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Analytical and Bioanalytical Chemistry (v.368, #8)
Carbohydrate analysis by high-performance anion-exchange chromatography with pulsed amperometric detection: The potential is still growing by T. R. I. Cataldi; C. Campa; G. E. De Benedetto (pp. 739-758).
This article reviews recent advances of carbohydrate analysis by high-performance anion-exchange chromatography with pulsed amperometric detection. Starting from the paper of Dennis C. Johnson [1] in which the great analytical promise of such a technique was anticipated, a multitude of exciting new research possibilities have recently emerged. The great attractiveness of high-performance anion-exchange chromatography is largely due to its compatibility with such a sensitive, selective and reliable detection method as pulsed amperometry. This very good match between liquid chromatography and electrochemical detection has allowed the determination of carbohydrates in a variety of complex matrices, for instance, foods, beverages, diary and biotechnological products, vegetal tissues, and also in the area of clinical diagnostics. For this reason, the introduction of HPAEC-PAD into regulated methods is becoming increasingly accepted. A comprehensive collection of applications to carbohydrates and samples of interest is given, with special focus on the separation of closely related sugar compounds using dilute alkaline eluents. Advances in pulsed potential waveforms are also discussed, and a comparison with other liquid chromatographic methods addressed.
A calix[4]arene based calcium-selective optode membrane: Measuring the absorbance maximum wavelength shift by J. M. Kürner; T. Werner (pp. 759-762).
An absorbance based calcium ion sensor is presented which applies a new immobilized chromogenic calix[4]arene. The membrane consists of a hydrogel/1,3-pentanedial mixture and the 1,3-bis(indoaniline)-derived 2,4-bis-[(ethylcarbonyl)methoxy]-calix[4]arene as calcium receptor. The indicator entrapped within the gel was not rapidly washed out. Upon calcium complexation a bathochromic shift up to 70 nm was observed along with an increase of the absorption coefficient. The dynamic range of calcium measurements is from 3 to 10 mM with a point of inflection of the calibration curve at a calcium concentration of about 7 mM. The concentration of calcium ions can be calculated from either absorbance at a distinct wavelength or – preferably when indicator leaching occurs – from the wavelength shift of the absorbance occurring when calcium levels are increased.
Study of the binding characteristics and transportation properties of a 4-aminopyridine imprinted polymer membrane by Hongsheng Guo; Xiwen He; Hong Liang (pp. 763-767).
Molecularly imprinted polymer membranes containing artificial recognition sites for 4-aminopyridine have been prepared by photopolymerization using 4-aminopyridine as template. Reference membranes were prepared with the same monomer mixture but in the absence of the template. The binding characteristics of the imprinted polymer membrane were investigated by a batch method and the transport properties of the membranes were investigated using diffusion chambers. The results showed that the binding amount of 4-aminopyridine is higher than that of 2-aminopyridine whereas the latter can transport the ¶4-aminopyridine imprinted polymer membrane faster than 4-aminopyridine.
A polystyrene based membrane electrode for cadmium(II) ions by A. Panwar; S. Baniwal; C. L. Sharma; A. K. Singh (pp. 768-772).
A polystyrene based membrane of 3,4 : 12,13-dibenzo-2,5,11,14-tetraoxo-1,6,10,15-tetraazacyclooctadecane shows a Nernstian response to Cd(II) ions over a wide concentration range (3.16 × 10–6–1.00 × 10–1 mol L–1) with a Nernstian slope of 29.8 mV/decade of concentration, between pH 2.0 and 6.0. This electrode has been found to be chemically inert and of adequate stability with a response time of 20s. The electrode gives reproducible results with a lifetime of 130 days. The membrane works satisfactorily in a partially non-aqueous medium up to a maximum 35% (v/v) content of methanol and ethanol. The practical utility of the proposed chemical sensor has been observed by using it as end-point indicator in the titration of Cd(II) ions with EDTA. The potentiometric selectivity coefficient values indicate that the membrane sensor is highly selective for Cd(II) ions over a number of cations. Small amounts of surfactants do not disturb the functioning of the sensor. This electrode has also been used to estimate cadmium ions in real samples.
Comparison of several spray chambers operating at very low liquid flow rates in inductively coupled plasma atomic emission spectrometry by J.-L. Todolí; S. Maestre; J. Mora; A. Canals; V. Hernandis (pp. 773-779).
Four different spray chambers were evaluated in ICP-AES at very low liquid flow rates: a double-pass (Scott type), a conventional cyclonic, and two low-volume cyclonic-type spray chambers (i.e., Cinnabar and Genie). A glass concentric pneumatic micro nebulizer (Atom Mist) was used in conjunction with all four chambers. The liquid flow rate was varied from 10 to 160 μL min–1. The conventional cyclonic spray chamber gave rise to coarser tertiary aerosols, higher analyte and solvent transport rates, higher sensitivity and lower limits of detection than the remaining ones. The low-volume spray chambers afforded analytical figures of merit similar to the double-pass one, despite their very different designs. However, these spray chambers exhibited shorter wash-out times. The matrix effects were significant only for the double-pass. This fact allowed the analysis of reference samples by employing aqueous standards at a minimum level of sample consumption. The recoveries obtained for the cyclonic spray chambers and several certified samples were close to 100%, being always lower in the case of the double-pass spray chamber.
Application of a modified simplex method to the multivariable optimization of a new FIA system for the determination of osmium by Hongping Xu; Huitao Liu; Huaiwen Wang; Lijun Dong; Xingguo Chen; Zhide Hu (pp. 780-785).
A methodology based on the coupling of experimental design and a modified simplex method is proposed for the optimization of a new flow injection-kinetic system for the spectrophotometric determination of Os (IV) with m-acetylchlorophosphonazo, which has for the first time been used as chromogenic reagent in the quantitative analysis of this element. An orthogonal array design is utilized to design the experimental protocol, in which six variables are varied simultaneously, and obtain the initial simplex using 25 experiments. A modified simplex method is applied to continuously optimize the data of the orthogonal array design; the search for optimum conditions of ¶6 variables using the modified simplex method required only 25 experiments. The efficiency and simplicity of the coupling of the experimental design and the modified simplex method are attractive for the development of new analytical methods. The method has been applied to the determination of Os (IV) in a refined ore as well as in a secondary alloy and provided satisfactory results.
Determination of the changes of the basic structures of silica species in dependence on the concentration of sodium chloride by FAB-MS by M. Tanaka; K. Takahashi (pp. 786-790).
The chemical species of silica in NaCl solutions of different concentrations were identified by FAB-MS (fast atom bombardment mass spectrometry). The basic structures of silica species, such as cyclic pentamer (Si5¶(OH)9O6 –), linear pentamer (Si5(OH)11O5 –), cyclic hexamer (Si6(OH)9O8 –, Si6(OH)11O7 –) and linear hexamer (Si6(OH)14O6 –), were identified, in addition to dimer (Si2(OH)5O2 –), trimer (Si3(OH)7O3 –) and cyclic tetramer (Si4(OH)7O5 –). The patterns of changes of the peak intensities of the silicate complexes relative to the dimer with increasing NaCl concentration were classified into two types: that represented by linear silicate complexes and the other by cyclic silicate complexes. The differences in the type of chemical species and their changes according to the NaCl concentration reflect the number of bonds necessary for polymerization and hydrolysis of the silica complexes. The differences between the linear and the cyclic silicate type have some implications on the dissolution mechanism of silicate complexes, the hydration of the molecules and the equilibrium between solubility, hydrolysis, polymerization and the salting-out effect in NaCl solution.
Polydiphenylamine-dodecyl sulfate films for the simultaneous amperometric determination of electroinactive anions and cations in ion-exclusion cation-exchange chromatography by Qun Xu; Chun Xu; Yanping Wang; Wen Zhang; Litong Jin; Kazuhiko Tanaka; Hiroki Haraguchi; Akihide Itoh (pp. 791-796).
An amperometric detector with two working electrodes both modified with polydiphenylamine-dodecyl sulfate (PDPA-DS) was successfully used for the simultaneous determination of electroinactive anions (SO4 2–, Cl–, NO3 –) and cations (Na+, NH4 + and K+) in single-column ion-exclusion cation-exchange chromatography (IEC-CEC). The PDPA-DS chemical modified electrode (CME) was based on the incorporation of dodecyl sulfate (DS) into PDPA by electropolymerization of diphenylamine in the presence of sodium dodecyl sulfate. The electrochemical responses against the anions and cations at the PDPA-DS CME in differential pulse voltammetry were studied. A set of well-defined peaks of electroinactive anions and cations were obtained. The anions and cations were detected conveniently and reproducibly in a linear concentration range 0.01–5.0 mmol/L and their detection limits were in the range 5–9 μmol/L at a signal-to-noise ratio of 3 (S/N = 3). The proposed method was quick, sensitive and simple and was successfully applied to the analysis of lake water samples. The working electrode was stable over one week period of operation with no evidence of chemical and mechanical deterioration.
Determination of low-level mercury based on a renewable-drops sensing technique by RongHua Yang; KeMin Wang; Dan Xiao; Kan Luo; XiaoHai Yang (pp. 797-802).
The design and characteristics of a novel drop-based fluorescence-detection technique for the determination of mercury(II) are described. The method, using a flow injection technique, is based on the renewable-drops of 3,3′,5,5′-tetramethylbenzidine(TMB), which are formed at the bottom tip of a silica capillary tube connected to the end of the flow system. An excitation beam from a high-pressure Hg lamp directly illuminates the drops, the fluorescence emission is conducted to a photodiode (PD) to convert the photocurrent into a voltage signal (mV). Optimum analytical conditions for Hg(II) assays have been established. In NaAc/HAc buffer at pH 3.09 this assay has a wide linear range for Hg(II) from 8.0 × 10–8 to 2.0 × 10–5 mol/L with a detection limit of 2.0 × 10–8 mol/L. The use of renewable drops allowing a fresh reaction surface for each sample is of particular value to solving the problems of ¶irreversible reactions. Besides its high sensitivity, the method permits a simple, fast, and inexpensive measurement with only micro-quantities of reagent consumption. The technique described provides a simple and sensitive way to fabricate sensors of feasible prospects and commercial advantages.
Arsenic speciation based on ion exchange high-performance liquid chromatography hyphenated with hydride generation atomic fluorescence and on-line UV photo oxidation by He Bin; Jiang Gui-bin; Xu Xiao-bai (pp. 803-808).
An on-line method capable of the separation of arsenic species was developed for the speciation of arsenite As(III), arsenate As(V), monomethylarsenic (MMA) and dimethylarsenic acid (DMA) in biological samples. The method is based on the combination of high-performance liquid chromatograph (HPLC) for separation, UV photo oxidation for sample digestion and hydride generation atomic fluorescence spectrometry (HGAFS) for sensitive detection. The best separation results were obtained with an anion-exchange AS11 column protected by an AG11 guard column, and gradient elution with NaH2PO4 and water as mobile phase. The on-line UV photo oxidation with 1.5% K2S2O8 in 0.2 mol L–1 NaOH in an 8 m PTFE coil for 40 s ensures the digestion of organoarsenic compounds. Detection limits for the four species were in the range of 0.11–0.15 ng (20 μL injected). Procedures were validated by analysis of the certified reference materials GBW09103 freeze-dried human urine and the results were in good agreement with the certified values of total arsenic concentration. The method has been successfully applied to speciation studies of blood arsenic species with no need of sample pretreatment. Speciation of arsenic in blood samples collected from two patients after the ingestion of realgar-containing drug reveals slight increase of arsenite and DMA, resulting from the digestion of realgar.
Three-phase double-arc plasma for spectrochemical analysis of environmental samples by M. M. Mohamed; Z. F. Ghatass; E. A. Shalaby; M. M. Kotb; M. El-Raey (pp. 809-815).
A new instrument, which uses a three-phase current to support a double-arc argon plasma torch for evaporation, atomization and excitation of solid or powder samples, is described. The sampling arc is ignited between the first and second electrode while the excitation arc is ignited between the second and third electrode. Aerosol generated from the sample (first electrode) is swept by argon gas, through a hole in the second electrode (carbon tubing electrode), into the excitation plasma. A tangential stream of argon gas is introduced through an inlet orifice as a coolant gas for the second electrode. This gas stream forces the excitation arc discharge to rotate reproducibly around the electrode surface. Discharge rotation increases the stability of the excitation plasma. Spectroscopic measurements are made directly in the current-carrying region of the excitation arc. An evaluation of each parameter influencing the device performance was performed. Analytical calibration curves were obtained for Fe, Al, K, and Pb. Finally, the present technique was applied for the analysis of environmental samples. The present method appears to have significant, low cost analytical utility for environmental measurements.
A liquid chromatography-tandem mass spectrometry method for fluazifop residue analysis in crops by E. Bolygo; A. Boseley (pp. 816-819).
An LC-MS-MS assay is described for fluazifop residue analysis in crops. The residues are extracted with acidified organic solvent, the esters and conjugates are hydrolysed with 6 M hydrochloric acid, then the extracts are cleaned-up by solid phase extraction using C2(EC) and Si cartridges in tandem. Quantitative analysis is performed by gradient liquid chromatography coupled to triple quadrupole mass spectrometer using atmospheric pressure chemical ionisation. All fluazifop-P-butyl, free fluazifop-P and any conjugates are quantified as fluazifop-P. The limit of quantification is 0.01–0.05 mg/kg depending on crop matrices. The clean-up method is also suitable for LC-UV analysis with a compromise in higher limit of quantification 0.05–0.2 mg/kg.
Surface characterization of polydimethylsiloxane treated pharmaceutical glass containers by X-ray-excited photo- and Auger electron spectroscopy by T. Mundry; P. Surmann; T. Schurreit (pp. 820-831).
The siliconization of pharmaceutical glass containers is an industrially frequently applied procedure. It is done by spreading an aqueous silicone oil emulsion film on the inner surface and successive heat curing treatment at temperatures above 300 °C for 10–30 min. It was often proposed that a covalent bonding of PDMS to the glass or branching of the linear PDMS occurs during heat treatment. The present study was performed for a detailed investigation of the glass and silicone (polydimethylsiloxane = PDMS) chemical state before and after heat-curing treatment and analysis of the bond nature. Combined X–ray excited photoelectron (XPS) and Auger electron spectroscopy as well as angle resolved XPS-measurements were used for analysis of the glass samples. The silicon surface atoms of the borosilicate container glass were transformed to a quartz-like compound whereas the former linear PDMS had a branched, two-dimensional structure after the heat curing treatment. It was concluded that the branching indicates the formation of new siloxane bonds to the glass surface via hydroxyl groups. Further evidence for the presence of bonded PDMS at the glass surface can be found in the valence band spectra of the siliconized and untreated samples. However, this bond could not be detected directly due to its very similar nature to the siloxane bonds of the glass matrix and the organosilicon backbone of PDMS. Due to the high variation of data from the siliconized samples it was concluded, that the silicone film is not homogeneous. Previously raised theories of reactions during heat-curing glass siliconization are supported by the XPS data of this investigation. Yet, the postulation of fixing or baking the silicone on the glass surface is only partially true since the bonded layer is very thin and most of the silicone originally on the surface after heat curing can be removed by suitable solvents. This fraction can therefore still interact with drug products being in contact to the siliconized container wall.
Voltammetric determination of mifepristone at a DNA-modified carbon paste electrode by K. Gu; J. Zhu; Y. Zhu; J. Xu; H.-Y. Chen (pp. 832-835).
A new strategy for the preparation of a DNA-modified carbon paste electrode is developed. It is found that the anodic response of mifepristone is greatly enhanced at the dsDNA-modified carbon paste electrode comparing with that obtained at the bare electrode, while the response at a ssDNA-modified electrode is similar to bare electrode. So the dsDNA-modified electrode is employed as a sensitive biosensor for the detection of mifepristone. A linear dependence of the peak currents on the concentration is observed in the range 2.0 × 10–7∼ 2.0 × 10–6 mol/L, with a detection limit of 1.0 × 10–7 mol/L. The relative standard deviation is 4.3% for six successive determinations of 1.0 × 10–6 mol/L mifepristone. The determination of mifepristone tablets is carried out and satisfactory results are obtained.
Determination of vitamin B12 in pharmaceutical preparations by a highly sensitive fluorimetric method by Hua-Bin Li; Feng Chen (pp. 836-838).
A fluorimetric method for the determination of vitamin B12 has been developed. The fluorescence emission was measured at λex/λem275/305 nm in phosphate buffer solution (pH 7.0), and the experimental variables and possible interference were studied. The linear calibration range was 1.000 ng/mL to 100.0 ng/mL with a correlation coefficient of 0.9994 and a detection limit of 0.1 ng/mL. The method is rapid, simple and highly sensitive. It was used to determine vitamin B12 in pharmaceutical preparations. The recovery was 96%–98% and the relative standard deviation was in the range of 1.8%–2.7%. The results agreed with those obtained by spectrophotometry.
Quantification of the metal distribution in metallothioneins of the human liver by HPLC coupled with ICP-AES by Ch. Wolf; U. Rösick; P. Brätter (pp. 839-843).
Fractions containing metallothioneins (MT’s), extracted from the liver cytosol of humans, were analysed to determine the complete distribution pattern of the metals copper, cadmium and zinc. Samples of cirrhotic livers which had come from organs removed during transplantation were examined for differences in the trace-element binding pattern. After the extraction of supernatants from the tissue samples, membrane ultrafiltration of the cytosolic solution was carried out to separate all high-molecular proteins with molecular weights >100 kDa. This procedure retains the metal content of the MT’s in its initial form, in contrast to the often-used heat treatment of samples, which changes the copper distribution significantly. The MT’s themself were isolated using size exclusion and anion exchange chromatography. Their metal content was determined simultaneously on-line by combination with an ICP-AES as element detector. Calibration of the procedure was performed by means of a column by-pass-injection of elemental standards into the separation system. The MT content in the samples was calculated using the determined metal concentrations and the generally accepted metal/protein ratios for Cu (12:1), Cd (7:1) and Zn (7:1). These values were compared with values resulting from a 109Cd-saturation-assay. When various liver samples of different pathogenesis were compared, the highest level of Cu-MT was found in primary biliary cirrhosis.
Determination of idarubicin in human urine by capillary zone electrophoresis with amperometric detection by Q. Hu; T. Zhou; L. Zhang; H. Li; Y. Fang (pp. 844-847).
A simple, reliable and reproducible method, based on capillary zone electrophoresis with amperometric detection, has been developed for the determination of idarubicin in human urine. A carbon disk electrode was used as working electrode. The optimal conditions of separation and detection were pH 5.6 phosphate buffer ¶(0.20 mol/L), 22 kV for the separation voltage and 1.00 V (vs. Ag/AgCl, 3 mol/L KCl) for the detection potential. The linear range was from 4.0 × 10–7 to 2.0 × 10–5 mol/L with a regression coefficient of 0.9986, and the detection limit was 8.0 × 10–8 mol/L. The method was directly applied to the determination of idarubicin in spiked human urine without any other sample pretreatment except filtration, and the assay results were satisfactory.
Resonance Rayleigh scattering method for the determination of trace amounts of cadmium with iodide-basic triphenylmethane dye systems by Sh. Liu; Zh. Liu; M. Li; N. Li; H. Luo (pp. 848-852).
In dilute phosphoric acid solution, cadmium (II) reacts with a large excess of I– to form [CdI4]2– which reacts further with basic triphenylmethane dyes such as crystal violet (CV), ethyl violet (EV), methyl violet (MV), brilliant green (BG) or malachite green (MG) to form an ion-association complex. This results in a significant enhancement of resonance Rayleigh scattering (RRS) intensity and the appearance of new RRS spectra. The characteristics of RRS spectra of the ion-association complexes, the influencing factors and the optimum conditions of these reactions have been investigated. The intensity of RRS is directly proportional to the concentration of cadmium from ¶0 to 60 ng mL–1 for EV and MV systems, 0 to 80 ng mL–1 for CV system, and 0 to 100 ng mL–1 for BG and MG systems. The methods exhibit high sensitivities and the detection limits for cadmium are between 0.35 and 2.00 ng mL–1 depending on the different reaction systems. The new RRS method was applied to the direct determination of traces of cadmium in pure zinc and synthetic water samples.
Rapid identification of carbendazim and linuron by adsorptive stripping on a carbon fiber ultramicroelectrode by M. J. González de la Huebra; P. Hernández; Y. Ballesteros; L. Hernández (pp. 853-856).
A method is described for the identification of a mixture of carbendazim and linuron. It is based on adsorptive stripping voltammetry at a carbon fiber ultramicroelectrode. Conditions for the determination of carbendazim in a mixture were optimized and the method was applied to soil samples. It was compared to HPLC with spectrophotometric detection, where similar results were obtained.