Immuno-affinity columns versus conventional clean-up: a method-comparison study for the determination of zearalenone in corn

The efficiency of a modern analytical method employing immuno-affinity columns (IACs) is compared to a well established traditional technique with respect to the determination of zearalenone (ZON) in corn in the μg/kg range. Despite of a constant error of about 4 μg/kg in the examined working range of 10–200 μg/kg, analytical data obtained from the analysis of spiked and naturally contaminated samples showed good correspondence for the compared methods. The performance characteristics of immuno-affinity-chromatography as a new clean-up technique for the determination of ZON in corn is reported for the first time and compared to a conventional clean-up procedure Received: 25 March 1997 / Revised: 5 May 1997 / Accepted: 12 May 1997     

Ex-vivo determination of blood glucose by microdialysis in combination with infrared attenuated total reflection spectroscopy

Several biosensors have been developed for continuous monitoring of human blood glucose, which is desirable for insulin-dependent diabetic patients. Developments in the field of quantitative assays using infrared attenuated total reflection spectroscopy allow the determination of metabolites at low concentrations. The microdialysis technique can provide a continuous sampling of extracellular body fluids. As only compounds of low molecular weight are passed on, infrared spectrometric quantitation is eased considerably. Samples were obtained by microdialysis of human blood plasma and aqueous glucose solutions. Multivariate calibration by partial least-squares was evaluated for its analytical performance in ex-vivo blood glucose monitoring. Mean squared prediction errors obtained by cross validation were 5.4 mg/dL for dialysate samples from different patients and 1.3 mg/ dL for dialysates from glucose solutions. Further investigations were carried out to achieve miniaturization of the measuring and detection device. Received: 5 December 1996 / Revised: 20 March 1997 / Accepted: 29 March 1997     

Validation of a computer program for atomic absorption analysis

 The approach to validation of a computer program for an analytical instrument as a component of the analytical method (using this instrument with the program) is discussed. This approach was used for validating a new program for atomic absorption analysis. The validation plan derived from this approach was based on minimising the influence of all steps of the analytical procedure on the analytical results obtained by the method. In this way significant changes in the results may be caused only by replacement of the previous program by the new one. The positive validation conclusion was based on the comparison of the results of the analysis of suitable reference materials obtained with the new program and with its precursor in the same conditions, and also on comparison of their deviations from the accepted reference values for these materials, with the corresponding uncertainties. Received: 25 January 1997 Accepted: 14 March 1997     

Laser-induced fluorescence determination of thallium in sediments

A simple dissolution procedure is decribed for sediments to be analyzed for thallium by Laser-Excited Atomic Fluorescence Spectrometry (LEAFS). It simply uses a nitric – hydrofluoric acid mixture at room temperature (a “cold dissolution” procedure as opposed to the hot acid digestion) followed by a dilution with water (as opposed to the tedious steps of separation and preconcentration). Excellent accuracy (91–106% recoveries) and precision (4–10% relative standard deviation) were demonstrated by the use of five sediment reference materials of diverse origins. The detection limit was estimated to be 0.5 ng/g of thallium. Additionally, a hot plate digestion procedure, using an in-house designed semi-enclosed Teflon beaker, was also investigated; its analytical results agreed with certified values and confirmed the adequacy of the cold dissolution technique. The method is being applied to study the sediment – water interactions in lake environments. Received: 30 December 1996 / Revised: 20 March 1997 / Accepted: 30 March 1997     

Determination of cobalt by substoichiometric extraction with β-hydroxy-naphthaldoxime

A substoichiometric radiochemical solventextraction method is described for the determination of cobalt, employing β-hydroxy-naphthaldoxime and chloroform as reagent and extractant, respectively. The extraction behaviour of the complex of cobalt with the reagent in the pH-range 8–9.5 and the effects of various metal ions on the extraction are critically studied. The method is used to determine the cobalt content in some pharmaceutical drugs. Received: 10 January 1997 / Revised: 11 March 1997 / Accepted: 25 March 1997     

A flow system for calibration of dissolved oxygen sensors

Well-defined oxygen standard solutions were obtained by the electrolysis of water in a coulometric oxygen generator. The generator was integrated into a flow system that includes the degassing of the carrier electrolyte, the generation of dissolved oxygen and the temperature control of the carrier electrolyte. The current efficiency of oxygen generation was found to be 100% by the Winkler titration method. Calibrations of a home made laboratory sensor and a WTW CellOx dissolved oxygen sensor have been made in a concentration range of 0.02 to 8 mg/L at temperatures from 5°C to 30°C. The calibration of the WTW sensor on water vapour saturated air was compared with the electrochemical calibration method. Both methods gave reliable results provided that the temperature equilibration between the sensor and the ambient air was successful. Received: 24 March 1997 / Revised: 15 May 1997 / Accepted: 15 May 1997     

Application of factor analysis in EDXRF

 The application of factor analysis in EDXRF as a method for evaluation of elemental concentrations and calculation of net peak areas is demonstrated in two examples. A quantitative PCR-analysis of sulphur interfered with by molybdenum could be performed by using the XRF-spectra as input with a standard error of analysis (SEA) below 0.2 mg/g for aqueous and 3.6 mg/g for solid samples. By using PCR-predicted net peak areas as input for the empirical evaluation method developed by Lucas-Tooth and Price, the SEA for solid samples could be decreased to 2.3 mg/g. The comparison of PCR to PLS showed no significant difference. Received: 25 October 1996/Revised: 6 March 1997/Accepted: 10 March 1997     

Sensitive determination of airborne diisocyanates by HPLC: 4,4′-Diphenylmethane-diisocyanate (MDI)

An HPLC/fluorescence method is described, which enables the sensitive determination of airborne monomeric 4,4′-diphenyl-methane-diisocyanate (MDI). A glass fiber filter coated with 1 mg 1-(2-pyridyl)-piperazine (2PP) is used for sampling. The urea derivative MDI-2PP, which shows a high molecular absorption coefficient and exhibits a sufficient fluorescence response, is extracted from the filter by use of a 90:10 acetonitrile/DMSO mixture. Linear calibration curves were obtained for the indoor range (7.8 ng/mL to 74.7 ng/mL) and the workplace range (27.7 ng/mL to 676.0 ng/mL). A detection limit of 9.0 ng/m³ can be achieved on a total sampling volume of 1000 L. The method is easy to handle and therefore highly suitable for a routine determination of MDI in the atmosphere of workplace areas and living environments. Received: 17 December 1997 / Revised: 2 March 1998 / Accepted: 4 March 1998     

Enhanced recovery of chlorophenols from surface waters using polymer based extraction cartridges

 The effectiveness of a new polymer based solid phase extraction cartridge (SDB 1) to recover phenolic compounds from aqueous samples has been evaluated by comparison of performance against conventional silica based cartridges. The polymer based material is found to be much more retentive, requiring a larger volume of solvent to achieve maximum recovery. Recovery efficiency is enhanced if the recovery solvent (methanol) is acidified to 0.1% with trifluoroacetic acid. The optimised extraction procedure has been applied to surface water samples and yields quantitative recovery at the 10 ng ml^-1 level of all nine phenols studied. Received: 26 November 1996/Revised: 21 March 1997/Accepted: 30 March 1997     

The effect of palladium modifier on the efficiency of antimony hydride trapping in graphite furnace atomic absorption spectrometry (AAS)

A slurry fluorination electrothermal vaporization (ETV)-ICP-AES method for the determination of Cu and Cr in SiO₂ powders has been developed. A polytetrafluoroethylene (PTFE) emulsion is used as fluorinating reagent; the matrix (Si) is partially separated from the sample by selecting the ashing temperature and time to reduce the interference. Moreover, the vaporization behaviour has been investigated in detail. The detection limits are 1.1 ng/mL with 3.8% of RSD (Cu) and 1.6 ng/mL with 3.2% of RSD (Cr). The method is applied to analyze the SiO₂ powders with satisfactory results. Received: 6 January 1997 / Revised: 13 March 1997 / Accepted: 28 March 1997     

Determination of total iron in ground waters and multivitamin tablets using a solid-phase reactor with tiron immobilised on amberlite ion-exchange resin in a flow injection system

A method is described for the flow injection determination of total iron as Fe(III) using a solid-phase reactor containing disodium-1,2-dihydroxybenzene-3,5-disulphonate (tiron) as substrate. The iron(III) reacted with tiron to form a complex which absorbs strongly at 667 nm, where it was measured spectrophotometrically. The system has a linear range of 1 to 50 mg L^–1 with a detection limit of 0.67 mg L^–1. It is suitable for the determination of total iron in multivitamin tablets and iron-rich ground waters, with a relative standard deviation of better than 1.1%. The results obtained compared favourably with the certified values and a standard ICP-AES method. Received: 12 November 1997 / Revised: 9 March 1998 / Accepted: 15 March 1998     

Liquid chromatographic isolation of coplanar PCB congeners on an activated carbon stationary phase

A rapid and uncomplicated method for the fractionation of PCBs leading to an isolation of the highly toxic non-ortho substituted PCBs is described. The liquid chromatographic separation was achieved on a stationary phase consisting of activated carbon and Celite 545. Using eluents with different polarity, isolation of the non-ortho substituted PCBs in a single fraction was achieved. The fractions were analysed by GC/MS. The method was tested by the determination of non-ortho substituted PCBs in technical mixtures (Aroclor 1254 and Aroclor 1242). The results were compared with those obtained by using an HPLC fractionation on a porous graphitic carbon column. Finally, the micro-column fractionation was used for the determination of non-ortho substituted PCBs in native soil samples. Received: 5 March 1997 / Revised: 4 June 1997 / Accepted: 6 June 1997     

Stochastic dynamics simulation of alanine dipeptide: Including solvation interaction determined by boundary element method

A merger of the Poisson–Boltzmann equation and stochastic dynamics simulation is examined using illustrative calculations of alanine dipeptide. The boundary element method (BEM) is used to calculate the hydration forces acting on the solute molecule based on the surroundings. Computational efficiency is achieved by the use of a simple hydration model and a coarse boundary element. Nonetheless, the conformational distribution obtained from this new method is reasonable compared with other theoretical and computational results. Detailed analysis has been accomplished in terms of the hydration interactions and solvation energies. The results indicate that the new simulation method provides an obvious improvement over the conventional stochastic dynamics simulation technique. The further improvement of the hydration model and future application to large molecules are also discussed. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1440–1449, 1997     

Analysis of N-dimensional data arrays from fluorescence spectroscopy of an intermediary sugar product

Unwanted formation of colour takes place during the production of crystalline sugar. The degree of colouration depends partly on the necessary processing conditions, e.g. heating and pH, and partly on the initial composition and condition of the sugar beets used as raw material. Reducing sugars are formed during the process. These are reactive compounds forming a variety of coloured complexes and strong precursors to further formation of colour and many of these compounds contain fluorophores. In the present work it is discussed if spectrofluorometric screening of intermediary sugar products prior to the final heating stages combined with a multi-way chemometric approach can provide information that significantly reflects the condition of the process and the beets. The model used is the N-way PCA (Principal Component Analysis) which is an exploratory model, not necessitating explicit modelling of single parameters nor any assumptions towards parameter interaction. By use of a 4-way PCA of order (3,2,3,3) satisfactory classification of 47 thick juice samples belonging to 5 factories has been obtained from a spectrofluorometric screening method. Also, a temporal trend has been found to evolve during the time of production. The investigation substantiates the use of modern models from data analysis for extracting significant information from large and complex data sets. Received: 13 January 1997 / Revised: 18 March 1997 / Accepted: 25 March 1997     

CAST/CNMR: highly accurate C NMR chemical shift prediction system considering stereochemistry

Accurate, practical prediction of ¹³C NMR chemical shifts has been achieved with a new system, CAST/CNMR, taking account of stereochemistry. The CAST/CNMR system has solved the critical problem of the accurate distinction of differences and similarities in stereochemical structures around a specific carbon, which has not yet been achieved by any other database-oriented system for prediction of ¹³C NMR chemical shifts. CAST/CNMR uses a three-dimensional structural database together with a ¹³C NMR spectral database. Absolute/relative configurational and conformational structural information are described by the CAST (CAnonical-representation of STereochemistry) coding method. This paper provides an overview of the CAST/CNMR system, and describes its application to two natural products as examples.     

Modern strategies for PC-supported spectral analysis of 1D NMR data

 Analysis of high-resolution NMR spectra elucidation has been known for many years. Hard-and software development now permits the implementation of such programs on personal computers. The structural information hidden in complex proton NMR spectra becomes easily accessible by using graphical user interfaces and direct data exchange between programs. A new mode has been implemented in 1D WIN-NMR to support the analysis of multiplet patterns with first order rules. Structure display, direct export mechanisms to the simulation program WIN-DAISY, and an archiving possibility complete the state-of-the-art data analysis. Some practical examples are given. Received: 25 October 1996/Revised: 6 March 1997/Accepted: 10 March 1997     

A new concept for the quasi non-destructive microsampling of historical glasses

A mobile and easily practicable microsampling technique for historical glasses and its application is presented. About 100 μg of material is scraped off the object with a fine grinding file. The analysis of main, minor and trace elements in the digested sample is performed by IC, GFAAS and FIA with photometric detection. The procedure has been verified by measurements of standard glasses. Investigations of baroque ruby glasses showed the suitability of the microsampling technique for archaeometrical application. Received: 6 January 1997 / Revised: 17 March 1997 / Accepted: 25 March 1997     

A new concept for the quasi non-destructive microsampling of historical glasses

A mobile and easily practicable microsampling technique for historical glasses and its application is presented. About 100 μg of material is scraped off the object with a fine grinding file. The analysis of main, minor and trace elements in the digested sample is performed by IC, GFAAS and FIA with photometric detection. The procedure has been verified by measurements of standard glasses. Investigations of baroque ruby glasses showed the suitability of the microsampling technique for archaeometrical application. Received: 6 January 1997 / Revised: 17 March 1997 / Accepted: 25 March 1997     

Use of a capacitively coupled microwave plasma (CMP) with Ar, N2 and air as working gases for atomic spectrometric elemental determinations in aqueous solutions and oils

A comparative study was performed of 600 W capacitively coupled microwave plasmas (CMP) with different plasma gases (Ar, N₂ and air) and aerosol generation with the aid of a Légère pneumatic nebulizer. Detection limits with the different working gases are in the order of 15–4000 ng/mL for Fe, Cr, Zn, Mg and Ca in aqueous solutions. The influence of organic solutions on the stability of the plasma is discussed. The determination of Co, Cr, Fe, Mg and Ni in different oil samples by OES is described, using an air-CMP and pneumatic nebulization after dilution of the oils by 20% with cyclohexane. The detection limits for these elements are in the 100–400 ng/g range. Results obtained for a waste motor oil for the elements mentioned in the concentration range of 4–50 μg/g were found to be in good agreement with those obtained by ICP-OES after digestion of the oils at high pressure in PTFE vessels. Received: 10 March 1997 / Revised: 23 May 1997 / Accepted: 30 May 1997     

Use of a capacitively coupled microwave plasma (CMP) with Ar, N2 and air as working gases for atomic spectrometric elemental determinations in aqueous solutions and oils

A comparative study was performed of 600 W capacitively coupled microwave plasmas (CMP) with different plasma gases (Ar, N₂ and air) and aerosol generation with the aid of a Légère pneumatic nebulizer. Detection limits with the different working gases are in the order of 15–4000 ng/mL for Fe, Cr, Zn, Mg and Ca in aqueous solutions. The influence of organic solutions on the stability of the plasma is discussed. The determination of Co, Cr, Fe, Mg and Ni in different oil samples by OES is described, using an air-CMP and pneumatic nebulization after dilution of the oils by 20% with cyclohexane. The detection limits for these elements are in the 100–400 ng/g range. Results obtained for a waste motor oil for the elements mentioned in the concentration range of 4–50 μg/g were found to be in good agreement with those obtained by ICP-OES after digestion of the oils at high pressure in PTFE vessels. Received: 10 March 1997 / Revised: 23 May 1997 / Accepted: 30 May 1997