Monitoring inorganic mercury and methylmercury species with liquid chromatography-piezoelectric detection

A piezoelectric detection system coupled with a liquid chromatographic system is developed for the speciation of inorganic mercury(II) and methylmercury. Piezoelectric detection has been demonstrated to be a very sensitive detection system for total mercury determination when a gold-coated piezoelectric quartz crystal was used. The analytical features of this detection unit make it very suitable to be used as a detector coupled with a liquid chromatographic system for monitoring mercury species. After separation by a chromatography column (Spherisorb ODS-2, 5 μm,  mm i.d.), mercury species are liberated and reduced, by using stannous chloride, and are detected as an amalgam on the gold-coated piezoelectric quartz crystal, the sensor subsequently was regenerated by passing a peroxydisulfate solution. This detector exhibits good sensitivity, it allows the determination of mercury at sub-ppb concentration levels (0.30-1.20 μg l⁻¹). The precision, expressed as relative standard deviation, was ±2.7% (n=11) for a 0.5 μg l⁻¹ total mercury concentration. The proposed method is free of interferences and it allowed the determination of inorganic mercury and methylmercury species in natural waters.     

Validation of an environmental friendly segmented flow method for the determination of phenol index in waters as alternative to the conventional one

Phenolic compounds are a sort of common pollutants in water. Phenol index becomes an expedite indicator for the evaluation of the contamination level of water samples, in spite of the knowledge of the individual phenol and its derivatives are also important.In this work, an environmental friendly method for the determination of phenols, using a segmented flow system based on the conventional method's reactions without the liquid-liquid extraction step, was validated.Three linear dynamic ranges using C₆H₅OH: 1-10 μg l⁻¹, 10-200 μg l⁻¹ and 0.2-2.5 mg l⁻¹, with a coefficient of variation lower than 2%, were obtained. Several method's performance parameters were determined: limits of detection, limits of quantification, precision through duplicate analysis and trueness using the reference materials purchased from LGC Promochem, RTC no. QCI-043-2 Lot:P1. Measurement uncertainty was evaluated using an interlaboratory approach based on proficiency testing data. Relative combined uncertainty for phenols in water samples, , of 0.054 were obtained, in according to those imposed by the Portuguese Legislation: target for 1 μg l⁻¹ of phenol (surface waters) and target for 500 μg l⁻¹ of phenol (wastewaters).A high efficiency reduction and elimination of reagents and wastes, reduction of analysis time and exposition of the analyst were also obtained.     

Determination of total bilirubin in human serum by chemiluminescence from the reaction of bilirubin and peroxynitrite

Peroxynitrous acid (ONOOH) was produced by the on-line reaction of acidified hydrogen peroxide with nitrite in a flow system, and peroxynitrite (ONOO⁻) was generated from ONOOH in NaOH solution. A weak chemiluminescent (CL) emission was observed due to the production of singlet oxygen ( ) during the decomposition of ONOO⁻. Bilirubin and its conjugate were found to enhance the CL emission of in a suitable micellar medium. For the first time, the feasibility of employing the present CL system for the sensitive and selective determination of total bilirubin contents in human serum was demonstrated and the results were compared with certified values. The present method showed a great improvement on overcoming bis(2,4,6-trichlorophenyl)oxalate CL highly insolubility in aqueous solution and exhibiting higher tolerance towards interferences than redox reaction of bilirubin with various oxidizing agents such as sodium hypochlorite and iodine. The recoveries of bilirubin were found to fall in the range between 95 and 108%. The detection limits (S/N=3) for bilirubin and its conjugate were determined to be 10 and 8 ng ml⁻¹, respectively. The relative standard deviations (R.S.D.) for the consecutive CL detection of a series of bilirubin (30 μg l⁻¹) and bilirubin ditaurite (25 μg l⁻¹) were 3.2 and 2.9% (n=11), respectively.     

Determination of chromium, cadmium and lead in food-packaging materials by axial inductively coupled plasma time-of-flight mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) with a time-of-flight (TOF) analyser was used for the determination of chromium, cadmium and lead in six food-packaging materials (paper and paper board). The samples (0.20-0.25 g) were digested in concentrated nitric acid in a high pressure microwave oven at 180 °C within 15 min. Two different plasma conditions were applied: cool plasma conditions (0.76 kW; 0.85, 0.89 and 15.5 l min⁻¹ nebuliser, auxiliary and plasma gas flow rate, respectively) for the determination of chromium and normal plasma conditions (1.21 kW; 0.66, 0.68 and 13.6 l min⁻¹ nebuliser, auxiliary and plasma gas flow rate, respectively) for the determination of cadmium and lead. External calibration was used in combination with rhodium (40 ng g⁻¹) as an internal standard. The detection limits (DL = 3S.D./sensitivity) under the conditions used corresponded to 0.01 ng g⁻¹ (), 0.06 ng g⁻¹ (), 0.07 ng g⁻¹ (), 0.03 ng g⁻¹ () and 0.02 ng g⁻¹ ( and ). The precision (R.S.D.) for six replicate determinations (10 s integration time) of 1 and 10 ng g⁻¹ of each analyte varied from 0.72% () to 4.43% (). The contents of chromium, cadmium and lead in the examined materials were evaluated using the signals of , and . They were in the range: 0.25-0.50 μg g⁻¹ for Cr, not detected (nd) to 0.12 μg g⁻¹ for Cd and 0.28-0.35 μg g⁻¹ for Pb in paper and 0.50-0.64 μg g⁻¹ for Cr, nd to 0.09 μg g⁻¹ for Cd and 0.67-0.99 μg g⁻¹ for Pb in paper board.     

Rapid high-performance liquid chromatographic determining technique of sulfamonomethoxine, sulfadimethoxine, and sulfaquinoxaline in eggs without use of organic solvents

A determining technique of sulfonamides (SAs) (sulfamonomethoxine (SMM), sulfadimethoxine (SDM), and sulfaquinoxaline (SQ)) in eggs, without use of organic solvents, is developed utilizing a high-performance liquid chromatography (HPLC) interfaced with a photo-diode array detector. The sample preparation was performed by homogenizing with perchloric acid solution using a handy ultrasonic-homogenizer followed by a centrifugal ultra-filtration unit. An analytical column and an isocratic mobile phase for HPLC are a reversed-phase C₄ column ( mm i.d.) and 0.18 mol l⁻¹ citric acid solution, respectively. The proposed technique was shown to be linear (r>0.998) over the concentration range 0.1-2.0 μg g⁻¹. Average recoveries of three SAs (spiked 0.05, 0.1, 0.15, and 0.2 μg g⁻¹) ranged from 80.3 to 88.4%, with relative standard deviations (R.S.D.s) between 3.4 and 5.8%. The practical detection limits and total time required for the analysis of one sample were < 0.05 μg g⁻¹ and <30 min, respectively. In all the processes, no organic solvents were used at all.     

Comparison of methods for the determination of total selenium in plasma by magnetic sector inductively coupled plasma mass spectrometry

Three sample preparation methods (dilution, microwave digestion and ethanol addition) were evaluated for the determination of Se in human plasma using magnetic sector inductively coupled plasma mass spectrometry (ICP-MS). A number of instrumental parameters were also considered, namely the choice of internal standard (Sc, Rh, In) and pre-defined spectral resolution (m/Δm ∼300 (low resolution, LR) and ∼7500 (high resolution, HR)). The isotopes and were selected for analysis avoiding the major and unresolvable Ar dimer interferences associated with other Se isotopes.Ethanol addition was found to be the most suitable and reliable sample preparation method. The optimum ethanol concentration for a 1+9 dilution of the plasma sample was 0.5% (v/v). Indium or Sc were selected over Rh as internal standards as Seronorm™ Level 1 target values were achieved at lower concentrations of ethanol modifier. Representative ICP-MS detection limits for this method using (HR) and (HR), were 0.1 and 0.2 μg l⁻¹.Accurate analysis of Se in Seronorm™ Level 1 (MI0181) was found using either or and HR (86±5 and 83±5 μg l⁻¹ respectively, n=5, In internal standard, target value=83±6 μg l⁻¹). Although offering improved precision (e.g. LR: 0-3% versus HR: 1-6%), accurate results were only obtained with LR for the Seronorm™ Level 1 sample when using (86±1 μg l⁻¹). The major interference precluded accurate Se analysis using and LR for all samples considered. Reliable Se concentrations were only found for a “real” pooled sample when using (HR), in part a result of non-negligible and unresolved interference when using LR. Consistently elevated Se concentrations were found under all conditions when Seronorm™ Level 2 (NO0371) was analysed. These results were confirmed by independent GF-AAS analysis.Magnetic sector ICP-MS with (HR), in combination with the ethanol addition sample preparation method, was used for the analysis of Se in human plasma samples as part of a small pilot study. Average measured selenium concentrations were 102±18 μg l⁻¹ (n=18).     

Determination of sulfur-containing amino acids by capillary electrophoresis dynamic reaction cell inductively coupled plasma mass spectrometry

Capillary electrophoresis dynamic reaction cell™ inductively coupled plasma mass spectrometry (CE-DRC-ICP-MS) for the determination of sulfur-containing amino acids is described. The sulfur-containing amino acids studied include l-cysteine, l-cystine, dl-homocystine and l-methionine. The species studied were well separated using a 70 cm length×75 μm i.d. fused silica capillary while the applied voltage was set at +22 kV and a 10 mmol l⁻¹ disodium tetraborate buffer (pH 9.8) containing 0.1 mmol l⁻¹ EDTA and 0.5 mmol l⁻¹ Triton X-100 was used as the electrophoretic buffer. The sulfur-selective electropherogram was determined at m/z 48 as by using its reaction with O₂ in the reaction cell. The method avoided the effect of polyatomic isobaric interferences at m/z 32 caused by and on by detecting as the oxide ion at m/z 48, which is less interfered. The detection limit of various species studied was in the range of 0.047-0.058 μg S ml⁻¹, which corresponded to the absolute detection limit of 1.3-1.6 pg S based on the injection volume of 27 nl. We determined the concentrations of selected sulfur-containing amino acids in urine and nutritive complement samples. The recovery was in the range of 92-128% for various species.     

Determination of arsenic, iron and selenium in moss samples using hexapole collision cell, inductively coupled plasma-mass spectrometry

Different collision gases (H₂, He and premixed 7% H₂ in He) used in the hexapole collision cell of an inductively coupled plasma-mass spectrometer (ICP-MS) were compared, and the gas-flow rates were optimized for the determination of arsenic (), iron () and selenium (). The study showed that the argon-based interferences at mass-to-charge ratios (m/z) of 56, 75 and 80 can be overcome by the optimized gas flows (7.5 ml min⁻¹ premixed 7% H₂ in He and 2 ml min⁻¹ H₂) in the hexapole collision cell. Detection limits of 15.5 ng l⁻¹ for iron () and 29 ng l⁻¹ for selenium () in 2% (v/v) HNO₃ were obtained under optimized collision cell conditions. The detection limit for arsenic () obtained in difficult hydrochloride acid matrix (5% HCl (v/v)) was 153 ng l⁻¹. The accuracy of the optimized method was confirmed by analyzing two moss reference materials. The results obtained by ICP-MS for arsenic, selenium and iron from both moss reference samples were, in most cases, in good agreement with the certified values.     

On-line preconcentration of palladium on alumina microcolumns and determination in urban waters by inductively coupled plasma mass spectrometry

A method for on-line preconcentration of palladium at ultra-trace level on alumina microcolumns and determination by inductively coupled plasma mass spectrometry (ICP-MS) has been developed. A sampling time of 10 min (30 ml) and an eluent (KCN) volume of 300 μl provides a limit of detection of 1 ng l⁻¹. The precision was 4% at the 25 ng l⁻¹ level. The proposed system allows the on-line removal of the primary interferents (Cu and Y) providing the credible accuracy of the results. The proposed method is suitable for palladium determination in urban water samples. Platinum concentration in the analysed urban water samples was also determined.     

Front face fluorescence spectroscopy and visible spectroscopy coupled with chemometrics have the potential to characterise ripening of Cabernet Franc grapes

The potential of front-face spectroscopy for grape ripening dates discrimination was investigated on Cabernet Franc grapes from three parcels located on the Loire Valley and for six ripening dates. The 18 batches were analysed by front-face fluorescence spectroscopy and visible spectroscopy. The excitation spectra (250-310 nm, emission wavelength = 350 nm) were characterised by a shoulder at 280 nm. Grapes spectra were classified by factorial discriminant analysis (FDA). Ripening dates were well predicted by fluorescence spectra: grapes before veraison were separated from grapes after veraison and almost every ripening date was identified. The common spectroscopic space obtained by CCSWA showed that wavelengths corresponding to anthocyanin absorption in the visible were correlated to fluorescence wavelengths around the starting and ending points of the shoulder (263 and at 292 nm). Then, regression models were investigated to predict total soluble solids (TSS), total acidity, malvidin-3G, total anthocyanins and total phenolics content from visible and fluorescence spectra. To predict technological indicators (TSS and total acidity), the PLS model with visible spectra (RMSECV = 0.82°Brix or 0.96 g L⁻¹ H₂SO₄) was better than those with fluorescence one (RMSECV = 1.39°Brix or 2.06 g L⁻¹ H₂SO₄). For malvidin-3G and total anthocyanins, all and were superior to 0.90 and RMSECV were low. Visible and fluorescence spectroscopies succeeded in predicting anthocyanin content. Concerning total phenolic, the best prediction was provided by fluorescence spectroscopy.     

Electroanalysis of dopamine at a gold electrode modified with N-acetylcysteine self-assembled monolayer

Voltammetric behavior of dopamine (DA) on a gold electrode modified with the self-assembled monolayer (SAM) of N-acetylcysteine has been investigated, and one pair of well-defined redox peaks of dopamine is obtained at the SAM modified gold electrode. The oxidation peak current increases linearly with the concentration of dopamine in the range of  mol l⁻¹. The detection limit is 8.0×10⁻⁷ mol l⁻¹. This method will be applicable to the determination of dopamine in injection of dopamine hydrochloride, and the good recovery of dopamine is obtained. Furthermore, The SAM modified gold electrode can resolve well the voltammetric responses of dopamine and ascorbic acid (AA), so it can also be applied to the determination of dopamine in the presence of ascorbic acid.     

Analysis of primary aliphatic short-chain monoamines by LC in water samples

Several derivatization procedures with o-phthaldialdehyde-N-acetylcysteine (OPA-NAC) were compared for a rapid analysis of primary aliphatic short-chain monoamines in water samples by HPLC using a LiChorospher analytical separation column (100RP₁₈ mm i.d., 5 μm). Both the solution and the solid-support assisted off-line derivatization on C₁₈ SPE cartridges were inadequate options because of beginning degradation processes of the instable isoindol derivatives during their transfer to the analytical column. This problem was precluded with the on-column or solid-support assisted on-line derivatization. In the last mentioned procedure, the derivatization took place in a Hypersil C₁₈ precolumn ( mm i.d., 30 μm) connected with an additional preconcentration step resulting in better detection limits (0.002-0.040 μg ml⁻¹ requiring only 150 μl of water sample) than in the on-column procedure (0.08-0.16 μg ml⁻¹). The improved sample handling, the better control of parameters affecting reaction rates, the fully automation of this method with only 10 min analysis time for each sample are further advantageous. The potential of the solid-support assisted on-line derivatization was outlined and applied to water samples from several sources. Recovery values near 100% were obtained.     

Non-aqueous capillary zone electrophoresis method for the analysis of paroxetine, tamoxifen, and their main metabolites in urine

The potential of non-aqueous capillary electrophoresis (NACE) was investigated for the simultaneous separation of paroxetine, tamoxifen, and their main metabolites. Baseline separation of the studied solutes was obtained on a  μm capillary using a non-aqueous buffer composed of 18 mM ammonium acetate and 1.1% acetic acid in 80:20 (v/v) methanol-acetonitrile, with a temperature and voltage of 22 °C and 15 kV, respectively. Clomipramine was used as internal standard. Aspects such as stability of the solutions, linearity, accuracy, precision and ruggedness were examined in order to validate the proposed method. Detection limits obtained for all the studied compounds ranged between 3.0 and 7.1 μg l⁻¹. The developed method is sensitive and robust and was used to determine paroxetine, tamoxifen, and their metabolites at clinically relevant levels in human urine. Before NACE determination, the samples were purified and enriched by means of an extraction-pre-concentration step with a pre-conditioned C₁₈ cartridge. Determination of these analytes in the urine of four females urines was demonstrated.     

Determination of trace alpha-fetoprotein variant by affinity adsorption solid substrate-room temperature phosphorimetry and its application to the forecast of human diseases

In the presence of ion perturber LiAc, 4-generation polyamidoamine dendrimers (4G-D) could emit strong and stable room temperature phosphorescence (RTP) signal at on nitrocellulose membrane (NCM), and Triton X-100 could sharply enhance the RTP signal of 4G-D. Triton X-100-4G-D was used to label concanavalin agglutinin (Con A) to get the labeling product Triton X-100-4G-D-Con A. Quantitative specific affinity adsorption (AA) reaction between Triton X-100-4G-D-Con A and α-fetoprotein variant (AFP-V) could be carried out on the surface of NCM, whose product Triton X-100-4G-D-Con A-AFP-V could emit strong and stable RTP and its ΔI_p was proportional to the content of AFP-V. According to the facts above, a new affinity adsorption solid substrate-room temperature phosphorimetry (AA-SS-RTP) for the determination of trace AFP-V by Con A labeled with Triton X-100-4G-D was established. Detection limits of this method were 0.23 fg spot⁻¹ (direct method, corresponding concentration: 5.8 × 10⁻¹³ g mL⁻¹) and 0.13 fg spot⁻¹ (sandwich method, corresponding concentration: 3.2 × 10⁻¹³ g mL⁻¹). It has been successfully applied to determine the content of AFP-V in human serum and forecast human diseases, for its high sensitivity, long RTP lifetime, good repeatability, high accuracy and little background perturbation with at the long wavelength area. Meanwhile, the mechanism for the determination of trace AFP-V using AA-SS-RTP was also discussed.     

Hetero dimer from tetrakisammonium cavitand and tetratopic crown ether cavitand

Hetero dimer between tetrakis(m-ammonium)cavitand and tetrakis(dibenzo-25-crown-8)cavitand 5 was formed in CDCl₃ at room temperature. The effects of solvent polarity and temperature on the stability of were studied and the thermodynamic parameters for the formation of are , ΔH⁰ = −67.4 kcal mol⁻¹ and ΔS⁰ = −201.6 cal mol⁻¹ K⁻¹.     

FI automatic method for the determination of copper(II) based on coproporphyrin I-Cu(II)/TCPO/H(2)O(2) chemiluminescence reaction for the screening of waters

In this paper, an automatic method for the screening of water samples containing Cu(II) was proposed, based on peryoxalate chemiluminescence reaction using coproporphyrin I as fluorophor compound to provide selectivity and a simple flow injection (FI) chemiluminescence detector (CLD). FI system conditions were chosen in order to distinguish samples over or under legislation limit established (50 μg l⁻¹) with high reliability. The detection limit found was 9 μg l⁻¹ and the linear dynamic range was 15-125 μg l⁻¹ of Cu(II). Repeatibility and reproducibility studies gave good precision and accuracy with recovery near 100%. Under these conditions, the method resulted selective and only Fe(II), Fe(III) and Pb(II) could interfere, but at a concentration level higher than their normal concentration in waters. The proposed method was found to be highly reliable for screening purposes and it was successfully applied to the screening of a variety of real water samples.     

Investigation of the luminescent properties of terbium-anthranilate complexes and application to the determination of anthranilic acid derivatives in aqueous solutions

The luminescent properties of terbium complexes with furosemide (FR), flufenamic (FF) acid, tolfenamic (TF) acid and mefenamic (MF) acid have been investigated in aqueous solutions. For all four compounds, complexation occurs when the carboxylic acid of the aminobenzoic group is dissociated and is greatly favoured in the presence of trioctylphosphine oxide as co-ligand and Triton X-100 as surfactant. Under optimum conditions, luminescence of the lanthanide ion is efficiently sensitised and the lifetime of the resonance level of terbium in the complex is ranging between 1 and 1.9 ms, against 0.4 ms for the aqua ion. The sensitivity of the method for the determination of anthranilic acid derivatives is improved by one to two orders of magnitude with respect to that achieved using native fluorescence or terbium-sensitised luminescence in methanol. The limits of detection are 2×10⁻¹⁰, 5×10⁻¹⁰ and 2×10⁻⁹ mol l⁻¹ for flufenamic acid, furosemide and tolfenamic acid, and mefenamic acid, respectively, with within-run RSD values of less than 1%. The method has been applied to the determination of flufenamic acid in spiked calf sera with and without sample pretreatment. Depending on the method and the analyte concentration, the recovery was ranging between 83 and 113% and the lowest concentration attainable in serum samples was close to 1×10⁻⁷ mol l⁻¹.     

Speciation and preconcentration of inorganic antimony in waters by Duolite GT-73 microcolumn and determination by segmented flow injection-hydride generation atomic absorption spectrometry (SFI-HGAAS)

A selective matrix removal/separation/enrichment method, utilizing a microcolumn of a chelating resin with SH functional groups (Duolite GT-73), was proposed for the determination of Sb(III) in waters by segmented flow injection-hydride generation atomic absorption spectrometry (SFI-HGAAS). The resin was selective to Sb(III) at almost all pH and acidity values employed, whereas Sb(V) was not retained at all and could be determined after a pre-reduction step with l-cysteine. Spike recoveries were tested at various concentration levels in different water types and were found to vary between 85 and 118%. Accuracy of the proposed methodology was checked by analyzing a standard reference material and a good correlation was found between the determined (13.3 ± 1.1 μg l⁻¹) and the certified value (13.79 ± 0.42 μg l⁻¹). The method was applied to several bottled drinking water samples for antimony determination with and without preconcentration and none of the samples were found to contain antimony above the permissible level (5 μg l⁻¹). The characteristic concentration (the concentration of the analyte corresponding to an absorbance of 0.0044) was 0.55 μg l⁻¹ and the 3 s limit of detection (LOD) based on five times preconcentration was 0.06 μg l⁻¹. The applicability of the microcolumn separation/preconcentration/matrix removal method for flow injection systems was also demonstrated.