Analytica Chimica Acta (v.510, #1)

15 N / 14 N isotopic ratio and statistical analysis: an efficient way of linking seized Ecstasy tablets by Fabien Palhol; Catherine Lamoureux; Martine Chabrillat; Norbert Naulet (1-8).
In this study, the 15 N / 14 N isotopic ratios of 106 samples of 3,4-methylenedioxymethamphetamine (MDMA) extracted from Ecstasy tablets are presented. These ratios, measured using gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS), show a large discrimination between samples with a range of δ15 N values between −17 and +19‰, depending on the precursors and the method used in clandestine laboratories. Thus, δ15 N values can be used in a statistical analysis carried out in order to link Ecstasy tablets prepared with the same precursors and synthetic pathway. The similarity index obtained after principal component analysis and hierarchical cluster analysis appears to be an efficient way to group tablets seized in different places.
Keywords: Nitrogen isotopic ratio; Gas chromatography; Combustion; Isotope ratio mass spectrometry; 3,4-Methylenedioxymethamphetamine; Seizures comparisons; Statistical analysis;

A flow-through reactor where a fine platinized platinum wire (Pt black wire) runs through the entire length of the PTFE tube was fabricated for the rapid decomposition of hydrogen peroxide (H2O2) at concentrations up to 1 M. Since the Pt black wire is directly electrically heated and the exterior of the tubular reactor is well insulated, the energy efficiency of this heater reactor is excellent. The temperature coefficient of resistance of the wire is significant (3280±40 ppm/°C). This provides a means to ascertain the mean temperature by measuring the resistance of the wire. The concentration of residual H2O2 was determined by the hematin-catalyzed oxidation of nonfluorescent thiamine to fluorescent thiochrome by H2O2. Essentially, quantitative (99.997%) decomposition of 1 M H2O2 could be achieved at a mean reactor temperature of 108 °C from a neutral aqueous solution with a mean residence time of ∼270 s.
Keywords: Hydrogen peroxide; Decomposition; Platinum black; Heated reactor;

Properties of the overtone mode of the quartz crystal microbalance in a low-viscosity liquid by Minoru Yoshimoto; Shin Tokimura; Kohya Shigenobu; Shigeru Kurosawa; Masayoshi Naito (15-19).
The effect of the immersion angle on the overtone mode of the quartz crystal ‘microbalance’ (QCM, piezoelectric quartz crystal) was investigated in a Newtonian liquid. The measurement using the impedance analyzer revealed that the resonant frequency shift of the Nth overtone mode of the QCM was depend on the immersion angle, and, at each immersion angle, was N times larger than that of the fundamental mode. These tendencies were also observed in the resistance of the Butterworth–Van Dyke equivalent circuit. Furthermore, on the basis of these results, we have discussed the immersion angle dependence of the resonant frequency shift and the resistance.
Keywords: QCM; Overtone mode; Immersion angle;

A flow-injection chemiluminescence (CL) method is described for the determination of fluoroquinolones including ciprofloxacin, norfloxacin and ofloxacin. The method is based on the enhancement by these compounds of the weak CL from peroxynitrous acid. The linear ranges are 1.0×10−7 to 1.0×10−5  mol l−1 for ciprofloxacin and norfloxacin, and 3.0×10−7 to 3.0×10−5  mol l−1 for ofloxacin, respectively. The detection limits (S/N=3) are 4.5×10−8  mol l−1 ciprofloxacin, 5.9×10−8  mol l−1 norfloxacin and 1.1×10−7  mol l−1 ofloxacin, respectively. The proposed method was applied to the determination of fluoroquinolones in pharmaceutical preparations.
Keywords: Peroxynitrous acid; Ciprofloxacin; Norfloxacin; Ofloxacin; Chemiluminescence; Flow-injection analysis;

Peroxynitrous acid (ONOOH) was produced by the on-line mixing of acidified hydrogen peroxide with nitrite in a flow system. A strong chemiluminescent (CL) emission was observed when ONOOH reacted with carbonate without any special CL reagents. When cotton was present in the CL cell, the CL emission was enhanced significantly. The method was developed to determine nitrite, which showed a key improvement that any CL reagents and sensitizers were not used, resulting in better selectivity. The applicability of the present CL system was demonstrated for the sensitive and selective determination of nitrite in natural water samples without any special pretreatment. Good agreements were obtained for the determination of nitrite in tap and well waters between the present approach and a standard spectrophotometric method. The average precision was 4.6% (n=7) and detection limit (S/N=3) was 1.0×10−7  M. Based on the CL spectrum, UV spectra, and dissolved oxygen measurement, a possible CL mechanism was proposed. ONOOH was an unstable compound in acidic solution and could be quenched into peroxynitrite (ONOO) in basic solution. ONOO reacted with CO2 to produce ONOOCO2 , which can rapidly decompose into •NO2 and •CO3 radicals. In the presence of H+, •CO3 radicals can protonate to bicarbonate radical (HCO3 •). The recombination of HCO3 • radicals and decomposition can lead to light emission.
Keywords: Solid surface enhancement; Chemiluminescence; Peroxynitrous acid; Nitrite; Natural water;

A new simple, rapid and cost effective flow injection (FI) electrochemiluminescence (ECL) method was described for the determination of acyclovir (9,2-hydroxyethoxy) methyl guanine. In the presence of acyclovir, the luminol electrochemiluminescence generated by a mini on-line galvanic cell could be greatly sensitized in alkaline medium. The relative electrochemiluminescence intensity was found to increase linearly with increasing concentration of acyclovir, which was corroborated by the calculated correlation coefficient value of 0.9994 (n=7). The limit of detection was 1.6×10−7  mol l−1 and the limit of quantification was 7.9×10−7  mol l−1. The proposed method was applied to the determination of acyclovir in pharmaceutical formulations. The reliability of the assay method was established by parallel determination and by standard-addition method. Experiment results demonstrated the described mini analysis system, while being simple and less time consuming, was accurate, precise and reproducible (R.S.D. = 1.6%, recoveries = 99 – 103%). Further experiments indicated that there was no significant difference between the results obtained by the proposed and official methods.
Keywords: Electrochemiluminescence (ECL); Acyclovir; On-line galvanic cell; Flow injection (FI);

Myo-inositol hexakisphosphate (phytate) is a substance present in urine with an important role in preventing calcium renal calculi development. In spite of this, the use of urinary phytate levels on stone-formers’ evaluation and treatment is still notably restricted as a consequence of the enormous difficulty to analyze this substance in urine. In this paper, a simple procedure for routinary urinary phytate determination based on phosphorus determination through inductively coupled plasma atomic emission spectrometry is described.The method only requires a previous separation of phytate from other components by column anion exchange chromatography. The working linear range used was 0–2 mg l−1 phosphorus (0–7 mg l−1 phytate). The limit of detection was 64 μg l−1 of phytate and the limit of quantification was 213 μg l−1. The relative standard deviation (R.S.D.) for 1.35 mg l−1 phytate was 2.4%. Different urine samples were analyzed using an alternative analytical methodology based on gas chromatography (GC)/mass detection used for inositol determination (phytate was previously hydrolyzed), resulting both methods comparable using as criterion to assess statistical significance P<0.05.
Keywords: Phytic acid; Urine; ICP-AES determination;

A novel method for inductively coupled plasma atomic emission spectrometry (ICP-AES) determination of trace amounts of Pt(II), Pd(II) and Rh(III), based on gaseous compounds introduction into the plasma as their diethyldithiocarbamate complexes by electrothermal vaporization (ETV), was developed. At the temperature of 1100 °C, the trace amounts of Pt, Pd and Rh were vaporized into plasma. The factors affecting the formation of the chelates and their vaporization behaviors, such as ashing temperature and time, vaporization temperature and time, pH and the concentration of chelating reagents were studied in detail. Under the optimized conditions, the limits of detection (LODs) (3σ) of Pt, Pd and Rh for tested solutions were 5.4, 1.4 and 0.8 ng ml−1, and for actual sample (auto-catalyst NIST SRM 2557) were 0.27, 0.07 and 0.04 μg g−1, respectively. The relative standard deviations (RSDs) for Pt, Pd and Rh were 1.4, 2.6 and 2.4% (C Pt=0.5 μg ml−1, C Pd,Rh=0.25 μg ml−1, n=7), respectively. The linear ranges of calibration graphs for Pt, Pd and Rh cover three orders of magnitude. Compared with conventional electrothermal vaporization technique, using the reagent of diethyldithiocarbamate as chemical modifier could not only enhance the analytical sensitivities, but also reduce the vaporization temperature. By combination with a separation/preconcentration step, the proposed method had been successfully applied to the analysis of the artificial seawater, tap water and urine with recoveries ranging from 91 to 106%. The two certified reference material meager platinpalladium ore GBW 07293 and auto-catalyst NIST SRM 2557 was also analyzed for validation, and the determined values obtained were in good agreement with the certified values.
Keywords: Low temperature electrothermal vaporization; ICP-AES; Chemical modifier; Pt, Pd and Rh;

A flow-injection biosensor system with an on-line microdialysis sampling is proposed for the simultaneous monitoring of glucose, l-lactate, and pyruvate in rat brain. In the first stage of the operation, the dialysate from the microdialysis probe is delivered to a sample loop of the six-way autoinjector by perfusing Ringer’s solution for 120 s at 2 μl min−1. In the second stage, the dialysate collected in the sample loop is automatically injected for 10 s into the flow-injection line with a triple enzyme electrode arranged in perpendicular for the flow direction. The triple enzyme electrode is constructed by hybridizing a poly(1,2-diaminobenzene) film to three sensing parts which respond selectively to glucose, l-lactate, and pyruvate, respectively, without any cross-reactivity. The three sensing parts of the triple enzyme electrode respond linearly to the concentrations of glucose, l-lactate, and pyruvate between 0.1 and 10 mM, without any interference from oxidizable species present in the dialysate. The proposed flow-injection analysis method can be successfully applied to the simultaneous in vitro and in vivo assays of three analytes in serum and in rat brain, respectively. The system can be automatically processed at an analytical speed of 28 dialysates h−1.
Keywords: In vivo analysis; Biosensor; Triple enzyme electrode; Flow-injection system; Microdialysis; Rat brain;

A novel and automated sequential injection procedure is proposed for the spectrophotometric determination of orthophosphate without requiring unstable chemical reducing species used in the classical molybdenum blue method. The flowing methodology is based on the on-line generation of the detectable species by electrochemical reduction of the 12-molybdophosphoric acid complex using a stainless steel tubular flow-through working electrode. The established method is linear up to 20 mg/l P, with coefficients of variation (n=10) of 2.4 and 1.8% for 2.0 and 10 mg/l P, respectively. The versatility of the sequential injection method to analyse samples containing high orthophosphate levels has been demonstrated by the implementation of a dilution chamber as well as flow-reversal techniques, yielding relative standard deviations (n=17) better than 2.0% for standards containing 200 and 800 mg/l P. The proposed analyser features an extremely wide dynamic range (viz., 0.3–800 mg/l) as well as improved tolerance to silicate interference, so that Si/P ratios higher than 50 are tolerated at the 5% level. Electrochemical conditions, reagent concentrations and physical variables have been thoroughly investigated. The method has been applied to the determination of orthophosphate in wastewaters as well as beverages and biological samples containing high concentrations of the target analyte. The t-test comparison of the means for the developed sequential injection system with electroreduction and both the molybdenum blue classical spectrophotometric batch procedure and inductively coupled plasma-optical emission spectrometric detection selected as external reference methods revealed that there is no evidence of significant differences between the obtained results at the 95% confidence level.
Keywords: Phosphate; Electroreduction; Molybdenum blue; Sequential injection analysis; Wastewater; Beverages; Urine;

Determination of catechins and catechin gallates in biological fluids by HPLC with coulometric array detection and solid phase extraction by Kai On Chu; Chi Chiu Wang; Michael Scott Rogers; Kwong Wai Choy; Chi Pui Pang (69-76).
Tea polyphenols are well known for their beneficial health effects that involve their anti-carcinogenic, anti-mutagenic, anti-pathogenic and anti-oxidative properties. The main polyphenols of green tea are favan-3-ols (catechins) and their corresponding gallate compounds, which constitute about one-third of the dry weight of tea leaves. Their main ingredients are (+)-catechin (C), (−)-epicatechin (EC), (−)-gallocatechin (GC), (−)-epigallocatechin (EGC), (−)-catechin gallate (CG), (−)-epicatechin gallate (ECG), (−)-gallocatechin gallate (GCG) and (−)-epigallocatechin gallate (EGCG). Each has slightly different biological properties. We have developed a method to simultaneously analyze all these compounds in plasma and urine. The samples were first incubated with β-d-glucuronidase and sulfatase to release the catechin residues from their corresponding conjugates for subsequent extraction by selective solid phase column, Waters Oasis HLB extraction cartridges. The extracted molecules were resolved by reversed phase HPLC and monitored by coulometric chemical detection on a CoulArray detector. All eight catechin compounds were analyzed in a single chromatogram within 25 min. For plasma and urine analyses, good linearity (>0.9950) was validated in the range 10–2000 and 10–5000 ng/ml, respectively. The coefficients of variance (CV) were less than 5%. Absolute recovery was greater than 85% and detection limit was 5 ng/ml. The chromatogram exhibited minimal interference as a result of the highly selective solid phase extraction and CoulArray detection.
Keywords: Solid phase extraction; Couloarray; HPLC; ECD; Catechin;

This paper describes employing capillary electrophoresis (CE) for the separation of gold colloids in nanometer-size regimes. Adding sodium dodecylsulfate (SDS) surfactant to the running buffer enhances the capability of CE to separate gold nanoparticles. We found that the optimized separation conditions involved SDS (70 mM), 3-cyclohexylamoniuopropanesulfonic acid (CAPS) buffer (10 mM), pH 10.0, and an applied voltage of 20 kV. We propose that the charged surfactants associate onto the surface of the gold nanoparticles and cause a change in the charge-to-size ratio of gold nanoparticle, which is a function of the surface area of nanoparticle and the surfactant concentration of running electrolyte. At high concentrations of the surfactant in the running electrolyte—i.e., when the surface of the gold nanoparticles is fully occupied with SDS—a linear relationship exists between the electrophoretic mobility and nanoparticles having diameters ranging from 5.3 to 38 nm. Based on the results of separating the 5.3 and 19 nm nanoparticles, we estimate that the size resolution (R s=1.0) is 5.0 nm. The relative standard deviations of the electrophoretic mobilities of the 5.3 and 19 nm gold nanoparticles are 0.97 and 0.54%, respectively.
Keywords: Gold nanoparticles; Separation; Capillary electrophoresis; Sodium dodecylsulfate;

Electroanalytical detection of zinc in whole blood by Jaanus Kruusma; Craig E Banks; Lembit Nei; Richard G Compton (85-90).
Three different electroanalytical techniques for the determination of zinc in blood are investigated. The direct determination in diluted blood via anodic stripping voltammetry at glassy carbon and the use of Nafion-coated glassy carbon mercury electrodes are shown to lack the necessary sensitivity whereas an acoustically assisted double extraction followed by sono-ASV using a glassy carbon electrode is found to be rapid, reliable and sensitive.
Keywords: Zinc; Blood; Nafion; Anodic stripping voltammetry; Ultrasound;

In situ measurements of copper and zinc using diffusive gradients in thin films (DGT) in two distinct natural water systems were compared to metal speciation assessed by competitive ligand exchange (CLE) and voltammetric measurements. In a dynamic river system, where dissolved metal concentrations vary significantly over short-time periods, DGT technique provided averaged values of the metal concentrations over time. In microcosms, at different total dissolved concentrations of copper and zinc, DGT technique measured a similar fraction as measurements of labile metal performed by voltammetry. The proportion of DGT and voltammetric-labile zinc to dissolved zinc was 61±4% and, respectively, 76±9%. DGT technique was measuring 81±8% of exchangeable copper (by exchange with catechol). These two fractions were similarly influenced by the addition of NTA. In the absence of NTA, copper measured by DGT represented 34±4% of dissolved copper whereas in the presence of NTA, this proportion raised to 57±2%. These measurements were compared to calculations performed with speciation programs using several models for the complexation by humic and fulvic substances, namely Model VI (WHAM), NICA-Donnan and SHM. The predicted speciation by these three models was similar. The prediction of free zinc ion and labile zinc concentrations were in agreement with experimental data. Calculated concentrations of free copper ion were overestimated because these models are not considering strong specific copper-binding ligands probably present in natural water.
Keywords: Copper; Zinc; Speciation; Freshwater; DGT; Voltammetry; Model;

Evaluation of an ultrasonic digestion procedure for total metal determination in sediment reference materials by Claudia Brunori; Ildiko Ipolyi; Laura Macaluso; Roberto Morabito (101-107).
In this work the possibility to use a simple and easily available laboratory device—routine ultrasonic bath—has been evaluated for total metal determination in sediments from different origin. The investigated instrumental parameters were time and temperature, whereas power was maintained constant set at 100% of nominal power. Four different sets of parameters were applied on a lake sediment reference material (RM), the results obtained for five elements—Cd, Cr, Cu, Ni and Zn—were statistically compared with those obtained by a previously optimised microwave acid digestion procedure on the same material. The optimal set of parameters—30 min sonication at ambient temperature—was chosen, and then applied to other five sediment RMs from different origin. In this case four additional elements—As, Pb, V and Fe—were also determined and the results were compared with reference and microwave values.The results obtained by the ultrasound digestion procedure were higher than 80% of the reference and/or microwave values in 40 out of 44 cases. In any case, the results obtained by ultrasonic procedure were statistically comparable to reference values (mean of means of interlaboratory exercises or certified values) in the 84% of the cases.
Keywords: Total metal content; Ultrasonic digestion; Sediments; Reference materials;

Extractable organic compounds in polyurethane foam with special reference to aromatic amines and derivatives thereof by Åsa Marand; Daniel Karlsson; Marianne Dalene; Gunnar Skarping (109-119).
Methods for determination of aromatic amines and related compounds in flexible toluene diisocyanate (TDI)-based polyurethane (PUR) foam were investigated. The foam was extracted using 0.1% (w/v) aqueous acetic acid (HAc). Extraction solutions were analysed and aromatic amines were determined as ethyl chloroformate (Et) and pentafluoropropionic acid anhydride (PFPA) derivatives. The determinations were performed using liquid chromatography (LC) and mass spectrometry (MS) detection with electrospray ionisation (ESI) or gas chromatography (GC)–MS with chemical ionisation monitoring negative ions (NCI). The Et derivatives were determined using LC–ESI+-MS with detection limit of 2 pg of toluenediamine (TDA). The PFPA derivatives were determined using LC–ESI-MS or GC–NCI-MS with detection limits of 0.1 and 0.02 pg of TDA, respectively. Using trideuterium labelled TDA as internal standard, linear calibration curves were obtained in the range of 0.01–0.50 μg ml−1 (n=7), with correlation coefficients >0.999. When plotting calibration curves for TDA–PFPA derivatives determined using LC–MS against TDA–PFPA using GC–MS and TDA–Et using LC–MS, linear curves were obtained. The relative standard deviation (R.S.D.) for determination of TDA in foam extraction solutions were 13%. LC–MS determination of PFPA derivatives was more selective, as compared to LC–MS of Et derivatives.In foam extraction solutions, 2,4- and 2,6-TDA, several isomers of methylenedianiline (MDA) and dimers of TDA/TDI were observed. 2,4-TDA and 4,4′-MDA are possible human carcinogens. Hydrolysis of the extraction solution revealed a large pool of TDA/TDI compounds and oligomers. The concentration of TDA in foam was affected by the extraction media, temperature and duration. The choice of derivatisation procedure also affected the determination of TDA. In extraction solutions from six different commercially available flexible foam qualities 2,4- and 2,6-TDA were found in the range of 0–7 and 0–6 μg g−1  foam, respectively. When flexible foam was heated, considerable higher concentrations of TDA were observed.
Keywords: Polyurethane; PUR; Toluenediamine; TDA; LC–MS;

Partial least squares modeling as a powerful multivariate statistical tool applied to spectrophotometric simultaneous determination of cobalt, copper, and nickel in aqueous solutions. The concentration range for cobalt, copper and nickel were 0.4–2.6, 0.6–3.4, 0.5–5.5 ppm, respectively. The experimental calibration set was composed with 36 sample solutions using a mixture design for three component mixtures. The absorption spectra were recorded from 470 to 600 nm. The effect of pH on the sensitivity and selectivity was studied according to net analyte signal (NAS). The values of root mean square difference (RMSD) for cobalt, copper and nickel using partial least squares (PLS) were 0.0192, 0.0263 and 0.0446 ppm, respectively. The effects of various cations and anions were investigated. The method was used to determination of cobalt, copper and nickel in two sample alloys based on copper, nickel and cobalt (known as cunico) and based on cobalt, nickel and iron (known as conife).
Keywords: Simultaneous determination; Cobalt; Copper; Nickel; PLS; Spectrophotometric; Cunife; Cunico; Alloys;