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Analytica Chimica Acta (v.570, #1)

Editorial Board (pp. co1).

CONTENTS (pp. v-vi).

Calendar of forthcoming meetings (pp. n1).

Visualization of electrophoretically mediated in-capillary reactions using a complementary metal oxide semiconductor-based absorbance detector by Maria Kulp; Pawel L. Urban; Mihkel Kaljurand; Edmund T. Bergström; David M. Goodall (pp. 1-7).

A method for real-time visualisation of reactions performed in-capillary by the technique of electrophoretically mediated microanalysis (EMMA) is described, using a two dimensional imaging detection system. The UV absorbance detector is based on a complementary metal oxide semiconductor (CMOS) active pixel sensor. Imaging of analyte peaks absorbing at 200nm and migrating over length of 14mm in the capillary dimension allowed measurement of velocities and lengths of reactant and product zones. By contrast with use of single point detection, velocities of species generated by reaction anywhere within the capillary are readily measured with CMOS imaging: this is of particular benefit for EMMA experiments where reaction occurs during zone overlap. For the oxidation of glutathione by hydrogen peroxide, reaction times were varied over the range 0.5–20s by changing voltages for electrokinetic injection and zone migration, and reactant and product peak areas were obtained for kinetic analysis of the reaction. The use of EMMA conditions with CMOS imaging allows the whole process of reaction, separation and quantification to be carried out in nanolitre volumes on-capillary in a single run on a time scale of less than 5min.

Keywords: In-capillary reactions; EMMA; CMOS imaging

Determination of avermectins in commercial formulations using microemulsion electrokinetic chromatography by Parinya Seelanan; Monpichar Srisa-art; Amorn Petsom; Thumnoon Nhujak (pp. 8-14).

Microemulsion electrokinetic chromatography (MEEKC) was developed for quantitative analysis of avermectins, such as abamectin, doramectin and ivermectin, in commercial formulations, using the microemulsion buffer containing a 50mM phosphate buffer at pH 2.5, 1.1% (v/v) n-octane as oil droplets, 180mM sodium dodecylsulphate as surfactant, 890mM 1-butanol as co-surfactant and 30% (v/v) ethanol as organic co-solvent. High accuracy and precision of the method were obtained. The contents of avermectins in commercial formulations determined by MEEKC were found to be insignificantly different with those determined by high performance liquid chromatography (HPLC). Therefore, MEEKC can be used an alternative method to HPLC for quantitative determination of avermectins.

Keywords: Avermectins; Abamectin; Doramectin; Ivermectin; Microemulsion electrokinetic chromatography; Capillary electrophoresis

Development of a fluorescence lifetime-based sol–gel humidity sensor by Orla McGaughey; José Vicente Ros-Lis; Adrian Guckian; Aisling K. McEvoy; Colette McDonagh; Brian D. MacCraith (pp. 15-20).

A sol–gel-based optical sensor for the measurement of relative humidity has been developed. It is based on the changes in fluorescence intensity and/or lifetime of the ruthenium complex, ruthenium(II)diphenylphenanthroline-dipyridophenazinehexafluorophosphate. Sensitivity to relative humidity has been demonstrated over the range 0–100% relative humidity. This sensor has been developed for application in the field of indoor air-quality monitoring and displays a limit of detection of 0.35% relative humidity and a resolution of 1.13% over the concentration range of interest (0–50% relative humidity). The effects of varying process parameters on the sensor performance were studied along with the effects of cross-sensitivity to molecular oxygen.

Keywords: Fluorescence lifetime; Relative humidity; Sol–gel; Sensor

Determination of nucleic acids based on the fluorescence quenching of Hoechst 33258 at pH 4.5 by Yuan Guan; Wen Zhou; Xiaohui Yao; Meiping Zhao; Yuanzong Li (pp. 21-28).

It was found the strong fluorescence emitted by the bis-benzimidazole derivative Hoechst 33258 at 490nm could be efficiently quenched in pH 4.5 buffer when nucleic acids were added. Analysis of fluorescence intensity showed that the procedure was a static quenching dominated one, which was also demonstrated by the electron absorption spectra and lifetime of the excited state. The binding constant and numbers of binding sites were obtained from the Scatchard plot. The decreased fluorescence intensity was in proportion to the concentration of nucleic acids in the range 40–1800ngml⁻¹ for dsDNA and 26–1700ngml⁻¹ for ssDNA. The limits of detection were 12 and 8ngml⁻¹, respectively. The sensitivity of the method was about 3.4 times higher for dsDNA detection and 5.4 times higher for ssDNA detection compared with the widely used fluorescence enhancement method using the same dye. Application results to synthetic samples showed simplicity, rapidity and satisfactory reproducibility of the presented method. Measurement of real samples extracted from leaves of Crassula argentea and E. coli genome also gave satisfactory results, which were in good agreement with those obtained using spectrophotometric method.

Keywords: Quantitative detection; Nucleic acids; Hoechst 33258; Fluorescence quenching

2-Carboxy-1-naphthyl phosphate as a substrate for the fluorimetric determination of alkaline phosphatase by Xiaojing Zhu; Qikui Liu; Chongqiu Jiang (pp. 29-33).

A new substrate, 2-carboxy-1-naphthyl phosphate (CNP), was developed for the fluorimetric determination of alkaline phosphatase (ALP) activity. The product of the enzyme reaction is 1-hydroxy-2-naphthoic acid (HNA), which is a strong fluorescent product. The amount of HNA generated is proportional to ALP activity. Optimal conditions for the determination of ALP were investigated. The linear range and detection limit for the determination of ALP are 0.01–4.8U/L and 7.44mU/L, respectively. This method is simple, practical and can be successfully applied to assess ALP in human serum with good accuracy and precision. The results were evaluated by comparison with a standard colorimetric assay using p-nitrophenyl phosphate as ALP substrate.

Keywords: Alkaline phosphatase; 2-Carboxy-1-naphthyl phosphate; Fluorimetry

Chemical imaging techniques for the analysis of complex mixtures: New application to the characterization of ritual matters on African wooden statuettes by Vincent Mazel; Pascale Richardin; David Touboul; Alain Brunelle; Philippe Walter; Olivier Laprévote (pp. 34-40).

Chemical imaging techniques, based on the combination of microscopy and spectroscopy, are well suited to study both the composition and the spatial organization of heterogeneous complex mixtures of organic and mineral matter. Time-of-flight secondary ion mass spectrometry (ToF-SIMS), followed by scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX) and Fourier transform infrared microscopy (FTIR microscopy) have been applied to non-destructive analysis of micro-samplings of ritual matters deposited on the surface of African wooden statuettes. With a very careful preparation, using ultramicrotomy on embedded samples, it was possible to perform successively all the measurements on a single fragment. Comparison and superposition of the different chemical images, obtained on a sample from a significant actual artefact, have allowed us to identify minerals (clays, quartz and calcium carbonate), proteins, starch, urate salts and lipids and to map their spatial distribution.

Keywords: Imaging techniques; Time-of-flight secondary ion mass spectrometry (ToF-SIMS); Scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX); Fourier transform infrared microscopy (FTIR microscopy); Cultural heritage; African art

Simultaneous determination of lamivudine, stavudine and nevirapine in antiretroviral fixed dose combinations by high performance liquid chromatography by Namita Kapoor; Sateesh Khandavilli; Ramesh Panchagnula (pp. 41-45).

An accurate, sensitive and specific reversed phase high performance liquid chromatographic method (RP-HPLC) for the simultaneous quantitative determination of the nucleoside reverse transcriptase inhibitors lamivudine, stavudine with the non-nucleoside reverse transcriptase inhibitor nevirapine in pharmaceutical fixed dose combinations is described. Chromatography was carried on C-18 column by gradient elution with two mobile phase components: mobile phase (A) comprising of 80% of 10mM acetate buffer adjusted to pH 3.5 with glacial acetic acid and 20% methanol and mobile phase (B) comprising of 50% acetonitrile with 50% isopropyl alcohol. Mobile phase was pumped at a flow rate of 0.6mlmin⁻¹ and UV detection was employed at 270nm. The average retention times for lamivudine, stavudine and nevirapine were 5.9, 8.8 and 14.2min, respectively. The calibration curves were linear ( r>0.999) in the range for each analyte. The method is accurate and precise with recoveries of lamivudine in the range of 98.7–100.4%, 99.2–100.6% for stavudine and 98.3–100.3% for nevirapine. No spectral or chromatographic interferences from the tablet excipients were found. This method which is rapid, simple and does not require any separation process has been successfully applied to the assay of commercial fixed dose formulations.

Keywords: Lamivudine (3TC); Stavudine (d4T); Nevirapine (NVP); HPLC; Fixed dose combinations (FDCs)

Simultaneous determination of 11 drugs belonging to four different groups in human urine samples by reversed-phase high-performance liquid chromatography method by Irena Baranowska; Piotr Markowski; Jacek Baranowski (pp. 46-58).

A new, accurate, sensitive and fast reversed-phase high-performance liquid chromatography (RP-HPLC) as an analytical method for the quantitative determination of 11 drugs in human urine was worked out, optimized and validated. The objects of analysis were imipenem (IMP), paracetamol (PAR), dipyrone (DPR), vancomycin (VCM), amikacin (AMK), fluconazole (FZ), cefazolin (CFZ), prednisolone (PRE), dexamethasone (DEX), furosemide (FUR) and ketoprofen (KET) belonging to four different groups (antibiotics, analgesic, demulcent and diuretic). For HPLC analysis, diode array (DAD) and fluorescence (FL) detectors were used. The separation of analyzed compounds was conducted by means of a LiChroCART^® Purospher^® C₁₈e (125mm×3mm, particle size 5μm) analytical column with LiChroCART^® LiChrospher^® C₁₈ (4mm×4mm, particle size 5μm) pre-column with gradient elution. Analyzed drugs were determined within 20min. The mobile phase was comprised of various proportions of methanol, acetonitrile and 0.05% trifluoroacetic acid in water. AMK was separated and determined from human urine using ortho-phthaldialdehyde–3-mercaptopropionic acid (OPA–3-MPA) as a fluorescent reagent by RP-HPLC-FL. The following retention times for drugs IMP, PAR, DPR, VCM, AMK, FZ, CFZ, PRE, DEX, FUR and KET in human urine were found: 4.01min, 4.86min, 6.71min, 8.14min, 9.46min, 10.01min, 10.90min, 13.34min, 14.06min, 16.03min and 18.98min, respectively. Excellent linearity was obtained for compounds in the range of concentration: 0.35–42μgml⁻¹, 0.5–45μgml⁻¹, 4.5–38μgml⁻¹, 0.25–25μgml⁻¹, 0.5–35μgml⁻¹, 0.25–22μgml⁻¹, 0.03–52μgml⁻¹, 0.15–25μgml⁻¹, 0.25–28μgml⁻¹, 0.05–18μgml⁻¹ and 0.15–35μgml⁻¹ for IMP, PAR, DPR, VCM, AMK, FZ, CFZ, PRE, DEX, FUR and KET, respectively. The limits of detection (LOD) and limits of quantification (LOQ) for analyzed drugs were calculated in all cases and recovery studies were also performed. Ten human urine samples obtained from patients treated in hospital have been tested. In analyzed samples, one or more drugs from the 11 examined drugs were detected. The concentrations of examined drugs in urine samples ranged between: 1.5–12μgml⁻¹ of PAR, 5.2–11.5μgml⁻¹ of DPR, 0.13–9.5μgml⁻¹ of CFZ and 0.1–8μgml⁻¹ of FUR. This method can be successfully applied to routine determination of all these drugs in human urine samples.

Keywords: Drugs; Human urine; Validations; Derivatization; RP-HPLC

Pharmacokinetics of protein-unbound linezolid in the blood and the mechanism of hepatobiliary excretion in the rat by Yun-Ju Chen; Lie-Chwen Lin; Ming-Hwang Shyr; Tung-Hu Tsai (pp. 59-64).

Linezolid (Zyvox), an oxazolidinones antibiotic, was developed for the treatment of infectious diseases caused by gram-positive pathogens. To investigate the mechanism of hepatobiliary excretion of linezolid, a parallel study design used two groups; in the control group, rats received linezolid alone (3 or 10mg/kg, i.v.). In the drug-treated groups, 10min prior to linezolid administration, cyclosporin A (CsA; 10mg/kg, i.v.), a P-glycoprotein (P-gp) inhibitor, was given in the rats. The microdialysis probes were implanted into the jugular vein toward right atrium and the bile duct of Sprague–Dawley rats for multiple biological fluid sampling. Separation was performed using a reversed phase C₁₈ (4.6mm×150mm i.d., 5μm) with mobile phase of acetonitrile–methanol-1% 1-octanesulfonic acid in water of 30:10:60 (v/v/v) at flow rate of 1ml/min. The UV detection for linezolid was set at a wavelength of 260nm. Following linezolid (10mg/kg, i.v.) administration, the concentration of linezolid in the brain was less than the limit of quantification and the area-under the concentration curve versus time curve (AUC) of blood and bile were 1780±50 and 2850±276 (minμg/ml), respectively. The bile-to-blood distribution ratio was 1.6±0.2 ( n=6), which was defined as AUC_bile/AUC_blood. The results demonstrated that the transportation of linezolid into bile might be mediated by active transport. However, after treatment with CsA, the linezolid AUC in bile was 3060±411 (minμg/ml) which did not indicate a significant difference with linezolid alone. These results suggest that the hepatobiliary excretion of linezolid might not be regulated by P-gp transportation.

Keywords: Cyclosporine A; Hepatobiliary excretion; Linezolid; Microdialysis; P-glycoprotein; Pharmacokinetics

Basic study on the determination of total boron by conversion to tetrafluoroborate ion (BF₄⁻) followed by ion chromatography by Junya Katagiri; Toshiaki Yoshioka; Tadaaki Mizoguchi (pp. 65-72).

The basic study on the determination of tetrafluoroborate ion (BF₄⁻) by ion chromatography, and total boron by conversion of boric acid to BF₄⁻ followed by ion chromatography of BF₄⁻ has been carried out. The results of thermodynamic calculations for the system of boric acid (H₃BO₃)–F⁻–H⁺ showed that the mole fraction of BF₄⁻ was higher than 99% at pH lower than 3.5 and 4.5 when the total free fluoride concentration (2[H₂F₂]+2[HF₂⁻]+[HF]+[F⁻]) was as high as 0.1 and 1.0M, respectively. The fraction of BF₄⁻ increased with increasing total free fluoride concentration. BF₄⁻ fraction values were higher than 99% at pH 0.75 and at total free fluoride concentration of 0.05M or higher. BF₄⁻ was hardly formed at pH>7 even when the total free fluoride concentration was as high as 1.0M. According to the experimental results, the fraction of BF₄⁻ at pH 0.7–0.8 was 51.2, 95.6 and 96.7% when the total fluoride concentration (2[H₂F₂]+2[HF₂⁻]+[HF]+[F⁻]+3[BF₃OH⁻]+4[BF₄⁻]) was 0.2, 1.0 and 3.3M, respectively. The formation reaction of BF₄⁻ from boric acid reached an equilibrium state within 20min regardless of reaction temperature, in the range of 20–50°C, when the total boron and total fluoride concentrations were 66.7mM and 1.0M, respectively. Although BF₄⁻ was formed only under acidic conditions, BF₄⁻, once formed, was very stable under alkaline conditions at least for several hours. We have concluded that BF₄⁻ could be analyzed by ion chromatography using sodium hydroxide solution as an eluent because BF₄⁻ was stable under chromatographic conditions. BF₄⁻ solution prepared from boric acid could be used as a standard solution in the ion chromatographic analysis of BF₄⁻ instead of the sodium tetrafluoroborate (NaBF₄) reagent available commercially, if a discrepancy of about 4–5% was allowed.

Keywords: Tetrafluoroborate ion; Boron; Fluorine; Analysis; Ion chromatography

Comparison of the volatile compounds of Atractylodes medicinal plants by headspace solid-phase microextraction-gas chromatography–mass spectrometry by Fang-Qiu Guo; Lan-Fang Huang; Shao-Yun Zhou; Tai-Ming Zhang; Yi-Zeng Liang (pp. 73-78).

Atractylodes macrocephala (baizhu) and Atractylodes lancea (cangzhu), which are two famous Atractylodes medicinal plants, have traditionally been used as important ingredient of several Chinese herbal medicines. The volatile constituents are the main active components in them. To avoid the traditional and time-consuming hydrodistillation, the analyses of volatile components in baizhu and cangzhu were carried out by means of headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography–mass spectrometry (GC–MS). The headspace volatiles were collected using a polydimethylsiloxane–divinylbenzene (PDMS–DVB, 65μm) fiber. The extraction conditions including extraction temperature, equilibrium time, extraction time and desorption time were optimized using the total peak areas as index. The best response was obtained when the extraction temperature, equilibrium time, extraction time and desorption time were 70°C, 30, 30 and 4min, respectively. Thirty-six components representing 90.72% of the total peak areas of baizhu were identified. The highest content component of the HS-SPME sample of baizhu was atractylone (40.12%). For cangzhu, 56 components representing 90.38% of the total peak areas of cangzhu were identified and the highest content component of the HS-SPME sample of cangzhu was eudesma-4(14),11-diene (16.49%). This study showed that baizhu and cangzhu have 23 common components. The result suggested the developed method could be used to compare the similarities and differences between the above-mentioned two Chinese herbs.

Keywords: HS-SPME; GC–MS; Atractylodes macrocephala; Atractylodes lancea; Volatile compound

Ternary ion-association complex based ion imprinted polymers (IIPs) for trace determination of palladium(II) in environmental samples by Sobhi Daniel; R.S. Praveen; Talasila Prasada Rao (pp. 79-87).

A new ion imprinted polymer (IIP) material was synthesized by co-polymerization of palladium–iodide–vinyl pyridinium/palladium–thiocyanate–vinyl pyridinium ion ternary ion-association complex taken in methanol/DMSO with 2-hydroxyethyl methacrylate (functional monomer) and ethylene glycol dimethacrylate (crosslinking monomer) in the presence of 2,2′-azobisisobutryonitrile (initiator). The imprinted anionic species [PdI₄]²⁻ or [Pd(SCN)₄]²⁻ were removed by leaching the dried and powdered materials particles for 18h with 6M HCl to obtain leached IIP particles. Non-imprinted/control polymers were also prepared in a similar fashion without the template. Various parameters that influence the percent extraction of palladium, viz. concentration of KI or KSCN, pH, weight of polymer particles, preconcentration and elution times, aqueous phase volume, etc., were systematically studied for both the systems, i.e., in batch as well as flow injection modes. As the on-line flow injection-flame atomic absorption spectrometric (FI-FAAS) allow offer higher enrichment factor, better precision and can analyze more samples for a given time, compared to batch method, this procedure is preferred for the analysis of palladium present in the street/fan blade dust samples collected from busy cities of India and the values obtained were compared with the standard ICPMS values.

Keywords: Solid phase extraction; Off-line and on-line techniques; Preconcentrative separation; Ion imprinted polymers; Palladium

Determination of chlorine, bromine and iodine in plant samples by inductively coupled plasma-mass spectrometry after leaching with tetramethyl ammonium hydroxide under a mild temperature condition by K. Tagami; S. Uchida; I. Hirai; H. Tsukada; H. Takeda (pp. 88-92).

A simple determination method for halogens (Cl, Br, and I) in plant samples using inductively coupled plasma-mass spectrometry (ICP-MS) was developed. In order to extract these halogens into aqueous solution, a leaching step with tetramethyl ammonium hydroxide (TMAH) under mild conditions was carried out, i.e. a 0.1-g dried sample was left overnight (ca. 12h) in contact with 1mL of 25% TMAH in a small PFA vial at 60°C. Then the sample was transferred to a 50-mL centrifuge tube and diluted to 50mL with deionised water. After centrifugation, halogens in the supernatant were determined by ICP-MS. When standard reference materials were measured by the method, the data were within the 95% confidence range of the certified values. The results also agreed well with the values obtained by neutron activation analysis with correlation factor r>0.99.

Keywords: Chlorine; Bromine; Iodine; TMAH; ICP-MS; Neutron activation analysis

Optimization of operating conditions of axially and radially viewed plasmas for the determination of trace element concentrations from ultrasound-assisted digests of soil samples contaminated by lead pellets by Ari Väisänen; Aki Ilander (pp. 93-100).

The method of ultrasound-assisted extraction followed by inductively coupled plasma optical emission spectrometry (ICP-OES) used for the determination of trace element concentrations (arsenic, copper, lead, antimony, and zinc) in shooting range areas was optimized. Optimization was achieved not only on the basis of the analysis of appropriate standard reference materials but also on that of 31 synthetic mixtures of matrix and analyte elements (aluminum, antimony, arsenic, calcium, copper, lead, iron, manganese, silicon, and zinc), in five concentrations. All the measurements were performed in robust plasma conditions which were tested by measuring the Mg II 280.270nm/Mg I 285.213nm line intensity ratio. The highest Mg II 280.270nm/Mg I 285.213nm line intensity ratios were observed when a nebulizer gas flow of 0.8Lmin⁻¹, auxiliary gas flow of 0.2Lmin⁻¹ and plasma power of 1400W were used for both the axially and radially viewed plasmas. The analysis of 31 synthetic mixtures of the selected elements showed that As concentrations could be accurately determined with axially viewed plasma alone. The determination of Pb and Sb could be performed with either axially or radially viewed plasma whereas, surprisingly, Cu could be determined with high accuracy using radial plasma alone with a power of 1400W. All the elements investigated were determined with high accuracy using robust plasma conditions and a combination of axially and radially viewed plasmas. The total recoveries of elements from SRM 2710 (Montana soil) and SRM 2782 (Industrial sludge) were highly comparable to leach recoveries certified by the National Institute of Standards and Technology (NIST).

Keywords: ICP-OES; Operating conditions; Ultrasound; Microwave; Trace elements

Anthocyanins profile as fingerprint of wines using atmospheric pressure photoionisation coupled to quadrupole time-of-flight mass spectrometry by J.L. Gómez-Ariza; T. García-Barrera; F. Lorenzo (pp. 101-108).

Present work shows for the first time the suitability of the atmospheric pressure photoionisation (APPI) coupled to quadrupole time-of-flight mass spectrometry (QqTOF) to characterise anthocyanins in wines. Results obtained are satisfactorily compared with the electrospray ionisation (ESI-MS) that has also been used. Parameters concerning the direct infusion-APPI-MS have been studied and optimised to generate information-rich mass spectra for wine fingerprinting.The proposed analytical methodology has been used to obtain a classification rule for unknown samples according to their anthocyanins profiles. In addition, the procedure shows high sample throughput since the time consuming sample treatment required for the extraction of anthocyanins from wines has been drastically reduced in this fingerprint-targeted approach.

Keywords: Young red wines; Vitis-vinifera; Anthocyanins; Mass spectrometry; Time-of-flight; Photospray ionisation

A novel histidine assay using tetraphenylporphyrin manganese (III) chloride as a molecular recognition probe by resonance light scattering technique by Zhanguang Chen; Jinbin Liu; Yali Han; Li Zhu (pp. 109-115).

A novel histidine-selective method has been developed for the determination of histidine in aqueous solutions by resonance light scattering (RLS) technique. At pH 8.0, the weak RLS intensity of tetraphenylporphyrin manganese (III) chloride [MnTPPCl] was greatly enhanced by the addition of histidine with the maximum peak located at 483nm. Under the optimum conditions, it was found that the enhanced RLS intensity was in proportion to the concentration of histidine in the range 7.8×10⁻⁷–2.4×10⁻⁵moll⁻¹. Low detection limit of 9.2×10^-8moll⁻¹ has been achieved. The histidine concentrations in synthetic samples and real samples were determined with satisfactory results. The sensitivity and selectivity of this method are high enough to permit the determination of trace amounts of histidine without any significant interference from high levels of other components such as common anions and especially, other amino acids.

Keywords: Resonance light scattering (RLS); Tetraphenylporphyrin manganese (III) chloride [MnTPPCl]; Amino acid; Histidine

Screening for testosterone, methyltestosterone, 19-nortestosterone residues and their metabolites in bovine urine with enzyme-linked immunosorbent assay (ELISA) by Huihui Lu; Grainne Conneely; Mark A. Crowe; Margaret Aherne; Miloslav Pravda; George G. Guilbault (pp. 116-123).

This work reports on the development of rapid enzyme-linked immunosorbent assay for testosterone, methyltestosterone, 19-nortestosterone and their metabolites in real samples of bovine urine. The assays were based on the competition between an immobilised testosterone–BSA conjugate and the analyte for corresponding antibodies, followed by the use of secondary anti-species (α-IgG-HRP) to determine the degree of competition. Urine samples were analysed after 10-fold dilution with the buffer, omitting extraction and hydrolysis. The limits of detection calculated for the original sample were ca. 74, 266 and 131pgml⁻¹ (ppt) for testosterone, methyltestosterone and 19-nortestosterone, respectively. In particular, testosterone and methyltestosterone assays offer the advantage to pick up both parent compounds and their major metabolites due to the high cross-reactivity pattern with corresponding antibody used in each assay. The concentration in bovine urine detected by developed method does indicate 19-nortestosterone administration to heifers. The developed assays were applied to urine samples of heifers treated with above androgens.

Keywords: Enzyme immunoassay; Steroids; Testosterone; Methyltestosterone; 19-Nortestosterone; Bovine urine

Spectrophotometric flow-injection determination of copper and nickel in plant digests exploiting differential kinetic analysis and multi-site detection by Diego Vendramini; Viviane Grassi; Elias A.G. Zagatto (pp. 124-128).

A novel strategy for implementing differential reaction-rate methods in flow-injection analysis is proposed and applied to the determination of copper and nickel in plant digests using 2-(5-brom-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP) as the color-forming reagent. Multi-site detection is involved, therefore the flow cell is displaced between two monitoring sites, and the analytical signals refer to different conditions of sample dispersion, reaction development and timing.The system handles 20samplesh⁻¹ and requires 0.32mg Br-PADAP per determination. Signal additivity was evaluated within 98 and 102%, and linear responses ( r>0.999; n=6) were verified for both copper and nickel up to 0.80mgl⁻¹. Detection limits of 0.01 and 0.04mgl⁻¹ Cu and Ni were estimated by considering the highest concentration of the counter analyte. Results are precise (R.S.D.<2%) and in agreement with ICP-OES (95% confidence level). Potentialities and limitations of the approach are discussed.

Keywords: Differential kinetic analysis; Flow analysis; Multi-site detection; UV–vis spectrophotometry; Plant analysis

A new method for determination of the oxidative stability of edible oils at frying temperatures using near infrared emission spectroscopy by Fabiano Barbieri Gonzaga; Celio Pasquini (pp. 129-135).

This work proposes a new method for determination of the oxidative stability of edible oils at frying temperatures using near infrared emission spectroscopy (NIRES). The method is based on heating an oil sample at a fixed temperature, followed by the acquisition of the emission spectra with time using a home-made spectrometer with an acousto-optical tunable filter (AOTF) as monochromator. The induction time, related to the oxidative stability, is determined by means of the emission band at 2900nm and its increase and broadening during the heating time. After the induction period, this band also provides information related to the oxidation rate of the sample. Twelve samples of edible oils, of different types and from different manufacturers, were analyzed for oxidative stability with mean repetitivity of 3.7%. The effects of nitrogen insertion, heating temperature and the presence of antioxidant compounds on the oxidative stability were evaluated.

Keywords: Near infrared emission spectroscopy; Edible oils; Oxidative stability; Instrumentation

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Analytica Chimica Acta (v.570, #1)