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Analytical and Bioanalytical Chemistry (v.368, #5)
Characterization of silicon wafers through deposition of self-assembled monolayers by B. Basnar; J. Schnöller; K. Föttinger; G. Friedbacher; U. Mayer; H. Hoffmann; L. Fabry (pp. 434-438).
AFM imaging of the adsorption of self-assembled octadecylsiloxane (ODS) monolayers has been utilized for probing surface properties of silicon wafers. It has been found that both growth rate of the organic films and island size of sub-monolayer films are influenced by the doping level of the wafers as well as by the surface finishing step during wafer production. Generally, higher doping levels led to lower adsorption rates and smaller islands. Variation of the sample pretreatment used for surface finishing of similarly doped wafers led only to significant changes of the island size, but not of the surface coverage. The results presented open up a valuable perspective for characterizing the surface homogeneity of silicon wafers which is an important parameter for monitoring-wafers in semiconductor industry.
Analytical applications of electrochemiluminescence: an overview by A. V. Kukoba; A. I. Bykh; I. B. Svir (pp. 439-442).
The chemical transformations of electrogenerated ion-radicals of a number of complex organic compounds may be accompanied by emission of photons. An electrochemiluminescence (ECL) quantum contains information both on the kinetics of the heterogeneous electrode processes and on the subsequent homogeneous chemical reactions in the solution. Application of ECL to solution analysis provides advantages in comparison to electrochemical methods. Using ECL for electrode surface analysis allows information to be obtained on the rate of an electrochemical process simultaneously at all points of the electrode under analysis in real time, and that is the main difference between this method and the point-by-point testing specific to electrochemical methods. The potential of ECL for analytical chemistry is examined concerning the homogeneous ECL-analysis of solutions and the heterogeneous ECL-analysis of electrode surfaces.
Simultaneous determination of trace metals by solid phase absorptiometry: application to flow analysis of some rare earths by Y. Tennichi; S. Matsuoka; K. Yoshimura (pp. 443-448).
Solid phase absorptiometry was applied to the simultaneous flow analysis of trace metals in combination with a micro black flow-through cell packed with ion exchanger beads and a multi-channel photodetector connected with optical fibers. A 4.0 cm3 sample solution containing five rare earth metal ions (Dy, Ho, Tm, Er and Nd) was introduced into a flow system and these metal ions were concentrated on a cation exchanger (Muromac 50W-X4) in a flow-through cell. The absorbance increases originating from the f-f or d-f transition bands of these metal ions were directly and continuously measured at 910 nm for Dy, at 530 nm for Ho, at 683 nm for Tm, 522 nm for Er and at 790 nm for Nd, respectively. A multi-variable analysis method was combined with the flow analysis because the absorption spectra of the five rare earth metal ions partly overlapped one another. Although no coloring reagents were used, the proposed method was about ¶200 times more sensitive than the corresponding solution method. The reproducibility of this method was less than ± 5%. The detection limits were 0.03, 0.40, 0.30, 0.35 and 0.23 mg dm–3 for Dy, Ho, Tm, Er and Nd, respectively. Five rare earth metal ions could be precisely determined in practical samples such as yttrium concentrate.
Modified helium pulse-operated microwave induced plasma for spectrochemical analysis of liquid samples by M. M. Mohamed; Z. F. Ghatass (pp. 449-455).
To minimize problems caused by sample introduction into helium pulse operated microwave-induced plasma (He-pulsed-MIP), a simple plasma torch was developed. This torch is constructed from commonly available components with an absolute minimum of machining. In this torch, plasma is kept operating by partially isolating it from the rest of the plasma (within the plasma chamber). This auxiliary plasma is by-passed during sample or solvent injection and is therefore not affected. The design of this discharge chamber was thoroughly examined and each parameter affecting its analytical performance was evaluated. Measurements reported include effect of helium flow rate, discharge tube position and microwave power on analytical performance. Analytical calibration curves and detection limits data are shown for Ca, Cd, Cr, Cu, Fe, Mg, Ni and Zn. Plasma excitation temperature was determined using iron and copper as thermometric species. Finally, the present technique was applied to the analysis of real biological samples (liver, brain, heart, bone, kidney, tests, serum, spleen and muscles of white albino rats). The results were compared with those obtained using flame atomic absorption spectroscopy.
Optimum conditions for pulse generation in diaphragm-free Karl Fischer coulometry by U. Nordmark; M. Rosvall; A. Cedergren (pp. 456-460).
A flexible instrument was designed in order to investigate the influence of current magnitude, current duration and the frequency of the pulse generation on the error obtained in coulometric Karl Fischer titrations carried out in diaphragm-free cells. For a given current magnitude the lowest errors were obtained for current durations more than 60% of the total time for the pulse cycle. No significant influence of the pulse frequency (5–1000 Hz) was found independently of the pulse current duration for three different types of reagents intended for diaphragm-free coulometry. For all reagents, the errors obtained with the home-built instrument were significantly smaller than those obtained with an optimized commercial titrator based on pulsed current generation. Using optimum conditions for the former instrument, in combination with an imidazole-buffered reagent at pH 10 containing chloroform as modifier, the accuracy was close to 100%. Thus, it is now possible to achieve the same high accuracy with diaphragm-free coulometry as with the conventional diaphragm based technique. The precision of the water determinations was affected by the size of the background.
Study of the binding characteristics of molecular imprinted polymer selective for cefalexin in aqueous media by Hongsheng Guo; Xiwen He (pp. 461-465).
A molecularly imprinted polymer was prepared using cefalexin as the template molecule and 2-(trifluoromethyl)acrylic acid as the functional monomer. The bulk polymer was ground, sieved and investigated in an equilibrium binding experiment to evaluate the binding characteristics of the cefalexin-imprinted polymer for a better understanding of the mechanisms of recognition in molecularly imprinted polymers. Scatchard analysis showed that two classes of binding sites were formed in the imprinted polymer under the concentration studied. The dissociation constants were estimated to be 0.14 mmol/L and 2.38 mmol/L. The polymer gave much higher binding capacity for cefalexin than the non-imprinted polymer with the same chemical composition. The selectivity was evaluated by distribution coefficients of cefalexin and other structurally similar compounds. The results showed that the imprinted polymer exhibited high affinity for cefalexin among the tested compounds.
Amperometric sensor for L-ascorbic acid determination based on MnO2 bulk modified screen printed electrode by E. Turkusic; V. Milicevic; H. Tahmiscija; M. Vehabovic; S. Basic; V. Amidzic (pp. 466-470).
A simple biosensor constructed by bulk-modification of carbon ink with manganese dioxide as a mediator was investigated for its ability to serve as amperometric detector for L-ascorbic acid in hydrodynamic mode. The sensor could be operated at pH 5.0 (0.05 M phosphate buffer) and exhibited excellent reproducibility and stability. Optimization of measurement parameters such as applied working potential and pH value were studied in detail. The screen printed electrode exhibited a linear amperometric increase with the concentration of ¶L-ascorbic acid from 50 mg L–1 to 250 mg L–1 and gave a (LOD = 3σ) detection limit of 0.2 mg L–1 (1.172 μmol L–1). The manganese dioxide modified screen printed electrode shows long term stability.
Stability of inorganic mercury and methylmercury on yeast-silica gel microcolumns: field sampling capabilities by Ma Perez-Corona (pp. 471-474).
The stability of methylmercury and inorganic mercury retained on yeast-silica gel microcolumns was established and compared with the stability of these species in solution. Yeast-silica gel columns with the retained analytes were stored for two months at three different temperatures: –20 °C, 4 °C and room temperature. At regular time intervals, both mercury species were eluted and quantified by cold vapor atomic absorption spectrometry (CVAAS). Methylmercury was found stable in the columns over the two-month period at the three different temperatures tested while the concentration of inorganic mercury decreased after one week’s storage even at –20 °C. These results are of great interest since the use of these microcolumns allows the preconcentration and storage of mercury species until analysis, thus saving laboratory space and avoiding the problems associated with maintaining species integrity in aqueous solution.
A sequential injection cold-vapor atomic absorption method for the determination of total mercury by W. E. Doering; R. R. James; R. T. Echols (pp. 475-479).
A sequential injection (SI) method for the determination of mercury via cold vapor atomic absorption spectrophotometry is presented. The method differs from flow injection (FI) cold vapor methods for the determination of mercury because of the simplicity of the system required for the method: one pump, one valve, a gas-liquid separator, and an atomic absorption spectrophotometer equipped with a quartz cell. Under optimal conditions, the method has the following figures of merit: a linear ¶calibration range of 1.0 to 20 μg L–1; a detection limit of 0.46 μg L–1; and a precision of 0.90% RSD (8 μg L–1). The procedure allows for a sampling rate of one injection per 80 s (excluding sample pretreatment). Results from the determination of mercury in water and fish specimens are also presented. The figures of merit of the method are compared to two other SI methods for the determination of mercury.
Separation of trace amounts of rhodium(III) with tri-n-butyl phosphate from nitric acid and sodium trichloroacetate media by Kazi Zakir Hossain; Takaharu Honjo (pp. 480-483).
A new method for the quantitative extraction and separation of trace amounts of rhodium from nitric acid and sodium trichloroacetate media has been established based on the formation of an ion-association complex of hexahydrated rhodium cation Rh(H2O)6 3+ and the trichloroacetate (TCA) anion in tri-n-butyl phosphate (TBP). The effect of various factors (solvent, pH, sodium trichloroacetate, shaking time, phase volume ratio, composition of the extracted species, foreign ions, transformation of rhodium chlorocomplexes into hexahydrated cation, etc.) on the extraction and back-extraction of rhodium has been investigated. The method can be combined with subsequent FAAS determination of rhodium. The procedure was applied to determine rhodium traces in chloroplatinic acid and palladium chloride.
Speciation of major arsenic species in seawater by flow injection hydride generation atomic absorption spectrometry by Jean Yves Cabon; Nolwenn Cabon (pp. 484-489).
Arsenic present at 1 μg L–1 concentrations in seawater can exist as the following species: As(III), As(V), monomethylarsenic, dimethylarsenic and unknown organic compounds. The potential of the continuous flow injection hydride generation technique coupled to atomic absorption spectrometry (AAS) was investigated for the speciation of these major arsenic species in seawater. Two different techniques were used. After hydride generation and collection in a graphite tube coated with iridium, arsenic was determined by AAS. By selecting different experimental hydride generation conditions, it was possible to determine As(III), total arsenic, hydride reactive arsenic and by difference non-hydride reactive arsenic. On the other hand, by cryogenically trapping hydride reactive species on a chromatographic phase, followed by their sequential release and AAS in a heated quartz cell, inorganic As, MMA and DMA could be determined. By combining these two techniques, an experimental protocol for the speciation of As(III), As(V), MMA, DMA and non-hydride reactive arsenic species in seawater was proposed. The method was applied to seawater sampled at a Mediterranean site and at an Atlantic coastal site. Evidence for the biotransformation of arsenic in seawater was clearly shown.
Determination of trace elements including platinum in tree bark by ICP mass spectrometry by J. Su. Becker; D. Bellis; I. Staton; C. W. McLeod; J. Dombovari; J. Sa. Becker (pp. 490-495).
The increasing emission of Pt-group metals from automobile catalytic converters requires the development of highly sensitive procedures for ultratrace analysis of environmental and biological systems. Tree bark, located close to motorway or industrial areas, was utilised as a substrate for collection of airborne particulate matter and samples after digestion (microwave assisted dissolution with HNO3 and HCl) were analysed by ICP mass spectrometry. The study targeted Pt and other metallic contaminants and involved analysis of some 57 tree bark samples using both quadrupole and double-focusing sector field ICP mass spectrometers. Detection limits for platinum determination in tree bark were 0.03 ng/g (DF-ICP-MS) and 0.2 ng/g (ICP-QMS). The platinum content of the bark samples ranged from 0.07–5.4 ng/g.
Individual sample conditioning in flow analysis. Determination of N-total in plant materials by J. M. T. Carneiro; R. S. Honorato; E. A. G. Zagatto (pp. 496-500).
A flow-batch system allowing in-line individual sample matrix matching is proposed for analysis of sample lots with high variability in acidity. The feasibility of the approach is demonstrated in the spectrophotometric determination of total nitrogen in Kjeldahl digests, using a column with a slightly soluble reagent (AgCl). The solutions are sequentially injected by means of an 8-port selecting valve and processed in a mixing chamber that is also used as a monitoring unit. The system yields reproducible results (r.s.d. usually < 2.5%) and the sampling rate is 14 samples/h. The analytical curve is linear within 1.00 and 6.00% N (dry basis), and the regression coefficient is > 0.999 (n = 6). Results are in agreement with certified values of standard reference materials and with results obtained by conductometry.
A highly sensitive fluorimetric method for the determination of fluoride in biological material with Al3+-calcein complex by Hua-Bin Li; Feng Chen (pp. 501-504).
A highly sensitive fluorimetric method for the determination of fluoride was established. The method was based on quenching of the fluorescence of the Al3+-calcein complex in CCl3COOH-CH3COOK buffer solution by fluoride. The fluorescence emission was measured at λex/λem 480/503 nm, and the experimental variables and interference in this determination were studied. The linear calibration range was 0.8 ng/mL to 150 ng/mL and the detection limit was 0.2 ng/mL. The method was applied to determine fluoride in biological materials. The recovery was in the range of 96.3% to 104.7% and the relative standard deviation was 4.6%. The results obtained from the certified reference material by the present method agreed with the certified values.
Direct determination of 1-naphthoxylactic acid in biological fluids by non-protected fluid room temperature phosphorimetry by J. A. Murillo Pulgarín; A. Alañón Molina (pp. 505-510).
A selective and sensitive room-temperature phosphorimetric method for the direct determination of 1-naphthoxylactic acid (NA) in biological fluids is described. It is based on obtaining a phosphorescence signal from NA using TlNO3 as a heavy atom perturber and Na2SO3 as a deoxygenator without a protective medium. This technique is named non-protected room-temperature phosphorescence (NP-RTP), which allows to determine analytes in complex matrices without the need for tedious prior separation. Optimization of the operational conditions resulted in a detection limit for NA of 9.6 ng/mL according to the error propagation theory. The repeatability and standard deviation were also determined. This method was successfully applied to the determination of NA in urine and human serum.
A novel method for the determination of total protein in human serum by near infrared fluorescence recovery by Hong Zheng; Chang-Qing Zhu; Dong-Hui Li; Qiu-Ying Chen; Huang-Hao Yang; Xiao-Lan Chen; Jin-Gou Xu (pp. 511-515).
A novel fluorometric method has been developed for the determination of total protein in human serum with a new near-IR reagent as a fluorescence probe, based on the fluorescence recovery of the cyanine-CTAB system in the presence of protein. Maximum fluorescence is produced with maximum excitation and emission wavelengths at 765 and 812 nm, respectively. Under optimal conditions, the calibration graphs are linear over the ¶range 0.4–12.0 μg/mL for protein. The detection limit is 70 ng/mL, and the relative standard deviation of six replicate measurements is 1.14% for 6.0 μg/mL protein. The results are satisfactory.
Determination of direct-bilirubin by a fluorimetric-enzymatic method based on bilirubin oxidase by Y. Andreu; J. Galbán; S. de Marcos; J. R. Castillo (pp. 516-521).
A method for the determination of direct bilirubin by reaction with bilirubin oxidase (BOx) is reported. The procedure is based on the changes in fluorescence which take place during the enzymatic reaction of BOx with any of the three forms of bilirubin (free, conjugated and with albumin) when the solution is excited at 240 nm and the emission is measured at 440 nm. The change in fluorescence was studied thoroughly. It seems mainly due to the fluorescence of one of the reaction products. A theoretical study was carried out to relate the changes in fluorescence observed to the species taking part in the reaction and to establish some of the enzymatic reaction constants. The optimum reaction conditions were studied for each of the three types of bilirubin together with their analytical characteristics (linear range and precision). Selective determination of direct bilirubin was carried out for various synthetic samples with good results. A linear response up to 7 mg L–1 of direct bilirubin was obtained. Using optimum conditions, the precision for free and conjugated bilirubin was 3.4% (n = 5) and 3.0% (n = 5), respectively.
Determination of the contents of water and moisture in milk powder by S. Rückold; K. H. Grobecker; H.-D. Isengard (pp. 522-527).
According to official methods the moisture content of milk powders is determined by drying techniques and the loss of mass defined as water content. The mass loss, detecting the volatiles evaporated under the applied conditions, is strongly dependent on the drying parameters. An ideal method should be able to determine “free water” without including “bound water” in the result. Two collaborative studies showed that drying methods are not capable of distinguishing between different binding forms of water and only the total water content, measured with Karl Fischer titration, provides results which can be attributed to a defined physical property. Results from two European collaborative studies are employed to evaluate three different drying techniques and Karl Fischer titration. Adsorption isotherms of skimmed milk powder at different temperatures were used to calculate the isosteric heat of sorption.
Modified on-line monitoring of total gaseous mercury in flue gases using Semtech® Hg 2000 analyzer by X. Feng; J. Sommar; M. Abul-Milh; B. Hong; D. Strömberg; O. Lindqvist (pp. 528-533).
The Semtech Hg 2000 analyzer continuously monitors the Hg0 content in flue gas. An on-line measurement method of total gaseous mercury in flue gas developed in our laboratory is described, which uses the absorption cell of the Semtech Hg Analyzer connected to a converter that is located in a furnace heated up to 650 °C. The converter can be heated up to 800 °C by both the furnace and an extra heating of a Ni-Cr alloy heating wire. Both the absorption cell and the converter are made of quartz. All gaseous Hg2+ species in flue gas are thermally reduced to Hg0 by the converter and detected by the Semtech Hg 2000 analyzer. The thermal reduction efficiencies of different conversion materials, which were filled in the converter, such as quartz chips, granular MgO, Ni and CoO powder, were tested using different flue gas conditions. Studies have shown that HCl is the major factor to inhibit the thermal reduction of Hg2+ to Hg0, and in the converter and the absorption cell Hg0 will react readily with HCl to form HgCl2. Both MgO and Ni could be used in the converter to absorb HCl in the flue gas, but Ni has better absorption efficiency. By using an original Semtech and a modified one, both Hg0 and total gaseous Hg contents in flue gas could be monitored simultaneously and continuously.
Development and validation of a near infrared method for the analytical control of a pharmaceutical preparation in three steps of the manufacturing process by M. Blanco; J. Coello; H. Iturriaga; S. Maspoch; N. Pou (pp. 534-539).
A near infrared diffuse reflectance spectroscopy (NIRS) procedure for the quantitative control analysis of the active compound (otilonium bromide) in a pharmaceutical preparation in three steps of the production process (blended product, cores and coated tablets) and a methodology for its validation are proposed. The analytical procedure is composed by two consecutive steps. First, the sample is identified by comparing its spectrum with a second derivative spectral library. If the sample is positively identified, the active compound is quantified by using a previously established partial least squares (PLS) calibration model. The procedure was validated by studying repeatability, intermediate precision, accuracy and linearity. To this end, an adaptation of ICH (International Conference on Harmonisation) validation methodology to an NIR multivariate calibration procedure is proposed. The relative standard error of prediction (RSEP) was ≤ 1% and the suitability of the procedure for control analysis was confirmed by the results obtained analysing new production samples produced over a three-month period.
Application of HPLC-NMR coupling using C30 phase in the separation and identification of flavonoids of taxonomic relevance by L. C. Santos; M. Dachtler; F. D. P. Andrade; K. Albert; W. Vilegas (pp. 540-542).
The on-line separation and identification of two important taxonomic markers for plant species of the Paepalanthus genus, the flavonoids 6-methoxykaempferol-3-O-β-D-glucopyranoside and 6-methoxykaempferol-3-O-β-D-6″(p-coumaroyl)glucopyranoside, has been performed with an HPLC-NMR coupling using C30 phase. 1D spectra have been recorded in the stopped-flow mode for the two predominant chromatographic peaks. This is the first application of HPLC-NMR coupling using C30 phase to a taxonomic problem. The technique drastically reduces the required amount of sampling for structure determination.