Multi-elemental analysis of non-food packaging materials by inductively coupled plasma-time of flight-mass spectrometry

Commercial non-food packaging materials of four different matrices (paper, low density polyethylene (LDPE), polyethylene-polypropylene (PE-PP) and high density polyethylene (HDPE)) were examined for the content of Cr, Ni, Cu, Zn, As, Mo, Cd, Sb, Ba, Hg, Tl, Pb and U. The examined samples (0.17–0.35 g) were digested in HNO₃ and H₂O₂ (papers, LDPE and PE-PP) and in HNO₃, H₂SO₄ and H₂O₂ (HDPE) using microwave assisted high pressure system. The inductively coupled plasma-time of flight-mass spectrometry (ICP-TOFMS) has been employed as the detection technique. All measurements were carried out using internal standardization. Yttrium and rhodium (50 ng g⁻¹) were used as internal standards. The detection and quantification limits obtained were in the range of 0.005 ng g⁻¹ (⁵²Cr) to 0.51 ng g⁻¹ (⁶⁶Zn) and 0.015 μg g⁻¹ (⁵²Cr) to 2.02 μg g⁻¹ (⁶⁶Zn) of dry mass, respectively. The evaluated contents (mg kg⁻¹) of particular elements in the examined materials were as follows: 0.22–219; <1.05–9.03; 1.25–112; <2.02–449; <0.98–<1.30; <0.36–2.06; <0.29–113; <0.22–44.1; <0.06–57.4; <0.66–<0.88; <0.08–0.24; <0.13–1222 and <0.08–0.44 for Cr, Ni, Cu, Zn, As, Mo, Cd, Sb, Ba, Hg, Tl, Pb and U, respectively.     

Micellar effects on photoinduced redox reactions of Fe(bpy)2(CN)2

Excitation of solutions of Fe(bipy)₂(CN)₂ by a 266-nm laser pulse produces a hydrated electron and the oxidized complex, Fe(bipy)₂ (CN)₂⁺, in the primary photochemical step, in homogeneous aqueous solution as well as in aqueous solutions containing cetyltrimethylammonium bromide (CTAB) or sodium dodecyl sulfate (SDS) micelles. In all cases nascent hydrated electrons react with ground state Fe(bipy)₂(CN)₂ to form Fe(bipy)₂(CN)₂⁻, and comparison of the decay constants in the three media (H₂O: k = 2.8 × 10¹⁰ M⁻¹ s⁻¹; CTAB: k = 2.9 × 10¹⁰ M⁻¹ s⁻¹; SDS: k = 5.5 × 10⁹ M⁻¹ s⁻¹), shows that the reaction is essentially unaffected by CTAB micelles but is much slower in SDS solution. Similar micellar effects were found for the back reaction between e_aq⁻ and Fe(bpy)₂(CN)₂⁺. Rate constants for the scavenging of the photogenerated hydrated electrons by methyl viologen (MV²⁺) cations and NO₃⁻ anions were measured in the three systems, and the results indicate that for scavenging by MV²⁺ the rate constants are decreased in the micelle systems (k in H₂O, 8.4 × 10¹⁰; CTAB, 3.5 × 10¹⁰ and SDS, 1.58 × 10¹⁰ M⁻¹ s⁻¹), whereas for NO₃⁻ the CTAB micelle decreases while the SDS micelle enhances the scavenging compared to water solution (k in H₂O, 8.3 × 10⁹; CTAB, 7 × 10⁸; and SDS, 2.05 × 10¹⁰ M⁻¹ s⁻¹). For the comproportionation reaction between Fe(bipy)₂(CN)₂⁺ and Fe(bipy)₂(CN)₂⁻ both micelles reduce the rate (k in H₂O, 3.3 × 10¹⁰; CTAB, 2.3 × 10¹⁰; and SDS, 1.05 × 10¹⁰ M⁻¹s⁻¹), but while the reaction of Fe(bipy)₂(CN)₂⁺ with MV⁺ is increased in CTAB compared to water, it is slowed in SDS (k in H₂O, 2.4 × 10¹⁰; CTAB, 8.9 × 10¹⁰; and SDS, 1.8 × 10¹⁰ M⁻¹s⁻¹). All effects observed in these microheterogeneous systems can be uniformly interpreted in terms of Coulombic interactions between the actual reactants and the charged surface of the micelles.     

Analytical procedures for the determination of selected major (Al, Ca, Fe, K, Mg, Na, and Ti) and trace (Li, Mn, Sr, and Zn) elements in peat and plant samples using inductively coupled plasma-optical emission spectrometry

A simple, robust and reliable analytical procedure for the determination of Al, Ca, Fe, K, Li, Mg, Mn, Na, Sr, Ti, and Zn in peat and plant materials by inductively coupled plasma-optical emission spectrometry (ICP-OES) was developed. A microwave heated high pressure autoclave was used to digest powdered sample aliquots (approximately 200 mg) with different acid mixtures including nitric acid (HNO₃), tetrafluoroboric acid (HBF₄) and hydrogen peroxide (H₂O₂). The optimized acid mixture for digestion of plant and peat samples consisted of 3 mL HNO₃ and 0.1 mL HBF₄, in addition to H₂O₂ which was sub-boiled into the PTFE digestion tubes during heating of the autoclave. Using HNO₃ alone, recoveries of Al and Ti were too low by 40 and 160%, respectively, because HNO₃ could not fully liberate the analytes of interest from the silicate fraction of the plant and peat matrix. However, for all other elements (such as Mn, Sr, and Zn), the use of HBF₄ was less critical. The accuracy of the analytical procedure developed was evaluated with peat and plant reference materials of different origin and composition. The ICP-OES instrument was optimized using solutions of plant reference materials considering RF power, nebulizer pressure, auxiliary gas flow and rinse time. Scandium was used as an online internal standard (IS) as it provided accurate results and showed less than 3% drift in sensitivity over time which was lower compared to other potential IS such as Rh (20%) and In (6%). The combination of most sensitive and less sensitive wavelengths allowed to obtain low detection limits and highest possible dynamic range. The achieved procedure detection limits ranged from 0.05 μg g⁻¹ (Li) to 15 μg g⁻¹ (Ca) and allowed a precise quantification of all elements. Comparative X-ray fluorescence spectrometric measurements of solid peat and plant samples generally agreed well with results obtained by digestion/ICP-OES. To overcome interferences caused by Na, K, and Li, a solution of 10 μg g⁻¹ CsCl₂ was successfully used as an ionization buffer. The good agreement between the found and certified concentrations in plant and peat reference materials indicates that the developed analytical procedure is well suited for further studies on the fate of major elements in plant and peat matrices.     

Flow injection determination of bismuth in urine by successive retention of Bi(III) and tetrahydroborate(III) on an anion-exchange resin and hydride generation atomic absorption spectrometry

Bismuth as BiCl₄⁻ and BH₄⁻ ware successively retained in a column (150 mm × 4 mm, length × i.d.) packed with Amberlite IRA-410 (strong anion-exchange resin). This was followed by passage of an injected slug of hydrochloric acid resulting in bismuthine generation (BiH₃). BiH₃ was stripped from the eluent solution by the addition of a nitrogen flow and the bulk phases were separated in a gas–liquid separator. Finally, bismutine was atomized in a quartz tube for the subsequent detection of bismuth by atomic absorption spectrometry. Different halide complexes of bismuth (namely, BiBr₄⁻, BiI₄⁻ and BiCl₄⁻) were tested for its pre-concentration, being the chloride complexes which produced the best results. Therefore, a concentration of 0.3 mol l⁻¹ of HCl was added to the samples and calibration solutions. A linear response was obtained between the detection limit (3σ) of 0.225 and 80 μg l⁻¹. The R.S.D.% (n = 10) for a solution containing 50 μg l⁻¹ of Bi was 0.85%. The tolerance of the system to interferences was evaluated by investigating the effect of the following ions: Cu²⁺, Co²⁺, Ni²⁺, Fe³⁺, Cd²⁺, Pb²⁺, Hg²⁺, Zn²⁺, and Mg²⁺. The most severe depression was caused by Hg²⁺, which at 60 mg l⁻¹ caused a 5% depression on the signal. For the other cations, concentrations between 1000 and 10,000 mg l⁻¹ could be tolerated. The system was applied to the determination of Bi in urine of patients under therapy with bismuth subcitrate. The recovery of spikes of 5 and 50 μg l⁻¹ of Bi added to the samples prior to digestion with HNO₃ and H₂O₂ was in satisfactory ranges from 95.0 to 101.0%. The concentrations of bismuth found in six selected samples using this procedure were in good agreement with those obtained by an alternative technique (ETAAS). Finally, the concentration of Bi determined in urine before and after 3 days of treatment were 1.94 ± 1.26 and 9.02 ± 5.82 μg l⁻¹, respectively.     

As, Cd, Cr, Ni and Pb pressurized liquid extraction with acetic acid from marine sediment and soil samples

Rapid leaching procedures by Pressurized Liquid Extraction (PLE) have been developed for As, Cd, Cr, Ni and Pb leaching from environmental matrices (marine sediment and soil samples). The Pressurized Liquid Extraction is completed after 16 min. The released elements by acetic acid Pressurized Liquid Extraction have been evaluated by inductively coupled plasma-optical emission spectrometry. The optimum multi-element leaching conditions when using 5.0 ml stainless steel extraction cells, were: acetic acid concentration 8.0 M, extraction temperature 100 °C, pressure 1500 psi, static time 5 min, flush solvent 60%, two extraction steps and 0.50 g of diatomaceous earth as dispersing agent (diatomaceous earth mass/sample mass ratio of 2). Results have showed that high acetic acid concentrations and high extraction temperatures increase the metal leaching efficiency. Limits of detection (between 0.12 and 0.5 μg g^− 1) and repeatability of the over-all procedure (around 6.0%) were assessed. Finally, accuracy was studied by analyzing PACS-2 (marine sediment), GBW-07409 (soil), IRANT-12-1-07 (cambisol soil) and IRANT-12-1-08 (luvisol soil) certified reference materials (CRMs). These certified reference materials offer certified concentrations ranges between 2.9 and 26.2 μg g^− 1 for As, from 0.068 to 2.85 μg g^− 1 for Cd, between 26.4 and 90.7 μg g^− 1 for Cr, from 9.3 to 40.0 μg g^− 1 for Ni and between 16.3 and 183.0 μg g^− 1 for Pb. Recoveries after analysis were between 95.7 and 105.1% for As, 96.2% for Cd, 95.2 and 100.6% for Cr, 95.7 and 103% for Ni and 94.2 and 105.5% for Pb.     

Determination of As, Cd, Pb and Se in DORM-1 dogfish muscle reference material using alkaline solubilization and electrothermal atomic absorption spectrometry with Ir+Rh as permanent modifiers or Pd+Mg in solution

In this work, tetramethylammonium hydroxide (TMAH) was used to solubilize the DORM-1 dogfish muscle certified reference material as a model substance for the determination of As, Cd, Pb and Se by electrothermal atomic absorption spectrometry (ET AAS). The sample was mixed with a small amount of TMAH and heated to 60 °C for 10 min in a water bath. After dissolution, As and Se were determined using palladium and magnesium nitrates as a chemical modifier added in solution. For Cd and Pb, best results were obtained with a mixture of 250 μg of each of iridium and rhodium as permanent modifiers. In both cases, the calibration was performed with aqueous solutions in 0.2% v/v HNO₃. The temperature program for each analyte was optimized using pyrolysis and atomization curves established with the fish reference material. The detection limits in dry samples and the characteristic mass values were: Cd 0.005 μg g⁻¹ and 0.9 pg; Pb 0.04 μg g⁻¹ and 7.6 pg; As 0.4 μg g⁻¹ and 13 pg and Se 0.6 μg g⁻¹ and 20 pg, respectively. Results from the determination of these elements in the DORM-1 certified fish reference material were within the 95% confidence interval of the certified values.     

Simultaneous separation and preconcentration of trace elements in water samples by coprecipitation on manganese dioxide using D-glucose as reductant for KMnO(4)

A field oriented and economical method of coprecipitation of trace elements like Al, Au, Bi, Cd, Co, Cu, Fe, Mo, Ni, Pb, Pd, Ti, V, W, Zn and REE has been developed. A novel reductant D-glucose, reduces KMnO₄ in solution to form a precipitate of MnO_2. Two liters of clear natural water sample is adjusted to pH 3.5–4.0, and is treated with 10 ml of 1% KMnO₄ and 20 ml of 0.1% D-glucose. The sample is heated at a temperature of 75–80 °C, MnO₂ is formed which coprecipitates the above trace elements. The precipitate is separated by filtration, dissolved in 2 ml of 50% HCl and 2 ml of 30% H₂O₂ and diluted to 25 ml for analysis using AAS and ICP-AES. The recoveries were found to be 96–105%. The preconcentration factor is 80. Limits of determination by the proposed method in natural waters are 1 μg l⁻¹ for Al, Cd, Mo, V, W, Ti and Zn, 5 μg l⁻¹ for Au, Bi, Co, Cu, Fe, Ni, Pb and Pd and 8 μg l⁻¹ for REE. The RSD of the present procedure (n=5) is 8% at 5 μg l⁻¹ level. Twenty water samples can be analyzed by an analyst in an 8-h day.     

The efficacy of nitrosonaphthol functionalized XAD-16 resin for the preconcentration/sorption of Ni(II) and Cu(II) ions

Amberlite XAD-16 resin has been functionalized using nitrosonaphthol as a ligand and characterized employing elemental, thermogravimetric analysis and FT-IR spectroscopy. The sorption of Ni(II) and Cu(II) ions onto this functionalized resin is investigated and optimized with respect to the sorptive medium (pH), shaking speed and equilibration time between liquid and solid phases. The monitoring of the influence of diverse ions on the sorption of metal ions has revealed that phosphate, bicarbonate and citrate reduce the sorption up to 10–14%. The sorption data followed Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherms. The Freundlich parameters computed are 1/n = 0.56 ± 0.03 and 0.49 ± 0.05, A = 9.54 ± 1.5 and 6.0 ± 0.5 mmol g⁻¹ for Ni(II) and Cu(II) ions, respectively. D–R isotherm yields the values of X_m = 0.87 ± 0.07 and 0.35 ± 0.05 mmol g⁻¹ and of E = 9.5 ± 0.23 and 12.3 ± 0.6 kJ mol⁻¹ for Ni(II) and Cu(II) ions, respectively. Langmuir characteristic constants estimated are Q = 0.082 ± 0.005 and 0.063 ± 0.003 mmol g⁻¹, b = (4.7 ± 0.2) × 10⁴ and (7.31 ± 0.11) × 10⁴ l mol⁻¹ for Ni(II) and Cu(II) ions, respectively. The variation of sorption with temperature gives thermodynamic quantities of ΔH = −58.9 ± 0.12 and −40.38 ± 0.11 kJ mol⁻¹, ΔS = −183 ± 10 and −130 ± 8 J mol⁻¹ K⁻¹ and ΔG = −4.4 ± 0.09 and −2.06 ± 0.08 kJ mol⁻¹ at 298 K for Ni(II) and Cu(II) ions, respectively. Using kinetic equations, values of intraparticle transport and of first order rate constant have been computed for both the metal ions. The sorption procedure is utilized to preconcentrate these ions prior to their determination in tea, vegetable oil, hydrogenated oil (ghee) and palm oil by atomic absorption spectrometry using direct and standard addition methods.     

Ablative and transport fractionation of trace elements during laser sampling of glass and copper

The fractionation of trace elements due to ablation and transport processes was quantified during Q-switched infrared laser sampling of glass and copper reference materials. Filter-trapping of the ablated product at different points in the sample introduction system showed ablation and transport sometimes caused opposing fractionation effects, leading to a confounded measure of overall (ablative + transport) fractionation. An unexpected result was the greater ablative fractionation of some elements (Au, Ag, Bi, Te in glass and Au, Be, Bi, Ni, Te in copper) at a higher laser fluence of 1.35 × 10⁴W cm⁻² than at 0.62 × 10⁴W cm⁻², which contradicted predictions from modelling studies of ablation processes. With glass, there was an inverse logarithmic relationship between the extent of ablative and overall fractionation and element oxide melting point (OMPs), with elements with OMPs < 1000°C exhibiting overall concentration increases of 20–1340%. Fractionation during transport was quantitatively important for most certified elements in copper, and for the most volatile elements (Au, Ag, Bi, Te) in glass. Elements common to both matrices showed 50–100% higher ablative fractionation in copper, possibly because of greater heat conductance away from the ablation site causing increased element volatilisation or zone refinement. These differences between matrices indicate that non-matrix-matched standardisation is likely to provide inaccurate calibration of laser ablation inductively coupled plasma-mass spectrometry analyses of at least some elements.     

Interactions of thorium isotopes with colloidal organic matter in oceanic environments

The phase speciation of thorium and consequences for the residence times of colloids have been examined in seawater of the Middle Atlantic Bight (MAB) and the Gulf of Mexico. Two fractions of colloidal organic matter (COM), 0.2 μm > COM₁ > 1 kD and 0.2 μm > COM₁₀ > 10 kD, were sampled using cross-flow ultrafiltration techniques and measured for their ²³⁴Th activity and organic carbon concentration. The ratios of mass concentrations of COM₁ to those of suspended particulate matter were as high as 10 in the MAB and 6–34 in the Gulf of Mexico. Higher concentrations of colloids may be of great importance in the biogeochemical cycling of many particle-reactive nuclides or trace elements owing to their high specific surface area and complexation capacity. A significant fraction of ²³⁴Th in the traditionally defined “dissolved” pool was found to be associated with colloids. On average, about 10% of “dissolved” ²³⁴Th was in the colloidal fraction of sizes between 10 kDa and 0.2 μm, and 50% was in the 1 kDa-0.2 μm fraction. Values of the partition coefficients [K_c: (0.5−4) × 10⁶ ml g⁻¹ for K_c1 and (0.5−7) × 10⁶ ml g⁻¹ for K_c10] of ²³⁴Th between truly dissolved (<1 kDa) and colloidal fractions approximated those for Th-particle interactions [K_p: (0.3−10) × 10⁶ ml g⁻¹], indicating that colloid and suspended particle surface sites are similar. The distribution of ²³⁴Th between dissolved, colloidal, and particulate phases was broadly similar to that of organic carbon in these oceanic environments. Thus, thorium isotopes might be used as tracers of marine organic carbon cycling. Residence times of colloids derived from ²³⁴Th:²³⁸U disequilibria were consistently short, ranging from 1 to 14 days for COM₁₀ and from 5 to 65 days for COM₁, suggesting that marine colloids are highly reactive in marine biogeochemical processes. The discrepancy between apparent turnover times of colloids (1 kDa) derived from Th scavenging and ¹⁴C measurements suggest that ²³⁴Th and ¹⁴C may trace different geochemical pathways of colloids in the ocean.     

Efficiency and mechanism of new poly(acryl-phenylamidrazone phenylhydrazide) chelating fiber for adsorbing trace Ga, In, Bi, V and Ti from solution

A new po1y(acrylphenylamidrazone phenylhydrazide) chelating fiber is synthesized from polyacrylonitrile fiber and used for preconcentration and separation of trace Ga(III), In(III), Bi(III), V(V) and Ti(IV) from solution (5–50 ng ml⁻¹ Ti(IV) or V(V) and 50–500 ng ml⁻¹ Ga(III), In (III) or Bi(III) in 1000–100 ml of solution can be enriched quantitatively by 0.15 g of fiber at a 4 ml min⁻¹ flow rate in the pH range 5–7 with recoveries >95%). These ions can be desorbed quantitatively with 20 ml of 4 M hydrochloric acid at 2 ml min⁻¹ from the fiber column. When the fiber which had been treated with concentrated hydrochloric acid and washed with distilled water until neutral was reused eight times, the recoveries of the above ions by enrichment were still >95%. Two-hundred-fold to 10 000-fold excesses of Cu(II), Zn(II), Ca(II), Mn(II), Cr(III), Fe(III), Ba(II) and Al(III) caused little interference in the determination of these ions by inductively coupled plasma-atomic emission spectrometers (ICP-AES). The relative standard deviations for enrichment and determination of 50 ng ml⁻¹ Ga, In or Bi and 10 ng ml⁻¹ V or Ti are in the range 1.2–2.7%. The contents of these ions in real solution samples determined by this method were in agreement with the certified values of the samples with average errors <3.7%.     

Hg(II)-imprinted thiol-functionalized mesoporous sorbent micro-column preconcentration of trace mercury and determination by inductively coupled plasma optical emission spectrometry

Hg(II)-imprinting thiol-functionalized mesoporous sorbent was prepared by a sol–gel method and characterized by X-ray diffraction (XRD), FT-IR spectroscopy and nitrogen gas adsorption–desorption. The static adsorption capacity of the Hg(II)-imprinted and non-imprinted sorbent was 78.5 and 26.6 mg g⁻¹, respectively. The breakthrough capacity was 4.46 mg g⁻¹, and the relative selectivity coefficient for Hg(II) in the presence of Cd and Pb was 3.3 and 3.9, respectively. A new method using a micro-column packed with Hg(II)-imprinting thiol-functionalized mesoporous sorbent has been developed for preconcentration of trace mercury prior to its determination by inductively coupled plasma optical emission spectrometry (ICP-OES). The effects of pH, sample flow rate and volume, elution solution and interfering ions on the recovery of the analyte have been investigated. The limit of detection was 0.39 ng ml⁻¹ with a concentration factor of 150 times. The developed method has been applied to the determination of trace mercury in some biological and environmental samples with satisfactory results. The accuracy was assessed through recovery experiments and analysis of certified reference material.     

Determination of fenoterol and salbutamol in pharmaceutical formulations by electrogenerated chemiluminescence

Fenoterol and salbutamol were determined by electrogenerated chemiluminescence (ECL) coupled with flow injection analysis (FIA), using Ru(bpy)₃²⁺ as the luminescent substance. Fenoterol and salbutamol oxidize together with the ruthenium 2,2-bipyridyl at a platinum electrode, which leads to an increase in the luminescent intensity, and this increase is proportional to the analyte concentration. For fenoterol a linear calibration curve within the range from 1.0 × 10⁻⁵ to 1.0 × 10⁻⁴ mol l⁻¹ was obtained with a correlation coefficient of 0.998 (n = 5) and for salbutamol the linear analytical curve was also obtained in this range with a correlation coefficient of 0.995 (n = 5). The relative standard deviation was estimated as ≤2.5% for 3 × 10⁻⁵ mol l⁻¹ for fenoterol solution and as ≤1.3% for 5.0 × 10⁻⁵ mol l⁻¹ salbutamol solution for 15 successive injections. The limit of detection for fenoterol was 2.4 × 10⁻⁷ mol l⁻¹ and for salbutamol was 4.0 × 10⁻⁷ mol l⁻¹. Fenoterol and salbutamol were successfully determined in drug tablets and the soluble components of the matrix did not interfere in the luminescent emission. The results obtained using the luminescent methodology were not statistically different from those obtained by UV-spectrophotometry at 95% confidence level.     

Comparison of AFS and ICP-MS detection coupled with gas chromatography for the determination of methylmercury in marine samples

Inductively coupled plasma mass spectrometry (ICP-MS) and atomic fluorescence spectrometry (AFS) coupled with gas chromatography (GC) have been evaluated as element specific detectors for the determination of methylmercury in marine samples. Detection limits for methylmercury chloride, obtained using ICP-MS and AFS, were 0.9 and 0.25 pg as Hg, respectively. Methylmercury was determined in marine tissue reference materials IAEA 142 and NIST 8044 mussel homogenate, and DOLT-2 dogfish liver by GC–AFS, with found values of 45±7, 26±4, and 671±41 ng g⁻¹, compared with certified values of 47±4, 28±2, and 693±53 ng g⁻¹. The analyses of IAEA 142 and NIST 8044 were repeated using GC–ICP-MS, with found values of 48±9 and 30±3 ng g⁻¹, respectively. Methylmercury was determined in real samples of ringed seal and beluga whale, with found values of 801±62 and 2830±113 ng g⁻¹, respectively.     

Square wave adsorptive stripping voltammetric determination of famotidine in urine

Electrochemical studies of famotidine were carried out using voltammetric techniques: cyclic voltammetry, linear sweep and square wave adsorptive stripping voltammetry. The dependence of the current on pH, buffer concentration, nature of the buffer, and scan rate was investigated. The best results for the determination of famotidine were obtained in MOPS buffer solution at pH 6.7. This electroanalytical procedure enabled to determine famotidine in the concentration range 1 × 10⁻⁹–4 × 10⁻⁸ mol L⁻¹ by linear sweep adsorptive stripping voltammetry (LS AdSV) and 5 × 10⁻¹⁰–6 × 10⁻⁸ mol L⁻¹ by square wave adsorptive stripping voltammetry (SW AdSV). Repeatability, precision and accuracy of the developed methods were checked. The detection and quantification limits were found to be 1.8 × 10⁻¹⁰ and 6.2 × 10⁻¹⁰ mol L⁻¹ for LS AdSV and 4.9 × 10⁻¹¹ and 1.6 × 10⁻¹⁰ mol L⁻¹ for SW AdSV, respectively. The method was applied for the determination of famotidine in urine.     

Optimisation of sample treatment for arsenic speciation in alga samples by focussed sonication and ultrafiltration

A procedure for arsenic species fractionation in alga samples (Sargassum fulvellum, Chlorella vulgaris, Hizikia fusiformis and Laminaria digitata) by extraction is described. Several parameters were tested in order to evaluate the extraction efficiency of the process: extraction medium, nature and concentration (tris(hydroxymethyl)aminomethane, phosphoric acid, deionised water and water/methanol mixtures), extraction time and physical treatment (magnetic stirring, ultrasonic bath and ultrasonic focussed probe). The extraction yield of arsenic under the different conditions was evaluated by determining the total arsenic content in the extracts by ICP-AES. Arsenic compounds were extracted in 5 mL of water by focussed sonication for 30 s and subsequent centrifugation at 14,000 × g for 10 min. The process was repeated three times. Extraction studies show that soluble arsenic compounds account for about 65% of total arsenic.

An ultrafiltration process was used as a clean-up method for chromatographic analysis, and also allowed us to determine the extracted arsenic fraction with a molecular weight lower than 10 kDa, which accounts for about 100% for all samples analysed.

Speciation studies were carried out by HPLC–ICP-AES. Arsenic species were separated on a Hamilton PRP-X100 column with 17 mM phosphate buffer at pH 5.5 and 1.0 mL min⁻¹ flow rate. The chromatographic method allowed us to separate the species As(III), As(V), MMA and DMA in less than 13 min, with detection limits of about 20 ng of arsenic per species, for a sample injection volume of 100 μL. The chromatographic analysis allowed us to identify As(V) in Hizikia (46 ± 2 μg g⁻¹), Sargassum (38 ± 2 μg g⁻¹) and Chlorella (9 ± 1 μg g⁻¹) samples. The species DMA was also found in Chlorella alga (13 ± 1 μg g⁻¹). However, in Laminaria alga only an unknown arsenic species was detected, which eluted in the dead volume.     

Unauthorised antibiotic treatments in beekeeping: Development and validation of a method to quantify and confirm tylosin residues in honey using liquid chromatography–tandem mass spectrometric detection

A liquid chromatographic–tandem mass spectrometric (HPLC-MS/MS) method is proposed for the identification and quantification of tylosin in honey. Sample treatment involves an extraction in a Tris buffer at pH 10.5, followed by a solid-phase clean up step on an Oasis HLB column. Roxithromycin was used as the internal standard. Chromatographic separation of tylosin and roxithromycin was performed on an XTerra MS C₁₈ column (100 mm × 2.1 mm i.d., 5 μm) using a gradient of aqueous 0.01 M ammonium acetate pH 3.5 and acetonitrile as the mobile phase, at a flow rate of 0.25 ml min⁻¹. The method was validated according to the guidelines laid down by the Commission Decision 2002/657/EC. Tylosin residues were confirmed by MS/MS experiments considering the appropriate identification points. All validation parameters such as Cc (lower than 3 ng g⁻¹), Ccβ (lower than 5 ng g⁻¹), recovery and precision were assessed on the basis of the “critical ion” (less intense ion permitting unambiguous identification of the analyte).     

Application of lead film electrode for simultaneous adsorptive stripping voltammetric determination of Ni(II) and Co(II) as their nioxime complexes

An adsorptive stripping voltammetric (AdSV) procedure for simultaneous determination of Ni(II) and Co(II) in the presence of nioxime as a complexing agent at an in situ plated lead film electrode was described. The Co(II) signal was enhanced by exploitation of the catalytic process in the presence of nitrite. Ni(II) and Co(II) signals are better separated than in the case of bismuth film electrodes. Calibration graphs for an accumulation time of 120 s are linear from 1 × 10⁻⁹ to 1 × 10⁻⁷ mol L⁻¹ and from 1 × 10⁻¹⁰ to 5 × 10⁻⁹ mol L⁻¹ for Ni(II) and Co(II), respectively. The proposed procedure was applied for Ni(II) and Co(II) determination in water certified reference materials.     

Effect of monascus pigment derivatives on the electrophoretic mobility of bacteria, and the cell adsorption and antibacterial activities of pigments

Various amino acid derivatives of monascus pigments were synthesized. The effects of pigment derivatives on the pigment adsorption ratio, electrophoretic mobility (EPM) of bacterial cells, and antibacterial activity were investigated under varying conditions of pigment type, pigment concentration, pH, and ionic strength. Two hydrophobic and two hydrophilic derivatives were selected as model pigments. There was a close relationship between the antimicrobial activity and the pigment adsorption ratio. Against Escherichia coli, the hydrophobic l-Tyr and l-Phe derivatives (log P = 3.18 and 3.57) exhibited high antimicrobial activities (MIC = 8 and 16 mg/L) and high cellular adsorption ratios (9.6 and 10.9 mg/L). The hydrophilic l-Glu and l-Asn derivatives (log P = 1.40 and 0.47) exhibited low activities (MIC = 64 and 128 mg/L) and low adsorption ratios (4.7 and 4.0 mg/L). The electrophoretic mobility of 11 different bacteria varied between −1.93 × 10⁻⁸ and −1.19 × 10⁻⁸ m² V⁻¹ s⁻¹ regardless of Gram⁺ or Gram⁻. The l-Phe derivative showed low MIC values (high antimicrobial activities) against bacteria with a high electrophoretic mobility. A positive linearity between the pigment adsorption ratio and the electrophoretic mobility was established. When the four pigment derivatives were added to E. coli solutions, the electrophoretic mobility of cells in all cases sharply increased with an increasing pigment concentration. The mobility value was high for hydrophobic pigment derivatives in descending order of l-Phe (0.8 × 10⁻⁸ m² V⁻¹ s⁻¹), l-Tyr (0.68 × 10⁻⁸ m² V⁻¹ s⁻¹), l-Glu (0.46 × 10⁻⁸ m² V⁻¹ s⁻¹), and l-Asn (0.44 × 10⁻⁸ m² V⁻¹ s⁻¹). Additional adsorption of the hydrophobic derivatives probably occurred due to a hydrophobic interaction between the pigment and the pigment-coated cells. The electrophoretic mobility decreased gradually with an increasing pH and/or ionic strength with both addition and no addition of the pigment derivatives. The pattern of change of the pigment adsorption ratio under varying pH and/or ionic strength values was similar to the pattern for electrophoretic mobility.     

Voltammetric determination of glucose based on reduction of copper(II)–glucose complex at lanthanum hydroxide nanowire modified carbon paste electrodes

A novel voltammetric method for the determination of β-d-glucose (GO) is proposed based on the reduction of Cu(II) ion in Cu(II)(NH₃)₄²⁺–GO complex at lanthanum(III) hydroxide nanowires (LNWs) modified carbon paste electrode (LNWs/CPE). In 0.1 mol L⁻¹ NH₃·H₂O–NH₄Cl (pH 9.8) buffer containing 5.0 × 10⁻⁵ mol L⁻¹ Cu(II) ion, the sensitive reduction peak of Cu(II)(NH₃)₄²⁺–GO complex was observed at −0.17 V (versus, SCE), which was mainly ascribed to both the increase of efficient electrode surface and the selective coordination of La(III) in LNW to GO. The increment of peak current obtained by deducting the reduction peak current of the Cu(II) ion from that of the Cu(II)(NH₃)₄²⁺–GO complex was rectilinear with GO concentration in the range of 8.0 × 10⁻⁷ to 2.0 × 10⁻⁵ mol L⁻¹, with a detection limit of 3.5 × 10⁻⁷ mol L⁻¹. A 500-fold of sucrose and amylam, 100-fold of ascorbic acid, 120-fold of uric acid as well as gluconic acid did not interfere with 1.0 × 10⁻⁵ mol L⁻¹ GO determination.