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Analytica Chimica Acta (v.592, #2)

Contents (pp. iii).

Calendar of forthcoming meetings (pp. n3).

Molecular imprinted polymer-based chemiluminescence imaging sensor for the detection of trans-resveratrol by Li Wang; Zhujun Zhang (pp. 115-120).

Sensitive, rapid and inexpensive chemiluminescence (CL) imaging has been developed based on molecular imprinted polymer (MIP) sensing elements. Imprinted uniform microspheres were synthesized by precipitation polymerization. Microtiter plates (96 wells) were coated with polymer microspheres imprinted with trans-resveratrol, which were fixed in place using poly(vinyl alcohol) (PVA) as glue. The amount of polymer-bound trans-resveratrol was quantified using imidazole (IMZ)-catalyzed peroxyoxalate chemiluminescence (PO-CL) reaction. The light produced was then measured with a high-resolution CCD camera. Calibration curve corresponding to analyte concentration ranging from 0.3 to 25μgmL⁻¹ was obtained with a limit of detection 0.1μgmL⁻¹. These results showed that the MIP-based CL imaging sensor can become a useful analytical tool for quick simultaneous detection of trans-resveratrol in a large number of real samples.

Keywords: Molecular imprinted polymer; Precipitation polymerization; Microspheres; Chemiluminescence imaging; Trans; -resveratrol

Analysis of berberine and total alkaloid content in Cortex Phellodendri by near infrared spectroscopy (NIRS) compared with high-performance liquid chromatography coupled with ultra-visible spectrometric detection by Chi-On Chan; Ching-Ching Chu; Daniel Kam-Wah Mok; Foo-Tim Chau (pp. 121-131).

This paper developed a rapid method using near infrared spectroscopy (NIRS) to differentiate two species of Cortex Phellodendri (CP), Cortex Phellodendri Chinensis (PCS) and Cortex Phellodendri Amurensis (PAR), and to predict quantitatively the content of berberine and total alkaloid content in all Cortex Phellodendri samples. Three alkaloids, berberine, jatrorrhizine and palmatine were analyzed simultaneously with a Thermo ODS Hypersil column by gradient elution with a new mobile phase under high-performance liquid chromatography–diode array detection (HPLC–DAD). Berberine content determined by HPLC–DAD was exploited as a critical parameter for successful discrimination between them. Multiplicative scatter correction (MSC), second derivative and Savitsky-Golay (S.G.) were utilized together to correct the scattering effect and eliminate the baseline shift in all near infrared diffuse reflectance spectra as well as to enhance spectral features in order to give a better correlation with the results obtained by HPLC–DAD. With the use of principal component analysis (PCA), samples datasets were separated successfully into two different clusters corresponding to two species. Furthermore, a partial least squares (PLS) regression method was built on the correlation model. The results showed that the correlation coefficients of the prediction models were R=0.996 for the berberine and R=0.994 for total alkaloid content. The influences of water absorption bands present in the NIR spectra on the models were also investigated in order to explore the practicability of NIRS in routine use. The outcome showed that NIRS possibly acts as routine screening in the quality control of Chinese herbal medicine.

Keywords: Cortex Phellodendri; Near infrared spectroscopy; Berberine; High-performance liquid chromatography

A comparative analysis of polyurethane hydrogel for immobilization of IgG on chips by Katarzyna Derwinska; Levi A. Gheber; Claudia Preininger (pp. 132-138).

Hydrogels are considered an optimum material for protein chip surfaces, since they provide a quasi-liquid environment which allows protein activity to be maintained and shows good spot morphology as well as excellent immobilization capacity. In the following, we present a polyurethane (PU) chip that electrostatically binds IgG. The PU surface is optimized with regard to layer thickness (∼200nm), hydrogel (2%) and immobilized antibody concentration (0.5mgmL⁻¹; 0.3ngspot⁻¹), pH and ionic strength of the print buffer as well as to blocking solution. Evaluation is done in a direct IgG immunoassay using the Nexterion slide H as a reference. It is shown that higher IgG loading is achieved on the PU chip than on slide H, no matter whether 1× PBS (pH 7.2), Sörensen (pH 5.8) or Nexterion buffer was used as a spotting solution. Moreover, the crossreactivity with goat IgG, human IgG and monoclonal anti-CRP spotted in Nexterion buffer was as low as ≤0.74% (slide H: ≤3.34%).

Keywords: Protein microarray; Polyurethane; Print buffer; Antibody immobilization

Quantification of very low enantiomeric impurity of efaroxan using a dual cyclodextrin system by capillary electrophoresis by Marie Lorin; Raphaël Delépée; Philippe Morin; Jean-Paul Ribet (pp. 139-145).

A rapid method for the enantiomeric purity determination of efaroxan has been developed by capillary electrophoresis (CE) using a dual cyclodextrin (CD) system. The influence of the nature and the concentration of CDs on separation parameters has been studied. High resolution ( R_s=7) and peak efficiency (104000–121000 theoretical plates) values were obtained for efaroxan enantiomers by adding two cyclodextrins, one neutral (7.5mM DM-β-CD) and the other negatively charged (3mM CM-β-CD) to the running buffer composed of 100mM phosphoric acid–triethanolamine (pH 3). These resolution and peak efficiencies values allowed the quantitation of the ( S)-enantiomer of efaroxan at very low enantiomeric excess even if the minor component migrates after the major one. This method was fully validated for the enantiomeric impurity determination of the ( S)-form of efaroxan at the 0.05% level. Calibration curve, expressed by the peak areas ratio versus the enantiomeric purity was linear over the 0.05–1% enantiomeric impurity range ( r²=0.9996). Limits of detection (LOD) and quantification (LOQ), expressed in term of ( S)-enantiomer impurity were 0.02% and 0.05%, respectively. The accuracy of the method at 0.12%, 0.50% and 0.80% enantiomeric impurity levels for the ( S)-form were determined. Recoveries were in 94–102% range for each quality control sample and were determined with good precision (intra-day R.S.D.=3.54%, inter-day R.S.D.=5.33%).

Keywords: Capillary electrophoresis; Dual cyclodextrin system; Enantiomeric excess; Enantiomeric purity; Validation; Efaroxan; Chirality

Glycosyl linkage characteristics and classifications of exo-polysaccharides of some regionally different strains of Lentinula edodes by amplified fragment length polymorphism assay and cluster analysis by Tiffany Chien Ting Lo; Ming Wei Kang; Bor Cheh Wang; C. Allen Chang (pp. 146-153).

We report here the first combined amplified fragment length polymorphism (AFLP) analysis of genomic DNA fingerprinting data and cluster analysis of the exo-polysaccharide glycosyl linkage data of 10 regionally different strains of Lentinula edodes to compare their genetic and structural similarities and differences. In addition, the monosaccharide compositions, molecular weights, glycosyl structural linkages were investigated for the exo-polysaccharides extracted from these different phylogenetic groups of regionally different L. edodes. All exo-polysaccharides had similar molecular weight distribution between 1×10⁴ and 3×10⁶Da and the monosaccharide composition analysis revealed the presence of heterogeneous materials containing glucose, mannose, xylose, galactose, fucose, rhamnose and arabinose in different ratios. Among these monosaccharides, the glucose contents are the highest for all but one strain, indicating that glucose probably is the building block of the backbones of these exo-polysaccharides. The AFLP assay data helped to classify the 10 L. edodes strains into three distinct genetic groups. Gas chromatographic and mass spectrometric (GC–MS) data revealed five different glycosyl linkage types for these exo-polysaccharides. Most of the exo-polysaccharide backbone structures contain (1→4)-linked-d-glucopyranosyl and (1→6)-linked-d-glucopyranosyl moieties. Arabinose 1→4 linkages and mannose 1→2 linkages also exist in all strains. The only differences among these linkages are their monosaccharide compositions leading to different degree of backbone and branch formations. Cluster analyses of the GC–MS data of the exo-polysaccharides of the 10 strains resulted in 10 dendrograms. However, four of the 10 dendrograms were identical and were obtained using the average, Ward and weighted linkage type method of Manhattan distance and using the Ward method of Euclidean distance. The results of cluster analyses were not very much different from that of the AFLP assay and allowed the comparison of genetic and structural similarities and differences.

Keywords: Lentinula edodes; Exo-polysaccharide; Glycosyl linkage; Amplified fragment length polymorphism; Cluster analysis; Genetics and structures

On-line purge and trap gas chromatography for monitoring of trihalomethanes in drinking water distribution systems by Michael A. Brown; Sarah Miller; Gary L. Emmert (pp. 154-161).

A method using an automated on-line purge and trap gas chromatograph with a dry electrolytic conductivity detector (DELCD) has been developed for monitoring four regulated trihalomethanes in drinking water distribution systems. This analyzer samples trihalomethanes from drinking water by pervaporation through a silicone capillary membrane contained within a gas extraction cell (GEC) followed by preconcentration using an adsorbent trap. Trihalomethanes are subsequently desorbed from the trap onto a capillary column, separated and detected. The analyzer operates in real-time, samples directly from the drinking water distribution system and is fully automated. The optimization, operation, and evaluation of the analyzer and method are discussed. Method detection limits (MDL) are less than 1.0μgL⁻¹ with acceptable estimates for accuracy, and precision. The results from two on-line monitoring studies in chlorinated and chloraminated distribution systems are presented. The performance of the method is compared directly to United Stated Environmental Protection Agency Method 502.2 and shows a very slight, but acceptable bias.

Keywords: Trihalomethanes; Drinking water; On-line monitoring; Gas chromatography; Disinfection by-products

A rapid quantitative method for humic substances determination in natural waters by Guo-Ping Sheng; Meng-Lin Zhang; Han-Qing Yu (pp. 162-167).

A simple and rapid method was proposed for humic substances (HS) determination at microgram levels in natural waters. This assay method is based on the binding of a dye, Toluidine Blue (TB), to HS molecules to produce a dye–HS complex, which causes a decrease in absorbance at 630nm. This method was calibrated with HS samples with up to a concentration of 40mgL⁻¹, which covered the range of dissolved HS concentrations present in natural waters. The detection limit was 0.8mgL⁻¹ of HS, and the relative standard deviation of 10 replicate measurements for a 20-mgL⁻¹ standard sample was 3.5%. From the Langmuir adsorption isotherm theory, the binding equilibrium constant and total number of binding sites at neutral pH were calculated to be (8.17±0.42)×10⁵Lmol⁻¹ and N of 1.45±0.04mmolg⁻¹ HS, respectively. The determination results with five water samples from lake, river and pond were consistent with those measured with the reference methods, demonstrating that this quantification method for HS determination was rapid, sensitive and feasible.

Keywords: Dye probe; Humic acids; Humic substances; Toluidine Blue; Water analysis

Determination of ketotifen by using calcein as chemiluminescence reagent by Nie Fei; Lu Jiuru (pp. 168-172).

Chemiluminescence (CL) was observed when potassium hexacyanoferrate(III) reacted with the mixture of calcein and ketotifen. Interestingly, the CL intensity would be enhanced by trace amounts of Mg²⁺ and the CL intensity was strongly dependent on ketotifen concentration. Based on this phenomenon, a flow injection CL method was established for the determination of ketotifen. The possible CL mechanism is proposed based on the kinetic characteristic of the CL reaction, CL spectrum, ultraviolet (UV) spectra and fluorescent spectra. The CL intensity was correlated linearly with concentration of ketotifen over the range of 6.0×10⁻⁹ to 2.0×10⁻⁷gmL⁻¹ and the detection limit was 3×10⁻⁹gmL⁻¹. The relative standard deviation was 1.8% for 2.0×10⁻⁸gmL⁻¹ ketotifen ( n=11). This method was applied to the determination of ketotifen in the tablets successfully.

Keywords: Chemiluminescence; Calcein; Ketotifen; Magnesium (II)

Flow-injection determination of zidovudine in plasma samples using multivariate curve resolution by Antonio Checa; Ramon Oliver; Santiago Hernández-Cassou; Javier Saurina (pp. 173-180).

This paper describes a spectrophotometric flow-injection method for the determination of an antiretroviral drug (zidovudine) in plasma samples. The main goal of this study is the development of feasible analytical method to monitor the plasmatic drug levels in a rapid and simple way as an alternative to chromatographic procedures. The flow-injection system proposed consists of a two-channel manifold with the injection of the sample into an acid carrier and on-line generation of a pH-gradient. The corresponding data are monitored over time using a diode array spectrophotometer. The discrimination of zidovudine species from plasma components is accomplished through chemometric data analysis based on the zidovudine features on both spectral and time domains. A pretreatment procedure consisting of liquid–liquid extraction is used for sample clean-up. However, despite the pretreatment, noticeable amounts of unknown substances acting as interferences are still present in the extracts. As relevant analytical parameters, the analyte recovery in the extraction process is 101% at 5.3μgmL⁻¹ and the detection limit is 0.013μgmL⁻¹. Multivariate curve resolution with alternating least squares is used to recover the analyte profiles for its further determination. As a result, the quantification of zidovudine in plasma can be accomplished even in the presence of plasma components with overall prediction error below 3%.

Keywords: Multivariate curve resolution-alternating least squares; Quantification; plasma samples; Acquired immunodeficiency syndrome drugs; Zidovudine; Matrix augmentation

Estimation of performance characteristics of a confirmation method for thyreostats in plasma by means of a weighted least-squares approach by P. Steliopoulos; E. Stickel (pp. 181-186).

A weighted linear regression-based approach was applied to ascertain analytical performance characteristics of a method for the quantitative determination of thyreostats in plasma by LC–MS. The weights were set equal to the reciprocal of the variances. A straightforward and practical procedure is presented that was used to model the variance of the replicate measurements as a function of concentration. Different function types were tested for their suitability.

Keywords: Weighted least-squares regression; Performance characteristics; Thyreostats

Determination of β-lactam antibiotics in milk using micro-flow chemiluminescence system with on-line solid phase extraction by Wei Liu; Zhujun Zhang; Zuoqin Liu (pp. 187-192).

In this paper, a chemiluminescence (CL) micro-flow system combined with on-line solid phase extraction (SPE) is presented for determination of β-lactam antibiotics (penicillin, cefradine, cefadroxil, cefalexin) in milk. It is based on the enhancement effect of β-lactam antibiotics on the luminol-K₃Fe(CN)₆ CL system. The micro-flow system was fabricated from two polymethyl methacrylate (PMMA) plates (50mm×40mm×5mm) with the microchannels of 200μm wide and 150μm deep. C₁₈-modified silica gel was packed into the microchannel (length: 10mm; width: 1mm; depth: 500μm) to serve as SPE device. Extraction and preconcentration of the analytes were carried out using on-line SPE micro-flow system and the selectivity of CL detection was improved. The detection limits were 0.5μgmL⁻¹ of penicillin, 0.04μgmL⁻¹ of cefradine, 0.08μgmL⁻¹ of cefadroxil and 0.1μgmL⁻¹ of cefalexin. The proposed method was also applied to analyze the β-lactam antibiotics in milk. Experimental results were in good agreement with those obtained by high performance liquid chromatography (HPLC) method with UV detection.

Keywords: Micro-flow system; On-line solid-phase extraction; Chemiluminescence; β-Lactam antibiotics

Automatic flow system for sequential determination of ABTS⁺ scavenging capacity and Folin-Ciocalteu index: A comparative study in food products by Luís M. Magalhães; Marcela A. Segundo; Salette Reis; José L.F.C. Lima; Ildikó V. Tóth; António O.S.S. Rangel (pp. 193-201).

In the present work, an automatic flow procedure for the sequential spectrophotometric determination of Folin-Ciocalteu reducing capacity (FC assay) and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS⁺) scavenging capacity expressed as the trolox equivalent (TEAC assay) is proposed for a comparative study of antioxidant properties in food products. Exploiting the flexibility of flow management associated to the computer control offered by multisyringe flow injection analysis, both methodologies were carried out in the same manifold using gallic acid and trolox as standard compounds. The proposed system configuration allowed the performance of each method separately or in tandem, providing 24 determinations per hour, which accounts for its application in routine analysis.The present methodology was applied to a large number of beverages ( n=72), namely red and white wines, herbal and tea infusions, juices and beers. The results obtained showed that FC reducing capacity and TEAC values of red wines were significantly different from those obtained for the other beverages, while tea infusions provided significantly higher TEAC values when compared to white wines, herbal infusions, juices and beers. A good correlation was found between TEAC and FC reducing capacity ( R>0.9) for red wines, herbal and tea infusions, and beers. For these beverages, similar slope values were found (106–140mgL⁻¹ of gallic acid per mM of Trolox), except for beers that showed a higher response for FC assay. These results provided evidence that the correlation between these assays vary according to the type of sample, reinforcing the idea that more than one method should be used for evaluation of antioxidant capacity.

Keywords: Multisyringe flow injection analysis; Folin-Ciocalteu assay; 2,2′-Azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation; Beverages

Enantiomeric quality control of antihistamines in pharmaceuticals by affinity electrokinetic chromatography with human serum albumin as chiral selector by M.A. Martínez-Gómez; S. Sagrado; R.M. Villanueva-Camañas; M.J. Medina-Hernández (pp. 202-209).

The present paper deals with the enantiomeric separation of six antihistaminic enantiomers by affinity electrokinetic chromatography (AEKC)-partial filling technique using human serum albumin (HSA) as chiral selector. A multivariate optimization approach of the most critical experimental variables in enantioresolution, running pH, HSA concentration and HSA plug length (SPL) was carried out since there are interactions between variables that could not be considered in an univariate optimization. The estimated and experimental resolution values obtained for antihistaminic enantiomers varied from 1.13 (for orphenadrine) to 2.15 (for brompheniramine). The optimum experimental conditions for enantioresolution of each compound were: brompheniramine, pH 8.5, [HSA] 180μM, SPL 180s; chlorcyclizine, pH 6.5, [HSA] 180μM, SPL 150s; chlorpheniramine, pH 8.25, [HSA] 160μM, SPL 150s; hydroxyzine, pH 7.0, [HSA] 180μM, SPL 150s; and orphenadrine, pH 7.8, [HSA] 160μM, SPL 150s. pH and the quadratic term of pH seem to be the most critical factors that determine enantioresolution of antihistamines. The validity of the developed methodologies to enantiomeric quality control of antihistamines in pharmaceutical formulations is demonstrated analyzing the content of brompheniramine, chlorpheniramine and hyroxyzine enantiomers in commercially available pharmaceutical formulations containing racemic mixtures of compounds. Resolution, accuracy, reproducibility, cost and sample throughput of the proposed methodologies make them suitable for quality control of the enantiomeric composition of antihistamines in pharmaceutical preparations.

Keywords: Affinity electrokinetic chromatography-partial filling technique; Human serum albumin; Antihistamines enantiomers; Enantiomeric quality control; Pharmaceutical preparations

Assessing the statistical validity of proteomics based biomarkers by Suzanne Smit; Mariëlle J. van Breemen; Huub C.J. Hoefsloot; Age K. Smilde; Johannes M.F.G. Aerts; Chris G. de Koster (pp. 210-217).

A strategy is presented for the statistical validation of discrimination models in proteomics studies. Several existing tools are combined to form a solid statistical basis for biomarker discovery that should precede a biochemical validation of any biomarker. These tools consist of permutation tests, single and double cross-validation. The cross-validation steps can simply be combined with a new variable selection method, called rank products. The strategy is especially suited for the low-samples-to-variables-ratio (undersampling) case, as is often encountered in proteomics and metabolomics studies. As a classification method, principal component discriminant analysis is used; however, the methodology can be used with any classifier. A dataset containing serum samples from Gaucher patients and healthy controls serves as a test case. Double cross-validation shows that the sensitivity of the model is 89% and the specificity 90%. Potential putative biomarkers are identified using the novel variable selection method. Results from permutation tests support the choice of double cross-validation as the tool for determining error rates when the modelling procedure involves a tuneable parameter. This shows that even cross-validation does not guarantee unbiased results. The validation of discrimination models with a combination of permutation tests and double cross-validation helps to avoid erroneous results which may result from the undersampling.

Keywords: Biomarker discovery; Classification; Curse of dimensionality; Statistical validation; Double cross-validation; Principal component discriminant analysis; Gaucher disease; Rank products; Permutation test; Surface enhanced laser desorption ionization time-of-flight mass spectrometry

Estimation of non-ionic, surface-active substances in aqueous solutions by means of the Controlled Growth Mercury Electrode by Bogusław Baś; Małgorzata Jakubowska (pp. 218-225).

In this paper, a quick and simple tensammetric method of estimation of non-ionic surfactants (NS) in aqueous solutions is proposed. The method makes use of the variation in the differential capacity of double layer in relation to the time of accumulation ( C_d– t_acc) of non-ionic surfactants at the hanging mercury drop electrode, generated by a single, very quick opening of the valve. Under such conditions, the capacity current measured at the potential of maximum adsorption diminishes with accumulation time of non-ionic surfactants. The proposed method, which was verified for model surfactant (Triton X-100), may also be applied in the determination of other NS.Modifications in construction of the CGME electrode and its improved metrological parameters played an important role in the presented procedure. In addition, other measurements were performed using standard electrochemical techniques, whereby current–time and differential capacity–potential curves were recorded.Satisfactory results were obtained in the determination of Triton X-100 in the range from 0.05 to 20mgL⁻¹ (R.S.D.=6%, recovery=94–103%, r=0.999, DL=0.15mgL⁻¹). Applicability of the method was presented using the water samples from Białka and Dunajec rivers, from which NS were removed by addition of fumed silica.

Keywords: Tensammetry; Non-ionic surfactants; Triton X-100; Controlled Growth Mercury Electrode

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Analytica Chimica Acta (v.592, #2)