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Analytical and Bioanalytical Chemistry (v.358, #4)


Filtering and integration of chromatographic data: a tool to improve calibration? by C. R. Mittermayr; H. Frischenschlager; E. Rosenberg; M. Grasserbauer (pp. 456-464).
The effect of filtering and automated integration of chromatographic data on the calibration curve and detection limit was assessed. In a first approach simulated chromatograms were used to quantify the effects of data processing. Three types of filters were used: Savitzky-Golay, Fourier and Wavelet filter. The filter parameters chosen have been optimized in a previous study. The simulated data have been integrated by a commercial software package. The use of applying the DIN 32645 concept for the determination of the detection limit of chromatographic data is discussed and opposed to the concept of the method detection limit. Under the conditions investigated, filtering can improve the limit of detection up to a factor of three. This can be explained by the fact that filtering reduces the variance of the peak area and height and the limit of detection is mainly determined by their variance. However, the integration algorithm practically limits the possible improvements by filtering the data.

Potentiometric titration of diprotic systems by G. Pezzatini; G. Loglio; S. Becagli (pp. 465-470).
 The approximate nature of Gran’s method of linearization of potentiometric titration curves applied to diprotic systems has been thoroughly investigated. A function involving pH and titrant volume V (which is linearly dependent on V and becomes zero at the first equivalent point of titration of a weak diprotic base with a strong monoprotic acid) has been critically examined and validated by means of widely extended simulated experiments. Accurate experimental confirmation of the theoretical expressions has been obtained by performing many real titrations of the primary standard Na2CO3 with HCl. This particular application, analytically significant itself, can be a prototype of analogous applications.

Rhodium and palladium β-diketonate determination with on-line supercritical fluid extraction-high performance liquid chromatography via solid phase extraction by B. W. Wenclawiak; Torsten Hees; Corinna E. Zöller; Hans-Peter Kabus (pp. 471-474).
 An on-line system of supercritical fluid extraction (SFE) and high performance liquid chromatography (HPLC) via solid phase extraction (SPE) is described for the determination of palladium and rhodium 2,2,6,6-tetramethyl-3,5-heptanedione-(thd) as well as rhodium-acetylacetonate-(acac) and benzylacetonate-(bzac) chelates. The chelates were extracted with supercritical CO2 from sand and humic acid, concentrated on SPE cartridges and analysed with HPLC. Two cartridge materials were tested and compared to off-line trapping. The percentage of the breakthrough and cartridge retained material were measured in liquid dichloromethane. The SFE conditions could be optimized to separate metal chelates during the extraction. The supercritical fluid (SF) behaviour of different ligands on rhodium were investigated.

Flow injection determination of silver with spectrophotometric detection by A. A. Ensafi; K. Zarei (pp. 475-479).
 A flow injection system is proposed for the rapid and sensitive determination of trace concentrations of silver(I) based on its catalytic effect on the oxidation of gallocyanine by peroxodisulphate in the presence of 1,10-phenanthroline as an activator with spectrophotometric detection. Silver can be determined in the range of 0.002–0.700 μg with a limit of detection of 0.001 μg. The relative standard deviation for ten replicate determinations of 0.035 and 0.170 μg of Ag(I) was 2.8% and 0.9%, respectively. The method was successfully applied to the determination of silver in real samples.

Catalytic determination of ultra trace amounts of vanadium with detection by linear sweep voltammetry by Ali A. Ensafi; B. Naderi (pp. 480-483).
Vanadium has a very strong catalytic effect on the bromate oxidation of gallocyanine at pH of 4.0. The oxidation product of gallocyanine exhibit a voltammetric wave at + 0.10 V vs. Ag/AgCl reference electrode in 0.10 mol/l KNO3 medium. The linear scan voltammetric behaviour of the reaction products at HMDE has been studied and selected as the indicator component for the reaction. A detection limit of 0.05 ng/ml and calibration graph from 0.30–200.00 ng/ml vanadium were obtained. Vanadium in water and gasoline samples was determined by this method, with satisfactory results.

Graphite furnace atomic absorption spectrometric (GFAAS) determination of Cu, Cd, Cr, Mn, Ni and Pb in tellurium metal using precipitation and ion-exchange procedures by N. N. Meeravali; J. Arunachalam (pp. 484-488).
 Two independent procedures have been developed for the determination of Cd, Cu, Ni, Mn, Cr and Pb in high-purity tellurium by GFAAS. In the first, tellurium is precipitated as TeO2 in the presence of EDTA at pH 4.5±0.2 to remove of 99.4% of tellurium as tellurium dioxide. The supernatant is analysed for impurities. In the second procedure, the trace impurities are preconcentrated on a Chelex-100 resin column at pH 9.4±0.2, and eluted by two column volumes of 2 mol/L HNO3. In this case a matrix separation coefficient (ks) of 1500 is achieved. The analyses are carried out by GFAAS. The relative standard deviations of the analyte concentrations in the samples are 4–8%. Separation of the matrix and recovery of the analytes are essentially complete as confirmed by standard addition of the analytes to the matrix.

Characterization of di(2-ethylhexyl)thiophosphoric acid by potentiometric titration and capillary zone electrophoresis by A. Merkoçi; A. Sastre; J. L. Cortina; C. Maccà (pp. 489-492).
 The acidity constant of di(2-ethylhexyl) thiophosphoric acid (DEHTPA) was investigated using potentiometric measurements with a pH glass electrode. Owing to the low solubility of DEHTPA in pure water, its concentration and acidity constants were determined by linearised pH-metric titration in 16.7% ethanol. A Ka value of (2.39±0.08)×10-4 was obtained. Quantitative determination of DEHTPA was performed by capillary zone electrophoresis (CZE) with carbonate buffer (pH 11.0) as a background electrolyte, operating at −20 kV with direct UV detection at 210 nm. The migration time was 8.97 min and the detection limit was 5 ppm.

A study of HPLC separation and spectrophotometric and voltammetric detection of 4′-substituted derivatives of 3-carboxy-4-hydroxy-6-acetylaminoazobenzene by Jir˘í Barek; Josef Cvac˘ka; Jir˘í Zima (pp. 493-499).
 Optimised conditions have been found for the separation of 3-carboxy-4-hydroxy-6-acetylaminoazo-benzene derivatives substituted in the position 4′ (4′-R-CHAAB, where R=–H, –CH3, –OCH3, –Cl, –COCH3, –NO2 and –NHCOCH3) using reversed phase HPLC with a C18 chemically bonded stationary phase. Suitable mobile phases are mixtures of 0.01 mol/L NaH2PO4 at pH 4 with methanol (1+1), 0.01 mol/L NaH2PO4 at pH 2 with acetonitrile (1+1) or 1% aqueous acetic acid with methanol (4+6). UV photometry is the most universal detection technique and yields limits of detection around 10-6 mol/L. Direct anodic voltammetry on a glassy carbon fibre array detector yields lower limits of detection for –COCH3 derivatives and higher limits of detection for –NO2 and –NHCOCH3 derivatives. When the analytes are chemically reduced using zinc powder in acetic acid, the voltammetric detection has limits of detection one order of magnitude lower than those obtained UV photometrically.

Determination of cationic surfactants by capillary electrophoresis by Katja Heinig; Carla Vogt; G. Werner (pp. 500-505).
A method is described for the separation of quaternary alkylbenzylammonium compounds as well as alkyl pyridinium salts by capillary electrophoresis using direct UV detection. The influence of the organic buffer modifier on the electrophoretic behaviour of the analytes is discussed. In addition to fused silica capillaries, also C8, C18 and neutral surface coatings are used. Separation is also performed in completely non-aqueous media. The results of method development are applied to the determination of cationic surfactants in cosmetics and pharmaceuticals. A comparison with HPLC with respect to efficiency, reproducibility and detection limits is presented.

Evaluation of contributions to the uncertainty of cholesterol determination in human serum by means of gas chromatography/(quadrupole-) mass spectrometry by A. Henrion; Gunther Dube; Wolfgang Richter (pp. 506-508).
 The uncertainty budget of the determination of cholesterol in a reference material (freeze-dried human serum) by isotope dilution mass spectrometry (IDMS) was evaluated. Measurements were run on a GC/quadrupole MS. A nested experimental design combined with a corresponding model for the analysis of variance (ANOVA) revealed the components making up the total uncertainty of the determinations. The coefficient of variation (CV) of the sole GC/MS-step was 0.47%, while that of the sample preparation including hydrolyzation, extraction and derivatization was 0.84%. This made the in-laboratory (overall) CV 0.96%. In addition, there was a vial-to-vial effect of 1.00% probably due to both inhomogeneity of the pooled material and lack of reproducibility of the filling procedure (including freeze drying) of the supplier as well as the reconstitution prior to use in the laboratory. These contributions sum up to an overall CV of a single determination of about 1.4%.

Second-derivative spectrophotometric study on the interactions of chlorpromazine and triflupromazine with bovine serum albumin by K. Kitamura; Hideyuki Mano; Yoshie Shimamoto; Yoshihiro Tadokoro; Koji Tsuruta; Shinji Kitagawa (pp. 509-513).
The second-derivative spectra of chlorpromazine (CPZ) or triflupromazine (TFZ) in buffer solutions (pH 7.4) containing various amounts of BSA (the reference solutions contained the same amount of BSA) showed derivative isosbestic points. The residual background signals derived from incomplete suppression of BSA signals can be entirely eliminated in the second-derivative spectra and BSA has spectrophotometrically one kind of binding site for CPZ or TFZ. The fractions of the drugs bound to BSA were calculated from the derivative intensity differences (ΔD values) of CPZ or TFZ before and after the addition of BSA. Scatchard plot experiments suggested that the binding of the drugs to BSA could be explained as a partition like non-specific binding model. The association constants (K) of CPZ or TFZ with BSA were calculated from the ΔD values according to the non-specific binding model by a nonlinear least-squares method. The K values were almost constant for all of the drug concentrations studied, and good reproducibility was obtained. The fractions predicted by the K values were in good coincidence to the observed values. These results confirm the usefulness of the proposed derivative method which does not need any separation procedures.

Sensitive determination of nucleotides and polynucleotides based on the fluorescence quenching of the Tb3+-Tiron complex by Dong-yuan Wang; Y. Zhao; Jin-gou Xu; Xiang-qun Guo (pp. 514-518).
 A sensitive method using fluorescence quenching for the determination of nucleotides (ATP, ADP, AMP, CTP, UTP) and polynucleotides[poly(A), poly(I), poly(U)] is proposed. It is based on the ability of nucleotides and polynucleotides to inhibit the formation of a strongly fluorescent complex of Tb3+ ion with Tiron. The possibilities of spectrofluorimetric measurements of these systems were studied under optimal conditions (pH 6.9 in hexamethylene tetramine-HCl buffer, 1.2×10-6 mol/L of Tb3+, 4.0×10-6 mol/L of Tiron, λex=317 nm, λem=546 nm). The results showed that the Tb3+-Tiron complex could be used as a fluorescence test for the phosphate moieties of nucleotides and polynucleotides. The detection limits are 0.3, 1.2, 3.7, 0.2, 0.3, 1.1, 0.6 and 0.9 ng/mL for ATP, ADP, AMP, CTP, UTP, poly(A), poly(I), and poly(U), respectively. The relative standard deviations (6 replicates) are within 4.0% in the middle of the linear range. The fluorescence quenching mechanism of these systems is also discussed.

Determination of trace chromium(VI) in water by graphite furnace atomic absorption spectrophotometry after preconcentration on a soluble membrane filter by Zhiqiang Li; Yanzhi Shi; Piying Gao; Xuexin Gu; T. Zhou (pp. 519-522).
 A new method for the concentration and determination of <0.1 μg/L of Cr(VI) in water by GFAAS is described. It is based on the formation of a chromium(VI)-salicylfluorone (SAF)-tetradecylpyridinium(TDP) ternary complex, the collection of the complex on a soluble membrane filter and the detection of the solution obtained after dissolving the membrane and analyte in a proper solvent. The ternary complex [Cr(VI)-SAF-TDP=1:2:2] is collected on a 0.45 μm nitrocellulose filter. This is dissolved in a small volume of sulphuric acid and the chromium is determined by GFAAS under the optimized conditions. Good linearity is observed over the range 0.010–0.150 μg Cr(VI) in 5.0 mL. The detection limit (three times the standard deviation of the blank) is 0.04 μg/L with 50-fold preconcentration. No interference from ions normally present in water was observed. The method has been applied to the concentration and determination of Cr(VI) in water samples from several sources and the recoveries of added Cr(VI) were 91–101%.

Analysis of trace elements in trunk wood by thick-target PIXE using dry ashing for preconcentration by L. Harju; Jan-Olof Lill; Kjell-Erik Saarela; Sven-Johan Heselius; Fredrik Joachim Hernberg; Alf Lindroos (pp. 523-528).
Thick-target Particle Induced X-ray Emission (TTPIXE) was used for the quantitative determination of trace-element concentrations in trunk wood. The wood samples were preconcentrated by dry ashing to improve the reliability of the sampling and the sensitivity of the analytical method. Samples of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) were collected from a polluted area (Harjavalta) as well as from a relatively nonpolluted area (Merimasku) in southwestern Finland. The elements studied were P, S, K, Ca, Mn, Fe, Ni, Cu, Pb, Rb, Sr, Ba, Cd and Ag. TTPIXE combined with dry ashing is a sensitive and reliable analytical technique for most elements studied. The method was validified by using several certified reference materials and also by ICP-MS analysis. Due to the low ash content (0.2–0.4%) in wood a high preconcentration factor can be obtained. Differences in trace-element uptake were observed between the two tree species studied. Trunk wood from the polluted area contained higher concentrations of heavy metal ions.

Determination of the provenance of majolica ceramics from Europe by thermoluminescence employing principal components by J. E. Vaz; J. J. LaBrecque; J. M. Cruxent (pp. 529-532).
Thermoluminescence data, obtained from majolica pottery after irradiation in the laboratory with gamma rays, were studied using the principal components technique to determine if the places of manufacture of this ceramic are differentiated one from another. A total of ten provenances in Holland, Spain and Italy was established by principal components. Six variables were used for the statistical analysis: the three glow-peaks positions, the relative intensity of the second peak to the first peak, the relative intensity of the third peak to the first peak, and the area under the glow curve.The precision for these parameters was about ± 5%, but the precision of the variables for a suite of standards was much higher. In addition, two groups of sherds collected in Latin America, and previously assigned to the provenances of Cataluna and Sevilla (Spain) by artistic criteria, were investigated in this study. All six samples of Cataluna agreed well with their previous assignment of provenance, but several of the samples assigned previously to Sevilla were not related unambiguously to this provenance, although they were with certainty excluded from other provenances.

Detection of reprocessing activities through stable isotope measurements of atmospheric noble gases by Y. Aregbe; K. Mayer; S. Valkiers; P. De Bièvre (pp. 533-535).
Noble gas stable isotope abundance measurements may provide a tool for detecting reprocessing activities of nuclear fuels. An approach has been made by carrying out blending calculations of released fission xenon and krypton in air using the Isotope Mixture Programs which have been developed at the IRMM. After having obtained a reliable approximation to the expected range of the isotope ratios in the blends and the respective detection limit thereof through these calculations, the potential application of ultra-accurate measurements of the isotopic composition of anthropogenic and atmospheric noble gases is taken into consideration. Also the important role of radiometric measurements of 85Kr and 133Xe for the detection of nuclear fuel reprocessing is taken into account. The information provided by such activity measurements is limited, therefore a method to calculate the initial isotopic composition of released fission noble gases, through measuring of their atmospheric mixing ratio, is presented and discussed. Highly accurate stable isotopic measurements of atmospheric noble gases might provide more detailed information on the “history” of the reprocessed nuclear fuel. Therefore they could serve, in combination with radiometric detection techniques, as an excellent tool for the identification of reprocessing activities.

Evaluation of gel permeation chromatography to Fourier transform infrared spectrometric detection using a modified thermospray for analysis of polystyrene samples by Mohammad A. Mottaleb; B. G. Cooksey; David Littlejohn (pp. 536-538).
A heated gas flow modified thermospray was used to couple gel permeation chromatography (GPC) to Fourier transform infrared spectrometry (FTIR) for the analysis of the standard polystyrene samples. Effluents from the GPC column were evaporated and the solutes were deposited as a series of spots on the surface of a moving stainless steel belt (0.025 mm thickness × 13 mm width). The belt continuously transferred the spots into the diffuse reflectance (DRIFT) accessory of the FTIR spectrometer, enabling identification of the deposited solutes by measurement of the diffuse reflectance IR spectrum. The IR spectra of the separated components showed excellent agreement of the spectral features to those of standard FTIR spectra and no thermal degradation was observed.

Potentiometric titration of anionic polyelectrolytes using a cationic surfactant solution as a titrant and a titrant-sensitive plasticized poly(vinyl chloride) membrane electrode by Takashi Masadome; T. Imato (pp. 538-540).
A potentiometric titration method for the direct determination of anionic polyelectrolytes using a plasticized poly(vinyl chloride) membrane electrode is described. A cationic surfactant solution is used as titrant. The method is based on ion association between the anionic polyelectrolyte in the sample and the cationic surfactant in the titrant. The end-point is detected as a sharp potential change due to an increase in the concentration of the free cationic surfactant at the equivalence point. The sharpness of the titration curve at the end-point is compared for several cationic surfactants; a solution of stearyltrimethylammonium ion has been found to be superior.

Quantitative determination of cadmium in polyethylene using total reflection X-ray fluorescence (TXRF) spectroscopy by U. Simmross; R. Fischer; F. Düwel; U. Müller (pp. 541-545).
A new application of total reflection X-ray fluorescence (TXRF) spectroscopy was tested for its use in the quantitative determination of element mass fractions (Z ≥ 12) in solid polyethylene samples. The experiments were conducted with four polyethylene reference materials from the Institute for Reference Materials and Measurements (IRMM) with cadmium mass fractions in the range from 40 to 400 mg/kg (VDA 001–004). Samples from each reference material were transferred as thin films straight onto quartz glass discs commonly used for TXRF analysis. Precision, accuracy and capability of the method are discussed on the basis of the current results and recent experiences with real samples. The method appears to be suitable for tasks in forensic science and polymer analysis.

Sequential flow-injection spectrophotometric determination of iron(II) and iron(III) by copper(II)-catalyzed reaction with Tiron by M. Endo; Shigeki Abe (pp. 546-547).
A flow injection method for the sequential determination of iron(II) and iron(III) was developed. It is based on the differential reaction kinetics of iron(II) and iron(III) with Tiron in a double-injection FI system. The proposed method employs the accelerating action of copper(II) for the oxidation of iron(II) in the presence of Tiron. A linear calibration graph is obtained for iron (II) and iron(III) in the concentration range 1.8 × 10–5– 1.8 × 10–4 mol/L; the throughput of samples is 30 injections/h.

A simple spectrophotometric procedure for the determination of antimony (III) and (V) in antileishmanial drugs by S. Rath; W. F. Jardim; J. G. Dórea (pp. 548-550).
A spectrophotometric method for the selective determination of antimony (III) and (V) in antileishmanial drugs is described. The procedure is based on the reaction of Sb(III) with bromopyrogallol red (BPR) in neutral solution. As a consequence of the Sb-BPR complex formed, the absorbance of BPR, at 560 nm, decreases proportionally to the amount of Sb(III) in the analyte solution. The calculated apparent molar absorptivity and determination limits are 3.67 × 104 L · cm–1 · mol–1 and 1.65 × 10–6 mol/L, respectively. Sb(V) is determined after reduction to Sb(III) by iodide. The Sb(V) content determined in ten samples of Glucantime varied from 75.40 ± 0.97 to 94.47 ± 1.0 mg/mL. Sb(III) was detected in all samples analyzed, and mean values ranged from 5.19 ± 0.16 to 10.52 ± 0.15 mg/mL. The method is suitable for the routine quality control of pharmaceutical formulations.

Determination of nitrite and bromate in disinfected water samples at the low μg/L level by means of a high-capacity anion exchanger by K. Köhler; M. Nowak; A. Seubert (pp. 551-553).
Bromate and nitrite are formed during the disinfection of water. The German threshold value for nitrite in drinking water is 100 μg/L, for bromate a limit below 50 μg/L has to be established. A self-made high-capacity resin with 2-(dimethylamino)-ethanol functionality in combination with a UV-transparent elution system based on perchloric acid allows the separation and sensitive photometric detection of nitrite and bromate, even if high chloride concentrations are present. The high capacity of the strongly basic resin allows sample volumes of up to 400 μL without disturbance of the separation. Detection limits for bromate and nitrite are 15 and 10 μg/L, respectively. The direct analysis of water samples with high salt contents, such as disinfected pool water, is possible by insertion of an on-line chloride removal step.

Determination of thiol drugs in pharmaceutical formulations as their S-pyridinium derivatives by high-performance liquid chromatography with ultraviolet detection by E. Bald; Stanisław Sypniewski (pp. 554-555).
Acetylcysteine and captopril can be determined in pharmaceutical formulations after precolumn derivatization of the thiol with 1-benzyl-2-chloropyridinium bromide (BCPB) by reversed-phase ion-pair HPLC separation and UV detection. The thiol group of the drugs reacts with BCPB in 0.1 mol/L phosphate buffer (pH 8) to form S-pyridinium derivatives showing an absorption maximum at 314 nm. The S-pyridinium derivative was separated isocratically on an Asahipak ODP-50 column at 45°C with 0.2 mol/L citrate buffer containing 10 mmol/L of sodium octanesulfonate (pH 2.5) and acetone (4:1, v/v). Calibration curves for both analytes were linear over the range of 2–20 μg/mL with variation coefficients of 3.12–1.28% for acetylcysteine and 9.22–1.51% for captopril.

Determination of procaine hydrochloride by ion-pairing flow injection analysis with piezoelectric detection by Z. Mo; J. Luo; Xiaohui Long; Ziling Xia (pp. 556-558).
A fast and simple method for the determination of procaine hydrochloride by ion-pairing flow injection analysis has been developed. It is based on the formation of an ion-pair with sodium dodecyl phenylsulphonate and piezoelectric detection. The calibration curve was linear between 0.02 and 2.00 mg/mL, with a detection limit of 0.01 mg/mL, a relative standard deviation of 0.3% (10 replicates) and a sampling frequency of 120/h. The proposed method has been satisfactorily applied to the determination of procaine hydrochloride in pharmaceutical preparations.

Separation of pesticides on an octadecyl-coated alumina column by T. Cserháti; Esther Forgács (pp. 558-560).
The retention times of 33 commercial pesticides were determined on an octadecyl alumina HPLC column using water-methanol mixtures. The retention of the pesticides decreased with an increasing concentration of methanol in the eluent proving the regular retention behaviour of the solutes. The retention characteristics of pesticides did not correlate to their hydrophobicity parameters indicating that the absorption centers of alumina not covered by the hydrophobic octadecyl ligand considerably influence the retention. The opposite linear correlation between the retention of pesticides on alumina and octadecyl alumina supports proves that octadecyl alumina supports behave as real reversed-phase supports, however, their retention characteristics differ considerably from those of traditional octadecylsilica supports.
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