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Analytical and Bioanalytical Chemistry (v.364, #6)
Electronic noses – A mini-review by D. J. Strike; M. G. H. Meijerink; M. Koudelka-Hep (pp. 499-505).
Electronic noses are a new class of analytical instruments anticipated to have an impact in many areas. They are based around an array of sensors each having a partial specificity and thus producing an odour fingerprint that can be identified by a pattern recognition system. In this review the technologies involved are discussed, giving particular emphasis to the sensors since these form the heart of the systems. The major sensor technologies are described, indicating both their strengths and their weaknesses. Finally, after a brief discussion of data processing technologies, the review ends with an assessment of the current state of the art and possible future directions.
Imprinting with sensor development – On the way to synthetic antibodies by F. L. Dickert; Oliver Hayden (pp. 506-511).
Molecular imprinting is an attractive tool for the development of artificial recognition systems. Even non-covalent imprinting provides universal interaction centers for sensoric applications. The coated chemical sensors have high stabilities under harsh conditions in both the gas and liquid phases. With adequate efforts optical and mass-sensitive sensors (quartz crystal microbalance, QCM, surface acoustic wave detector, SAW) are suitable for analysis down to the ppb (nL/L) range. PAHs, isomer VOCs as well as complex oil mixtures are appropriate analytes.
Application of non-specific fluorescent dyes for monitoring enantio-selective ligand binding to molecularly imprinted polymers by Sergey A. Piletsky; Ewald Terpetschnig; Håkan S. Andersson; Ian A. Nicholls; O. S. Wolfbeis (pp. 512-516).
The displacement of non-specific dyes from molecularly imprinted polymer (MIP) chromatographic stationary phases has been used for the detection and quantification of ligand-polymer binding events. A blank polymer and an L-phenylalaninamide-imprinted polymer were prepared using methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as a crosslinker. The MIP is first loaded with dye, and a solution of the dye in the eluent is passed through the MIP. If analyte is injected into the dye solution in the eluent, part of the dye is competitively replaced by the analyte from the MIP. Specifically, the competitive displacement of rhodamine B by amino acids and phenylalaninamide (Phe-NH2), respectively, has been studied under polar and hydrophobic elution conditions. Enantioselective binding of Phe and Phe-NH2 to the imprinted polymer was shown to occur in the micromolar concentration range. It is proposed that the displacement of non-specific dyes from MIPs be used for the development of multisensors based upon these highly specific and stable materials, which provide promising alternatives to the use of biological macromolecules in sensor technology.
Effect of pulsations of a plasma torch on the radial distribution of temperature by R. Toukhvatoulline; G. Feldmann (pp. 517-520).
The influence of the pulsation of a plasma torch over the lateral intensity of the radiation and the radial temperature profile was studied. For the case of pulsation of the axis of a torch following a Gaussian distribution the exact integral equation was obtained relating the lateral intensity with and without pulsation. For a particular case the lateral distributions of radiation intensity were calculated for three different values of the Gaussian standard deviation. For the spectral line ArI 435.8 nm the radial temperature distributions with and without pulsations were calculated. The results show how pulsations can affect experimental results.
The determination of arsenic and selenium in standard reference materials using sector field ICP-MS in high resolution mode by Ashley T. Townsend (pp. 521-526).
Sector field ICP-MS was used to analyse As and Se in a range of standard reference materials (NIST 1643d Water, NIST 1573a Tomato Leaves, NIST 1566a Oyster Tissue, NIST 2704 Buffalo River Sediment and Bio-Rad Reference Urine Level 2). A spectral resolution of m/Δm = 7500 enabled 75As and 77Se to be separated from problematic ArCl interferences. Following microwave acid digestion, solid samples were typically diluted 1 + 99 prior to analysis, while the urine sample was diluted 1 + 9. The water sample was analysed undiluted and diluted 1 + 9. Despite near baseline spectral separation, 75As and 77Se were still found to be influenced by ArCl at high Cl concentrations, the effect being most pronounced for 77Se. When necessary 82Se was also monitored to determine the accuracy of the 77Se results. Detection limits (LOD, based on 3σ of 10 replicates) for 75As, 77Se and 82Se in ultra-pure water, 1% (w/w) HNO3 and 1% (w/w) HCl were ∼ 0.1, ∼ 0.2 and ∼ 0.5 ng g–1, respectively. Although signal intensities when using high resolution were ∼ 1% of that found when using low resolution mode (m/Δm = 300), measured As concentrations and certified values were found to agree to within ± 11% for all samples analysed. The concentration of Se in NIST 1566a Oyster Tissue, NIST 2704 Buffalo River Sediment and Bio-Rad Reference Urine were found to be in agreement with certified values to within ± 15– 20%, as measured by 77Se. However, closer agreement (± 5%) was found when these samples were analysed using 82Se. The Se concentration in NIST 1643d Water was found to agree to within ± 5% of the certified value (depending on dilution factor). Due to the low concentration of Se in NIST 1573a Tomato Leaves, quantitation was not possible (below LOQ, 10σ). As a consequence of the lower ion transmission when using resolution 7500, analytical precisions were found to be elevated over that normally observed using low resolution mode, typically ± 5–20% (depending on analyte concentration and isotopic abundance).
Application of a fractionary factorial design to the determination of tin in lubricating oils by continuous flow hydride generation-atomic absorption spectrometry by M. Begoña Martín-García; Dolores Bellido-Milla; Andrés Jimenez-Jimenez; María Purificación Hernández-Artiga (pp. 527-532).
The determination of wear metals and metalloids in used lubricating oils allows the prediction of equipment failure. A number of procedures to determine wear metals in lubricating oils by atomic spectrometry has been published. Industry has lately shown a special interest in the determination of tin, since its appearance at certain levels in used oils indicates severe engine wear. Therefore, a method for the determination of the total tin content in used lubricating oils by hydride generation-atomic absorption spectrometry (HG-AAS) is described. Unused marine lubricating oils spiked with the analyte were digested in closed vessels in a microwave oven and the diluted product was used for continuous stannane generation. There are many factors that influence effective SnH4 generation; therefore, fractionary factorial design was used to obtain an adequate sensitivity and also to stabilize the signal. Six variables were taken into account and a 26–2 IV design was used with spiked samples containing 30 ng g–1 Sn. The reproducibility, stability, calibration curve and limit of detection were established. The method was applied to different kinds of used lubricating oils. In all cases, the results were higher than those obtained in the industry by simple dilution.
Direct analysis of solid samples by GFAAS – determination of trace heavy metals in barytes by R. Nowka; I. L. Marr; T. M. Ansari; H. Müller (pp. 533-540).
Solid sampling graphite furnace atomic absorption spectroscopy (SS-GFAAS) has been used for the determination of traces of heavy metals (Cd, Pb, Cu, Cr, Ni, V and As) in barytes over a wide concentration range, e.g. Cd from 0.023 to 27.0 μg/g and Pb from 1.54 to 3509 μg/g.The necessity of determining heavy metals in commercial barytes (naturally occurring barium sulfate), a mineral important to the oil industry because of its use in drilling muds, is discussed. The problems presented by the analysis of this difficult matrix are elegantly solved by using SS-GFAAS for the direct determination of heavy metals. A high-performance graphite furnace AAS with D2-background correction system and a transversely heated graphite atomizer was used for the investigations. The spectrometer was combined with a mechanical sampling module and an ultramicrobalance. The transfer of solid samples (sample weights 0.031–0.686 mg) into the atomizer was carried out by using an optimized graphite platform as the sample carrier. Calibration curve techniques and standard addition methods were employed using external standards (CRMs). Problems associated with signal deformations like multiple peaks, tailing or shoulders are also discussed and possibilities to solve the problems are given. The influence of the homogeneity of solid samples on the precision and accuracy are shown in a real example. The results obtained by SS-GFAAS were compared with results by other methods like X-ray fluorescence spectroscopy (XRF) and flame AAS after aqua regia microwave extraction. This study has demonstrated that SS-GFAAS is a very powerful and easy-to-use method for quick and accurate analysis of barytes.
Determination of cadmium in coal fly ash, soil and sediment samples by GFAAS with evaluation of different matrix modifiers by I. Rucandio; D. Petit (pp. 541-548).
The determination of cadmium in different samples such as coal fly ashes, soils and sediments by Graphite Furnace Atomic Absorption Spectrometry (GFAAS) was studied. The best analytical conditions and instrumental parameters were deduced. Different types of matrix modifiers were tested and an optimization of several conditions (pyrolysis and atomization temperatures, heating rate, use of L’vov platform, etc.) was carried out. A mixture of 2% NH4H2PO4 + 0.4% Mg(NO3)2 in 0.5 mol L–1 HNO3 as matrix modifier provided the highest sensitivity and an efficient behaviour for the three types of samples. A detection limit of 26 ng g–1 was achieved and other figures of merit are shown. Analytical results obtained by direct calibration using standard samples prepared in the laboratory and by standard addition method were comparable.
Mutual interference coefficients obtained for 639 emission lines of 68 elements in routine analysis by ICP-AES by Yûetsu Danzaki; Kunio Takada; Kazuaki Wagatsuma; Masaoki Oku (pp. 549-550).
In our previous report [1], a practical method to obtain spectral interference coefficients and to select analytical lines in ICP-AES has been suggested.The coefficients were defined as apparent mass of the analyte corresponding to the spectral interference observed for unit mass of the interferent. In this report, data of the experimentally obtained mutual interference coefficients among 639 emission lines of 68 elements are presented. The data would be also useful for different resolution spectrometers in routine analysis, they are presented on 69 Tables as Supplementary Electronic Material.
Direct determination of trace copper and chromium in silicon nitride by fluorinating electrothermal vaporization inductively coupled plasma atomic emission spectrometry with the slurry sampling technique by Tianyou Peng; Zucheng Jiang; Bin Hu; Zhenghuan Liao (pp. 551-555).
A method has been developed for the determination of trace impurities in silicon nitride (Si3N4) powders by fluorination assisted electrothermal vaporization (ETV) /ICP-AES using the slurry sampling technique. Polytetrafluoroethylene (PTFE) emulsion as a fluorinating reagent not only effectively destroys the skeleton of Si3N4, but also carries out selective volatilization between the impurity elements (Cu, Cr) and the matrix (Si). The experimental parameters influencing fluorination reactions were optimized. The detection limits for Cu and Cr are 1.05 ng/mL ( Cu) and 1.58 ng/mL (Cr), the RSDs are in the range of 1.9–4.2%. The proposed method has been applied to the determination of Cu and Cr in Si3N4 ceramic powders. The analytical results were compared with those obtained by independent methods.
Study on the direct analysis of solid powder biological samples using fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry with PTFE slurry modifier by Shizhong Chen; Feng Li; Zhenhuan Liao; Tianyou Peng; Z. Jiang (pp. 556-559).
A method has been described for the direct determination of Ti, Cu, Mn, Cr and Cd in solid biological samples without any chemical pretreatment by fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES) with slurry sampling. A polytetrafluorethylene (PTFE) emulsion was used as a fluorinating reagent to promote the vaporization of the analytes from the graphite furnace. The interface between furnace device and ICP torch and the main factors affecting the analytical signal were investigated systematically. The detection limits for the determination of Ti, Cu, Mn, Cr and Cd are 6.3, 4.7, 10, 13 and 278 ng/mL, respectively; the relative standard deviations are in the range of 1.5 (Mn) ∼4.0% (Cd) after optimization of the operating conditions. The recommended approach has been applied to directly determine the trace elements of interest in the Chinese traditional medicine Loulu and in the solid biological standard reference material (peach leaves, GBW 08501) with satisfactory results.
Microdetermination of proteins by enhanced Rayleigh light scattering spectroscopy with morin by Ya-Ting Wang; Feng-Lin Zhao; Ke-An Li; Shen-Yang Tong (pp. 560-564).
Under acidic conditions, the reaction between 3,5,7,2′,4′-pentahydroxyflavone (morin) and proteins enhances the weak light scattering of morin drastically. The enhanced light scattering intensity is proportional to the content of proteins. This fact is the basis of a new method for the quantitative analysis of proteins. The linear range is 0.45–7.15 and 0.46–11.14 μg/mL for BSA and HSA, respectively. The relative standard deviation is 3.76% (n = 12) for BSA in the middle of the linear range. The results of this assay for human serum samples were comparable with those from the traditional method (CBB method). There is almost no interfere from amino acids and most of the metal ions. The scattering spectrum of morin was also discussed.
HPLC online reductive scanning voltammetric detection of diquat, paraquat and difenzoquat with mercury electrodes by I. Rühling; H. Schäfer; W. Ternes (pp. 565-569).
To establish an electrochemical HPLC detection system which is suitable for the voltammetric characterisation of unknown contaminants and food components at working potentials lower than –1 V, a modified flow-through cell for the use of a hanging mercury drop electrode (HMDE) is described. The introduction of silanised glass capillaries and a new flow-channel design provide a high HMDE lifetime, which is recommended in HPLC detection. As test system the herbicides diquat, paraquat and difenzoquat and ethylviologen as internal standard were measured using differential pulse voltammetry (DPV) detection to improve selectivity. Spiked water samples were analysed with voltammetric and UV-detection and results agreed well.
Determination of Diazepam and associated compounds in pharmaceutical preparations by J. J. Berzas; G. Castañeda; M. J. Pinilla (pp. 570-575).
A method for determining Diazepam and its associated compounds in pharmaceutical products by micellar electrokinetic chromatography (MEKC) is described. The separation was carried out at 30 °C and 25 kV, using a 25 mM borate buffer (pH 9.6) and 35 mM sodium dodecylsulfate (SDS) water solution. Under these conditions the analysis was carried out within 12 min with acceptable limits of detection and quantification. The method has been applied for quantifying Diazepam in different commercial formulations when it is the active drug and when it is employed associated with other drugs (Nortriptyline, Pyridoxine hydrochloride and Sulpiride).
Fractionation of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and planar polychlorinated biphenyls by high performance liquid chromatography on a pyrenyl-silica column by M. Martínez-Cored; E. Pujadas; J. Díaz-Ferrero; M. Coll; R. Martí; F. Broto-Puig; L. Comellas; M. C. Rodríguez-Larena (pp. 576-583).
Analytical procedures for the determination of polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated dibenzofurans (PCDF) and non-ortho polychlorinated biphenyls (PCB) require a fractionation step to separate PCDD/F from planar PCB and the bulk of PCB. An HPLC method which achieves the separation of the bulk of PCB (0–6 mL of hexane), mono-ortho PCB (6–8 mL of hexane), non-ortho PCB (8–15 mL of hexane) and PCDD/F (15–50 mL of toluene) on a PYE column (2-(1-pyrenyl) ethyldimethylsilylated silica gel) in a single step without the use of backflush as other authors proposed was developed. The method shows a good accuracy and precision and it is linear in the range studied, e.g from 5.8 to 2420 pg injected in HPLC for TCDD/F, from 28.8 to 12100 pg for PeCDD/F, HxCDD/F, HpCDD/F and from 57.6 to 24200 pg for OCDD/F. It has been successfully applied to the analysis of technical mixtures of PCB (Aroclors), a pine wood sample and several water samples of different origins.
Development of a dipstick immunoassay for quantitative determination of 2,4-dichlorophenoxyacetic acid in water, fruit and urine samples by N. V. Cuong; T. T. Bachmann; R. D. Schmid (pp. 584-589).
A sensitive dipstick assay for 2,4-dichlorophenoxyacetic acid (2,4-D) detection was developed. The assay was based on the competitive reaction of 2,4-D and enzyme tracer with monoclonal antibodies immobilised on an Ultrabind® membrane. The binding of enzyme tracer on the test strip was determined by a simple, portable reflectometer as remission at 657 nm. Using this technique, 2,4-D could be detected in a concentration range of 0.5 μg/L to 100 μg/L. The center point of the 2,4-D test was found at a concentration of 6 μg/L. Cross-reactivity with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) as determined by this dipstick assay was 2.5% and 3% by standard ELISA technique using microtiter plates. The assay was applied in the detection of 2,4-D in real water samples, and sensitivity was comparable to spiked water samples. If combined with an effective extraction procedure that results in recovery rates of 90%, the dipstick assay can be used to monitor human exposure to 2,4-D from contamination in water, from oranges and in testing urine samples.
Voltammetric study of nifuroxazide at unmodified and Sephadex-modified carbon paste electrodes by A. Radi (pp. 590-594).
The electrooxidation of nifuroxazide was investigated by cyclic and differential-pulse voltammetry at carbon paste and Sephadex-modified carbon paste electrodes. Nifuroxazide is irreversibly oxidized at all pH values and gives rise to a well-defined oxidation peak. The modification of the carbon paste surface with Sephadex allowed a preconcentration process to take place for nifuroxazide such that higher sensitivity was achieved compared with the bare surface. The influence of the scan rate, time of accumulation, modifier loading, solution conditions and pH on the adsorptive step at the modified carbon paste electrodes was investigated. The direct determination of the drug in urine is also discussed.
A nitrate-selective microelectrode based on a lipophilic derivative of iodocobalt(III)salen by P. G. Verschuren; Juul L. van der Baan; Rolf Blaauw; Dirk de Beer; Johannes C. van den Heuvel (pp. 595-598).
The synthesis of iodo{2,2′-[1,2-octadecanediylbis(nitrilomethylidyne)]diphenolato}cobalt is described. Liquid membrane microelectrodes based on this carrier exhibit Nernstian behaviour with a selectivity sequence according to the Hofmeister series: I– > NO3 – > NO2 – > Cl– > HCO3 – > AcO–. The selectivity coefficient of nitrate over nitrite and chloride amounts to –1.6 and –2.7, respectively. The detection limit for nitrate in water amounts to 10–5.2 mol/L. A nitrate profile measured in a nitrifying biofilm is presented as a practical application.
Determination of aluminium in the edible part of fish by GFAAS after sample pretreatment with microwave activated oxygen plasma by R. Ranau; J. Oehlenschläger; H. Steinhart (pp. 599-604).
An analytical method for the determination of aluminium in the edible part of fish was developed using a new pre-treatment method in a microwave activated oxygen plasma and graphite furnace atomic absorption spectrometry. The linearity of the calibration line as well as of different standard addition lines were very good within the measurement area of 0–60 μg Al/L. The recovery with spiked ocean perch fillet was good. The unsatisfactory recovery of aluminium with the reference-material (mussel tissue) may be due to high quantities of insoluble aluminium-silicates. An installed quality-control-card indicated that the method showed no significant fluctuation as well as contamination over the complete analysis time. The limit of detection calculated as 3 times the standard deviation of the blank absorbance divided by the slope of the calibration line was 1 μg Al/L.
Polymeric encapsulated membrane for optrodes by Bambang Kuswandi; R. Narayanaswamy (pp. 605-607).
Highly efficient and simple reagent immobilisation procedure for an optrode membrane has been developed. The preparation procedure combines two well-known physical immobilisation procedures, viz. adsorption and encapsulation techniques, applied sequentially which, in turn, produce a combined optical sensing layer. The sensitive polymeric encapsulated membrane (PEM) contains the polymeric resin, which can adsorb a large amount of indicator dye, encapsulated within porous polymeric structure. The procedure has been tested in the preparation of a pH sensor.