cu/⁶⁵Cu ratios by quadrupole inductively coupled plasma mass spectrometry (ICP-MS) to measure labile pools of Cu in soils using E value techniques. Mass spectral interferences in detection of ⁶³Cu/⁶⁵Cu ratios in soil extracts were found to be minimal. Isotope ratios determined by quadrupole ICP-MS compared well to those determined by high-resolution (magnetic sector) ICP-MS. E values determined using the stable isotope technique compared well to those determined using the radioisotope for both uncontaminated and Cu-contaminated soils.

Keywords: Soil; Copper; Labile pool; Isotope dilution; Isotope ratios; ICP-MS

Efficient and rapid method for extraction of intact phospholipids from sediments combined with molecular structure elucidation using LC–ESI-MS–MS analysis by Klaus-G. Zink; Kai Mangelsdorf (pp. 798-812).

This paper presents the application of an efficient method for extraction and fractionation of intact phospholipids (PLs) from complex sediment matrices and elucidation of their molecular structure by normal-phase HPLC–ESI-MS–MS. Flow-blending extraction was tested with different solvent mixtures and the best recovery of all PLs classes from the sediment matrix was achieved by using methanol–dichloromethane–buffer, 2:1:0.8. The applied LC–ESI-MS system has linearity of R²=0.98 and a detection limit of 0.5 ng/PL, sufficient for reliable identification of complex mixtures of PLs. MS–MS analyses using a triple-quadrupole mass spectrometer enables detection of individual PL side-chain composition and, hence, characterization of the living organisms contributing to the sedimentary organic material. Parallel GC–MS analysis of the hydrolysed phospholipid fatty acids supports the characterized fatty acid patterns determined from intact PLs. The PL inventory of different investigated lacustrine surface sediments shows predominantly high abundance of phosphatidylglycerols and phosphatidylethanolamines and phosphatidyl-mono- and dimethyl-ethanolamines with fatty acyl side-chains typically known from bacteria. In a sample from Lake Baikal intense signals of bacterial 14:0-acyl-PGs were also identified, for the first time in sediments as far as we are aware.

Keywords: Intact phospholipids; Sediments; LC–ESI-MS; Bacteria; Fatty acids

Three-step extraction procedure for determination of heavy metals availability to vegetables by Agnieszka Moćko; Witold Wacławek (pp. 813-817).

A three-step sequential extraction procedure was used to determine the concentration of heavy metal speciation forms in soil. The procedure allows one to identify the pool of heavy metals that can be potentially mobilised under changes in soil pH value or redox potential. It has been shown that similar portions of heavy metals are present in reducible, oxidisable and residual fractions. It was found that soil chemical properties significantly affected the distribution of heavy metals among different fractions and their uptake by vegetables. Cadmium was a dominant element which occurred in the exchangeable fraction—the most bioavailable and potentially toxic.

Keywords: Extraction procedure; Heavy metals; Bioavailability; Soil; Vegetables

Ozone monitoring in a Mediterranean forest using diffusive and continuous sampling by Franco De Santis; Donatella Zona; Raffaella Bellagotti; Francesca Vichi; Ivo Allegrini (pp. 818-823).

Ambient ozone was measured in a forest in Castelporziano (Italy) characterised by the prevailing presence of Holm-oak trees (Quercus ilex L.) from June to November 2003. Two methods for measuring ozone were used: long-term monitoring using diffusive samplers at three heights within the canopy, and continuous monitoring at two heights using the UV method. Results for one week mean ozone levels above and below the canopy from the diffusive samplers were compared to those obtained using the automatic analyser at the same levels. A good correlation between the two sampling techniques was found. Continuous monitoring showed a daily cycle with a midday maximum and a nocturnal minimum. While the forest floor consistently had the lowest ozone concentration, there were no differences during most daytime hours. The midday maximum is clearly due to downward mixing with O₃-rich air from above. The night-time ozone decay within the canopy is the result of dry deposition of O₃ and most likely due to reaction with biogenically produced NO. AOT40 within and above the canopy mostly exceeded the critical levels.

Keywords: Ozone (vertical profile); Diffusive sampling; Mediterranean forest

Determination of benzene, toluene, ethylbenzene and xylenes in air by solid phase micro-extraction/gas chromatography/mass spectrometry by Simonetta Tumbiolo; Jean-François Gal; Pierre-Charles Maria; Orfeo Zerbinati (pp. 824-830).

The aim of the study was to analyse BTEX compounds (benzene, toluene, ethylbenzene, xylenes) in air by solid phase micro-extraction/gas chromatography/mass spectrometry (SPME/GC/MS), and this article presents the features of the calibration method proposed. Examples of real-world air analysis are given. Standard gaseous mixtures of BTEX in air were generated by dynamic dilution. SPME sampling was carried out under non-equilibrium conditions using a Carboxen/PDMS fibre exposed for 30 min to standard gas mixtures or to ambient air. The behaviour of the analytical response was studied from 0 to 65 μg/m³ by adding increasing amounts of BTEX to the air matrix. Detection limits range from 0.05 to 0.1 μg/m³ for benzene, depending on the fibre. Inter-fibre relative standard deviations (reproducibility) are larger than 18%, although the repeatability for an individual fibre is better than 10%. Therefore, each fibre should be considered to be a particular sampling device, and characterised individually depending on the required accuracy. Sampling indoor and outdoor air by SPME appears to be a suitable short-delay diagnostic method for volatile organic compounds, taking advantage of short sampling time and simplicity.

Keywords: Solid phase micro-extraction; GC/MS; Calibration device; Gas standard; Air analysis; BTEX

Simultaneous determination of multiple constituents in real beer samples of different origins by capillary zone electrophoresis by Sonia Cortacero-Ramírez; Antonio Segura-Carretero; Carmen Cruces-Blanco; Maria Luisa Romero-Romero; Alberto Fernández-Gutiérrez (pp. 831-837).

Simultaneous determination of alcohols, amines, amino acids, flavonoids, and purine and pyrimidine bases in bottled beer samples directly without any pre-treatment was carried out by capillary zone electrophoresis with diode-array detection. Electrolyte conditions such as pH, composition and concentration of the buffer, working voltage and type and time of injection were checked. The best separation of the cited analytes was achieved in 70 mM sodium borate solution and pH 10.25. The detection limits were from 2.1 to 5.6 mg L⁻¹ for the 18 compounds studied. The developed method is rapid, sensitive and quantitative and has been applied to seven types of international bottled beers of different origins bought locally.

Keywords: Capillary zone electrophoresis; Multicomponent determination; Beers

Characterisation of the interface of sputter-deposited copper coatings on nitrogen plasma-treated carbon substrates by M Rosner; E Neubauer; Ch Eisenmenger-Sittner; H Bangert; H Hutter (pp. 838-842).

The adhesion of copper coatings to carbon substrates is very poor, because of lack of diffusion or reaction between the constituents. Because there is technological interest in enhancing the adhesion and improving the interface between copper and carbon, plasma treatment of the carbon substrate was employed in this study. For modification of the carbon surface a nitrogen plasma was used. It was confirmed by pull-off tests that the strength of adhesion of the copper coating can be improved by a factor of more than 10 by plasma pretreatment, even after treatment for a very short time (1 min). To obtain more information about the mechanisms of the processes occurring at the interface SIMS investigations were performed on samples which had been treated for different times (between 1 and 60 min). These measurements confirmed that nitrogen is located on the interface. With increasing pretreatment time the amount of nitrogen detected on the interface increased. Besides characterisation of as-deposited samples, another focus was to study the mechanisms of diffusion of nitrogen if the samples are heat treated at 500°C.

Keywords: PVD; SIMS; Adhesion; Nitrogen-plasma

Measurement of water by oven evaporation using a novel oven design. 2. Water in motor oils and motor oil additives by Sam A. Margolis; Kevin Vaishnav; John R. Sieber (pp. 843-852).

The measurement of water in lubricating oils is important because water accelerates the corrosion of metal parts and bearings in motors. Some of the additives added to lubricating oils to improve their performance react with the Karl Fischer reagent (KFR) causing a positive bias in the water measurement. A new oven evaporation technique for measuring water in oils has been developed that is automated, requires less sample handling, is easily calibrated, and is capable of measuring relatively small mass fractions of water (≥50 mg/kg sample). A series of motor oils was analyzed with the standard KFR, a reagent that detects interfering substances that reduce iodine, and the aldehyde–ketone reagent that does not detect substances that react with methanol and form water. The oil samples were heated to 107°C and then reheated to 160°C. At both temperatures, material was measured by both KFRs, but only zinc dithiophosphate released sulfur compounds that would react with the reagent that detects interfering substances. Mass fractions of between 20 and 70% of the volatile material released at either temperature were measured with the standard KFR but not with the aldehyde–ketone reagent. These results demonstrate that there are a number of sources of positive bias in the measurement of water in motor oils and that the standard KFR cannot be used to measure water in motor oils and motor oil additives. These results also indicate that some of the material reacts with methanol to form water. Finally, these results suggest that some of the material that is volatile at 160°C and not at 107°C may be water that is physically occluded or may be substances that react with diethyleneglycol monomethylether to produce water.

Keywords: Water; Karl Fischer; Oven evaporation; Motor oils; Motor oil additives

Applicability of solid-phase microextraction combined with gas chromatography atomic emission detection (GC-MIP AED) for the determination of butyltin compounds in sediment samples by J. Carpinteiro; I. Rodríguez; R. Cela (pp. 853-857).

The performance of solid-phase microextraction (SPME) applied to the determination of butyltin compounds in sediment samples is systematically evaluated. Matrix effects and influence of blank signals on the detection limits of the method are studied in detail. The interval of linear response is also evaluated in order to assess the applicability of the method to sediments polluted with butyltin compounds over a large range of concentrations. Advantages and drawbacks of including an SPME step, instead of the classic liquid–liquid extraction of the derivatized analytes, in the determination of butyltin compounds in sediment samples are considered in terms of achieved detection limits and experimental effort. Analytes were extracted from the samples by sonication using glacial acetic acid. An aliquot of the centrifuged extract was placed on a vial where compounds were ethylated and concentrated on a PDMS fiber using the headspace mode. Determinations were carried out using GC-MIP AED.

Keywords: Butyltin compounds; SPME; GC-MIP AED; Sediments

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Analytical and Bioanalytical Chemistry (v.380, #5-6)