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Analytica Chimica Acta (v.588, #1)

Editorial Board (pp. co1).

Contents (pp. v-vi).

Review of recent applications of flow injection spectrophotometry to pharmaceutical analysis by Paraskevas D. Tzanavaras; Demetrius G. Themelis (pp. 1-9).

Pharmaceutical analysis is one of the most important fields in analytical chemistry. The discovery of new drugs and the on-going update of international regulations for the safety and efficacy of pharmaceutical formulations demand the continuous development of new analytical methods. Inevitably, automation plays an important role, especially when a lot of samples have to be analyzed in the minimum of time. The present study reviews the applications of flow injection (FI) spectrophotometry to the determination of active pharmaceutical ingredients (APIs) in their respective formulations. However, the topic covered in this study is important not only to pharmaceutical analytical scientists. The principles, figures of merit and “chemistry” of the presented methods can be of interest to bio-analytical and clinical chemists as well for the analysis of biological samples, to environmental analysts that study the up-to-date demand of the determination of the fate of pharmaceuticals in the environment and even to toxicologists and forensic scientists. This review covers scientific contributions published later than 2000. A variety of FI procedures based on homogeneous (direct UV measurements, colour-forming reactions, metal–drug interactions) and heterogeneous (optical sensors and solid-phase reactors) systems are discussed. A third section covers on-line sample pretreatment (solid-phase extraction, liquid–liquid extraction, on-line digestion, etc.).

Keywords: Flow injection analysis; Spectrophotometry; Active pharmaceutical ingredients; Pharmaceutical formulations; Quality control

Determination of verapamil hydrochloride with 12-tungstophosphoric acid by resonance Rayleigh scattering method coupled to flow injection system by Dongpo Xu; Shaopu Liu; Zhongfang Liu; Xiaoli Hu (pp. 10-15).

A flow injection analysis (FIA) method coupled to resonance Rayleigh scattering (RRS) detection for the determination of verapamil hydrochloride (VP) was proposed. In pH 1.0 acidic medium, 12-tungstophosphoric acid (TP) reacted with VP to form an ion-association complex, which resulted in a significant enhancement of RRS intensity. The maximum scattering peak was located at 293nm. RRS intensity was proportional to the concentration of VP in the range of 0.017–13.0μgmL⁻¹, and the detection limit (3 σ) was 5.1ngmL⁻¹. The proposed method exhibited satisfactory reproducibility with a relative standard derivation (R.S.D.) of 2.1% for 11 successive determinations of 5.0μgmL⁻¹ VP. Therefore, a novel method for the determination of VP by FIA–RRS was developed. The optimum reaction conditions and the parameters of the FIA operation such as flow rate, injection volume, reactor length, and so on had been optimized in this paper. The present method had been applied to the determination of VP in serum samples and pharmaceuticals with satisfactory results. The maximal sample throughput in the optimized system was 80h⁻¹.

Keywords: Resonance Reyleigh scattering; 12-Tungstophosphoric acid; Verapamil hydrochloride; Flow injection analysis

Determination of dissolved sulphides in waste water samples by flow-through stripping chronopotentiometry with a macroporous mercury-film electrode by A. Manova; M. Strelec; F. Cacho; J. Lehotay; E. Beinrohr (pp. 16-19).

Sulphides in water samples were determined by stripping chronopotentiometry in a computer controlled flow system with a flow-through electrochemical cell. The working electrode was a porous glassy carbon electrode coated with Nafion and mercury. The sample was diluted with 0.1molL⁻¹ NaOH and analysed. Sulphides in the sample were collected in the porous electrode as mercury sulphide and then stripped by a current of −500μA. The limit of detection was found to be 1.6μgL⁻¹ and 0.5μgL⁻¹ for 1mL and 5mL of preconcentrated sample, respectively. The linear range for 1mL sample was found to be 5–400μgL⁻¹. The repeatability and reproducibility was found to be 2.6% and 4.8%, respectively. The method was applied to analyses of waste water samples from a tannery.

Keywords: Sulphide; Waste water; Tannery; Stripping chronopotentiometry

Rapid multi-residue method for the quantitative determination and confirmation of glucocorticosteroids in bovine milk using liquid chromatography–electrospray ionization–tandem mass spectrometry by Mark McDonald; Kristina Granelli; Pernilla Sjöberg (pp. 20-25).

Dexamethasone, betamethasone and prednisolone are synthetic glucocorticosteroids authorised for therapeutic use in bovine animals within the European Union. Dexamethasone and betamethasone are used mainly for the treatment of metabolic and inflammatory diseases. Prednisolone is used to treat bovine mastitis. Maximum residue limits (MRLs) of 0.3μgkg⁻¹ for both dexamethasone and betamethasone and 6.0μgkg⁻¹ for prednisolone in bovine milk have been established. 6α-Methylprednisolone and flumethasone are not authorised for use in bovine animals and are completely banned in bovine milk. The proposed method is based on deprotenisation of milk using 20% (w/v) trichloroacetic acid. Samples are filtered using glass microfibre filters and subject to clean-up using OASIS HLB solid phase extraction. Separation was achieved on a Hypercarb 100mm×2.1mm×5μm column. Mobile phase was: 90/10 acetonitrile/0.1% formic acid in water; flow rate was 600μLmin⁻¹. The method allowed the rapid identification and confirmation of the five glucocorticosteroids according to the criteria laid down in Commission Decision 2002/657/EC. Matrix calibration curves for all compounds were linear in the interval 0.0MRL to 2.0MRL with a correlation coefficient ( r²) higher than 0.96. Relative recoveries ranged from 97% for betamethasone to 111% for prednisolone. Precision at the MRL ranged from 3.8% for prednisolone to 13.8% for betamethasone. Decision limits, CCα, and detection capability, CCβ have been calculated for all compounds.

Keywords: Synthetic glucocorticosteroids; Dexamethasone; Betamethasone; Prednisolone; 6α-Methylprednisolone; Flumethasone; Milk; Liquid chromatography tandem mass spectrometry; Validation

Gold nanoparticle-based electrochemical detection of protein phosphorylation by Kagan Kerman; Miyuki Chikae; Shohei Yamamura; Eiichi Tamiya (pp. 26-33).

In this report, we demonstrate the application of Au nanoparticles in the electrochemical detection of protein phosphorylation. The method is based on the labeling of a specific phosphorylation event with Au nanoparticles, followed by electrochemical detection. The phosphorylation reaction is coupled with the biotinylation of the kinase substrate using a biotin-modified adenosine 5′-triphosphate [γ]-biotinyl-3,6,9-trioxaundecanediamine (ATP) as the co-substrate. When the phosphorylated and biotinylated kinase substrate is exposed to streptavidin-coated Au nanoparticles, the high affinity between the streptavidin and biotin resulted in the attachment of Au nanoparticles on the kinase substrate. The electrochemical response obtained from Au nanoparticles enables monitoring the activity of the kinase and its substrate, as well as the inhibition of small molecule inhibitors on protein phosphorylation. We determined the activity of Src non-receptor protein tyrosine kinase, p60^c-Src and protein kinase A in combination with their highly specific substrate peptides Raytide™ EL and Kemptide, respectively. The detection limits for Raytide™ EL and Kemptide were determined as 5 and 10μM, (S/N=3), and the detection limits for the kinase activity of p60^c-Src and protein kinase A (PKA) were determined as 5 and 10UmL⁻¹, (S/N=3), respectively. Tyrosine kinase reactions were also performed in the presence of a well-defined inhibitor, 4-amino-5-(4-chlorophenyl)-7-( t-butyl) pyrazolo[3,4-d]pyrimidine (PP2), and its negative control molecule, 4-amino-7-phenylpyrazol[3,4-d] pyrimidine (PP3), which had no inhibition effect. Based on the dependency of Au nanoparticle signal on inhibitor concentration, IC₅₀ value, half-maximal inhibition of the inhibitors was estimated. IC₅₀ values of PP2, genistein and herbimycin A to p60^c-Src were detected as 5nM, 25μM and 900nM, respectively. The inhibition of PKA activity on Kemptide using ellagic acid was monitored with an IC₅₀ of 3.5μM. The performance of the biosensor was optimized including the kinase reaction, incubation with streptavidin-coated Au nanoparticles, and the small molecule inhibitors. Kinase peptide-modified electrochemical biosensors are promising candidates for cost-effective kinase activity and inhibitor screening assays.

Keywords: Protein phosphorylation; Tyrosine kinase; Small molecule kinase inhibitors; Electrochemical biosensor; Colloidal gold nanoparticles

A general phase transfer protocol for synthesizing alkylamine-stabilized nanoparticles of noble metals by J. Yang; Jim Yang Lee; Heng-Phon Too (pp. 34-41).

The ethanol-mediated phase transfer protocol was extended herein to prepare alkylamine-stabilized nanoparticles of several noble metals by transferring them from aqueous environment into toluene. This method relies on the use of ethanol as a mediator to provide and maintain adequate contact between dodecylamine and metal nanoparticles during the transfer process and involves first mixing the metal hydrosols and an ethanol solution of dodecylamine and then extracting the dodecylamine-stabilized metal nanoparticles into toluene. Alkylamine-stabilized Ag, Pd, Rh, Ir and Os nanoparticles with 7.09, 3.45, 6.89, 2.42 and 4.52nm in diameter, respectively, could be prepared this way. The self-assembly of dodecylamine-stabilized Ag and Rh nanoparticles was also detected by transmission electron microscopy (TEM).

Keywords: Phase transfer; Alkylamine; Noble metal nanoparticles; Self-assembly

Fiber optic pH sensing with long wavelength excitable Schiff bases in the pH range of 7.0–12.0 by Sibel Derinkuyu; Kadriye Ertekin; Ozlem Oter; Serpil Denizalti; Engin Cetinkaya (pp. 42-49).

Most of the fluorescent pH probes work near neutral or acidic regions of the pH scale. In this work, two different fluorescent Schiff bases, chloro phenyl imino propenyl aniline (CPIPA) and nitro phenyl imino propenyl aniline (NPIPA), have been investigated for pH sensing in the alkaline region. Absorption and emission based spectral data, quantum yield, fluorescence lifetime, photostability and acidity constant (p K_a) of the Schiff bases were determined in conventional solvents and in PVC. The long wavelength excitable immobilized Schiff bases CPIPA ( λ_ex=556nm) and NPIPA ( λ_ex=570nm) exhibited absorption and emission based optical response to proton in the pH range of 8.0–12.0 and 7.0–12.0, respectively. Response of the CPIPA was fully reversible within the dynamic working range. The response times were between 3–13min. A relative signal change of 95% and 96% have been achieved for sensor dyes of CPIPA and NPIPA, respectively. The CPIPA displayed better fluorescence quantum yield ( ϕ_F=3.7×10⁻¹) and higher matrix compatibility compared to NPIPA ( ϕ_F=1.6×10⁻¹) in immobilized PVC. The CPIPA and NPIPA exhibited a slight cross sensitivity to the ions of Hg⁺ and Fe³⁺, respectively.

Keywords: Fiber optic pH sensor; Fluorescent pH indicator; Schiff base

Separation and determination of diversiform phytosterols in food materials using supercritical carbon dioxide extraction and ultraperformance liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry by Baiyi Lu; Ying Zhang; Xiaoqin Wu; Jiayi Shi (pp. 50-63).

This paper presents at first time that the ultra-performance™ liquid chromatographic atmospheric pressure chemical ionization mass spectrometer (UPLC-APCI–MS) was used as an efficient method for the identification and quantification of diversiform phytosterols in food materials. The sample preparation consisted of extraction by supercritical carbon dioxide fluid extraction (SCE) and saponification by refluxing with ethanolic KOH, and then the non-saponificable fraction was extracted with petroleum ether. This fraction was subjected to solid phase extraction (SPE) on silica gel cartridge and then the sterols were eluted with hexane-ethyl acetate. Sterols were separated on an Acquity UPLC™ BEH C18 column (100mm×1.0mm, 1.7μm particle size) with a gradient of methanol/water (1% acetonitrile) at a flow of 0.1mLmin⁻¹. The determination was performed in selective ion monitoring mode. The quality parameter of the developed method was established using 6-ketocholestanol as internal standard. Limits of quantification (LOQ) were 0.1754, 0.0341, 0.0500, 0.0205, 0.0225, 0.3674, 0.0241, 0.0272, 0.0076μgL⁻¹ and 0.1525μgmL⁻¹ for 6-ketocholestanol, desmosterol, ergosterol, cholesterol, lanosterol, cholestanol, campesterol, stigmasterol, β-sitosterol, and stigmastanol, respectively. The intra- and inter-day determination precision for the 10 phytosterols were less than 5 and 6% in relative standard deviations, and their recoveries were located in the range of 94–107%. The developed approach has been applied successfully for efficient determination of diversiform phytosterols in food materials, including corn, sesame, oat and peanut.

Keywords: Abbreviations; UPLC-MS; ultra-performance™ liquid chromatographic-mass spectrometer; APCI; atmospheric pressure chemical ionization; SIM; selective ion monitoring; LOD; limits of detection; LOQ; limits of quantification; SCE; supercritical carbon dioxide extraction; SPE; solid phase extractionPhytosterols; Separation and determination; Supercritical carbon dioxide fluid extraction; Ultra-performance™ liquid chromatography-mass spectrometer

Enrichment of phenols from water with in-situ derivatization by in-tube solid phase microextraction–solvent desorption prior to off-line gas chromatographic determination with large-volume injection by Jacek Olejniczak; Jacek Staniewski (pp. 64-72).

Sorption of phenols from water into the stationary phase of open tubular columns (named in-tube solid phase microextraction) as an enrichment method for gas chromatographic (GC) analysis of aqueous samples was studied. The effect of operating conditions (stationary phase polarity, swelling of the stationary phase by solvents, number of sampling cycles, salting-out effect, sampling velocity, flow rate of desorption solvent) on the process efficiency was evaluated. Real water samples were also used in this study. Swelling of the stationary phase by organic solvent enables the volume of the stationary phase to be increased and its properties to be modified. The use of toluene or tetrachloromethane for the purpose results in high extraction efficiencies for most phenols. The results demonstrated a direct relationship between the extracted amount of phenols and its initial concentration in the sample. The limit of detection in off-line analyses applying large-volume injection was lower than 0.04μgL⁻¹.These results of the use of in-tube solid phase microextraction with solvent desorption as a non-exhaustive (equilibrium sorptive) enrichment method show a great potential for on-line chromatographic analysis of micropollutants in real water samples.

Keywords: Capillary gas chromatography; Enrichment method; Open-tubular extraction; In-tube solid phase microextraction; Phenols; Water analysis

Synthesis of novel chitosan resin derivatized with serine diacetic acid moiety and its application to on-line collection/concentration of trace elements and their determination using inductively coupled plasma-atomic emission spectrometry by Lukman Hakim; Akhmad Sabarudin; Mitsuko Oshima; Shoji Motomizu (pp. 73-81).

A novel chelating resin functionalized with serine diacetic acid moiety was synthesized by using chitosan as base material, and applied to the collection/concentration of trace elements in environmental water samples, followed by the determination using inductively coupled plasma-atomic emission spectrometer (ICP-AES). The synthesized resin, crosslinked chitosan serine diacetic acid (CCTS-SDA), showed good adsorption behavior toward trace amounts of Cd, Pb, Cu, Ni, V, Ga, Sc, In, and Th in a wide pH range. Additionally, rare earth elements also can be retained on the resin at neutral pH region. The adsorbed elements can be easily eluted with 1molL⁻¹ of nitric acid, and their recoveries were found to be 90–100%. The CCTS-SDA was packed in a mini-column, which was then installed in a computer-controlled auto-pretreatment system (Auto-Pret System) for on-line trace elements collection and determination with ICP-AES. Experimental parameters which related to the improvement of sensitivity and reproducibility were optimized. The limits of detection (LOD) for 13 elements were found to be in sub-ppb level. The proposed method with CCTS-SDA resin was successfully applied to the determination of trace elements in river water samples. The method was validated by determining a certified reference material of river water, SLRS-4.

Keywords: Chelating resin; Chitosan; Serine diacetic acid moiety; Trace elements; On-line pretreatment; Computer control; Inductively coupled plasma-atomic emission spectrometry; SLRS-4

Admicelle-mediated collection followed by flotation for the preconcentration of trace metals in fresh waters by Hiroaki Matsumiya; Yosuke Yatsuya; Masataka Hiraide (pp. 82-87).

Dithizone-impregnated admicelles were prepared by mixing silica particles with dithizone and cetyltrimethylammonium chloride in 0.1molL⁻¹ aqueous ammonia. The resulting admicelles were added to 1000mL of sample solution and dispersed by stirring for 15min. Traces of Ni(II), Cu(II), Ga(III), Cd(II), Pb(II) and Bi(III) in the solution were simultaneously incorporated into the admicelles at pH 7.5–9. With the aid of a rising stream of numerous tiny bubbles, the admicelles were floated on the solution surface and collected in a small sampling vessel by suction. The metals were desorbed from the admicelles with dilute nitric acid and determined by inductively coupled plasma-mass spectrometry. The proposed method offered a 100-fold multielement preconcentration and it was applicable to the analysis of river and pond waters.

Keywords: Admicelle; Flotation; Preconcentration; Trace metal; Fresh water; Inductively coupled plasma-mass spectrometry

Spectrophotometric determination of ascorbic acid by the modified CUPRAC method with extractive separation of flavonoids–La(III) complexes by Mustafa Özyürek; Kubilay Güçlü; Burcu Bektaşoğlu; Reşat Apak (pp. 88-95).

The proposed method for ascorbic acid: AA (Vitamin C) determination is based on the oxidation of AA to dehydroascorbic acid with the CUPRAC reagent of total antioxidant capacity assay, i.e., Cu(II)-neocuproine (Nc), in ammonium acetate-containing medium at pH 7, where the absorbance of the formed bis(Nc)-copper(I) chelate is measured at 450nm. The flavonoids (essentially flavones and flavonols) normally interfering with the CUPRAC procedure were separated with preliminary extraction as their La(III) chelates into ethylacetate (EtAc). The Cu(I)-Nc chelate responsible for color development was formed immediately with AA oxidation. Beer's law was obeyed between 8.0×10⁻⁶ and 8.0×10⁻⁵M concentration range, with the equation of the linear calibration curve: A450_nm=1.60×10⁴ C (moldm⁻³)−0.0596. The relative standard deviation (R.S.D.) in the analysis of N=45 synthetic mixtures containing 1.25×10⁻²mM AA with flavonoids was 5.3%. The Cu(II)-Nc reagent is a lower redox-potential and therefore more selective oxidant than the Fe(III)-1,10-phenanthroline reagent conventionally used for the same assay. This feature makes the proposed method superior for real samples such as fruit juices containing weak reductants such as citrate, oxalate and tartarate that may otherwise produce positive errors in the Fe(III)-phen method when equilibrium is achieved. The developed method was applied to some commercial fruit juices and pharmaceutical preparations containing Vitamin C+bioflavonoids. The findings of the developed method for fruit juices and pharmaceuticals were statistically alike with those of HPLC. The proposed spectrophotometric method was practical, low-cost, rapid, and could reliably assay AA in the presence of flavonoids without enzymatic procedures open to interferences by enzyme inhibitors.

Keywords: Ascorbic acid determination; CUPRAC method; Copper(II)-neocuproine; Spectrophotometry; La(III) chelation; Solvent extraction; Flavonoids separation

Colored inks analysis and differentiation: A first step in artistic contemporary prints discrimination by Anna Vila; Nuria Ferrer; Jose F. García (pp. 96-107).

Prints are the most popular artistic technique. Due to their manufacturing procedure, they are also one of the most frequently falsified types of artwork. In terms of their economic and historic value, the chemical analysis and characterisation of coloured inks and their principal constituent materials (pigments), together with the historical and aesthetic information available in the Catalogues Raisonées, are important tools in distinguishing originals from non-original prints.The chemical characterisation and discrimination of coloured inks has test in this study. Analysis using Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and X-ray diffraction (XRD) has been done on blue pigments and inks, due to this colour is one of the most representative for the presence of organic and inorganic materials in their composition. Conclusion obtained for this colour would demonstrate the capability of the approach when it is applied to any other coloured set of inks.

Keywords: Infrared spectroscopy; Scanning Electron microscopy; Blue inks; Blue pigments; Prints

Comparative study of mobile Raman instrumentation for art analysis by P. Vandenabeele; K. Castro; M. Hargreaves; L. Moens; J.M. Madariaga; H.G.M. Edwards (pp. 108-116).

In archaeometry, one of the main concerns is to extract information from an art object, without damaging it. Raman spectroscopy is being applied in this research field with recent developments in mobile instrumentation facilitating more routine analysis. This research paper evaluates the performances of five mobile Raman instruments (Renishaw RA100, Renishaw Portable Raman Analyser RX210, Ocean Optics RSL-1, Delta Nu Inspector Raman, Mobile Art Analyser - MArtA) in three different laboratories. A set of samples were collected, in order to obtain information on the spectral performances of the instruments including: spectral resolution, calibration, laser cut-off, the ability to record spectra of organic and inorganic pigments through varnish layers and on the possibilities to identify biomaterials. Spectra were recorded from predefined regions on a canvas painting to simulate the investigation of artworks and the capabilities to record spectra from hardly accessible areas was evaluated.

Keywords: Raman spectroscopy; Archaeometry; Art analysis; Raman instrumentation; Mobile equipment; Fibre optic; Comparative study

A sensitive spectrophotometric method for determination of carbon tetrachloride with the aid of ultrasonic decolorization of methyl orange by Wei Luo; Zhifei Chen; Lihua Zhu; Fang Chen; Limin Wang; Heqing Tang (pp. 117-122).

A sensitive method for carbon tetrachloride (CCl₄) determination has been developed with the aid of ultrasonic oxidation decolorization of methyl orange (MO). It is found that the ultrasonic oxidation decolorization rate of MO can be significantly promoted by adding a little amount of CCl₄. The increased ultrasonic decolorization rate of MO is strongly dependent on the concentration of CCl₄ added, and a linear correlation is observed between the amount of CCl₄ and the decolorization rate of MO in the ultrasonic oxidation process. Thus, the CCl₄ determination is transformed to a simple and direct determination of the decoloration extent of MO solution at a given concentration. As an indirect spectrophotometric determination of CCl₄, the new method is sensitive and easy of operation with a maximum wavelength of 508nm, molar absorptivity of 3.83×10⁴Lmol⁻¹cm⁻¹, and a Sandell sensitivity of 7.96×10⁻³μgcm⁻². Under optimized conditions, Beer's law is obeyed in the range of 0.4–20mgL⁻¹ of CCl₄ (DL=0.19mgL⁻¹, r=0.9996). The concentrations of CCl₄ in several practical samples have been determined satisfactorily by using this method.

Keywords: Carbon tetrachloride determination; Spectrophotometry; Methyl orange; Ultrasonic

Synthesis and investigation on the interaction with calf thymus deoxyribonucleic acid of a novel fluorescent probe 7-oxobenzo[ b][1,10]phenanthroline-12(7H)-sulfonic acid by Longhua Guo; Bin Qiu; Guonan Chen (pp. 123-130).

In this paper, the synthetic route of a potential antitumor reagent, benzo[ b][1,10] phenanthrolin-7(12H)-one (BPO), was improved. A sulfonic group was introduced to BPO to form a new compound, 7-oxobenzo[ b][1,10]phenan-throline-12(7H)-sulfonic acid (OPSA), in order to enhance its water-solubility. The molecular structure of OPSA has been confirmed by IR, UV, MS,¹H NMR and elements analysis. It was proved in our experiments that DNA could quench the fluorescence of OPSA and the maximum quenched intensity appeared at 408nm ( λ_ex=284nm). The quenched fluorescence intensity was proportional to the concentration of DNA. Based on this phenomenon, OPSA had been used as the fluorescent probe for detection of calf thymus DNA (ct-DNA) and the corresponding linear response range was from 1.0 to 150.0μgmL⁻¹ and the limit of detection (LOD) was 3.8ngmL⁻¹. Its interaction with ct-DNA was investigated by fluorescence, absorption and viscosity measurements. When binding to ct-DNA, OPSA showed obvious fluorescence quenching and the quenched intensity was stable with the presence and absence of NaCl. The absorption spectra of OPSA had no evidence of increasing or decreasing when ct-DNA was added. The viscosity of OPSA and ct-DNA mixture showed no obvious change comparing with the viscosity of ct-DNA along. The results suggested that the interaction between OPSA and ct-DNA was groove binding in nature. Scatchard plots constructed from fluorescence titration data gave a binding constant of 8.9×10⁵Lmol⁻¹ and a binding site size of 0.35 base pairs per bound drug molecule.

Keywords: Antitumor reagent; Benzophenanthrolinone; Fluorescence probe; Deoxyribonucleic acid

Simultaneous enzymatic kinetic determination of pesticides, carbaryl and phoxim, with the aid of chemometrics by Yongnian Ni; Dongxia Cao; Serge Kokot (pp. 131-139).

A sensitive and selective enzymatic kinetic method for the simultaneous determination of mixtures of carbaryl and phoxim pesticides was researched and developed. It was based on the inhibitory effect of the pesticides on acetylcholinesterase (AChE), and the use of 5,5′-dithiobis(2-nitrobenzoic) acid (DTNB) as a chromogenic reagent for the thiocholine iodide (TChI) released from the acetylthiocholine iodide (ATChI) substrate. The DTNB-thiocholine reaction was investigated by a spectrophotometric-kinetic approach. The complex rate equation for the formation of the chromogenic product, P, was solved under certain experimental conditions, which enabled the absorbance ( A_P, at λ_max=412nm) from the mixtures of the two pesticide inhibitors to be directly related to their concentrations provided the absorbance additivity was followed. The spectra were measured for mixtures of carbaryl and phoxim at different concentrations, and at t=904s, T=35°C, pH=7.5, c_ATChI=0.14, and c_AChE=0.10mgmL⁻¹. The detection limits of the enzymatic kinetic spectrophotometric procedures for the determination of the carbaryl and phoxim were 4.7 and 0.59μgL⁻¹, respectively.Calibration models for chemometrics methods, such as principal component regression (PCR), partial least squares (PLS) and radial basis function-artificial neural network (RBF-ANN) were constructed and verified with synthetic samples of the mixtures of the two pesticides. The best performing model was based on the RBF-ANN method yielding at approximately 10ppb analyte concentrations, %RPE_T (carbaryl=5.2; phoxim=6.5), %Recovery (approx.105%) and %RPE_T (6.5). Various spiked town-water samples produced recoveries in the range of 98.8–103% for each pesticide.

Keywords: Acetylcholinesterase; Enzymatic kinetic method; Pesticides; Carbaryl; Phoxim; Chemometrics; Radial basis function-artificial neural network

Determination of various alcohols based on a new immobilized enzyme fluorescence capillary analysis by Yong-Sheng Li; Xiu-Feng Gao (pp. 140-146).

A novel method for the determination of ethanol in tequila based on the immobilized enzyme fluorescence capillary analysis (IE-EFCA) has been proposed. Alcohol dehydrogenase (ADH) was immobilized in inner surface of a capillary and an immobilized enzyme capillary bioreactor (IE-ECBR) was formed. After nicotinamide adenine dinucleotide (NAD⁺) as an oxidizer is mixed with alcohol sample solution, it was sucked into the IE-ECBR. The fluorescence intensity of the mixed solution in the IE-ECBR was detected at λ_ex=350nm and λ_em=459nm. The experimental conditions are as follows: The reaction time is 20min; temperature is 40°C; the concentrations of phosphate buffer solution (pH 7.5) and NAD⁺ are 0.1molL⁻¹ and 5mmolL⁻¹, respectively; immobilization concentration of ADH is 10UL⁻¹. The determination range of ethanol is 2.0–15.0gL⁻¹ ( F=10.44C+6.6002, r>0.9958); its detection limit is 1.11gL⁻¹; and relative standard deviation is 1.9%. IE-EFCA method is applicable for the determination of the samples containing alcohol in medicine, industry and environment.

Keywords: Immobilized enzyme; Fluorescence capillary analysis; Ethanol determination

In situ gas generation for micro gas analysis system by Shin-Ichi Ohira; Kiyoshi Someya; Kei Toda (pp. 147-152).

This manuscript describes an easy, simple and small system for gas generation. The aim of this work was to establish gas generation for on-site checking or on-site calibration of a micro gas analysis system, μGAS. The new technology, μGAS, achieves real-time measurement of trace level gases in the field. To make the measurement more reliable and convenient, a small gas generation system has been developed. Source reagent solution and generator solution are made to flow by micropumps, mixed in a miniature coil, and then introduced into a microchannel gas desorber. The gas desorber is comprised of a honeycomb-shaped microchannel covered with a thin porous polytetrafluoroethylene membrane. A good generation factor is obtained due to the wide vaporization area and thin solution layer of the microchannel desorber. Generation of H₂S, SO₂, CH₃SH and NH₃ gases were examined. Concentrations of the gases are easily controlled by the source reagent concentration and the solution flow rates. At 100μLmin⁻¹ flow rates for both the source and generator solutions, 30ppbv to 2ppmv concentrations are formed with a gas flow rate of 200mLmin⁻¹. The gas concentration is proportional to the source concentration. The gas generation can be performed only when needed. The gas generation system is combined with μGAS for on-site calibration.

Keywords: Standard gas in situ generation; On-site calibration; Micro gas analysis system; Microchannel gas desorber; Hydrogen sulfide; Sulfur dioxide; Methyl mercaptan; Ammonia; Micro flow analysis

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Analytica Chimica Acta (v.588, #1)