Validation of a computer-program for the interpretation of infrared spectra

The capability of a modern interpretation system for IR spectra has been tested, in which the process of structural assignment is modelled by methods of fuzzy logic. Figures of merit were generated for different interpretation algorithms. These figures of merit permit the validation as well as a comparison of independent interpretation systems. The influence of the sample preparation practice onto the information content of the resulting spectrum has been evaluated as well. Automatically generated band tables show only restricted reliability. Received: 13 February 1997 / Revised: 1 April 1997 / Accepted: 3 April 1997     

Field method for the micro-quantitative determination of tetracycline in human urine

A simple, fast and sensitive titrimetric method has been developed for the determination of tetracycline hydrochloride in human urine using m-dinitrobenzene as color agent and Dowex 1 × 8 as detection medium. Received: 26 February 1997 / Revised: 23 April 1997 / Accepted: 29. April 1997     

Development of a modified beta-cyclodextrin based fluorosensor for dipyridamole

2,6-O-diethyl-β-cyclodextrins were prepared and immobilized onto silica gel to develop a fluorosensor for dipyridamole. The analytical performance characteristics of the proposed sensor for analysis of dipyridamole were as follows: the detection limit was 0.8 nmol/L with a relative standard deviation of 1.4% for 10 determinations of 50 nmol/L of dipyridamole. The modification of β-CD improved the sensitivity and selectivity for measuring dipyridamole. The recommended method has been successfully tested for the determination of dipyridamole in clinical samples (urine and pharmaceutical preparations). Received: 23 January 1997 / Revised: 14 April 1997 / Accepted: 21 April 1997     

MS-Pep: a computer program for the interpretation of mass spectra of peptide libraries

Electrospray mass spectrometry (ESI-MS) is an established method for the qualitative analysis of synthetic peptide libraries and combinatorial mixtures or collections of small organic compounds. However, the calculation of the mass distribution of even small peptide mixtures is a time-consuming and error-proned task. Therefore, the computer program MS-Pep has been developed, which calculates the masses of expected peptides, byproducts and the mass distributions of peptide libraries. Received: 2 December 1996 / Revised: 17 April 1997 / Accepted: 21 April 1997     

Performance comparison between packed column supercritical fluid chromatography (SFC) and HPLC using cyclandelate as the model analyte

A reproducible and fast method has been developed for the assay of cyclandelate in bulk and drug forms using packed column supercritical fluid chromatography using dicyclohexyl phthalate (DCHP) as internal standard. The drug and the internal standard were resolved by elution with supercritical fluid carbon dioxide doped with 14.29% (v/v) methanol on an RP-C₁₈ column and detected spectrophotometrically at 228 nm. Chromatographic figures of merit using C₈, C₁₈, cyano and phenyl columns have been assessed. Parallel experiments have been performed by HPLC and the data have been compared. Supercritical fluid extraction using CO₂ modified with a small amount of methanol was found to give quantitative analytical recoveries of cyclandelate from a dosage form. SFC has been shown to be a viable, faster alternative technique to HPLC generating less disposable waste. Received: 20 June 1997 / Revised: 20 October 1997 / Accepted: 26 October 1997     

Ion trap MS/MS of polychlorinated dibenzo-p-dioxins and dibenzofurans: confirming the concept of the molar response

It has been shown that the concept of molar response, which is applicable to single ion monitoring of M⁺, can also be employed for ion trap MS/MS measurements, simplifying the determination of PCDD/PCDF by an extended IDA approach. Received: 22 April 1997 / Revised: 16 June 1997 / Accepted: 18 June 1997     

Size and phase fractionation of water components by membrane filtration Distribution patterns for arsenic, iron and manganese in aqueous effluents of tin ore settling plant

The possibility of on-line membrane size-fractionation of water components and simultaneous separation of particulate and dissolved matter at each filtration stage has been shown. The distribution patterns have been studied for As, Fe and Mn in effluent samples of tin ore tailings (Altenberg, Saxony, Germany). The seepage composition is characterized by high concentrations of Fe and As. The particulate and dissolved components were separated in five fractions between 0.025 and 8 μm. It was suggested that the distribution patterns of As and Fe compounds depend on the chemical conditions at the sampling sites. Manganese exists mainly in solvated forms in the liquid fractions. Received: 8 January 1997 / Revised: 8 April 1997 / Accepted: 9 April 1997     

A new proposal for a parameter-free integration software

An algorithm is presented that has successfully been utilized in practice for several years. It improves data analysis in chromatography. The program runs in an extremely reliable way and evaluates chromatographic raw data with an acceptable error. The algorithm requires a minimum of preliminaries and integrates even unsmoothed noisy data correctly. Received: 7 April 1997 / Revised: 23 May 1997 / Accepted: 4 June 1997     

Enantioseparation of four-membered rings by gas chromatography; an overview

The separation of enantiomers by gas chromatography on a chiral stationary phase is stored and conveniently retrieved in the molecular database Chirbase/GC. According to the present information content (version 3/96), a great variety of analytes has been published in several hundred journals. A selected review is given on 364 enantiomer separations of 102 different molecules containing at least one four-membered saturated carbocyclic ring. Factors determining the degree of enantioseparation are outlined and analyzed. Received: 16 November 1996 / Revised: 17 April 1997 / Accepted: 30 April 1997     

Enantioseparation of four-membered rings by gas chromatography; an overview

The separation of enantiomers by gas chromatography on a chiral stationary phase is stored and conveniently retrieved in the molecular database Chirbase/GC. According to the present information content (version 3/96), a great variety of analytes has been published in several hundred journals. A selected review is given on 364 enantiomer separations of 102 different molecules containing at least one four-membered saturated carbocyclic ring. Factors determining the degree of enantioseparation are outlined and analyzed. Received: 16 November 1996 / Revised: 17 April 1997 / Accepted: 30 April 1997     

Isothermal pressure dependence of the solubility of some triazines in supercritical CO2

 The solubility of two related series of each three triazine compounds has been determined in supercritical CO₂, at 40 °C and pressures between 80 and 220⋅10⁵ Pa. A high pressure small volume cell with adjustable optical path and built-in circulation pump has been constructed to be used with quartz windows in a Perkin Elmer UV-VIS spectral photometer. At 220 bar solubilities are between 0.3 and 25 g/L, dependent on the specific triazine structure. The isothermal pressure dependence of the solubility could be modelled using the pressure dependent dielectric constant of CO₂ as the only variable. Received: 30 October 1996/Revised: 3 April 1997/Accepted: 13 April 1997     

Analytical methodologies for chromium speciation in solid matrices: a survey of literature

The analytical literature about chromium speciation in solid samples has been surveyed. From 451 articles published on the speciation of chromium from 1983 to 1997, the methodologies to do speciation in solids after sample pretreatment are discussed, through consideration of the types of samples and their dissolution, the analytical techniques employed for chromium measurement, and the figures of merit of the 86 papers reported in the Analytical Abstracts data base. Received: 6 February 1998 / Revised: 6 March 1998 / Accepted: 7 March 1998     

Substrate inhibition in an enzymatic ordered bireactant system: non-linear modelling of the kinetics of hypoxanthine-guanine-phosphoribosyltransferase

Hypoxanthine-guanine-phosphoribosyltransferase (HGPRT; EC 2.4.2.8) was determined as an enzyme following an ordered bireaction in the presence of substrate inhibition due to hypoxanthine. This kind of inhibition has not been postulated for HGPRT so far. The mechanism and the kinetic constants of the reaction of HGPRT from Saccharomyces cerevisiae were investigated by initial velocity studies involving a non-linear regression analysis. In addition, two kinds of experimental designs were compared: the variation of hypoxanthine concentrations over wide ranges at different of fixed levels of 5-phosphoribosyl-1-pyrophosphate, and the use of five appropriate sets of experimental conditions each characterized by different hypoxanthine and 5-phosphoribosyl-1-pyrophosphate concentrations. Both experimental designs were consistent with an ordered bi bi mechanism including a dead-end-complex between the enzyme and hypoxanthine. Received: 25 April 1997 / Revised: 9 June 1997 / Accepted: 16 June 1997     

Speciation of vanadium (IV) and vanadium (V) with Eriochrome Cyanine R in natural waters by solid phase spectrophotometry

The separation and preconcentration of vanadium (IV) and vanadium (V) using Sephadex DEAE A-25 with Eriochrome Cyanine R has been studied, based on the preconcentration of vanadium (IV) in the first step and V(V) after reduction with ascorbic acid in the second step. Factors affecting the optimum fixation of the complex were investigated. The absorbance of the solid phase is measured directly at 563 nm for V(IV), at 585 nm for V(V) and at 750 nm for both. The proposed method provides a simple and specific procedure for the separation of vanadium in natural waters. The calibration graph is linear up to 150 ng/mL, with RSD of 4.7% for V(IV) and 4.0% for V(V). The detection limits are 1.6 and 1.4 ng/mL for V(IV) and V(V), respectively. Received: 21 November 1996 / Revised: 15 April 1997 / Accepted: 18 April 1997     

Development of a highly sensitive enzyme-immunoassay for the determination of triazine herbicides

A monoclonal antibody (Mab) with extraordinary sensitivity and high class selectivity to triazine herbicides is described. With an enzyme-linked immunosorbent assay (ELISA) using Mab 4A54 IC₅₀ values for terbuthylazine, atrazine, propazine and simazine below 0.1 μg/L (the EU maximum admissible concentration for individual pesticides) have been obtained. Detection limits of 0.004 μg/L for terbuthylazine, 0.006 μg/L for atrazine, 0.003 μg/L for propazine, 0.01 μg/L for simazine and 0.05 μg/L for deethylterbuthylazine could be achieved. Therefore, Mab 4A54 allows a sum screening of these five triazines in a relevant concentration range. To our knowledge, this is the most sensitive antibody to terbuthylazine at all and also the most sensitive Mab to all these four triazines. Another monoclonal antibody resulting from the same immunization, clone 4A118, exhibits best sensitivity for propazine (detection limit: 0.02 μg/L) at lower cross-reactivity to terbuthylazine and atrazine compared to clone 4A54. Affinity constants of both Mabs towards several triazines have been calculated. The application of both Mabs for the analysis of triazines in water samples of different origin has been tested and their resistance towards humic acid influence could be shown. A good correlation of the analysis of water samples with GC and ELISA was observed. Received: 17 February 1997 / Revised: 1 April 1997 / Accepted: 3 April 1997     

Platinum speciation with hyphenated techniques: high performance liquid chromatography and capillary electrophoresis on-line coupled to an inductively coupled plasma-mass spectrometer – application to aqueous extracts from a platinum treated soil

1. An on-line hyphenation of reversed phase high-performance liquid chromatography (RP-HPLC) with inductively coupled plasma-mass spectrometry (ICP-MS) is applied, using an ultrasonic nebuliser combined with a membrane desolvator as the interface. Thus, organic solvents (e.g. methanol, hexane) or gradients (e.g. methanol/water) as well as aqueous NaHCO₃/NaCl mixtures can be directly used without influence on the plasma. The high resolution power of HPLC enables the separation of Pt-species, whereas ICP-MS is taken for element specific detection with low detection limits. 2. Additionally, a powerful on-line coupling of capillary electrophoresis (CE) and ICP-MS [1, 2] was used for platinum speciation in parallel. With these two methods, independent from each other, first characterisation is achieved about the nature of Pt species formed by interaction with a soil. Aqueous extracts of a clay-like humic soil, treated with a Pt contaminated tunnel dust and Pt model compounds [3] were examined to elucidate transformation processes of Pt-species in a soil. Received: 19 February 1997 / Revised: 15 April 1997 / Accepted: 18 April 1997     

Platinum speciation with hyphenated techniques: high performance liquid chromatography and capillary electrophoresis on-line coupled to an inductively coupled plasma-mass spectrometer – application to aqueous extracts from a platinum treated soil

1. An on-line hyphenation of reversed phase high-performance liquid chromatography (RP-HPLC) with inductively coupled plasma-mass spectrometry (ICP-MS) is applied, using an ultrasonic nebuliser combined with a membrane desolvator as the interface. Thus, organic solvents (e.g. methanol, hexane) or gradients (e.g. methanol/water) as well as aqueous NaHCO₃/NaCl mixtures can be directly used without influence on the plasma. The high resolution power of HPLC enables the separation of Pt-species, whereas ICP-MS is taken for element specific detection with low detection limits. 2. Additionally, a powerful on-line coupling of capillary electrophoresis (CE) and ICP-MS [1, 2] was used for platinum speciation in parallel. With these two methods, independent from each other, first characterisation is achieved about the nature of Pt species formed by interaction with a soil. Aqueous extracts of a clay-like humic soil, treated with a Pt contaminated tunnel dust and Pt model compounds [3] were examined to elucidate transformation processes of Pt-species in a soil. Received: 19 February 1997 / Revised: 15 April 1997 / Accepted: 18 April 1997     

Experience with wheat and wheat flour CRMs

The Chemical Section of OHM [1–2] embarked on the preparation of a wheat sample series as CRMs in 1992. The certification process has been carried out according to the recommendations of ISO. Since then a series of wheat flour samples has been developed as well. The investigations of the long-term stability and the application of wheat and flour CRMs are presented. Received: 23 May 1997 / Revised 8 September 1997 / Accepted: 16 September 1997     

Study and application of a method for the determination of metallic elements by ICP-AES with preconcentration on an active carbon-silica gel microcolumn in a FI system

Using active carbon-silica gel as adsorbent and sodium diethyldithiocarbamate (NaDDTC) as chelating reagent in a flow injection system, an ICP-AES method has been developed for preconcentration and determination of trace metallic elements in high purity rare earth oxides. The experimental parameters such as pH, flow rate, amount of adsorbent, length of reaction coil and eluent acidity were optimized. At pH 4.6 Al,Cr,Cu,Fe,Pb,V,Zn could be preconcentrated, and subsequently determined by ICP-AES. This method can eliminate matrix effects. Its enrichment factors were 8.1–12.6 with detection limits in the ng/mL range and RSD of 2.3–5.0. This method was applied to the analysis of high purity of La₂O₃ and Eu₂O₃ with satisfactory results. Received: 24 April 1997 / Revised: 22 September 1997 / Accepted: 7 October 1997     

Experiments to determine the escape probability of photoelectrons

A novel experimental method for the assessment of the escape probability of photoelectrons as a function of depth and their mean escape depths is described and illustrated for photoelectrons leaving an aluminium oxide surface. The results are compared with those of the straight line approximation model calculations. Received: 30 July 1997 / Revised: 7 April 1998 / Accepted: 8 April 1998