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Analytical and Bioanalytical Chemistry (v.375, #5)

The sky is not falling...accepting failure to create innovation in experimentation by John Fetzer (pp. 597-598).

Structural characterization of neutral oligosaccharide mixtures through a combination of capillary electrochromatography and ion trap tandem mass spectrometry by Amy H. Que; Milos V. Novotny (pp. 599-608).

A CEC/ESI-MS/MS combined system has been developed for the separation and on-line structural analysis of neutral oligosaccharides. Various types of isomeric oligosaccharides were first successfully separated by CEC using polar monolithic columns, while the on-line tandem mass spectrometry has been explored to differentiate and elucidate the structures of isomeric oligosaccharides. The experimentally obtained tandem spectra usually provide sequence, branching, and linkage information. Oligosaccharide isomers with a different monomeric composition and branching showed different patterns of glycosidic linkage cleavage (B- and Y-ion series), allowing us to deduce their sequence and branching points. Isomers with different linkages were distinguished by identifying cross-ring fragment ions (A-ion series). While (1→4) linkages yielded dominant ^0,2A ions, (1→6) linkages showed an extensive and complete cross-ring cleavage series: ^0,2A, ^0,3A, and ^0,4A ions. Although the anomeric configurations and monosaccharide identification are rarely obtained from tandem MS, the relevant mixture components can be completely resolved with high-efficiency CEC columns featuring a polar functionality.

Keywords: Capillary electrochromatography Monolithic columns Isomeric oligosaccharides Tandem mass spectrometry

Quantification of bile acids directly from urine by MALDI–TOF–MS by DebraLynn Mims; David Hercules (pp. 609-616).

The ability to quantify mixtures of bile acids using matrix-assisted laser desorption/ionization time-of-flight (MALDI–TOF) mass spectrometry directly from urine has been demonstrated. Six cholic acid derivatives were selected for analysis: taurocholic acid (TCA), taurochenodeoxycholic acid (TCDCA), taurolithocholic acid (TLCA), glycocholic acid (GCA), glycochenodeoxycholic acid (GCDCA), and glycolithocholic acid (GCDCA). Urine samples were pre-concentrated and purified using solid-phase extraction (SPE) columns. The method was optimized to eliminate suppression effects, and proved to be reproducible from day to day. Calibration curves averaged from three days were obtained for the bile acids directly from urine, and then tested for their ability to accurately determine concentrations from one measurement. In summary, a simple, rapid method has been developed for the quantification of bile salts from urine with SPE clean-up by MALDI-MS.

Keywords: Bile acids MALDI SPE Quantification Urine

Determination of hydrocortisone, polymyxin B and Zn-bacitracin in pharmaceutical preparations by micellar electrokinetic chromatography by J. M. Lemus Gallego; J. Pérez Arroyo (pp. 617-622).

A new, simple and accurate micellar electrokinetic chromatography (MEKC) method is established for quantification of hydrocortisone, polymyxin B and Zn-bacitracin in local pharmaceutical preparations. The separation was carried out at 25 °C and 25 kV, using a 15 mmol L⁻¹ phosphate–15 mmol L⁻¹ borate buffer (pH 8.2), 60 mmol L⁻¹ sodium dodecylsulfate (SDS), and 10% methanol-water (v/v) as background electrolyte. Under these conditions the analysis takes about 23 min. The method has been applied for quantifying these compounds in two different commercial pharmaceutical products and the method gave good results when compared with a reference spectrophotometric multivariate calibration method.

Keywords: Hydrocortisone Polymyxin B Zn-bacitracin Micellar electrokinetic chromatography (MECK)

Direct determination of four fluoroquinolones, enoxacin, norfloxacin, ofloxacin, and ciprofloxacin, in pharmaceuticals and blood serum by HPLC by V. F. Samanidou; C. E. Demetriou; I. N. Papadoyannis (pp. 623-629).

A rapid, accurate and sensitive method has been developed for the quantitative determination of four fluoroquinolone antimicrobial agents, enoxacin, norfloxacin, ofloxacin and ciprofloxacin, with high in-vitro activity against a wide range of Gram-negative and Gram-positive organisms.A Kromasil 100 C₈ 250 mm×4 mm, 5 μm analytical column was used with an eluting system consisting of a mixture of CH₃CN–CH₃OH–citric acid 0.4 mol L⁻¹ (7:15:78 %, v/v). Detection was performed with a variable wavelength UV–visible detector at 275 nm resulting in limits of detection: 0.02 ng per 20 μL injection for enoxacin and 0.01 ng for ofloxacin, norfloxacin and ciprofloxacin. Hydrochlorothiazide (HCT) was used as internal standard at a concentration of 2 ng μL⁻¹. A rectilinear relationship was observed up to 2 ng μL⁻¹ for enoxacin, 12 ng μL⁻¹ for ofloxacin, 3 ng μL⁻¹ for norfloxacin, and 5 ng μL⁻¹ for ciprofloxacin. Separation was achieved within 10 min. The statistical evaluation of the method was examined by performing intra-day (n=8) and inter-day precision assays (n=8) and was found to be satisfactory with high accuracy and precision. The method was applied to the direct determination of the four fluoroquinolones in human blood serum. Sample pretreatment involved only protein precipitation with acetonitrile. Recovery of analytes in spiked samples was 97±6% over the range 0.1–0.5 ng μL⁻¹.

Keywords: Fluoroquinolones Antibiotics Enoxacin Norfloxacin Ofloxacin Ciprofloxacin HPLC Pharmaceuticals Biological fluids Human blood serum

Solid-state ²⁹Si MAS NMR studies of diatoms: structural characterization of biosilica deposits by R. Bertermann; N. Kröger; R. Tacke (pp. 630-634).

Four different diatom species (Chaetoceros debilis, Chaetoceros didymum, Cylindrotheca fusiformis, Nitzschia angularis) were studied by solid-state ²⁹Si MAS NMR spectroscopy. To determine the Q²:Q³:Q⁴ ratios in the biosilica deposits of the diatoms, quantitative ²⁹Si MAS NMR experiments were performed. This analysis did not reveal any differences regarding the molecular architecture of the silica (i.e. the degree of condensation of the SiOH units (2 ≡SiOH → ≡Si–O–Si≡ + H₂O)) from the different diatom species. However, complete cells showed significantly smaller Q⁴:Q³ ratios (1.8–1.9) than extracted cell walls (2.5–2.8), indicating the existence of intracellular pools of less condensed silica.

Keywords: Biomineralization Biosilica Cell wall Diatoms Solid-state NMR

Separation of positional isomers by the use of coupled shape-selective stationary phase columns by Yajing Shao; Philip Marriott (pp. 635-642).

The successful separation of 2- and 3-methyl-substituted positional isomers of butanol, butyl acetate, and butanoic acid and its ethyl ester, is reported. These compounds are of interest in the study of wine flavour, however the separation of the 2- and 3-methyl isomers may present problems, and more so in the presence of the wine matrix components, when single capillary column gas chromatography (GC) is used. The strategy to achieve separation was based on the use of shape-selective cyclodextrin derivative (CDD) capillary columns (commonly referred to as chiral columns). These columns provide simultaneous resolution of the enantiomeric pairs of the 2-methyl isomers, and at the same time the ability to separate the 3-methyl isomer from the 2-methyl is achieved in all but the case of the (S)-2- and 3-methylbutanol. The advantages of using shape-selective columns to perform this study is demonstrated, with coupling of two CDD columns giving improved separations of these compounds. Although these compounds are relatively volatile, cryogenic modulated comprehensive two-dimensional GC was shown to provide good pulsed peak profiles with chiral separation in the first dimension when a thicker film trapping column segment was employed. The components of interest were well separated from other wine matrix components.

Keywords: Comprehensive two-dimensional gas chromatography GC×GC Cyclodextrin phase Shape selectivity Geometrical isomer Cryogenic modulation Enantiomer separation Solid phase microextraction

Characterisation of quaternary mixtures by the apparent content curves method: identification of tocopherols in vegetable oils by A. R. Maurí-Aucejo; M. Llobat-Estellés; R. Marín-Saez (pp. 643-652).

A procedure for identification of the compounds in quaternary mixtures has been developed. The proposed procedure is based on the apparent content curves method. From these curves and using the Q parameter, work conditions are selected and quaternary mixtures treated as "pseudoternary" mixtures.A simple strategy to test matrix effects at working wavelengths has been developed, identification limits established and following the identification table quaternary mixtures were easily characterised. The procedure has been applied to the identification of phenols in mixtures by UV–visible spectrophotometry and tocopherols in edible oils by fluorimetry. Results obtained for edible oils are in agreement with the composition obtained by use of the reference method.

Keywords: Apparent content curves Identification Tocopherols Edible oils

A comparative study of the correction of systematic errors in the quantitation of pyrethroids in vegetables using calibration curves prepared using standards in pure solvent by M. Martínez-Galera; T. López-López; M. D. Gil-García; J. L. Martínez-Vidal; D. Picón-Zamora; L. Cuadros-Rodríguez (pp. 653-660).

A comparative study of two mathematical approaches was performed in order to correct systematic errors due to the presence of the unexpected interferences which appear when the quantitation of the analyte in real samples is carried out with calibration curves built using standards in pure solvent. These methods consisted in the establishment of different mathematical expressions which transform the concentration (Cs) obtained using calibration graphs built using pure solvent into the corrected concentration (C_M) that should be obtained if the quantitation is carried out with calibration curves built using standards dissolved in blank matrix extracts. In the two approaches the correction is performed from the results of an intermediate precision study which was carried out using both calibration graphs (prepared using pure solvent and blank matrix extract). By using ANCOVA to compare the slope of both solvent-based and matrix-matched calibration graphs, matrix effect was found in the determination of deltamethrin in tomato and acrinathrin in tomato and pepper. In these cases, both approaches led to good results.

Keywords: Pyrethroids Photochemically induced fluorescence Vegetables Matrix effect ANCOVA HPLC

Spectrofluorimetric determination of formaldehyde by a flow-injection method based on its catalytic effect on the acridine yellow–bromate reaction by T. Pérez-Ruíz; C. Martínez-Lozano; V. Tomás; J. Fenoll (pp. 661-665).

A flow-injection configuration for the determination of formaldehyde is proposed. The method is based on the enhancing effect of formaldehyde on the oxidation of acridine yellow by bromate in acidic medium. The proposed procedure is simple, inexpensive, sensitive and suitable for concentrations of formaldehyde between 1 and 56 μg mL⁻¹. A sampling-rate of 60 samples h⁻¹ was achieved. The effect of several organic and inorganic species was studied. The method was applied to the determination of formaldehyde in pharmaceuticals, milk and air in work environments. The accuracy of the method was confirmed by comparing the results with those obtained using the standard acetylacetone method.

Keywords: Formaldehyde Flow-injection analysis Spectrofluorimetry Air Milk

The effect of the presence of volatile organoselenium compounds on the determination of inorganic selenium by hydride generation by Mª. Eva Moreno; Concepción Pérez-Conde; Carmen Cámara (pp. 666-672).

As a result of microbiological activity it is possible to find dimethylselenium (DMSe) and dimethyldiselenium (DMDSe) in a wide type of environmental samples, such as soils, sediments, sewage sludges and plants where methylation can take place.Selenium determination by hydride-generation (HG) techniques requires its presence as Se(IV). Consequently, inorganic speciation by hydride generation techniques is done by first determining Se(IV) and then, after reduction of Se (VI) to Se(IV), the total selenium. Therefore, the concentration of Se (VI) is evaluated as the difference between total inorganic selenium and Se(IV). In the present work it could be demonstrated that DMSe and DMDSe are forming other volatile species by reaction with sodium borohydride, applying the same reduction condition as for inorganic selenium. These species are subsequently detected by several atomic techniques (atomic absorption AAS, atomic fluorescence AFS and inductively coupled plasma–mass spectrometry ICP–MS). The error that their presence can cause in determination of inorganic selenium has been evaluated. The magnitude of this error depends on the specific analytical detector used.The coupling of pervaporation–atomic fluorescence is proposed for the identification of these species and pervaporation–gas chromatography–atomic fluorescence for their individual quantification.

Keywords: Dimethylselenium Dimethyldiselenium Hydride generation Pervaporation Capillary gas chromatography Atomic fluorescence spectrometer

Microwave sample-digestion procedure for determination of arsenic in moss samples using electrothermal atomic absorption spectrometry and inductively coupled plasma mass spectrometry by Matti Niemelä; Paavo Perämäki; Juha Piispanen (pp. 673-678).

Arsenic in moss samples was determined by electrothermal atomic absorption spectrometry (ETAAS) after microwave-assisted sample digestion. Two different sample masses (500 mg and 1000 mg) and three different microwave ovens were used in the digestion. There was a slight difference in the digestion efficiency, as determined by the residual carbon concentrations of 500 mg digested samples, between the microwave ovens. The arsenic results obtained for moss reference samples were, in most cases, satisfactory. However, phosphorus was found to have a reducing influence on the arsenic peak area in the ETAAS determination. According to the results, it was not possible to reduce the phosphorus interference by increasing the amount of Mg(NO₃)₂ in the Pd–Mg chemical modifier. The arsenic results obtained by ETAAS were compared to those obtained by inductively coupled plasma mass spectrometry (ICP–MS).

Keywords: Arsenic ETAAS ICP–MS Moss samples Microwave sample digestion Phosphorus interference

Separation of arsenic species by capillary electrophoresis with sample-stacking techniques by Zu Liang Chen; Jin-Ming Lin; Ravendra Naidu (pp. 679-684).

A simple capillary zone electrophoresis procedure was developed for the separation of arsenic species (AsO₂ ²⁻, AsO₄ ²⁻, and dimethylarsinic acid, DMA). Both counter-electroosmotic and co-electroosmotic (EOF) modes were investigated for the separation of arsenic species with direct UV detection at 185 nm using 20 mmol L⁻¹ sodium phosphate as the electrolyte. The separation selectivity mainly depends on the separation modes and electrolyte pH. Inorganic anions (Cl⁻, NO₂ ⁻, NO₃ ⁻ and SO₄ ²⁻) presented in real samples did not interfere with arsenic speciation in either separation mode. To improve the detection limits, sample-stacking techniques, including large-volume sample stacking (LVSS) and field-amplified sample injection (FASI), were investigated for the preconcentration of As species in co-CZE mode. Less than 1 μmol L⁻¹ of detection limits for As species were achieved using FASI. The proposed method was demonstrated for the separation and detection of As species in water.

Keywords: As species CZE Sample stacking Natural water

Solid-phase spectrophosphorimetric determination of the pesticide o-phenylphenol in water and vegetables by L. F. Capitán-Vallvey; M. K. A. Deheidel; R. Avidad (pp. 685-691).

A phosphorimetric method for the determination of o-phenylphenol (OPP) using filter paper as solid support and Tl(I) as heavy metal enhancer of the phosphorescent signal is proposed. The phosphorescence measurements were carried out by placing the paper with the sample between two plates of quartz, thus avoiding the quenching effect produced by atmospheric oxygen and moisture. The linear dynamic range of the method was 0.5–4.0 mg L⁻¹ and the detection and quantification limits were 0.03 and 0.11 mg L⁻¹, respectively. The precision of the method (expressed as relative standard deviation) was 1.7% for a sample containing 2.0 mg L⁻¹ of analyte. The method has been applied to the determination of OPP in different types of water, lettuce, string beans and peppers, with recoveries ranging between 97.1 and 100.7%

Keywords: Solid-phase phosphorescence o-Phenylphenol determination Water and vegetables analysis

PVC-membrane ion-selective bulk optode for Ag⁺ ion based on hexathia-18-crown-6 and 1,2-benzo-3-octadecanoylimino-7-diethylaminophenoxazine by Mojtaba Shamsipur; Shohreh Rouhani; Ali Mohajeri; Mohammad Reza Ganjali (pp. 692-697).

A silver-selective optode membrane incorporating hexathia-18-crown-6 for cation recognition and a lipophilic chromoionophore 1,2-benzo-3-octadecanoylimino-7-diethylaminophenoxazine for transduction has been prepared. The PVC membrane composition was optimized to result in the largest working concentration range. The response range of the proposed optode is 5.0×10⁻⁹–5.0×10⁻⁵ mol L⁻¹ Ag⁺ with a limit of detection of 1.0×10⁻⁹ mol L⁻¹. The probe works well at pH 5.0 and revealed small ion interference and good selectivity, reproducibility and stability.

Keywords: Silver analysis PVC-membrane ion-selective bulk optode Hexathia-18-crown-6 1,2-Benzo-3-octadecanoylimino-7-diethylaminophenoxazine

Solid-phase extraction–spectrophotometric determination of uranium(VI) in natural waters by Susan Sadeghi; Darush Mohammadzadeh; Yadollah Yamini (pp. 698-702).

A method for the extraction and determination of uranyl ion in natural waters using octadecyl bonded silica membrane disks modified with piroxicam and spectrophotometry with arsenazo(III) is proposed. The perconcentration step was studied with regard to experimental parameters such as amount of extractant, type and amount of eluent, pH, flow rates and tolerance limit of diverse ions on the recovery of uranyl ion. The limit of detection of the proposed method is 0.4 µg L⁻¹ of uranyl. The method was applied to the recovery of uranyl from different water samples.

Keywords: Uranyl preconcentration Octadecyl silica disk Piroxicam Spectrophotometric determination

Simultaneous determination of 2-nitrophenol and 4-nitrophenol based on the multi-wall carbon nanotubes Nafion-modified electrode by Wensheng Huang; Chunhai Yang; Shenghui Zhang (pp. 703-707).

In this work, multi-wall carbon nanotubes (MWNT) were conveniently dispersed into Nafion–ethanol solution, and the MWNT–Nafion-modified glassy carbon electrode (GCE) was described for the simultaneous determination of 2-nitrophenol and 4-nitrophenol. At pH 4.0 phosphate buffer, the reduction peak currents of 2-nitrophenol (at –0.8 V) and 4-nitrophenol (at −1.0 V) increase significantly at the MWNT–Nafion-modified GCE, in comparison with that at the Nafion-modified GCE and the bare GCE. The experimental parameters, such as solution pH of phosphate buffer, accumulation potential and time, and the amounts of MWNT–Nafion onto the GCE surface, were optimized. The reduction peak currents are linear with the concentration of 2-nitrophenol from 5×10⁻⁸ to 1×10⁻⁵ mol L⁻¹ and with that of 4-nitrophenol from 1×10⁻⁷ to 1×10⁻⁵ mol L⁻¹. The detection limits after 3-min accumulation are 1×10⁻⁸ mol L⁻¹ for 2-nitrophenol and for 4×10⁻⁸ mol L⁻¹ for 4-nitrophenol. This modified electrode was applied to direct determination of 2-nitrophenol and 4-nitrophenol in lake water samples.

Keywords: Carbon nanotubes Nafion Chemically modified electrodes 2-Nitrophenol 4-Nitrophenol

Co²⁺-selective membrane electrode based on the Schiff Base NADS by Mohammad Hossein Mashhadizadeh; Iran Sheikhshoaie (pp. 708-712).

A new PVC membrane electrode for cobalt(II) ions based on a recently synthesized Schiff base of 5-((4-nitrophenyl)azo)-N-(2′,4′-dimethoxyphenyl)salicylaldimine is reported. The electrode exhibits a Nernstian response for Co²⁺ ions over a wide concentration range (9.0×10⁻⁷–1.0×10⁻² M) with a slope of 29(±1). The limit of detection is 8.0×10⁻⁷ M. The proposed sensor revealed good selectivities over a wide variety of other cations including hard and soft metals. This electrode could be used in a pH range of 3.5–6.0. It was used as an indicator electrode in potentiometric titrations of cobalt(II) ions and can be used in the direct determination of Co²⁺ in aqueous solutions.

Keywords: Cobalt(II) ions Ion-selective electrode Schiff base PVC membrane Potentiometry

CD spectrometric methods for the simultaneous determination of ethisterone and its Δ⁵-isomer by D. Szegvári; P. Horváth; A. Gergely; S. Németh; S. Görög (pp. 713-717).

Quick and accurate direct and indirect circular dichroism (CD) spectrometric methods were developed for the simultaneous determination of ethisterone (17α-ethinyl-17-hydroxy-4-androstene-3-one) and its Δ⁵-isomer (Δ⁵-ethisterone). The direct method is based on the selective negative Cotton effect of the Δ⁴-3-oxo group in ethisterone (negative maximum at 348 nm in dioxan) and measurement of the ellipticity at 296 nm (positive maximum of Δ⁵-ethisterone), where the measured ellipticity is the sum of those of the two isomers. In the indirect procedure Δ⁵-ethisterone is transformed to ethisterone by base-catalysed isomerization and the ellipticities are measured at 339 nm in ethanol before and after isomerization. Preliminary experiments show the usefulness of CD detector in the HPLC determination of the mixture of the isomers. A major advantage of the direct CD spectrometric and the HPLC/CD methods is that the Δ⁵-isomer with extremely low UV activity can also be directly measured with high sensitivity.

Keywords: Circular dichroism Ellipticity Chiroptical detector Ethisterone Isomerization

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Analytical and Bioanalytical Chemistry (v.375, #5)