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Analytical and Bioanalytical Chemistry (v.381, #4)

Microfluidics in China by Zhao-Lun Fang (pp. 807-808).

Lab-on-valve mesofluidic analytical system and its perspectives as a “world-to-chip” front-end by Jianhua Wang (pp. 809-811).

Rapid authentication of ginseng species using microchip electrophoresis with laser-induced fluorescence detection by Jianhua Qin; Frederick C Leung; Yingsing Fung; Derong Zhu; Bingcheng Lin (pp. 812-819).

Ginseng is one of the most expensive Chinese herbal medicines and the effectiveness of ginseng depends strongly on its botanical sources and the use of different parts of the plants. In this study, a microchip electrophoresis method coupled with the polymerase chain reaction (PCR)–short tandem repeats (STR) technique was developed for rapid authentication of ginseng species. A low viscosity hydroxypropyl methylcellulose (HPMC) solution was used as the sieving matrix for separation of the amplified STR fragments. The allele sizing of the amplified PCR products could be detected within 240 s or less. Good reproducibility and accuracy of the fragment size were obtained with the relative standard deviation for the allele sizes less than 1.0% (n=11). At two microsatellite loci (CT 12, CA 33), American ginseng had a different allele pattern on the electropherograms compared with that of the Oriental ginseng. Moreover, cultivated and wild American ginseng can be distinguished on the basis of allele sizing. This work establishes the feasibility of fast genetic authentication of ginseng species by use of microchip electrophoresis.

Keywords: Ginseng; Short tandem repeats (STR); Microchip; Electrophoresis; Molecular authentication

DNA separation with low-viscosity sieving matrix on microfabricated polycarbonate microfluidic chips by Mei-Ying Ye; Xue-Feng Yin; Zhao-Lun Fang (pp. 820-827).

Microfluidic devices have been fabricated on polycarbonate (PC) substrates by use of a hot embossing method using a silicon master template. By adding auxiliary lines around the functional channel on the silicon master, its lifetime was significantly prolonged and the bonding strength of the PC cover plate to the microfluidic chip was greatly improved. More than 300 polycarbonate microfluidic chips have been replicated with the same silicon mold. CE separation of Φ X-174/HaeIII DNA restriction fragments, with high resolution efficiency and good reproducibility, was achieved on these devices using the low-viscosity sieving matrix HPMC-50. Temperature was found to have a significant effect on separation efficiency.

Keywords: Hot embossing; Polycarbonate; Microchip; DNA; Electrophoresis

Enhancing effect of DNA on chemiluminescence from the decomposition of hydrogen peroxide catalyzed by copper(II) by Meilin Liu; Baoxin Li; Zhujun Zhang; Jin-Ming Lin (pp. 828-832).

In the absence of any special luminescence reagent, emission of weak chemiluminescence has been observed during the decomposition of hydrogen peroxide catalyzed by copper(II) in basic aqueous solution. The intensity of the chemiluminescence was greatly enhanced by addition of DNA and was strongly dependent on DNA concentration. Based on these phenomena, a flow-injection chemiluminescence method was established for determination of DNA. The chemiluminescence intensity was linear with DNA concentration in the range 2×10⁻⁷−1×10⁻⁵ g L⁻¹ and the detection limit was 4.1×10⁻⁸ g L⁻¹ (S/N=3). The relative standard deviation was less than 3.0% for 4×10⁻⁷ g L⁻¹ DNA (n=11). The proposed method was satisfactorily applied for determination of DNA in synthetic samples. The possible mechanism of the CL reaction is discussed.

Keywords: Chemiluminescence; DNA; Hydrogen peroxide; Copper(II)

Electrochemical DNA sensing based on gold nanoparticle amplification by Zhi-Ling Zhang; Dai-Wen Pang; Hong Yuan; Ru-Xiu Cai; Héctor D. Abruña (pp. 833-838).

A hybridization signal-amplified method based on a gold nanoparticle-supported DNA sequence for electrochemical DNA sensing has been investigated by cyclic voltammetry, differential-pulse voltammetry, and atomic-force microscopy (AFM). Quantitative analysis showed that the peak current increment (ΔIp) is linearly dependant on the concentration of the gold nanoparticle-supported DNA sequence Au2 over the range 0.51–8.58 pmol L⁻¹. AFM results indicated that the extent of surface hybridization was dependent on the concentration of the gold-nanoparticle-supported DNA sequence. Moreover, a new pair of peaks, which might arise from the special configuration of the gold-nanoparticle-supported DNA sequence, appeared in the cyclic voltammogram after hybridization. Although quite sensitive, this DNA sensing surface was not easily regenerated, so this kind of amplified method was suitable for disposable DNA sensors and chip-based gene diagnosis sensors.

Keywords: Gold nanoparticle; Electrochemical DNA sensing; Nanoparticle amplification; AFM

Feature characterization of microfabricated microfluidic chips by PDMS replication and CCD imaging by Jing Dai; Yan-Xia Guan; Shi-Li Wang; Zhi-Yong Wu; Zhao-Lun Fang (pp. 839-843).

This paper presents a new approach for the metrological characterization of microfabricated features on microfluidic chips, based on a combination of poly(dimethylsiloxane) (PDMS) replication and charge-coupled device (CCD) imaging. A PDMS replicate was cast from the original chip sample, and a 2-mm thick sample slice was cut from the replica at the cross-section to be studied. The digital image of the revealed structural profile was captured by a CCD camera under a microscope, and the image was processed using specially-developed algorithms for CCD image calibration and edge detection. Depth and width measurements obtained using the method agreed well with those gained using a stylus profiler and universal measuring microscope, with a deviation of below 0.9 μm, while profile distortions of deeper structures using stylus profilers were avoided. The method is reliable, non-destructive, and cheap and simple to implement in any analytical laboratory.

Keywords: Microfluidics; Chips; PDMS replication; CCD-imaging; Metrology

Investigation of the recovery of selenomethionine from selenized yeast by two-dimensional LC–ICP MS by Aleksandra Połatajko; Barbara Banaś; Jorge Ruiz Encinar; Joanna Szpunar (pp. 844-849).

Determination of selenomethionine in selenized yeast by HPLC–ICP MS has been revisited with the focus on recovery of this amino acid during the proteolytic digestion and chromatography steps. Recovery of the extracted selenium from an anion-exchange column was 100% but selenomethionine quantified by the method of standard additions accounted only for 67% of the selenium injected. Analysis (by size-exclusion LC–ICP MS) of the eluate collected before and after the selenomethionine peak showed the presence of oxidized selenomethionine (ca. 3%) and selenomethionine likely to be unspecifically associated with the biological matrix continuum (ca. 11%). This finding was validated by two-dimensional LC–ICP MS using a different elution order, i.e. size-exclusion anion-exchange. The approach developed enabled demonstration that more than 80% of selenium in the selenized yeast is actually present in the form of selenomethionine and suggests that many results reported elsewhere for the concentration of this vital amino acid in selenized yeast may be negatively biased. The research also provided insight into speciation of selenium in the solid residue after proteolytic extraction but the additional amount of selenomethionine recovered was negligible (<1.5%).

Keywords: Selenomethionine determination; Selenized yeast; Two-dimensional chromatography; ICP MS

A global indicator as a tool to follow airborne molecular contamination in a controlled environment by Stéphane Cariou; Jean-Michel Guillot; Laurence Pépin; Pascal Kaluzny; Louis-Paul Faure (pp. 850-853).

The impact of pollutants on production quality in nanotechnology necessitates reduction of contaminant levels in cleanrooms. So, devising a global airborne-pollutant indicator (GAPI) for rapid determination of the level of pollution and its danger to the process is justified. This tool used relative impact weights of the different molecules to quantify the pollution. A calculation of impact weight is proposed in this paper. Impact weights could take into account several characteristics of the molecules (molecular volume, sticking coefficient, ...). They could also be combined to be as close as possible to reality. An example of calculations of the impact of molecular volumes on air quality is given.

Keywords: Air quality; Pollutant impact; Cleanroom; VOC; Measurement

Simultaneous speciation of mercury and butyltin compounds in natural waters and snow by propylation and species-specific isotope dilution mass spectrometry analysis by M. Monperrus; E. Tessier; S. Veschambre; D. Amouroux; O. Donard (pp. 854-862).

A robust method has been developed for simultaneous determination of mercury and butyltin compounds in aqueous samples. This method is capable of providing accurate results for analyte concentrations in the picogram per liter to nanogram per liter range. The simultaneous determination of the mercury and tin compounds is achieved by species-specific isotope dilution, derivatization, and gas chromatography–inductively coupled plasma mass spectrometer (GC–ICP–MS). In derivatization by ethylation and propylation, reaction conditions such as pH and the effect of chloride were carefully studied. Ethylation was found to be more sensitive to matrix effects, especially for mercury compounds. Propylation was thus the preferred derivatization method for simultaneous determination of organomercury and organotin compounds in environmental samples. The analytical method is highly accurate and precise, with RSD values of 1 and 3% for analyte concentrations in the picogram per liter to nanogram per liter range. By use of cleaning procedures and SIDMS blank measurements, detection limits in the range 10–60 pg L⁻¹ were achieved; these are suitable for determination of background levels of these contaminants in environmental samples. This was demonstrated by using the method for analysis of real snow and seawater samples. This work illustrates the great advantage of species-specific isotope dilution for the validation of an analytical speciation method—the possibility of overcoming species transformations and non-quantitative recovery. Analysis time is saved by use of the simultaneous method, because of the use of a single sample-preparation procedure and one analysis.

Keywords: Speciation; Mercury and butyltin compounds; Isotope dilution; Sodium tetrapropylborate; Environmental aqueous samples

Development of a procedure for the sequential extraction of substances binding trace elements in plant biomass by Daniela Pavlíková; Milan Pavlík; Soňa Vašíčková; Jiřina Száková; Karel Vokáč; Jiří Balík; Pavel Tlustoš (pp. 863-872).

This work investigates how the amounts of some important substances in a plant, and their behaviour inside the plant, depend on the levels of stress placed on the plant. To this end, model plant spinach (Spinacia oleracea L.) was cultivated on soil treated with sewage sludge. The sewage sludge contained various trace elements (As, Cd, Cu, Zn), and the uptake of these trace elements placed the plant under stress. Following this, a sequential extraction procedure was employed to determine the levels and distributions of trace elements within the most important groups of compounds present in the spinach plants. Since the usual five-step sequential extraction procedure provides only general information on the distributions of elements within individual groups of organic compounds, due to the wide range of organic compounds within the individual fractions, this scheme was extended and improved through the addition of two solvent extraction steps—a butanol step (between the ethyl acetate and methanol solvent steps) and an H₂O step (after the methanol+H₂O solvent step). The distributions and levels of the trace elements within the main groups of compounds in spinach biomass was investigated using this new seven step sequential extraction (water free solvents: petroleum ether (A) → ethyl acetate (B) → butanol (C) → methanol (D) → water solvents: methanol+H₂O (1+1; v/v) (E) → H₂O (F) → methanol+H₂O+HCl (49.3+49.3+1.4; v/v/v) (G)). The isolated fractions were characterized using IR spectroscopy and the trace element contents were determined in the individual fractions. Lipophilic compounds with low contents of Cd, Cu and Zn were separated in the first two fractions (A, B). Compounds with higher As contents (11.5–12.8% of total content) were also extracted in the second fraction, B. These two fractions formed the smallest portion of the isolated fractions. Low molecular compounds from secondary metabolism and polar lipids were separated in the third (C) and fourth (D) fractions, and high molecular compounds (mainly polypeptides and proteins) separated in the fifth and sixth fractions (E, F). The addition of the H₂O solvent step was particularly useful for separating compounds that have a significant impact on trace element bounds. The methanol fraction was dominant for all treatments, and a significant decrease in the spinach biomass separated in this fraction was observed when the soil was treated with sewage sludge. Most of the As (35.5–38.8% of total content), Cu (45.0–51.6%) and Zn (39.8–47.2%) was also determined in this fraction. The G fraction (obtained after acid hydrolysis) contained polar compounds. Most of the Cd was also found in this fraction, as was a significant amount of Zn. Non-extractable residues formed the last fraction (polysaccharides, proteins).

Keywords: Sequential extraction; Spinach plant; Trace elements; Organic compounds binding trace elements

Analytical phosphorus fractionation in sewage sludge and sediment samples by J. J. González Medeiros; B. Pérez Cid; E. Fernández Gómez (pp. 873-878).

The Standards, Measurements and Testing (SMT) harmonized procedure for phosphorus fractionation in freshwater sediments (SMT protocol), which was developed within the framework of the Standards, Measurements and Testing (SMT) Programme of the European Commission, has been applied to different environmental samples such as sewage sludge, river and marine sediments. The phosphorus contents in the extracts were spectrophotometrically determined; the measurement conditions and the matrix effects were evaluated for each fraction. The partitioning patterns obtained for sewage sludge and sediment samples reveal that the distribution between inorganic and organic phosphorus forms is independent of the matrix composition of the samples. In addition, a higher available phosphorus content was found in sewage sludges due to the higher percentages of labile phosphorus forms, which suggests possible internal phosphorus release. Finally, one simplified pseudototal microwave digestion method was performed for total phosphorus determination which was validated by its application to the reference material BCR-684.

Keywords: SMT protocol; Phosphorus fractionation; Eutrophication; Sewage sludges; Sediments

Square-wave voltametric method for determination of molinate concentration in a biological process using a hanging mercury drop electrode by M. Fátima Barroso; O. C. Nunes; M. Carmo Vaz; C. Delerue-Matos (pp. 879-883).

A square-wave voltammetric (SWV) method using a hanging mercury drop electrode (HMDE) has been developed for determination of the herbicide molinate in a biodegradation process. The method is based on controlled adsorptive accumulation of molinate for 10 s at a potential of −0.8 V versus AgCl/Ag. An anodic peak, due to oxidation of the adsorbed pesticide, was observed in the cyclic voltammogram at ca. −0.320 V versus AgCl/Ag; a very small cathodic peak was also detected. The SWV calibration plot was established to be linear in the range 5.0×10⁻⁶ to 9.0×10⁻⁶ mol L⁻¹; this corresponded to a detection limit of 3.5×10⁻⁸ mol L⁻¹. This electroanalytical method was used to monitor the decrease of molinate concentration in river waters along a biodegradation process using a bacterial mixed culture. The results achieved with this voltammetric method were compared with those obtained by use of a chromatographic method (HPLC–UV) and no significant statistical differences were observed.

Keywords: Hanging mercury drop electrode; Square-wave voltammetry; Molinate; Biodegradation

The state of conservation of painted surfaces in the presence of accelerated ageing processes monitored by use of FT-Raman spectroscopy and multivariate control charts by Emilio Marengo; Maria Cristina Liparota; Elisa Robotti; Marco Bobba; Maria Carla Gennaro (pp. 884-895).

A new method has been developed for monitoring the degradation of paintings. Two inorganic pigments (ultramarine blue and red ochre) were blended with linseed oil and spread on canvas. Each canvas was subjected to simulated accelerated ageing in the presence of typical degradation agents (UV radiation and acidic solution). Periodically the painted surfaces were analysed by FT-Raman, to investigate the status of the surface. The data obtained were analysed by principal component analysis (PCA). Finally the Shewhart and cumulative sum control charts based on the relevant principal components (PC) and the so called scores monitoring and residuals tracking (SMART) charts were built. The method based on the use of PC to describe the process was found to enable identification of the presence of relevant modification occurring on the surface of the samples studied.

Keywords: FT-Raman; PCA; Multivariate control charts; Degradation monitoring

A new and sensitive resonance-scattering method for determination of trace nitrite in water with rhodamine 6G by Zhi-Liang Jiang; Shuang-Jiao Sun; Cai-Yan Kang; Xi Lu; Jie Lan (pp. 896-900).

In the medium HCl–KI–rhodamine dye, NO₂⁻ reacts with excess I⁻ to form I₃⁻ and the I₃⁻ and rhodamine dye combine to form an association particle which gives three resonance-scattering (RS) peaks at 320 nm, 400 nm, and 595 nm. In systems containing rhodamine 6G (Rh6G), rhodamine B (RhB), rhodamine S (RhS), and butyl rhodamine B (BRhB) the resonance scattering intensity at 400 nm is proportional to nitrite concentrations in the range 2.3–276 ng mL⁻¹, 9.2–184 ng mL⁻¹, 9.2–184 ng mL⁻¹, and 9.2–92 ng mL⁻¹, respectively. Because of the high sensitivity, wide linear range, and good stability of the Rh6G system, it has been used for determination of nitrite in water samples, with satisfactory results. The spectral results have been used to verify that the formation of (Rh6G·I₃)_n association particles and their interface with the system are main factors that cause the RS enhancement.

Keywords: Nitrite; Rhodamine 6G; Association particle; Resonance scattering

High-resolution Hadamard transform microscope fluorescence imaging: quantifying the DNA content in single cells by Hongwu Tang; Meina Luo; Yongpan Xiong; Guanquan Chen (pp. 901-906).

This study presents a novel miniaturized Hadamard transform fluorescence imaging microscope, by combining a conventional fluorescence microscope with Hadamard transform multiplexing encoding using a one-dimensional movable mask to realize spatial resolution and a linear CCD for multichannel detection. The microscope can provide high-resolution automatically-generated 0–255 gray level HT images for morphological analysis and visualization of a single cell, and normalized HT images for cellular quantitative measurements. The microscope’s imaging capability was applied to measure the DNA content in human lymphocyte, chicken erythrocyte and eel erythrocyte, and a comparative study was performed. The results show that the calibrated DNA content in a chicken erythrocyte is 2.32 pg when human lymphocyte is used as the standard, and eel erythrocyte may be a potentially reliable and novel standard for determining DNA contents in other species because it has a stable DNA value of 2.06 pg, with a CV of 4.3% when 20 eel erythrocytes are measured. The results also demonstrate that the HT imaging microscope should be valuable in the fields of medicine and cell biology.

Keywords: Hadamard transform; Fluorescence imaging; Microscopy; Single-cell analysis

Capillary zone electrophoresis for simultaneous determination of seven nonsteroidal anti-inflammatory drugs in pharmaceuticals by Yen-Ling Chen; Shou-Mei Wu (pp. 907-912).

A simple capillary zone electrophoresis (CZE) method has been developed for analyzing seven nonsteroidal anti-inflammatory drugs (NSAIDs)—sulindac (SU), ketoprofen (KE), indomethacin (IN), piroxicam (PI), nimesulide (NI), ibuprofen (IB), and naproxen (NA). The separation was run using borate buffer (60 mmol L⁻¹, pH 8.5) containing 13% (v/v) methanol at 20 kV, and detected at 200 nm. Several conditions were studied, including concentration and pH of borate buffer, methanol percentage, and separation voltage. In method validation, the calibration plots were linear over the range 40.0–500.0 μmol L⁻¹. In intra-day and inter-day analysis, relative standard deviations (RSD) and relative errors (RE) were all less than 5%. The limits of detection were 10 μmol L⁻¹ for SU, IN, PI, and 20 μmol L⁻¹ for KE, NI, IB, NA (S/N = 3, sampling 6 s by pressure). All recoveries were greater than 95%. This method was applied to the quality control of six NSAIDs in pharmaceuticals using NI as internal standard (IS). The assay results were within the labeled amount required by USP 25.

Keywords: NSAIDs; Pharmaceuticals; Capillary zone electrophoresis

Comparing chemical fingerprints of herbal medicines using modified window target-testing factor analysis by Zhong-Da Zeng; Yi-Zeng Liang; Cheng-Jian Xu (pp. 913-924).

A “chromatographic fingerprint” of a herbal medicine is essentially its chromatographic spectrum: a characteristic representation of its chemical components, some of which are pharmacologically active. Since a wide variety of factors, such as the geographical location, the harvest season, and the part used can influence the chemical constituents (and therefore the pharmacological activity) of any particular herbal medicine and its products, these fingerprints provide a way to compare and contrast the compositions of different variants of the same herbal medicine. In particular, it is possible to ascertain whether particular components present in one herbal fingerprint are also present in another fingerprint. In this work we use a novel method—modified window target-testing factor analysis (MWTTFA), based on the use of target factor analysis (TFA), fixed-size moving window evolving factor analysis (FSMWEFA) and a Gaussian shape correction to the chromatographic profiles—to achieve this end. To demostrate the strategy, the fingerprints of samples from garlics produced in different geographical locations were compared, as well as the fingerprints of samples taken from above-ground and below-ground parts of Houttuynia cordata Thunb. The results from these comparisons clearly show that four chemical components present in Hunan common edible garlic are absent in Xingping base garlic, while seven components are present in Xingping base garlic but absent in Hunan common edible garlic. Also, eleven components are present in the sample from the above-ground part of Houttuynia cordata Thunb but not in the sample from the below-ground part, while seven components are present in the sample from the below-ground part of Houttuynia cordata Thunb that are not present in the sample from the above-ground part. These interesting conclusions should be very useful for future pharmacological and clinical research into these herbal medicines, and the novel MWTTFA technique can also be used for quality control purposes.

Keywords: Fingerprint; Herbal medicines; Window target-testing factor analysis; Garlic; Houttuynia cordata thunb; GC MS

Flow injection chemiluminescence determination of naftopidil based on potassium permanganate oxidation in the presence of formaldehyde or formic acid by Alan Townshend; José A. Murillo Pulgarín; M. Teresa Alañón Pardo (pp. 925-931).

A flow injection method is proposed for the determination of naftopidil based upon the oxidation by potassium permanganate in a sulfuric acid medium and sensitized by formaldehyde and formic acid. The optimum chemical conditions for the chemiluminescence emission were 0.25 mM potassium permanganate and 4.0 M sulfuric acid. Two manifolds were tested and instrumental parameters such as the length of the reactor, injection volume and flow rate were compared. When using the selected manifold in the presence of 0.4 M formaldehyde, naftopidil gives a second-order calibration graph over the concentration range 0.1–40.0 mg L⁻¹ with a detection limit calculated (as proposed by IUPAC) of 92.5 ng mL⁻¹ and a standard deviation of 0.12 mg mL⁻¹ for ten samples of 10.0 mg L⁻¹ naftopidil. In the presence of 1.15 M formic acid, naftopidil gives a second-order calibration graph over the concentration range 0.05–40.0 mg L⁻¹ with a detection limit of 14.2 ng mL⁻¹ and a standard deviation of 0.37 mg mL⁻¹ for ten samples of 10.0 mg L⁻¹ naftopidil. In both cases, the determination is free from interferences from common excipients such as sucrose, glucose, lactose, starch and citric acid.

Keywords: Naftopidil; Chemiluminescence; Flow injection

Solid-phase reactor flow-injection on-line oxidizing spectrofluorimetry for determination and dissolution studies of folic acid by Zhi-Qi Zhang; Ying Tang (pp. 932-936).

A simple, sensitive and specific flow-injection spectrofluorimetric method has been developed for the determination of folic acid in pharmaceuticals. The method is based on use of a lead dioxide solid-phase reactor for on-line oxidation of folic acid into a strongly fluorescent compound with a maximum excitation wavelength of 281 nm and an emission wavelength of 450 nm. Under optimum conditions the fluorescence intensity of oxidation product is proportional to the concentration of folic acid over the range 0.008–2.5 μg mL⁻¹. The detection limit is 0.0001 μg mL⁻¹, the relative standard deviation is 0.85% for 11 replicate determinations of 0.05 μg mL⁻¹ folic acid, and the sample throughput is 20 h⁻¹. In combination with an on-line filter and dilution, an automated drug-dissolution system was established. The proposed method has been successfully applied to the determination of folic acid in pharmaceutical preparations and dissolution testing.

Keywords: Folic acid; Flow-injection analysis; Spectrofluorimetry; Dissolution; Solid-phase reactor

Stable isotope dilution analysis of wine fermentation products by HS-SPME-GC-MS by Tracey E. Siebert; Heather E. Smyth; Dimitra L. Capone; Corinna Neuwöhner; Kevin H. Pardon; George K. Skouroumounis; Markus J. Herderich; Mark A. Sefton; Alan P. Pollnitz (pp. 937-947).

The aim of this study was to quantify, in a single analysis, 31 volatile fermentation-derived products that contribute to the aroma of red and white wine. We developed a multi-component method based on headspace solid-phase microextraction coupled with gas chromatography mass spectrometry (HS-SPME-GC-MS). The 31 volatile compounds analysed include ethyl esters, acetates, acids and alcohols. Although these compounds have a range of functional groups, chemical properties, volatilities, affinities for the SPME fibre, and are found in wine at various concentrations, the accuracy of the analysis was achieved with the use of polydeuterated internal standards for stable isotope dilution analyses (SIDA). Nine of the labelled standards were commercially available, while 22 were synthesised. The method was validated by a series of duplicate spiked standard additions to model, white and red wine matrices over the concentration range relevant for each compound in wine. This demonstrated that the appropriate use of SIDA helped to account for matrix effects, for instance potential sources of variation such as the relative response to the MS detector, ionic strength, ethanol content and pH of different wine matrices. The resultant calibration functions had correlation coefficients (R²) ranging from 0.995 to 1.000. Each compound could be quantified at levels below its aroma threshold in wine. Relative standard deviations were all <5%. The method was optimised for the best compromise (over the 31 compounds) of wine dilution factor, level of sodium chloride addition, SPME fibre, SPME temperature, SPME time, GC column and MS conditions. Confirmation of identity was achieved by retention time and peak shape, and measurement of at least three ions for each analyte and internal standard with the MS operating in selected ion monitoring mode to facilitate more precise quantitation with a high sampling rate. The method is a valuable research tool with many relevant applications. A novel method for the combined chiral separation and SIDA quantification of 2- and 3-methylbutanoic acid is also demonstrated.

Keywords: GC/MS; SPME; Wine; SIDA; Fermentation; Aroma

Polypyrrole modified stainless steel frits for on-line micro solid phase extraction of ochratoxin A by Jorn C. C. Yu; Edward P. C. Lai (pp. 948-952).

Polypyrrole (PPy) was electrochemically synthesized on stainless steel frits as a sorbent for the micro solid phase extraction (μSPE) of ochratoxin A (OTA). Using 20 μl of standard solution under a fast flow rate of 0.5 ml/min, 80% recovery of OTA was achieved in the concentration range from 0.1–10 pg/μl. This good recovery was achieved within a short residence time of 1.2 s. A binding capacity of 1 ng OTA was estimated for each PPy-modified frit, or 2 ng OTA for two frits in series. The bound OTA could be pulsed eluted (PE) with 20 μl of 1% triethylamine in acetonitrile. On-line coupling of this PPy-on-a-frit and PE technique to high performance liquid chromatography (HPLC) was straightforward. On-line μSPE-PE-HPLC results clearly demonstrated the capability of PPy-on-a-frit to bind OTA in the presence of red wine, beer, and orange juice components.

Keywords: Polypyrrole; Stainless steel frit; Micro solid phase extraction; Ochratoxin A; Pulsed elution; High performance liquid chromatography

Study of spectral analytical data using fingerprints and scaled similarity measurements by M. Urbano Cuadrado; M. D. Luque de Castro; M. A. Gómez-Nieto (pp. 953-963).

A new chemoinformatic model has been developed for enlarging the differences between spectra and applied to differentiation of wines according to the criteria grape origin and variety and ageing process. The model is based on generation of fingerprints from normalised spectra, using empirical parameters and a set of 120 samples. After generation of the fingerprints, similarity matrixes were built on the basis of the Tanimoto similarity index between the fingerprints of the samples. Calculation of the Tanimoto index was modified to adapt the index to the characteristics of the analytical measurements. Thus, scaling factors taking into account pattern fingerprints generated from a group of samples with common characteristics were used. In addition, a modified expression for calculating the Tanimoto index was employed. Principal-components analysis (PCA) and soft independent modelling of class analogy (SIMCA) were applied to the similarity matrixes. The results obtained are discussed as a function of the normalisation method employed, the empirical factor used in generation of the fingerprints, and selection of samples for building the pattern fingerprint, etc. Finally, results from differentiation of wines are compared with those obtained by applying PCA to the unprocessed spectra as stated by the proposed model.

Keywords: Similarity calculation; Fingerprints; Attenuated total reflection mid infrared; Wine differentiation

Calibration of NO sensors for in-vivo voltammetry: laboratory synthesis of NO and the use of UV–visible spectroscopy for determining stock concentrations by Finbar O. Brown; Niall J. Finnerty; Fiachra B. Bolger; Julian Millar; John P. Lowry (pp. 964-971).

The increasing scientific interest in nitric oxide (NO) necessitates the development of novel and simple methods of synthesising NO on a laboratory scale. In this study we have refined and developed a method of NO synthesis, using the neutral Griess reagent, which is inexpensive, simple to perform, and provides a reliable method of generating NO gas for in-vivo sensor calibration. The concentration of the generated NO stock solution was determined using UV–visible spectroscopy to be 0.28±0.01 mmol L⁻¹. The level of NO₂⁻ contaminant, also determined using spectroscopy, was found to be 0.67±0.21 mmol L⁻¹. However, this is not sufficient to cause any considerable increase in oxidation current when the NO stock solution is used for electrochemical sensor calibration over physiologically relevant concentrations; the NO sensitivity of bare Pt-disk electrodes operating at +900 mV (vs. SCE) was 1.08 nA μmol⁻¹ L, while that for NO₂⁻ was 5.9×10⁻³ nA μmol⁻¹ L. The stability of the NO stock solution was also monitored for up to 2 h after synthesis and 30 min was found to be the time limit within which calibrations should be performed.

Keywords: Nitric oxide; Laboratory synthesis; UV–visible spectroscopy; In-vivo voltammetry; Electrochemical sensors; Calibrations

A new, improved sensor for ascorbate determination at copper hexacyanoferrate modified carbon film electrodes by Rasa Pauliukaite; Mariana Emilia Ghica; Christopher M. A. Brett (pp. 972-978).

A new, improved sensor for the electrocatalytic determination of ascorbate has been developed that has both a low applied operating potential and a low detection limit. The sensor was constructed by depositing copper hexacyanoferrate film either electrochemically or chemically onto carbon film electrode, and it was then characterised by cyclic voltammetry and electrochemical impedance spectroscopy. Chemically deposited films were shown to be the best for ascorbate determination and were used as an amperometric sensor at +0.05 V versus SCE to determine ascorbate in wines and juice. The linear range extended to 5 mM with a limit of detection of 2.1 μM, the sensor was stable for more than four months, and it could be used continuously for at least 20 days.

Keywords: Ascorbate; Amperometric sensor; Carbon film electrodes; Copper hexacyanoferrate; Vitamin C in foods

A comparison of different types of gold–carbon composite electrode for detection of arsenic(III) by Andrew O. Simm; Craig E. Banks; Shelley J. Wilkins; Nikos G. Karousos; James Davis; Richard G. Compton (pp. 979-985).

A study has been conducted using abrasively modified basal and edge-plane graphite, carbon-paste, and carbon–epoxy electrodes to create gold–carbon composite electrodes. Using either nano or micro-sized gold particles their suitability for use in detecting arsenic(III) is assessed. It was found that gold arrays prepared from micron-sized particles gave the best performance for arsenic detection. In particular micron arrays produced in carbon-paste electrodes with an easily renewable surface work well for detection of arsenic, producing a detection limit of 5(±2)×10⁻⁹ mol L⁻¹, with a high sensitivity of 10(±0.1) A mol⁻¹ L.

Keywords: Arsenic(III); Carbon-paste electrodes; Anodic stripping voltammetry; Gold microarrays; Gold nanoarrays

A new determining method of copper(II) ions at ng ml⁻¹ levels based on quenching of the water-soluble nanocrystals fluorescence by Chen Bo; Zhong Ping (pp. 986-992).

CdTe nanocrystals (NCs) were prepared and modified in aqueous solution by using 3-mercaptopropionic acid (MPA). Compared with previous fluorescent sensors based on organic fluorophores, these NCs have the following merits. First, they are sensitive and the synthetic procedure is simple; second, they have narrow, tunable, symmetric emission spectra and are photochemically stable. The applicability of these NCs to the determination of Cu(II) ions was studied successfully. Maximum fluorescence intensity was produced at pH 7.8, with excitation and emission wavelengths at 365 and 532 nm, respectively. Under optimal conditions, linear relationships were found between the relative fluorescence intensity and the concentration of Cu(II) ions in the range 0–256 ng ml⁻¹ and the limit of detection was 0.19 ng ml⁻¹. This method was applied to determine real samples successfully. In addition, the quenching mechanism is also described.

Keywords: Fluorescence spectra; Nanocrystals; Cu(II) ions

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Analytical and Bioanalytical Chemistry (v.381, #4)

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Analytical and Bioanalytical Chemistry (v.381, #4)