Analytica Chimica Acta (v.428, #1)

Microscale on-line production of l-malic acid from fumaric acid using on-line immobilized fumrase is developed. Fumaric acid is aspirated continuously through immobilized fumarase using a flow injection manifold. A simple and rapid flow injection chemiluminescence system based on an immobilized malate dehydrogenase, methylene blue and luminol system is developed to monitor the production of malic acid. The log-log calibration graph for malate is linear from 4.0×10−6 to 8.0×10−5  M. The detection limit (3σ) is 4.0×10−6  M. The RSD of 5 replicate injections of 3.2×10−5  M malate is 3%. The conversion yield of malic acid is 30–95% depending on the concentration of fumaric acid used.
Keywords: Flow injection; Malate; Chemiluminescence; Immobilized enzyme;

A simultaneous flow injection method for the determination of malic and lactic acids in wines based on the coupling of dialysis-enzymic derivatisation with either photometric or fluorimetric detection is proposed. A study of the dialysis selectivity and efficiency as a function of the membrane features was previously carried out. After separation by dialysis, the malic and lactic acids are collected into a nicotinamide adenine dinucleotide (β-NAD+) acceptor stream. The oxidation of the coenzyme is catalysed by malic and lactic dehydrogenases immobilised on controlled pore glass in two different enzymatic reactors and the reduced form of the coenzyme (NADH) is monitored either spectrophotometrically (340 nm) or fluorimetrically (λ ex=340 nm, λ em=460 nm). Discrimination between the two analytes is achieved by dividing the dialysed into two aliquots by trapping a portion of the solution in the loop of an auxiliary injection valve and leading each aliquots to one or the bioreactors with the help of a selection valve. The linear determination range is 0.05–1.0 g l−1 for malic acid and 0.1–1.0 g l−1 for lactic acid with 3σ limits of detection (LODs) of 0.03 and 0.05 g l−1, respectively, for spectrophotometric detection and 0.02–1.5 g l−1 for malic acid and 0.05–1.5 g l−1 for lactic acid and LODs of 0.015 and 0.01 g l−1, respectively, when fluorimetric detection is used. When applied to different Spanish wines the results compared well with those of the official methods.
Keywords: Malic acid; Lactic acid; Wine; Flow injection; Dialysis; HPLC; Immobilised enzyme; Photometry; Fluorimetry;

New method is developed for the determination of traces (<10−9  M) of thallium(I) in aqueous solutions. The method is based on an effect of thallium(I) ions on transient chaotic regimes in the Belousov–Zhabotinskii oscillating chemical reaction. The optimum conditions for the determination has been determined. The detection limit is ≤10−12  M. There are few interferences at low concentrations.
Keywords: Thallium; Kinetic methods; Transient chaos; Belousov–Zhabotinskii reaction;

A new simple and rapid reagent-injection method is reported for the spectrophotometric determination of citric acid in beverages and pharmaceutical formulations. The method is based on the inhibitory effect of citric acid upon the Fe(III) catalytic oxidation of 2,4-diaminophenol (DAP) by H2O2. Citric acid forms stable complexes with Fe(III), thus, reducing its catalytic effect. The decrease in absorbance of the oxidation product is monitored at 500 nm. The various chemical and physical variables of the FI system were optimized and a study of interfering ions was also carried out. A linear calibration graph was obtained from 0 to 1000 mg l−1 citric acid. The precision was very good (s r=1.9%) and the detection limit was satisfactory (c L=0.96 mg l−1). The sampling rate was 90 injections per hour. The average accuracy was evaluated by comparison of the results with those obtained by the Boehringer–Mannheim UV-method test combination kit for citric acid and it was also very good (e r=0.96%). The method was found to be adequately selective considering the ions the samples contain, and has been successfully applied to the determination of citric acid in commercial beverages and pharmaceutical formulations.
Keywords: Citric acid; Spectrophotometry; Inhibitory effect; Reagent injection; Beverages; Pharmaceutical formulations;

Basis sets for multivariate regression by John H. Kalivas (31-40).
Estimates of regression coefficients for a multivariate linear model have been the subject of considerable discussion in the literature. A purpose of this paper is to discuss biased estimators using common basis sets. Estimators of focus are least squares, principal component regression, partial least squares, ridge regression, generalized ridge regression, continuum regression, and cyclic subspace regression. Variations of these methods are also proposed. It is shown that it is not the common basis set used to span the calibration space or the number of vectors from the common basis set used to form respective calibration models that are important, i.e. a parsimony emphasis. Instead, it is suggested that the size and direction of the calibration subspace used to form the models is essential, i.e. a harmony consideration. The approach of the paper is based on representing estimated regression vectors as weighted sums of basis vectors.
Keywords: Multivariate calibration; Regression model; Near infrared spectroscopy; Basis set;

Near-infrared spectroscopy is a promising technique for the rapid monitoring of submerged culture bioprocesses. However, despite the key role of mycelial (filamentous fungal and bacterial) micro-organisms in the manufacture of antibiotics and other valuable therapeutics, there is little information on the application of the technique to monitor mycelial bioprocesses. In part, this is due to the complex and spectroscopically challenging matrices, which result from the growth of these micro-organisms. Moreover, there is a particular lack of any detailed mechanistic information on how models for the prediction of the concentration of key analytes (e.g. biomass, substrates, product) can be constructed, evaluated and improved using the spectral data arising from such complex matrices. We investigated the near-infrared spectra of culture fluid from a submerged fungal bioprocess, for monitoring the concentrations of mycelial biomass and other key analytes. Several empirical models were developed for predicting the concentration of the analytes, using multivariate statistical techniques. Despite the filamentous nature of the biomass and the resulting complexity of the spectral variations, empirical models could be developed for the prediction of this analyte, using biomass ‘specific’ information. SEP values of <1 g/l could be achieved on external validation, for models developed in the concentration range of 0–20 g/l. The concentrations of the substrates, total sugars (as glucose equivalents) and ammonium, could also be predicted, simultaneously. However, the product (penicillin) and by product (extracellular proteins) levels had to be monitored on the cell free culture fluid, due to their relatively low concentration. Here we report upon how the spectral information can be deconvoluted for predicting the levels of the analytes and upon how the ‘analyte specific’ information in the spectral data can be used to inform and assist the modelling process, in order to increase confidence in exactly what is being modelled.
Keywords: Fermentation; Penicillium chrysogenum; Spectroscopy; Mycelial biomass; Multivariate calibration;

Determination of biogenic volatile organic compounds (C8–C16) in the coastal atmosphere at Mace Head, Ireland by J.H. Sartin; C.J. Halsall; B. Davison; S. Owen; C.N. Hewitt (61-72).
A methodology describing the sampling and analysis of biogenic volatile organic compounds (VOCs) in ambient coastal air is presented. Air samples were collected during a field campaign (September 1998) at Mace Head on the west coast of Ireland. In addition, air samples from seaweed enclosures were taken to assess the VOC source potential of macro-algae at low tide. VOC identification was confirmed using GC–MS and an n-alkane retention index, with quantification carried out using GC–FID. A suite of compounds (C8–C16) were routinely quantified; these included a series of n-alkanes (C11–C16) and oxygenated hydrocarbons (C8–C14). Their mixing ratios in coastal air ranged from <10–400 parts per trillion (pptv). The most abundant oxygenates included 2-ethyl-1-hexanol (mean=175 pptv) and two ubiquitous ketones (geranyl acetone and 6-methyl-5-hepten-2-one) with average mixing ratios of 123 and 28 pptv, respectively. Air mass back trajectories indicated higher levels of the oxygenates when air flow was off the land (easterly continental) rather than from the ocean, although the opposite was observed for the n-alkanes. Mixing ratios of the n-alkanes (>C12) were significantly higher in the seaweed enclosure air than in ambient air, suggesting seaweed to be a source of long chain n-alkanes. Oxygenates, however, did not show a significant difference between enclosure and ambient air. Unlike studies carried out in the vicinity of woodlands, no monoterpenes or sesquiterpenes were detected in this study.
Keywords: Marine air; n-Alkanes; Oxygenates; Seaweed enclosures;

Kováts retention indices determined on four different capillary columns (OV-1, HP-50, DB-210 and HP-Innowax) were correlated with molecular structural parameters calculated by a semiempirical quantum-chemical method PM3. Multivariate techniques: principal component analysis and cluster analysis were applied to extract the data structure. Multiple linear regression was made in forward stepwise manner to select suitable variables in the model. Basic correlations were found between the retention indices on different columns and the molecular surface, energies of highest occupied and lowest unoccupied molecular orbitals {E(HOMO) and E(LUMO)}, polarizability, and dipole moments. These correlations provide insights into the mechanism of chromatographic retention on a molecular level. They support the view: the more polar is the stationary phase, the greater is the effect of the polarity (polarizability and dipole moment) of solute molecules on the retention phenomena.
Keywords: Gas chromatography; Kováts retention indices; Semiempirical quantum-chemical calculations; Aldehydes; Ketones; Molecular descriptors;

Sucrose effect on reversed-phase liquid chromatography solute retention by Eric Peyrin; Yves Claude Guillaume; Catherine Grosset; Annick Villet; Anne Ravel; Josette Alary (83-88).
The reversed-phase liquid chromatography retention of a series of benzoate ester molecules was investigated over a wide range of sucrose concentrations (c) 0.01–0.8 M using a C18 as the stationary phase and a methanol–water mixture with high organic fraction (60/40, v/v) as the mobile phase. A theoretical treatment was developed to investigate the effect of sucrose molecules on the equilibrium between the solutes and the C18 phase and the methanol–water medium, respectively. This was found to be adequate to accurately describe the benzoate ester retention behavior when c varied. It was expected that the addition of sucrose was responsible for two main opposite contributions to solute retention, (i) a net interaction between the solute and the modifier in the mobile phase determining a decrease in k′ values with c up to 0.2 M; and (ii) an increase in the solute affinity for the C18 stationary phase due to the salting-out effect governing a retention increase above 0.2 M. Thermodynamic parameter variations were calculated using van’t Hoff plots and discussed in relation to this retention model to confirm the respective effects of the modifier on the solute affinity towards the two phases.
Keywords: Sucrose; Reversed-phase liquid chromatography; Benzoate ester;

Properties of 4-(1′-n-tridecyl)pyridine N-oxide in the extraction and polymer inclusion membrane transport of Cr(VI) by Barbara Wionczyk; Wies aw Apostoluk; Krystyna Prochaska; Cezary Koz owski (89-101).
The N-oxide of 4-(1′-n-tridecyl)pyridine (TDPNO) is a novel agent which could be used for the separation of Cr(VI) from aqueous solutions of sulphuric acid. The distribution constants (K D) of TDPNO in the systems: toluene/0.5 M (Na, H)2SO4 and toluene-n-heptane (3:1) mixture/0.5 M (Na, H)2SO4, were found to be 2350±30 and 2180±20, respectively. The protonation constant of TDPNO (K H=12.0±0.1) was also determined. The interfacial activity of TDPNO in the systems hydrocarbon/water was found to be strongly dependent upon the Lewis basicity of hydrocarbons. The chromium(VI) extraction and transport with TDPNO in the CTA-based polymer inclusion membrane system were found to be strongly dependent upon the concentration of sulphuric acid in the aqueous and/or source phase, respectively. The complex L·H2CrO4, where L stands for TDPNO, was found to occur in the organic phase and/or at the source phase/membrane phase boundary.
Keywords: Chromium(VI); 4-(1′-n-Tridecyl)pyridine; Sulphuric acid;

The partition coefficients (K p) between lipid bilayers of dimyristoyl-l-α-phosphatidylcholine (DMPC) unilamellar liposomes and water were calculated for four drugs, chlordiazepoxide (a benzodiazepine), isoniazid and rifampicin (tuberculostatic drugs) and griseofulvin (an antifungal antibiotic), using spectrophotometric data and two different approaches. In one, spectrophotometric data were obtained in liposome suspensions and the values of K p were determined from second derivative intensities. In the other, the aqueous and lipid phases were separated by filtering through a Centricon filter unit prior to spectrophotometric determination of drug concentration in each phase. Both methods provide precise and accurate values for the partition coefficient of the drugs in water (Hepes)/DMPC media. None of them presents a clear advantage in the total time needed for the determinations, but for drugs which absorb near or below 275 nm, the need to eliminate liposome scattering may favour the phase separation method.
Keywords: Partition coefficient; Unilamellar liposomes; DMPC; Derivative spectrophotometry;

The solid phase microextraction (SPME) associated with microwave assisted extraction (MAE) for organochlorine pesticides (OCPs) in medicinal plants were studied. The influence of SPME extraction time, desorption time and temperature, and gas chromatography (GC) inlet conditions for the SPME fiber coated with poly(dimethylsiloxane) (PDMS) were investigated. Extraction time of 90 min, desorption time of 2 min and desorption temperature of 270°C were selected for SPME. Heating time of 10 min and heating power of 80% were the optimum conditions for MAE. Three different commonly used medicinal plants were tested including atractylodis rhizoma, glycyrrhizae radix, and poria. The associated SPME and MAE using water as the extracting solvent shows good results for the medicinal plants. The method detection limits were below 0.13 ng/g using GC electron capture detection. The reproducibility of the technique was less than 24% R.S.D.
Keywords: Organochlorine pesticide; Medicinal plants; Microwave assisted extraction; Solid phase microextraction; GC/ECD;

Removal of heavy metals in industrial wastewaters by ion-exchanger grafted textiles by Stella Lacour; Jean-Claude Bollinger; Bernard Serpaud; Pierre Chantron; Richard Arcos (121-132).
A special class of grafted textiles was studied in order to remove heavy metals from industrial wastewaters. Three cation-exchanger textiles (CET) were tested in a batch reactor, each carrying carboxylate (RCOO, Na+), sulfonate (RSO3 , Na+) or phosphate (ROPO3 2−, 2Na+) functional groups. The study of their behaviour towards Cu(II) and Cd(II) was carried out as a function of time (exchange kinetics) and at equilibrium with increasing metal concentrations (exchange isotherms). After determining the exchange capacities and selectivity coefficients of CET, the influence of different parameters (the counter-ion and functional group nature, the metal concentration, the presence of different competitors in the solution) on the removal of Cu(II) and Cd(II) was shown. The optimal use conditions of CET were therefore well defined and compared with those of conventional resins. Finally, desorption studies were performed with various regenerating solutions in order to determine the best conditions for textile regeneration and an optimal heavy metal concentration. These cation-exchanger textiles offer an interesting alternative for water treatment by ion-exchange technique.
Keywords: Grafted textiles; Ion-exchange; Industrial water treatment; Heavy metal removal; Desorption;

A study has been carried out on the separation of fission products from spent pressurized water reactor (PWR) fuels and their quantitative determination using inductively coupled plasma atomic emission spectrometry (ICP-AES). Plutonium and uranium were separated from fission products using anion exchange and tri-n-butylphosphate (TBP) extraction chromatography, respectively. Americium was separated and fission products such as Sr, Ba, Cd, La, Ce, Pr, Nd, Sm, Eu, Gd and Y were quantitatively recovered using di(2-ethylhexyl)phosphoric acid (HDEHP) extraction chromatography. An ICP-AES/shielding system, which was specially designed and built for the analysis of radioactive materials, was employed and the analytical precision for all metal elements studied was found to be <5%. Three spent PWR fuels whose burnup rates were between 15,000 and 35,000 MWd/MTU were analysed and then the relation between the burnup and the quantity of the fission products was compared to that calculated by burnup code, ORIGEN 2.
Keywords: Spent PWR fuels; Fission products; Anion exchange; TBP; HDEHP; Extraction chromatography; ICP-AES/shielding system;

Thickness-shear mode acoustic sensor for atrazine using molecularly imprinted polymer as recognition element by Chunhua Luo; Mengqin Liu; Yunchun Mo; Jingnian Qu; Yonglan Feng (143-148).
A new thickness-shear mode (TSM) acoustic sensor for the determination of atrazine was fabricated using a molecularly imprinted polymer (MIP) as recognition element. The influence of functional monomers on sensor response was investigated. The experiment conditions such as pH and the amount of coating were optimized. The sensor showed high sensitivity and selectivity to the template atrazine. At the range of concentrations detected, the relationship between the frequency shift (−Δf) and log(C) was obtained with a polynomial fitting programme. The determination limit was 2.0×10−6  mol/l. This method seems to be applicable for the development of mass sensor, combining the advantages of both biological receptors and synthetic imprinted polymers.
Keywords: TSM acoustic sensor; Atrazine; Molecularly imprinted polymer; Recognition element;

The residual hydration number of the metal ion in the 1,10-phenanthroline adducts of tris[1,1,1-trifluoro-5,5′-dimethyl-2,4-hexanedionato]lanthanoids in chloroform has been determined by coulometric Karl–Fischer titration and also by the luminescence lifetime of europium(III) in the complex. The residual hydration number was essentially zero for all lanthanoids across the series. This data and the hydration number of the lanthanoids(III) complexed with the β-diketone can be used to explain the trend of the variation of the formation constants of the adducts across the lanthanoid series.
Keywords: Hydration number; Lanthanoids(III); β-Diketonato chelates; 1,10-Phenanthroline; Organic solvents; Pivaloyltrifluoroacetone;