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Analytica Chimica Acta (v.572, #1)

Editorial Board (pp. co1).

Contents (pp. v-vi).

Calendar of forthcoming meetings (pp. n1).

Editorial Board (pp. co1).

Calendar of forthcoming meetings (pp. n1).

Contents (pp. v-vi).

Novel potentiometric and optical silver ion-selective sensors with subnanomolar detection limits by Zsófia Szigeti; Adam Malon; Tamás Vigassy; Viktor Csokai; Alajos Grün; Katarzyna Wygladacz; Nan Ye; Chao Xu; Vincent J. Chebny; István Bitter; Rajendra Rathore; Eric Bakker; Ernö Pretsch (pp. 1-10).

Ten Ag⁺-selective ionophores have been characterized in terms of their potentiometric selectivities and complex formation constants in solvent polymeric membranes. The compounds with π-coordination show much weaker interactions than those with thioether or thiocarbamate groups as the coordinating sites. Long-term studies with the best ionophores show that the lower detection limit of the best Ag⁺ sensors can be maintained in the subnanomolar range for at least 1 month. The best ionophores have also been characterized in fluorescent microspheres. The so far best lower detection limits of 3×10⁻¹¹M (potentiometrically) and 2×10⁻¹¹M Ag⁺ (optically) are found with bridged thiacalixarenes.

Keywords: Ion-selective electrodes; Fluorescent microspheres; Silver sensors; Complex formation constants; Lower detection limit; Long-term stability

A disposable immunosensor for detection of 17β-estradiol in non-extracted bovine serum by G. Volpe; G. Fares; F. delli Quadri; R. Draisci; G. Ferretti; C. Marchiafava; D. Moscone; G. Palleschi (pp. 11-16).

This paper reports the assembly of a disposable immunosensor based on the direct competitive enzyme-linked immunosorbent assay (ELISA), for simple and fast measurement of 17β-estradiol (17β-E₂) in bovine serum, using screen-printed electrodes (SPEs) and a Palm-Sens portable electrochemical detector. The immunosensor strip was assembled immobilising, by passive adsorption, anti-rabbit IgG onto the surface of the working SPE electrode. After the interaction between anti-rabbit IgG and rabbit anti-17β-E₂ polyclonal antibodies (PAb), the competition was performed using 17β-estradiol–alkaline phosphatase conjugate (17β-E₂–AP) synthesised in our laboratory. The enzymatic substrate used for signal generation was 1-naphthylphosphate and its conversion to an electroactive product (1-naphthol) was measured using differential pulse voltammetry (DPV). To develop a prototype for field measurements, the entire competitive protocol has been optimised directly in a blank non-extracted bovine serum.According to the new EU criteria established by the Commission Decision 2002/657/EC for qualitative and quantitative screening methods, the detection capability (CCβ), was determined. The CCβ value resulted below the action limit (40pgmL⁻¹) fixed for 17β-E_2.Spiked and real samples were analysed using the electrochemical immunostrips obtaining precision values (relative standard deviation, R.S.D.%) ranging from 8.6 to 17.0% and a recovery ( R%) from 88.2 to 120.0%.Results obtained on real samples were confirmed by liquid chromatography coupled on-line with tandem mass spectrometry (LC-MS/MS) using an atmospheric pressure chemical ionisation (APCI) source and a heated nebulizer (HN) interface; this is the method currently used to confirm illegal hormone administration for regulatory purposes. The disposable immunosensor appears suitable as a screening tool for field analysis of bovine serum estradiol.

Keywords: 17β-Estradiol; Electrochemical disposable immunosensor; Non-extracted bovine serum

Electrochemical deposition of sol–gel films for enhanced chromium(VI) determination in aqueous solutions by Nathan A. Carrington; Li Yong; Zi-Ling Xue (pp. 17-24).

A pyridine-functionalized sol–gel film has been formed by electrodeposition at a glassy carbon electrode surface. When this protonated film is exposed to a Cr(VI) solution, the Cr(VI) anions are preconcentrated at the electrode surface. Using square wave voltammetry, the Cr(VI) species are reduced to Cr(III), and a peak current corresponding to this reduction is generated at 0.17V. The peak currents can be correlated with the Cr(VI) concentration. The functionalized sol–gel films demonstrated an enhanced sensitivity for Cr(VI) in aqueous solutions, providing a limit of detection at the low ppb level. Interference studies also displayed the high selectivity of the films for Cr(VI), and the system was able to tolerate a large excess of Cr(III) with no adverse affects. The reported electrodeposition method of film formation uses commercially available reagents and yields films quickly and reproducibly. The growth of these sol–gel films was monitored using an electrochemical quartz crystal microbalance (EQCM), and they were characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The reported work shows the promise of such an electrode for use in Cr(VI) sensing applications.

Keywords: Sol–gel; Chromium(VI); Electrodeposition

Electrochemical deposition of sol–gel films for enhanced chromium(VI) determination in aqueous solutions by Nathan A. Carrington; Li Yong; Zi-Ling Xue (pp. 17-24).

Keywords: Sol–gel; Chromium(VI); Electrodeposition

Preventing inhibition of tyrosinase with modified electrodes by Isıl Narlı; Senem Kiralp; Levent Toppare (pp. 25-31).

Wines, especially red wines, contain numerous biologically active compounds, the most important of which are polyphenols, whose nutritional importance is attributed to their antioxidant power. Because of this, the detection of the amount of phenolic compounds in red wines becomes extremely important. However, using free enzyme in the determination of phenolic compounds in wines cannot reflect the actual values since there are also naturally found inhibitors in red wines. In this study, benzoic acid, cinnamic acid, and sorbic acid were utilized to understand the behavior of immobilized polyphenol oxidase in the conducting polymer matrices toward inhibition. Cinnamic acid was found to be the most powerful inhibitor for both free and immobilized enzyme in copolymer matrix of poly(terephthalic acid bis-(2-thiophen-3-yl-ethyl) ester) (PTATE) with polypyrrole (PPy). In the case of immobilized enzyme in PPy matrix, it was observed that sorbic acid is a stronger inhibitor than cinnamic acid. The inhibitory effects of these inhibitors on PPO were compared with respect to both the structural differences of inhibitors and conducting polymer matrices.

Keywords: Enzyme; Tyrosinase; Biosensor; Inhibition; Immobilization; Wine

Preventing inhibition of tyrosinase with modified electrodes by Isıl Narlı; Senem Kiralp; Levent Toppare (pp. 25-31).

Keywords: Enzyme; Tyrosinase; Biosensor; Inhibition; Immobilization; Wine

Speciation analysis of selenium in natural water using square-wave voltammetry after preconcentration on activated carbon by Franco A. Bertolino; Angel A.J. Torriero; Eloy Salinas; Roberto Olsina; Luis D. Martinez; Julio Raba (pp. 32-38).

A simple, accurate, sensitive and selective method was described for rapid determination of ultra-trace quantities of selenium. Selenium(IV) was collected on activated carbon (AC) after reduction to elemental Se byl-ascorbic acid. The collected selenium was then dissolved by oxidation reaction with bromate in acidic media and was indirectly determined through the bromide formation using square-wave voltammetry (OSWV). The total amount of Se(IV) and Se(VI) was collected on AC after its reduction by hydrazine. Selenium in the range 0.01–20μgL⁻¹ could be determined by this method. The method was used to the determination of Se(IV) and Se(VI) in natural water with satisfactory results.

Keywords: Selenium; Activated carbon; Preconcentration; Square-wave voltammetry; Cyclic voltammetry; Natural water

Ultrasonic acoustic wave detection of single or capillary electrophoretically resolved underivatized amino acids by Wa Lok (Jacky) Chou; Paul C.H. Li (pp. 39-46).

Acoustic wave detection of various underivatized amino acids that were hydrodynamically introduced into and electrokinetically migrated along a capillary tube has been achieved. The detection principle is based on the measurement of the ultrasonic absorption and density change of the aqueous amino acid samples as they pass by the detection zone. Acoustic wave detection of underivatized leucine was obtained in the ultrasonic frequency range of 100kHz to 20MHz. This was accomplished by measuring the insertion loss from the vector ratio of the signal voltage to the source voltage obtained at the generating and receiving piezoelectric transducers. Linear concentration dependence of the insertion loss of underivatized leucine was established. The effects of capillary internal diameter, capillary geometry (square and circular), buffer concentration, buffer pH and acoustic wave frequency on the insertion loss were investigated. Subsequently, separations of underivatized amino acids (leucine/histidine and leucine/tryptophan) were performed under different buffer conditions and different capillary geometry.

Keywords: Acoustic wave detection; Ultrasonic absorption; Underivatized amino acids; Insertion loss; Capillary electrophoresis

Ultrasonic acoustic wave detection of single or capillary electrophoretically resolved underivatized amino acids by Wa Lok (Jacky) Chou; Paul C.H. Li (pp. 39-46).

Keywords: Acoustic wave detection; Ultrasonic absorption; Underivatized amino acids; Insertion loss; Capillary electrophoresis

Analysis of fatty acids in lung tissues using gas chromatography–mass spectrometry preceded by derivatization-solid-phase microextraction with a novel fiber by Dongmei Cha; Mingming Liu; Zhaorui Zeng; Dong’e Cheng; Guoqing Zhan (pp. 47-54).

In this article, a laboratory-made sol–gel derived fiber with butyl methacrylate/hydroxy-terminated silicone oil (BMA/OH-TSO) coating was first used for headspace solid-phase microextraction (HS-SPME) of medium and long chain fatty acids after derivatization and applied to the analysis of fatty acids in lung tissues by coupling to gas chromatography–mass spectrometry (GC–MS). The experimental parameters for derivatization, HS-SPME and desorption were optimized. Fatty acids in cancerous lung tissues from five patients with lung cancer were determined under the optimized conditions. Normal lung tissues from the same five patients were used as controls. This fiber showed higher extraction efficiency for fatty acids after derivatization when compared with commercial polydimethylsiloxane (PDMS) and polydimethylsiloxane–divinylbenzene (PDMS/DVB) fibers due to the three-dimensional network in the coating. The method presented in this paper showed satisfactory precision, accuracy, linearity and limits of detection (LODs). The relative standard deviation values were below 13.3% ( n=5) and the recoveries obtained ranged from 76.35% to 107.0%. The results obtained using the SPME method were also compared with those got by using liquid–liquid extraction (LLE) technique. It was found that the sensitivity could be enhanced by the SPME method. The analysis of the cancerous lung tissues and normal controls from five patients with lung cancer indicated that the main components of lung tissue were palmitic acid (C_16:0), stearic acid (C_18:0) and lignoceric acid (C_24:0). A comparison between the levels of the fatty acids in cancerous lung tissues and normal controls from the same a patient with lung cancer shows that most of the saturated fatty acids showed higher levels in cancerous lung tissues, while unsaturated fatty acids showed higher levels in normal controls on the whole.

Keywords: Fatty acids; Derivatization; Solid-phase microextraction; Gas chromatography–mass spectrometry; Lung tissue

On-line preconcentration and separation of Co, Ni and Cd via capillary microextraction on ordered mesoporous alumina coating and determination by inductively plasma mass spectrometry (ICP-MS) by Wenling Hu; Bin Hu; Zucheng Jiang (pp. 55-62).

In this paper, an ordered mesoporous alumina coating was prepared and applied to capillary microextraction (CME) of trace Co, Ni and Cd for the first time. The coated capillary was used for on-line coupling CME with inductively plasma mass spectrometry (ICP-MS) for the determination of trace metals of Co, Ni and Cd. The porous structure of Al₂O₃ coating was examined by SEM and TEM. The effects of the extraction parameters including pH, sample flow rate and volume, elution solution and interfering ions on the recovery of analytes have been investigated and optimized. Under the optimized conditions, the limits of detection were 0.33, 1.5 and 1.4ngL⁻¹ for Co, Ni and Cd, respectively, with a preconcentration factor of 10 times. The precisions for all investigated elements were 2.7, 4.1 and 2.5% ( c=0.05ngL⁻¹, n=7), for Co, Ni and Cd, respectively, and the sample frequency was 8h⁻¹.The proposed method was successfully applied for the analysis of trace metals in water, rice and urine samples with the recovery of 94–105%. In order to validate the proposed method, two certified reference materials of GBW 0913 human urine and NIES No.10-b rice flour were analyzed, and the determination values are in good agreement with the certified values. The ordered mesoporous Al₂O₃ coated capillary can be used more than 20 times without decreasing the extraction efficiency.

Keywords: Capillary microextraction; Inductively plasma mass spectrometry (ICP-MS); Ordered mesoporous Al; ₂; O; ₃; coating; Trace metals

A study of the analytical behaviour of selected synthetic and naturally occurring quinolines using electrospray ionisation ion trap mass spectrometry, liquid chromatography and gas chromatography and the construction of an appropriate database for quinoline characterisation by F. O’Donnell; V.N. Ramachandran; W.F. Smyth; C.J. Hack; E. Patton (pp. 63-76).

Mass spectral fragmentation of quinoline alkaloids of significance in plants has been investigated using electrospray ionisation ion trap mass spectrometry (ESI–MSⁿ) with a view to characterisation of molecules of unknown structure isolated from these natural sources. This investigation has led to the generation of an appropriate database incorporating data from ESI–MSⁿ and also from gas liquid chromatography (GLC) and liquid chromatography (HPLC) for these low molecular mass quinolines. This has been put to practical application in the identification of quinoline alkaloids in a plant extract. Thus, an acid extraction of the leaves of Choisya ternata containing such tertiary alkaloids was analysed by liquid chromatography–electrospray ionisation mass spectrometry (HPLC–ESI–MS) and the resulting behaviour of the quinolines was compared with that of the quinoline alkaloids in the database.

Keywords: Quinolines; Electrospray ionisation ion trap mass spectrometry; Fragmentation patterns; High performance liquid chromatography; Gas liquid chromatography; Quinoline database; Choisya ternata

Feasibility study on qualitative and quantitative analysis in tea by near infrared spectroscopy with multivariate calibration by Quansheng Chen; Jiewen Zhao; Haidong Zhang; Xinyu Wang (pp. 77-84).

This study attempted the feasibility to use near infrared (NIR) spectroscopy as a rapid analysis method to qualitative and quantitative assessment of the tea quality. NIR spectroscopy with soft independent modeling of class analogy (SIMCA) method was proposed to identify rapidly tea varieties in this paper. In the experiment, four tea varieties from Longjing, Biluochun, Qihong and Tieguanyin were studied. The better results were achieved following as: the identification rate equals to 90% only for Longjing in training set; 80% only for Biluochun in test set; while, the remaining equal to 100%. A partial least squares (PLS) algorithm is used to predict the content of caffeine and total polyphenols in tea. The models are calibrated by cross-validation and the best number of PLS factors was achieved according to the lowest root mean square error of cross-validation (RMSECV). The correlation coefficients and the root mean square error of prediction (RMSEP) in the test set were used as the evaluation parameters for the models as follows: R=0.9688, RMSEP=0.0836% for the caffeine; R=0.9299, RMSEP=1.1138% for total polyphenols. The overall results demonstrate that NIR spectroscopy with multivariate calibration could be successfully applied as a rapid method not only to identify the tea varieties but also to determine simultaneously some chemical compositions contents in tea.

Keywords: Near infrared (NIR) spectroscopy; Tea; Multivariate calibration; Soft independent modeling of class analogy (SIMCA); Partial least squares (PLS)

Feasibility study on qualitative and quantitative analysis in tea by near infrared spectroscopy with multivariate calibration by Quansheng Chen; Jiewen Zhao; Haidong Zhang; Xinyu Wang (pp. 77-84).

Keywords: Near infrared (NIR) spectroscopy; Tea; Multivariate calibration; Soft independent modeling of class analogy (SIMCA); Partial least squares (PLS)

The potential of Raman spectroscopy for characterisation of the fatty acid unsaturation of salmon by Nils Kristian Afseth; Jens Petter Wold; Vegard Herman Segtnan (pp. 85-92).

Raman spectroscopy has been evaluated for characterisation of the degree of fatty acid unsaturation (iodine value) of salmon ( Salmo salar). The Norwegian Quality Cuts from 50 salmon samples were obtained, and the samples provided an iodine value range of 147.8–170.0gI₂/100gfat, reflecting a normal variation of farmed salmon. Raman measurements were performed both on different spots of the intact salmon muscle, on ground salmon samples as well as on oil extracts, and partial least squares regression (PLSR) was utilised for calibration. The oil spectra provided better iodine value predictions than the other data sets, and a correlation coefficient of 0.87 with a root mean square error of cross-validation of 2.5gI₂/100gfat was achieved using only one PLSR component. The ground samples provided comparable results, but at least two PLSR components were needed. Higher prediction errors were obtained from Raman spectra of intact salmon muscle, and this may partly be explained by sampling uncertainties in the relation between Raman measurements and reference analysis. All PLSR models obtained were based on chemically sound regression coefficients, and thus information regarding fatty acid unsaturation is readily available from Raman spectra even in systems with high contents of protein and water. The accuracy, the robustness and the low complexity of the PLSR models obtained suggest Raman spectroscopy as a promising method for rapid in-process control of the degree of unsaturation in salmon samples.

Keywords: Raman spectroscopy; Salmon; Iodine value; Partial least squares regression; Sampling; In-process control

The potential of Raman spectroscopy for characterisation of the fatty acid unsaturation of salmon by Nils Kristian Afseth; Jens Petter Wold; Vegard Herman Segtnan (pp. 85-92).

Keywords: Raman spectroscopy; Salmon; Iodine value; Partial least squares regression; Sampling; In-process control

Improving the robustness of a partial least squares (PLS) model based on pure component selectivity analysis and range optimization: Case study for the analysis of an etching solution containing hydrogen peroxide by Youngbok Lee; Hoeil Chung; Mark A. Arnold (pp. 93-101).

Pure component selectivity analysis (PCSA) was successfully utilized to enhance the robustness of a partial least squares (PLS) model by examining the selectivity of a given component to other components. The samples used in this study were composed of NH₄OH, H₂O₂ and H₂O, a popular etchant solution in the electronic industry. Corresponding near-infrared (NIR) spectra (9000–7500cm⁻¹) were used to build PLS models. The selective determination of H₂O₂ without influences from NH₄OH and H₂O was a key issue since its molecular structure is similar to that of H₂O and NH₄OH also has a hydroxyl functional group. The best spectral ranges for the determination of NH₄OH and H₂O₂ were found with the use of moving window PLS (MW-PLS) and corresponding selectivity was examined by pure component selectivity analysis. The PLS calibration for NH₄OH was free from interferences from the other components due to the presence of its unique NH absorption bands. Since the spectral variation from H₂O₂ was broadly overlapping and much less distinct than that from NH₄OH, the selectivity and prediction performance for the H₂O₂ calibration were sensitively varied depending on the spectral ranges and number of factors used. PCSA, based on the comparison between regression vectors from PLS and the net analyte signal (NAS), was an effective method to prevent over-fitting of the H₂O₂ calibration. A robust H₂O₂ calibration model with minimal interferences from other components was developed. PCSA should be included as a standard method in PLS calibrations where prediction error only is the usual measure of performance.

Keywords: Near-infrared (NIR) spectroscopy; Pure component selectivity analysis (PCSA); Net analyte signal (NAS); Moving window partial least squares (PLS); Standard clean 1 (SC1) etching solution

Robustness study of a reversed-phase liquid chromatographic method for the analysis of carboxylic acids in industrial reaction mixtures by E. Destandau; J. Vial; A. Jardy; M.-C. Hennion; D. Bonnet; P. Lancelin (pp. 102-112).

The robustness study of the reversed-phase liquid chromatographic method developed for the quantitative analysis of carboxylic acids is a real asset to prepare method transfer because it provides an indication of its reliability during routine use. Indeed, it was possible to predict the consequences of small variations in operating conditions on the responses. The design of experiments approach was applied to model the effects and interactions of a high number of factors varying simultaneously with a limited number of runs. First we identified the factors which potentially affect the chromatographic responses used for carboxylic acids quantitation: detection wavelength ( λ), column temperature ( T), acetonitrile ratio in mobile phase (Me), duration of the plateau before the gradient ( L) and gradient slope ( S). Then we estimated the order of magnitude of realistic variations to assign factor levels. Finally a central composite design was carried out around the nominal conditions defined during method optimization. The statistical treatment of responses (retention factors, and concentrations) showed that the column temperature, the acetonitrile ratio in the mobile phase, the duration of the plateau before the gradient and the gradient slope were the most influent factors. The building of the robust domain from response-surfaces allowed us to give tolerance limits for the factors (216nm< λ<222nm, 49.3°C< T<51.4°C, 4.90%L<5.4min, 9%< S<11%) for which the performances of the method were maintained.

Keywords: Reversed-phase liquid chromatography; Carboxylic acids; Robustness study; Design of experiments; Response-surfaces

Development and validation of an analytical method for the determination of semicarbazide in fresh egg and in egg powder based on the use of liquid chromatography tandem mass spectrometry by Szilard Szilagyi; Beatriz de la Calle (pp. 113-120).

In this work the development of a method to determine semicarbazide (SEM) in fresh whole egg and in whole egg and egg white powders as those used in the food industry, by using LC–MS/MS is described. The method is based on a recently validated one for the determination of SEM in baby food. SEM is extracted from egg with 0.2molL⁻¹ hydrochloric acid and derivatised with 2-nitrobenzaldehyde. The extract is neutralised and purified by passing through a solid phase extraction (SPE) cartridge. The 2-nitrobenzaldehyde derivative is eluted with ethyl acetate. The eluate is evaporated to dryness and the residue re-dissolved in methanol:water mobile phase. SEM is determined by reversed-phase LC–MS/MS. The “in-house�? validation of this method has been performed taking into account the “ Harmonized guidelines for single-laboratory validation of methods of analysis�? (IUPAC Technical report) and the Commission Decision (2002/657/EC). The performance characteristics of the method were established by in-house validation procedures employing assays with standard solutions, sample blanks and spiked samples. Linearity, matrix effect, trueness, precision, selectivity, limits of detection and of quantification were determined. The fitness for purpose of this method was assessed based on its performance characteristics. LOD's of 0.15 and 0.4μgkg⁻¹ for whole fresh egg and industrial egg powders, respectively, were obtained. The LOQ for fresh whole egg was 0.2μgkg⁻¹ and for industrial egg powders 0.8μgkg⁻¹. Linear calibration curves were obtained in the ranges 1–100 and 0.8–400μgkg⁻¹ for fresh whole egg and the egg powders, respectively.

Keywords: Semicarbazide; Nitrofurazone; Nitrofurans; Egg; Liquid chromatography tandem mass spectrometry

In this work the development of a method to determine semicarbazide (SEM) in fresh whole egg and in whole egg and egg white powders as those used in the food industry, by using LC–MS/MS is described. The method is based on a recently validated one for the determination of SEM in baby food. SEM is extracted from egg with 0.2molL⁻¹ hydrochloric acid and derivatised with 2-nitrobenzaldehyde. The extract is neutralised and purified by passing through a solid phase extraction (SPE) cartridge. The 2-nitrobenzaldehyde derivative is eluted with ethyl acetate. The eluate is evaporated to dryness and the residue re-dissolved in methanol:water mobile phase. SEM is determined by reversed-phase LC–MS/MS. The “in-house” validation of this method has been performed taking into account the “ Harmonized guidelines for single-laboratory validation of methods of analysis” (IUPAC Technical report) and the Commission Decision (2002/657/EC). The performance characteristics of the method were established by in-house validation procedures employing assays with standard solutions, sample blanks and spiked samples. Linearity, matrix effect, trueness, precision, selectivity, limits of detection and of quantification were determined. The fitness for purpose of this method was assessed based on its performance characteristics. LOD's of 0.15 and 0.4μgkg⁻¹ for whole fresh egg and industrial egg powders, respectively, were obtained. The LOQ for fresh whole egg was 0.2μgkg⁻¹ and for industrial egg powders 0.8μgkg⁻¹. Linear calibration curves were obtained in the ranges 1–100 and 0.8–400μgkg⁻¹ for fresh whole egg and the egg powders, respectively.

Keywords: Semicarbazide; Nitrofurazone; Nitrofurans; Egg; Liquid chromatography tandem mass spectrometry

Method validation approach on the basis of a quadratic regression model by P. Steliopoulos; E. Stickel; H. Haas; S. Kranz (pp. 121-124).

A method validation approach that bases on a quadratic regression model in which two types of error are incorporated is presented and applied to an experimental data set. The validation approach enables the determination of analytical performance characteristics referred to in Commission Decision 2002/657/EC (i.e., repeatability, within-laboratory reproducibility, decision limit, detection capability).

Keywords: Method validation; 2002/657/EC; Quadratic regression model

Method validation approach on the basis of a quadratic regression model by P. Steliopoulos; E. Stickel; H. Haas; S. Kranz (pp. 121-124).

Keywords: Method validation; 2002/657/EC; Quadratic regression model

Common components and specific weights analysis: A tool for monitoring the molecular structure of semi-hard cheese throughout ripening by Romdhane Karoui; Éric Dufour; Josse De Baerdemaeker (pp. 125-133).

Twelve semi-hard (Raclette) cheeses, belonging to four brand products, namely A ( n=3), B ( n=3), C ( n=3) and D ( n=3), were produced during summer period and ripened at an industrial scale. Tryptophan, riboflavin and vitamin A fluorescence spectra were scanned on the 12 cheeses at 2, 30 and 60 days of ripening. The physico-chemical analyses were performed only at the end of the ripening stage (60 days). Common components and specific weights analysis (CCSWA) were applied on the four data tables. CCSWA showed that the common component 1 ( q₁), discriminating cheeses labelled A, B and C from those labelled D, expressed 94.4 and 59% of the inertia of vitamin A and tryptophan fluorescence spectra and a less amount for riboflavin fluorescence spectra and physico-chemical data (24.2 and 13.2%, respectively). Common component 3 ( q₃), differentiating between cheeses labelled B and those labelled A and C, explained 34.6 and 23.9% of the inertia of the physico-chemical data and tryptophan fluorescence spectra, respectively, and a tiny part of the inertia of riboflavin and vitamin A fluorescence spectra (3.2 and 0.7%, respectively). The CCSWA showed its ability to describe the overall information collected from fluorescence and physico-chemical data tables and to extract relevant information at the molecular level throughout ripening of the investigated semi-hard cheeses.

Keywords: Semi-hard cheese; Ripening; Tryptophan; Vitamin A; Riboflavin; Chemometrics

Synchronous-scan fluorescence as a selective detection method for sodium dodecylbenzene-sulfonate and pyrene in environmental samples by Xianli Liu; Shu Tao; Nansheng Deng; Yu Liu; Bingjun Meng; Bei Xue; Guanghong Liu (pp. 134-139).

Synchronous-scan fluorescence spectra of dodecylbenzene sulfonic acid sodium salt (SDBS) and pyrene in aqueous solution were studied. The concentration ranges of SDBS and pyrene in aqueous solutions were 0.01–10.00 and 0.001–0.050mgL⁻¹, respectively. The optimized wavelength differences (Δ λ) of 46–55 and 38nm were maintained between excitation and emission wavelengths for SDBS and pyrene, respectively, and they were found to be suitable for effective determination of SDBS and pyrene without mutual interferences; the peaks were observed at λ_ex 229–232nm (SDBS) and λ_ex 335nm (pyrene). Linear relationships between synchronous-scan fluorescence spectroscopy (SFS) intensity and concentration of SDBS or pyrene in aqueous solution (Milli-Q water, river water, and mucus of fish gills) were established. It was demonstrated that SFS method was effective for simultaneous analyses of SDBS and pyrene in mixed solution.

Keywords: Synchronous-scan fluorescence spectroscopy; Dodecylbenzene sulfonic acid sodium salt; Pyrene; Mixed solution; Analysis; Linear relationship

Enzymatic chemiluminescent assay of glucose by sequential-injection analysis with soluble enzyme and on-line sample dilution by Anastasios Economou; Polyxeni Panoutsou; Demetrius G. Themelis (pp. 140-147).

This work reports a sequential-injection analysis (SIA) method for the enzymatic assay of glucose with soluble glucose oxidase (GOD) and on-line sample dilution with chemiluminescence (CL) detection. A zone of sample was aspirated in the holding coil of the SIA manifold and, if necessary, was diluted on-line by means of an auxiliary dilution conduit. Then, a zone of GOD was aspirated adjacent to the sample zone and a stopped-flow period was applied to allow the enzymatic reaction to proceed with production of hydrogen peroxide. Then, zones of a catalyst (Co(II) solution) and alkaline luminol were aspirated into the holding coil. Finally, the flow was reversed and the stacked zones were sent to a flow-cell located in front of a photomultiplier tube (PMT) that monitored the CL intensity. The linear dynamic range was 1×10⁻⁵–1×10⁻³molL⁻¹ glucose, the coefficient of variation at 8×10⁻⁵molL⁻¹ of glucose was s_r=3.1% ( n=8), the limit of detection at the 3 σ level was c_L=1×10⁻⁶molL⁻¹ and the sampling frequency was 28h⁻¹. With on-line dilution by a factor of 1/200, the linear range could be extended up to 0.2molL⁻¹ glucose. The advantages of the proposed method are the simple manifold and instrumentation used, the scope for automated on-line dilution, the low consumption of sample and reagents and the elimination of enzyme immobilisation procedures. The method was applied to the analysis of commercial drinks and honey with percent relative errors in glucose determination in the range 100±6.1%.

Keywords: Glucose; Chemiluminescence; Sequential-injection analysis; Glucose oxidase; On-line sample dilution

Multi-pumping flow system for the determination of dissolved orthophosphate and dissolved organic phosphorus in wastewater samples by Carmen Pons; Ildikó V. Tóth; António O.S.S. Rangel; Rafael Forteza; Víctor Cerdà (pp. 148-154).

A multi-pumping flow system (MPFS) for the spectrophotometric determination of dissolved orthophosphate and dissolved organic phosphorus in wastewater samples is proposed. The determination of orthophosphate is based on the vanadomolybdate method. In-line ultraviolet photo-oxidation is employed to mineralise organic phosphorus to orthophosphate prior to detection. A solenoid valve allows the deviation of the flow towards the UV-lamp to carry out the determination of organic phosphorus.Calibration was found to be linear up to 20mgPL⁻¹, with a detection limit (3 s_b/ S) of 0.08mgPL⁻¹, an injection throughput of 75 injections h⁻¹ and a repeatability (R.S.D.) of 0.6% for the direct determination of orthophosphate. On the other hand, calibration graphs were linear up to 40mgPL⁻¹, with a detection limit (3 s_b/ S) of 0.5mgPL⁻¹, an injection throughput of 11 injections h⁻¹ and a repeatability (R.S.D.) inferior to 2.3% for the procedures involving UV photo-oxidation.

Keywords: Multi-pumping flow system; Orthophosphate; Organic phosphorus; UV photo-oxidation

Flow-injection spectrophotometric determination of reverse transcriptase inhibitors used for acquired immuno deficiency syndrome (AIDS) treatment by Antonio Checa; Ramon Oliver; Javier Saurina; Santiago Hernández-Cassou (pp. 155-164).

This paper describes a rapid method for the quantification of reverse transcriptase inhibitors in mixtures of therapeutic interest containing zidovudine, zalcitabine and nevirapine. The method is based on a pH-gradient flow-injection system with diode array detection and further data analysis using multivariate curve resolution. Data matrices of unknown samples mixtures have been analyzed simultaneously with those of standards and background via the construction of augmented data matrices. In this case, the spectral domain has been chosen for performing column-wise (i.e., wavelength-wise) matrix augmentation. The quantification is accomplished from the comparison of the analyte peaks resolved for unknown mixtures and standards, being peak areas the quantitative information to be correlated with the concentration in both calibration and prediction steps. The influence of background signal on the response is tackled through two main strategies involving modelling or subtraction. The potentiality of this method for the analysis of drugs in the presence of unknown interferences is demonstrated. Results obtained in the analysis of drug samples have proven the excellent performance of this method. Overall prediction errors in the quantification of two- and three-component mixtures are about 5–10%.

Keywords: Multivariate curve resolution method based on alternating least squares (MCR-ALS); Acquired immuno deficiency syndrome (AIDS) treatment; Reverse transcriptase inhibitors; Drug mixtures

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Analytica Chimica Acta (v.572, #1)

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Analytica Chimica Acta (v.572, #1)