Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Analytical and Bioanalytical Chemistry (v.374, #1)
No Title by J. van Staden; Raluca I. Stefan (pp. 3-12).
The need to measure several quantities rapidly in the same sample has prompted the development of automated methods of analysis that in both the continuous and discontinuous modes offer the possibility of simultaneous determinations. The application of pH gradients and differential kinetic determinations dominate the simultaneous determination of two or more closely related species in mixtures without prior separation. Various options enable use of kinetic-based measurements for the simultaneous determination of different analytes in flow systems. Some possible general reactions are given and discussed. The scope of sequential injection kinetic analysis is illustrated with examples.
Keywords: Kinetic Sequential injection analysis Simultaneous analyses
No Title by Lucian Copolovici; Ioan Baldea (pp. 13-16).
A kinetic method for the determination of aromatic amines is reported. The method involves the formation of an azo dye between 1-(4-hydroxy-6-methylpyrimidin-2-yl)-3-methylpyrazolin-5-one and a diazonium salt formed from the amine in the presence of nitrite in weakly acidic media. The reaction is monitored via the initial rate of change of the absorbance of the azo dye at 420 nm, because this is proportional to the aniline concentration.The optimum acidity and concentration of reagents were established. The concentration ranges for which the calibration lines are linear are quite large. Detection limits were estimated. The effect of several metal ions usually present in real samples, e.g. waste water, was examined to assess interference.
Keywords: Kinetic methods Aromatic amines Azo dye
No Title by A. Rustoiu-Csavdari; S. Bâldea; D. Mihai (pp. 17-24).
A kinetic method is presented to determine micro-molar amounts of Pb(II) from various river and wastewater samples, in the presence of trace copper. The procedure is based on the catalytic effect of both species on the oxidation of mercaptosuccinic acid by chromate in acidic media. The extent of the reaction is followed spectrophotometrically at 420 nm and pseudo-first-order rate coefficients of the rate-determining step are determined as a function of catalyst concentrations. The optimum operating conditions (ionic strength, temperature, and concentration of reagents) regarding sensitivity towards lead were established. Interference by several ionic species has been studied. The effect of Fe(III), the only severe interferent, is suppressed by complexation with 1,10-phenantroline. The bi-component calibration model employs an artificial neural network to compute the Pb(II) concentration from a k obsd value and the a priori-known Cu(II) concentration of the sample. Working concentration ranges are 20–2160 µg L–1 for Pb(II) and 80–650 µg L–1 for Cu(II), respectively. Detection limits are 20 µg L–1 Pb(II) and 80 µg L–1 Cu(II), respectively. The relative standard deviations (3 measurements) for four different testing points are lower than 2.5%. The method was applied to samples of river and wastewater of the mining region of Baia-Mare, Northern Romania. The results were compared to those obtained by an officially standardized AAS method. Good agreement was achieved. The method is inexpensive, fairly rapid, and sensitive. Its working range covers the exact range of concentrations usually encountered in the mentioned geographic area.
Keywords: Kinetic catalytic method Spectrophotometry Pb(II) and Cu(II) determination Water analysis Bi-component calibration Artificial neural networks
No Title by Alina Avramescu; Silvana Andreescu; Thierry Noguer; Camelia Bala; Daniel Andreescu; Jean-Louis Marty (pp. 25-32).
Graphite electrodes fabricated by screen-printing have been used as amperometric detectors in biosensors based on NAD+-dependent dehydrogenases, tyrosinase, or genetically modified acetylcholinesterases. The mono-enzyme sensors have been optimized as disposable or reusable devices for detection of a variety of substrates important in the food industry (D-lactic acid, L-lactic acid, acetaldehyde) or in environmental pollution control (phenols and dithiocarbamate, carbamate and organophosphorus pesticides). The sensors were prepared in four configurations differing in enzyme confinement, enzyme immobilization and location of the immobilization agent in the biosensor assembly. Tests on real samples have been performed with the biosensors; D-lactic acid and acetaldehyde have been detected in wine and phenols in air.
Keywords: Screen-printing Graphite ink Configuration Mono-enzyme sensors
No Title by H. Iturriaga; J. Coello; S. Maspoch; M. Porcel (pp. 33-38).
A kinetic–spectrophotometric method for the determination of theophylline, dyphylline and proxyphylline, based on their azo coupling reaction with the diazonium ion of sulfanilic acid after a treatment with alkali, is proposed. The absorbance is recorded from 340 to 600 nm every second during reaction for 90 s, and calibration is performed by partial least-squares regression, using first derivative spectra values. Mixtures containing 2.5–13 µg mL–1 dyphylline and proxyphylline, and 2–9 µg mL–1 theophylline were successfully resolved with root mean squared errors of prediction (RMSEP) of 0.4, 0.3, and 0.2 for dyphylline, proxyphylline, and theophylline, respectively. The proposed method was satisfactorily applied to the determination of the three compounds in a commercially available pharmaceutical preparation and provided results similar to those obtained by HPLC.
No Title by Silvana Andreescu; Alina Avramescu; Camelia Bala; Vasile Magearu; Jean-Louis Marty (pp. 39-45).
Two-enzyme systems based on acetylcholinesterase (AChE) – a mono-enzyme system based on AChE, with p-aminophenyl acetate as substrate, and a bi-enzyme system based on AChE and tyrosinase, with phenyl acetate as substrate – have been studied for detection of organophosphate insecticides. The analytical performance and detection limits for determination of the pesticides were compared for the two AChE configurations. The enzyme loading, pH, and applied potential of the bi-enzyme system were optimised. When phenyl acetate was used as substrate for AChE activity the phenol generated by enzymatic hydrolysis was determined with a second enzyme, tyrosinase. Amperometric measurements were performed at 100 mV and –150 mV relative to the Ag/AgCl reference electrode for the mono-enzyme and bi-enzyme systems. Screen-printed sensors were used to detect the organophosphorus pesticides paraoxon and chlorpyrifos ethyl oxon; the detection limits achieved with phenyl acetate as substrate were 5.2×10–3 mg L–1 and 0.56×10–3 mg L–1, respectively.
Keywords: Substrates of acetylcholinesterase Tyrosinase Insecticides Inhibition Screen-printed biosensor
No Title by Z. Moldovan; L. Alexandrescu (pp. 46-50).
A method for the determination of phenyl-β-naphthylamine (PBN) in ternary mixtures by second-derivative spectrophotometry is described. The procedure works without any separation step of PBN from the other polymer additives. By applying the second-derivative spectrophotometry, Beer's law was valid over the range 0.25–10 µg mL–1. The proposed method has been applied to the determination PBN in synthetic ternary mixtures and rubber samples. A comparative study of the results obtained using the second and the third-derivative spectrophotometric methods is presented and evaluated. The derivative spectrophotometric method indicated that the amount of PBN found after extraction from the rubber samples was 0.97±0.02 g/100 g of sample.
Keywords: Phenyl-β-naphthylamine Antioxidant Rubber mixture Derivative spectrophotometry
Determination of para-aminobenzoic acid, a degradation product of procaine hydrochloride, by zero-crossing first-derivative spectrometry by Irinel Badea; Dana Moja; Luminita Vladescu (pp. 51-53).
A first derivative spectrometric method has been developed for the determination of the para-aminobenzoic acid (PABA), a related substance and degradation product of the local anesthetic procaine hydrochloride (PH). The wavelength selected for the determination of para-aminobenzoic acid in the presence of procaine was 290 nm. At this wavelength the calibration graphs relating the amplitude of the signals to the concentration of para-aminobenzoic acid were linear up to 10 mg L–1. The detection limit of para-aminobenzoic acid was 0.70 mg L–1. The method is simple and rapid and does not require preliminary treatment of the sample. The method was validated.
Keywords: Procaine para-Aminobenzoic acid Derivative spectrometry
No Title by Jane Goh; Richard W. Loo; Richard A. McAloney; Cynthia M. Goh (pp. 54-56).
The principles of diffraction are utilized to enable the simultaneous detection of multiple analytes in solution, forming the basis of a multi-analyte sensor. Probe molecules are immobilized on a substrate such that each type of molecule defines a specific pattern within the same region of substrate. The binding of a target molecule to its complementary probe is heralded by a characteristic diffraction image. This principle is demonstrated using antibody conjugates.
Keywords: Biosensor Diffraction Immunoassay Micro-contact printing Multi-analyte
No Title by T. Guerlavais; A. Meyer; F. Debart; J.-L. Imbach; F. Morvan; J.-J. Vasseur (pp. 57-63).
MALDI–TOF mass spectrometry has been used to characterize solid-supported oligonucleotides containing natural and non-natural and non-nucleoside moieties and a variety of internucleosidic linkages including phosphate and phosphite triesters and H-phosphonate diesters. This technique was used to follow the reactions involved in oligonucleotide synthesis; this enabled direct control of the elongation and optimization of the coupling process.
Keywords: MALDI–TOF MS Oligonucleotides Analogs Solid-phase synthesis
No Title by Xing-Fang Li; Mingsheng Ma; Yun K. Tam (pp. 64-68).
A 2-cm cartridge has been used for separation before electrospray mass spectrometric analysis of pharmaceutical compounds in cell culture media, alleviating the need for sample extraction and desalting procedures. Nine representative pharmaceuticals listed in the biopharmaceutical classification system (BCS) were chosen as the candidate compounds and Hank's balanced salt solution with Hepes buffer (HBSS–Hepes buffer) was used as the cell-culture medium in an effort to study permeability of chemicals through cell monolayers. Effects of several conditions, e.g. pH and buffer concentration in the mobile phase, flow rate, and temperature on separation efficiency were examined. The nine pharmaceuticals were separated within 2 min by use of a 2-cm C8 cartridge. Relative standard deviations (RSD) from repeated analysis within the same day or over five days were 0.03–0.2% for retention times and 0.6–5.3% for peak areas; antipyrine was used as internal standard. Calibration curves based on peak-area measurements were linear over the range 0.1–20 µmol L–1. The HBSS–Hepes buffer did not interfere with separation and detection; identical separation and peak intensity were obtained when the samples were separately prepared in distilled water or in the culture medium.
Keywords: Cartridge separation Electrospray mass spectrometry Pharmaceuticals Fast analysis
No Title by Thuvan Nguyen; Zeev Rosenzweig (pp. 69-74).
This paper describes the preparation and characterization of calcium ion sensitive fluorescent liposomes and their application for the determination of calcium ions in aqueous samples. Calmodulin (CaM), a calcium ion-binding protein labeled with the fluorophore Alexa-488 is embedded in the membrane of unilamellar liposomes. Upon calcium ion binding, calmodulin undergoes a conformational change that exposes its hydrophobic core and affects the fluorescence intensity of the attached fluorophore. Characterization studies of Alexa-CaM-containing liposomes reveal that embedding calmodulin molecules in the bilayer membrane of liposomes extends the lifetime of the calcium ion binding activity of calmodulin by about fourfold compared to the lifetime of its calcium-binding activity in free solution. Moreover, the calcium ion response of Alexa-CaM-containing liposomes is about threefold higher than the calcium ion response of Alexa-CaM in solution. The improvement in the calcium ion detection properties is attributed to the interaction between calmodulin, a membranal protein, and the hydrophobic phospholipids of the liposomes. The analytical properties of the calcium ion sensitive fluorescent liposomes are discussed.
Keywords: Calcium ion detection Fluorescence Calmodulin
No Title by Masanobu Mori; Wenzhi Hu; Kiyoshi Hasebe; Shunitz Tanaka; Kazuhiko Tanaka (pp. 75-79).
With conventional capillary electrophoresis (CE), it was difficult to directly analyze samples containing proteins as a result of the irreversible adsorption of proteins onto the inner surface of the capillary column. This difficulty, however, was completely overcome by adding N-dodecylphosphocholine (DPC, a phosphobetaine-type zwitterionic surfactant) to the background electrolyte (BGE). DPC made two essential contributions to the determination of common inorganic cations in the protein-containing samples: protein adsorption onto the capillary walls was completely avoided, and the resolution of the analyte cations was essentially improved. The optimal BGE for analysis of biological samples was found to be 5 mM DPC, 5 mM copper(II) acetate/10 mM ethylenediamine (pH 8). The detection limits (signal-to-noise ratio =3 and UV at 215 nm) of sodium, potassium, calcium, magnesium, and ammonium ions were 25, 31, 24, 45, and 60 µM, respectively. These five species of the common inorganic cations in human saliva samples were detected successfully within 2 min by the proposed system with direct sample injection.
Keywords: Zwitterionic surfactant Capillary electrophoresis Human saliva Alkali and alkaline earth metal ions Ammonium ion
No Title by Joachim König; Roland Grasser; Heather Pikor; Kurt Vogel (pp. 80-87).
A simple, robust and highly reproducible method for the determination of xylanase, β-glucanase, and cellulase in commercial feed enzyme preparations is described. The method is based on measurement of reducing moieties released by the enzymes from arabinoxylan, β-glucan, or carboxymethylcellulose (CMC) and is independent of enzyme standards.
Keywords: Xylanase, β-glucanase and celulase activity Linear kinetics Substrate dependence, ring test of method
No Title by Jerry W. King; Zhouyao Zhang (pp. 88-92).
Supercritical fluid carbon dioxide (SC-CO2) has been used to dissolve derivatizing agents (e.g. heptafluorobutyric anhydride, HFBA, and pyridine), which also act as a modifier in the fluid phase, for simultaneous extraction and derivatization of carbamates from the sample matrix. The derivatized carbamate pesticides (carbaryl, 3-hydroxycarbofuran, carbofuran, aldicarb, methiocarb) were then analyzed by GC–ECD or GC–MS with excellent sensitivity. Extraction and conversion of the carbamates was complete, as indicated by HPLC with post-column hydrolysis and o-phthalaldehyde derivatization then fluorescence detection. GC-MS (ion trap) was also used to confirm the formation of the carbamate derivatives. Compared with the same HFBA reaction in an organic solvent the derivatization reaction time was considerably shorter in SC-CO2. The described approach, combining both extraction and derivatization, simplifies the analysis of carbamate pesticides and eliminates the use of organic solvents associated with the derivatization step.
Keywords: Carbamate Derivatization Extraction Pesticide Supercritical fluid
No Title by Q. Zhang; X. Liang; J. Chen; P. Lu; A. Yediler; A. Kettrup (pp. 93-102).
A method has been developed for peak identification of PCBs in GC with ECD detection under different temperature programs and isothermal conditions on two commonly used columns (DB-5 and DB-1701). This was achieved by means of accurate calibration of retention times based on the concept of the relative retention index P i and retention times of the selected PCB internal standards. The P i was calculated from the predicted retention times with the database of the retention parameters (A, B) and the migration equations. Through comparison of the calibrated and experimental retention times of PCBs in technical samples, it was shown that the developed method was effective for correct PCB comprehensive, quantitative, congener-specific (CQCS) analyses.
Keywords: Polychlorinated biphenyls (PCBs) Identification Chromatography with ECD
No Title by A. Filgueiras; I. Lavilla; C. Bendicho (pp. 103-108).
A single extraction method based on the reagents employed in the SM&T (standards, measurement and testing programme) sequential extraction scheme for partitioning of Cd, Cr, Cu, Ni, and Pb in sediments has been developed. Small-scale extractions adapted to electrothermal atomic absorption spectrometric determinations (i.e. 25 mg mass in 1 mL extractant) have been used for the first time in conjunction with selective reagents using conventional operating conditions (i.e. conductive heating, magnetic stirring) or ultrasound-assisted extraction. Small-scale slurry preparations were implemented for determination of the residual/total metal content. The methodology developed enabled drastic reduction of extraction times, yielding extractable contents in accordance with those obtained by application of the conventional SM&T method, which can be regarded as a standard method. An important saving in the amount of sample and reagents is also achieved with small-scale extractions. Homogeneity of sediments at the mg level proved acceptable – precision was similar for between-batch and within-batch measurements. Method development was performed with CRM BCR 601 lake sediment for which extractable amounts of several metals are known. An application to a "real-world" sediment is also presented.
Keywords: Small-scale extractions SM&T scheme Cu, Cr, Cd, Pb, Ni Ultrasonic treatment Sediments
No Title by L. Kleiber; H. Fink; R. Niessner; U. Panne (pp. 109-114).
The potential of laser ablation inductively coupled mass spectrometry (LA-ICP-MS) was investigated for the inorganic characterization of different coal samples pressed into pellets. Reference analysis was performed by microwave-assisted digestion of the ground samples followed by ICP-MS analysis of the resulting solutions. Two different laser ablation sampling procedures were compared. For continuous sampling, three sites of the pellet were sampled for approximately one minute, whereas for sequential sampling 15 sites were sampled for two seconds, respectively. The qualitative results of the two procedures were equivalent, but continuous sampling allowed faster analysis and better precision (RSD about 10%) than sequential sampling (RSD 10–20%). Different normalization procedures with internal and extrinsic standards were investigated and allowed a quantitative determination of Al, Ti, Zn, Ni, and V with measurement uncertainties below 10% and Fe, Si, and Sn with measurement uncertainties below 20%.
Keywords: Laser ablation ICP-MS Coal Normalization
No Title by M. Baranguan; F. Laborda; J. Castillo (pp. 115-119).
A method is proposed for the determination of lead by generation of its hydride and detection by quartz-tube AAS using a reagent injection FIA system based on the injection of sodium tetrahydroborate. Lead hydride generation was carried out using a combination of 0.5 M nitric acid, 10% m/v hydrogen peroxide and 10% m/v sodium tetrahydroborate. The characteristic concentration obtained was 3.1 ng mL–1 and the detection limit was 2.6 ng mL–1 for an injected volume of 0.125 mL of tetrahydroborate.
Keywords: Reagent injection FIA Plumbane Quartz-tube AAS Hair analysis
No Title by J. González-Rodríguez; P. Pérez-Juan; M. Luque de Castro (pp. 120-125).
An easily automatable sequential flow-injection–pervaporation method is proposed for the photometric determination of methanol and iron in vinegar. The method is based on separation of the methanol from the sample matrix by pervaporation followed by its oxidation to formaldehyde with permanganate, decolouration of the latter with S2O5 2–, and subsequent reaction of formaldehyde with p-rosaniline to yield a violet reaction product with maximum absorption at 567 nm. Iron is determined by an existing method based on reaction with thiocyanate in acidic medium and monitoring at 508 nm. After optimisation by either the univariate or multivariate approaches, as required, the linear range was established for methanol (4–1000 mg L–1) and iron (0.18–20 mg L–1). The proposed method was then compared with reference methods for methanol and iron in terms of repeatability (2.452 mg L–1 and 0.245 mg L–1, respectively), reproducibility (4.435 mg L–1 and 0.356 mg L–1, respectively), detection limit (LOD=82 and 0.234 mg L–1, respectively), and traceability. The throughput was nine samples per hour.
Keywords: Vinegar Pervaporation Flow injection Spectrophotometry Methanol Iron
No Title by Shu Chen; Zhi Zhang; Hua Yu (pp. 126-130).
Bismuth hydride gas was collected on-line and determined via a new flow injection-hydride generation collection-flame atomic absorption spectrometry system. The performance of the gas-liquid separator, hydride gas collection time, acidity of the sample solution, NaBH4 concentration, and the effects of concomitant interferents were investigated to optimize the conditions of this new method. Interferences from concomitant elements were investigated, and recoveries of 94.7–105.3% for 10 ng mL–1 Bi were obtained after the addition of 0.2% ascorbic acid-thiourea masking reagents. The sensitivity of this new method was one order of magnitude higher than the continuous flow-hydride generation-flame atomic absorption method with a detection limit of 0.25 ng mL–1 and a precision of 2.3%. The method was evaluated by determining trace bismuth in standard biological reference material human hair GBW07601, and the results were consistent with the certified value. The proposed method was then employed to determine trace bismuth in ten colored gelatin samples; recoveries of 94.2–105.8% were obtained.
Keywords: Hydride collection Gas-liquid separator Bismuth Atomic absorption spectrometry
No Title by C. Bruhn; F. Pino; V. Campos; J. Nóbrega (pp. 131-140).
A flow injection system with a pre-concentration minicolumn based on a chelating resin was coupled to a flame atomic absorption spectrometer. The focus of this work was the investigation of interference effects and the analytical applicability of the azo-immobilized 8-hydroxyquinoline on controlled-pore glass for the determination of Cr and Mn in mussel and non-fat milk powder. All studied concomitants affected the retention of Cr(III). These effects are probably related to the formation of hydroxo-complexes at the optimum pH range 9.0–10. The positive effect caused by Ca(II) was exploited to increase the retention of Cr(III) species and to improve the slope by 70%. The interferences on Mn(II) retention were less severe. The quantification of Cr and Mn was performed by standard additions. The proposed methodology was validated by analysis of three certified reference materials of mussels (Cr and Mn) and non-fat milk powder (Mn) with a mean relative percent error of <6.5% and mean relative standard deviation of <13%. Chromium and Mn were determined in typical Chilean mussels samples, and Mn was determined in non-fat milk powder samples. Results agreed at the 95% confidence level with those obtained by electrothermal atomic absorption spectrometry (ETAAS) using graphite furnace atomization. The method detection limits for a 30 s pre-concentration time were 0.9 and 1.1 µg L–1 for Mn, and 2.2 and 2.5 µg L–1 for Cr in acid digested solutions of mussel and non-fat milk, respectively. The methodology is simple, fast (sampling frequency 60–72 h–1), reliable, of low cost, and can be applied to the determination of traces of Cr (≥0.18 µg g–1) and Mn (≥0.6 µg g–1) in mussel samples, and Mn (≥0.37 µg g–1) in non-fat milk powder.
Keywords: On-line pre-concentration FI-FAAS Immobilized 8-hydroxyquinoline Chromium Manganese Mussels Non-fat milk powder
No Title by J. van Staden; Mulalo G. Mashamba; Raluca I. Stefan (pp. 141-144).
An on-line potentiometric sequential injection titration process analyser for the determination of acetic acid is proposed. A solution of 0.1 mol L–1 sodium chloride is used as carrier. Titration is achieved by aspirating acetic acid samples between two strong base-zone volumes into a holding coil and by channelling the stack of well-defined zones with flow reversal through a reaction coil to a potentiometric sensor where the peak widths were measured. A linear relationship between peak width and logarithm of the acid concentration was obtained in the range 1–9 g/100 mL. Vinegar samples were analysed without any sample pre-treatment. The method has a relative standard deviation of 0.4% with a sample frequency of 28 samples per hour. The results revealed good agreement between the proposed sequential injection and an automated batch titration method.
Keywords: Potentiometric sequential injection titration Acetic acid Sodium hydroxide Process analyser
No Title by Supalax Srijaranai; Rodjana Burakham; Tipwan Khammeng; Richard L. Deming (pp. 145-147).
The sequential simplex strategy has been used to optimize the mobile phase used for separation of inorganic anions by micellar chromatography on a C18-µBondapak column, with absorption detection at 230 nm. The amount of acetonitrile and the concentration of phosphate buffer (pH 6.0) were chosen for optimization. The optimum mobile phase was found to be 38% acetonitrile in 18.2 mmol L–1 phosphate buffer (pH 6.0) containing 10 mmol L–1 cetyltrimethylammonium bromide (CTAB); this optimum was achieved within seven experiments. The separation of the five anions (nitrite, nitrate, iodide, thiocyanate, and thiosulfate) was accomplished in 18 min.
Keywords: Simplex optimization Anion analysis Micellar chromatography
No Title by Tom Fricke; Jürgen Hamann; Müfit Bahadir; Burkhard König (pp. 148-154).
Competitive carrier-mediated co-extraction and co-transport of a variety of anions and their counter ions into an organic phase or through supported liquid hydrophobic membranes from aqueous mixtures of salts have been monitored by ion chromatography. The method enables rapid screening of the anion co-transport or co-extraction ability of new potential ionophores and carrier molecules.
Keywords: Ion chromatography Anion binding Ionophores Membrane transport
No Title by Waldemar Ternes; Edburga L. Krause (pp. 155-160).
A new analytical method for the determination of piperine and its isomers in egg yolk and albumen is described here. All four isomers were separated by HPLC and detected using UV, DAD and electrochemical detection. The absolute detection limit (UV detection, S/N=3) of a standard solution of piperine was 370 pg piperine. The correlation coefficients for the linear calibration graphs (concentration range: c=100 ng–10 µg piperine isomer/mL) are generally better than 0.996. The piperine isomers were characterized and identified by spectroscopy (MS, 1H-NMR, FT-IR). The method was successfully applied to the determination of piperine deposits in eggs (egg yolk and albumen) after feeding hens with piperine-spiked feed. The detection limit for piperine (24.8(±0.2) ng/g egg yolk and 37.9(±4.9) ng/g albumen) and the recoveries (70.3(±7.7)% (egg yolk) and 75.7(±1.9)% (albumen)) of piperine were determined.
Keywords: Piperine Isopiperine Chavicine Isochavicine HPLC Egg Blood
No Title by Lea Pallaroni; Christoph von Holst; Cecilia Eskilsson; Erland Björklund (pp. 161-166).
A microwave-assisted extraction (MAE) method has been developed for determination of zearalenone in wheat and corn by LC–MS with an atmospheric pressure chemical ionization interface (APCI). Matrix effects were minimized by use of matrix-matched standard curves for quantification of the analyte. The limit of quantification (LOQ) of the method was 30 ng g–1 in wheat and 20 ng g–1 in corn. The rapid LC–MS method enabled analysis of the extracts without clean-up, thereby reducing analyte losses, the time required for the analytical procedure, and costs. A factorial design approach was used to examine the effect on extraction efficiency of the main extraction conditions – time, temperature, and solvent. On the basis of results from statistical assessment extraction was performed with 1:1 (v/v) methanol–acetonitrile at 80 °C for 5 min. When these extraction conditions were applied to a wheat sample from a recently conducted international proficiency test, 92% (103 ng g–1) of the assigned zearalenone concentration (112 ng g–1) in the test material was obtained. This result was within the uncertainty (u) range of the assigned value of the test material (u=±15.8 ng g–1, α=0.05) thereby demonstrating the accuracy of the method was sufficient. The precision of the whole method was also confirmed to be adequate, because the observed relative standard deviation (RSD) of 12% (n=10) also fulfils the quality criteria recommended by European guidelines for in-house method validation.
Keywords: Zearalenone Microwave-assisted extraction Mycotoxin Liquid chromatography–mass spectrometry Food analysis
No Title by Barbara Muik; Andrea Edelmann; Bernhard Lendl; María Ayora-Cañada (pp. 167-172).
An automated method for measuring the primary amino acid concentration in wine fermentations by sequential injection analysis with spectrophotometric detection was developed. Isoindole-derivatives from the primary amino acid were formed by reaction with o-phthaldialdehyde and N-acetyl-L-cysteine and measured at 334 nm with respect to a baseline point at 700 nm to compensate the observed Schlieren effect. As the reaction kinetic was strongly matrix dependent the analytical readout at the final reaction equilibrium has been evaluated. Therefore four parallel reaction coils were included in the flow system to be capable of processing four samples simultaneously. Using isoleucine as the representative primary amino acid in wine fermentations a linear calibration curve from 2 to 10 mM isoleucine, corresponding to 28 to 140 mg nitrogen/L (N/L) was obtained. The coefficient of variation of the method was 1.5% at a throughput of 12 samples per hour. The developed method was successfully used to monitor two wine fermentations during alcoholic fermentation. The results were in agreement with an external reference method based on high performance liquid chromatography. A mean-t-test showed no significant differences between the two methods at a confidence level of 95%.
Keywords: Yeast assimilable nitrogen content Primary amino acids Fermentation monitoring Sequential injection analysis Wine analysis
No Title by Ermanno Vasca; Stefano Materazzi; Tonino Caruso; Osvaldo Milano; Cecilia Fontanella; Carla Manfredi (pp. 173-178).
An investigation on the complex formation equilibria between divalent metal ions Me (with Me=Mn, Co, Ni, Cu, Cd, and Pb) and phytic acid (H12L) is presented. Experiments were performed through a potentiometric methodology by measuring, at 25 °C, the proton and, in some cases (Cu2+, Cd2+, and Pb2+), also the metal ion activity at equilibrium in solutions containing, besides the metal and the ligand, 3 M NaClO4 as the ionic medium. Unhydrolyzed solutions of the metal ion at millimolar concentration levels were titrated with solutions of about 10 mM sodium phytate, until the formation of a solid phase took place (always at pH ≈2.5, except in the case of Cu2+, which formed soluble complexes up to pH ≈3.3). Coulometry was employed to produce very dilute solutions of either Cu2+, Cd2+, or Pb2+ of accurately known composition. The emf data were explained by assuming, in the acidity interval explored, the formation of the complexes of general stoichiometry MeH5L5– and Me2H3L5–. Coordination compounds in the solid state were also synthesized and characterized by elemental analysis, thermal analysis, and ICP spectroscopy. The solids had a general stoichiometry Me6H t LCl t ·x H2O, with the following t and x values for each metal investigated: Me (t; x) = Mn (4; 2); Co (4; 2); Ni (4; 2); Cu (2; 2.5); Zn (2; 1); Sn (6; 6).
Keywords: Phytate Metal complexes Potentiometric method Coulometric method Thermogravimetric method