Flow-injection in-line complexation for ion-pair reversed phase high performance liquid chromatography of some metal-4-(2-pyridylazo) resorcinol chelates

Flow injection (FI) was coupled to ion-pair reversed phase high performance liquid chromatography (IP-RPHPLC) for the simultaneous analysis of some metal-4-(2-pyridylazo) resorcinol (PAR) chelates. A simple reverse flow injection (rFI) set-up was used for in-line complexation of metal-PAR chelates prior to their separation by IP-RPHPLC. The rFI conditions were: injection volume of PAR 85 μL, flow rate of metal stream 4.5 mL min⁻¹, concentration of PAR 1.8 × 10⁻⁴ mol L⁻¹ and the mixing coil length of 150 cm. IP-RPHPLC was carried out using a C₁₈ μBondapak column with the mobile phase containing 37% acetonitrile, 3.0 mmol L⁻¹ acetate buffer pH 6.0 and 6.2 mmol L⁻¹ tetrabutylammonium bromide (TBABr) at a flow rate of 1.0 mL min⁻¹ and visible detection at 530 and 440 nm. The analysis cycle including in-line complexation and separation by IP-RPHPLC was 16 min, which able to separate Cr(VI) and the PAR chelates of Co(II), Ni(II) and Cu(II).     

The effect of signal suppression and mobile phase composition on the simultaneous analysis of multiple classes of acidic/neutral pharmaceuticals and personal care products in surface water by solid-phase extraction and ultra performance liquid chromatography-negative electrospray tandem mass spectrometry

A new multi-residue method for the determination of 25 acidic/neutral pharmaceuticals (antibiotics, anti-inflammatory/analgesics, lipid regulating agents, diuretics, triazides, H2-receptor antagonists, cardiac glicozides and angiotensin II antagonists) and personal care products (sunscreen agents and preservatives) in surface water with the usage of a new technique: ultra performance liquid chromatography–negative electrospray tandem mass spectrometry (UPLC–MS/MS) was developed and validated. The novel UPLC system with 1.7 μm particle-packed column allowed for good resolution of analytes with the application of low mobile phase flow rates (0.05 mL min⁻¹) and short retention times (from 4.7 min to 13.3 min) delivering a fast and cost-effective multi-residue method. SPE with the usage of Oasis MCX strong cation-exchange mixed-mode polymeric sorbent was chosen for sample clean-up and concentration. The influence of mobile-phase composition, matrix assisted ion suppression and SPE recovery on the sensitivity of the method was identified and quantified. The instrumental limits of quantification varied from 0.2 μg L⁻¹ to 30 μg L⁻¹. The method limits of quantification were at low nanogram per litre levels and ranged from 0.3 ng L⁻¹ to 30 ng L⁻¹. The instrumental and method intra-day and inter-day repeatabilities were on average less than 5%. The method was successfully applied for the determination of PPCPs in River Taff. Thirteen compounds were determined in river water at levels ranging from a single to a few hundred nanograms per litre. Among them were ten pharmaceuticals (aspirin, salicylic acid, ketoprofen, naproxen, diclofenac, ibuprofen, mefenamic acid, furosemide, sulfasalazine and valsartan) and three personal care products (methyl- and ethylparaben and 4-benzophenone).     

Use of silica gel chemically modified with zirconium phosphate for preconcentration and determination of lead and copper by flame atomic absorption spectrometry

An analytical method using silica gel chemically modified with zirconium (IV) phosphate for preconcentration of lead and copper, in a column system, and their sequential determination by flame atomic absorption spectrometry (FAAS), was developed. Sample solutions are passed through a glass column packed with 100 mg of the sorbent material, at pH 4.5, and lead and copper are eluted with 1.0 mol l⁻¹ HNO₃ at a flow rate of 2.0 ml min⁻¹. The extraction of copper is affected by Fe(II), Mn(II), Zn(II), Ni(II) and Co(II) while only Fe(II) interferes in the lead determination. These interferences may be overcome with an appropriate addition of a KI or NaF solution. An enrichment factor of 30 was obtained for both metals. While the limits of detection (3σ) were 6.1 and 1.1 μg l⁻¹, for Pb and Cu, respectively, the limits of determination were 16.7 and 3.3 μg l⁻¹. The precision expressed as relative standard deviation (R.S.D.) obtained for 3.3 μg l⁻¹ of Cu and 16.7 μg l⁻¹ of Pb were 4.3 and 4.7%, respectively, calculated from ten measurements. The proposed method was evaluated with reference material and was applied for the determination of lead and copper in industrial and river waters.     

Investigation of on-line coupling electrothermal atomic absorption spectrometry with flow injection sorption preconcentration using a knotted reactor for totally automatic determination of lead in water samples

A flow injection on-line sorption preconcentration electrothermal atomic absorption spectrometric system for fully automatic determination of lead in water was investigated. The discrete non-flow-through nature of ETAAS, the limited capacity of the graphite tube and the relatively large volume of the knotted reactor (KR) are obstacles to overcome for the on-line coupling of the KR sorption preconcentration system with ETAAS. A new FI manifold has been developed with the aim of reducing the eluate volume and minimizing dispersion. The lead diethyldithiocarbamate complex was adsorbed on the inner walls of a knotted reactor made of PTFE tubing (100 cm long, 0.5 mm i.d.). After that, an air flow was introduced to remove the residual solution from the KR and the eluate delivery tube, then the adsorbed analyte chelate was quantitatively eluted into a delivery tube with 50 μl of ethanol. An air flow was used to propel the eluent from the eluent loop through the reactor and to introduce all the ethanolic eluate onto the platform of the transversely heated graphite tube atomizer, which was preheated to 80°C. With the use of the new FI manifold, the consumption of eluent was greatly reduced and dispersion was minimized. The adsorption efficiency was 58%, and the enhancement factor was 142 in the concentration range 0.01–0.05 μg l⁻¹ Pb at a sample loading rate of 6.8 ml min⁻¹ with 60 s preconcentration time. For the range 0.1–2.0 μg l⁻¹ of Pb a loading rate of 3.0 ml min⁻¹ and 30 s preconcentration time were chosen, resulting in an adsorption efficiency of 42% and an enhancement factor of 21, respectively. A detection limit (3σ) of 2.2 ng l⁻¹ of lead was obtained using a sample loading rate of 6.8 ml min⁻¹ and 60 s preconcentration. The relative standard deviation of the entire procedure was 4.9% at the 0.01 μg l⁻¹ Pb level with a loading rate of 6.8 ml min⁻¹ and 60 s preconcentration, and 2.9% at the 0.5 μg l⁻¹ Pb level with a 3.0 ml min⁻¹ loading rate and 30 s preconcentration. Efficient washing of the matrix from the reactor was critical, requiring the use of the standard addition method for seawater samples. The analytical results obtained for seawater and river water standard reference materials were in good agreement with the certified values.     

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%.     

Separation and determination of amitriptyline and nortriptyline by dispersive liquid-liquid microextraction combined with gas chromatography flame ionization detection

Dispersive liquid–liquid microextraction (DLLME) coupled with gas chromatography–flame ionization detection (GC–FID) was applied for the determination of two tricyclic antidepressant drugs (TCAs), amitriptyline and nortriptyline, from water samples. This method is a very simple and rapid method for the extraction and preconcentration of these drugs from environmental sample solutions. In this method, the appropriate mixture of extraction solvent (18 μL Carbon tetrachloride) and disperser solvent (1 mL methanol) are injected rapidly into the aqueous sample (5.0 mL) by syringe. Therefore, cloudy solution is formed. In fact, it is consisted of fine particles of extraction solvent which is dispersed entirely into aqueous phase. The mixture was centrifuged and the extraction solvent is sedimented on the bottom of the conical test tube. 2.0 μL of the sedimented phase is injected into the GC for separation and determination of TCAs. Some important parameters, such as kind of extraction and disperser solvent and volume of them, extraction time, pH and ionic strength of the aqueous feed solution were optimized. Under the optimal conditions, the enrichment factors and extraction recoveries were between 740.04–1000.25 and 54.76–74.02%, respectively. The linear range was (0.005–16 μg mL⁻¹) and limits of detection were between 0.005 and 0.01 μg mL⁻¹ for each of the analytes. The relative standard deviations (R.S.D.) for 4 μg mL⁻¹ of TCAs in water were in the range of 5.6–6.4 (n = 6). The performance of the proposed technique was evaluated for determination of TCAs in blood plasma.     

Reverse flow injection spectrophotometric determination of iron(III) using chlortetracycline reagent

A simple reversed flow injection colourimetric procedure for determining iron(III) was proposed. It is based on the reaction between iron(III) with chlortetracycline, resulting in an intense yellow complex with a suitable absorption at 435 nm. A 200 μl chlortetracycline reagent solution was injected into the phosphate buffer stream (flow rate 2.0 ml min⁻¹) which was then merged with iron(III) standard or sample in dilute nitric acid stream (flow rate 1.5 ml min⁻¹). Optimum conditions for determining iron(III) were investigated by univariate method. Under the optimum conditions, a linear calibration graph was obtained over the range 0.5–20.0 μg ml⁻¹. The detection limit (3σ) and the quantification limit (10σ) were 0.10 and 0.82 μg ml⁻¹, respectively. The relatives standard deviation of the proposed method calculated from 12 replicate injections of 2.0 and 10.0 μg ml⁻¹ iron(III) were 0.43 and 0.59%, respectively. The sample throughput was 60 h⁻¹. The proposed method has been satisfactorily applied to the determination of iron(III) in natural waters.     

Enantioseparation and impurity determination of the enantiomers of novel phenylethanolamine derivatives by high performance liquid chromatography on amylose stationary phase

Simple and efficient analytical HPLC methods using Chiralpak AS-H as chiral stationary phase were developed for direct enantioseparation of 11 novel phenylethanolamine derivatives. The chromatographic experiments were performed in normal phase mode with n-hexane–ethanol–triethylamine (TEA) as mobile phase. Excellent baseline enantioseparation was obtained for most of compounds. The effects of the concentration of organic modifiers and column temperature were studied for the enantiomeric separation. The mechanism of chiral recognition was discussed based on the relationship between the thermodynamic parameters and structures of compounds. It was found that the enantioseparations were all enthalpy driven, and the tert-butyl groups of compounds had significant influence on the chiral recognition. Trantinterol enantiomers were resolved (R_s = 2.73) within 14 min using n-hexane–ethanol–TEA (98:2:0.1, v/v/v) as mobile phase with a flow rate of 0.8 mL min⁻¹ at 30 °C. The optimized method was validated for linearity, precision, accuracy and stability in solution and proved to be robust. The limits of detection (LOD) and quantification (LOQ) for (+)-trantinterol were 0.15 and 0.46 μg mL⁻¹. The method was applied for enantiomeric impurity determination of (−)-trantinterol bulk samples.     

A peroxidase-tetrathiafulvalene biosensor based on self-assembled monolayer modified Au electrodes for the flow-injection determination of hydrogen peroxide

The construction and performance under flow-injection conditions of an integrated amperometric biosensor for hydrogen peroxide is reported. The design of the bioelectrode is based on a mercaptopropionic acid (MPA) self-assembled monolayer (SAM) modified gold disk electrode on which horseradish peroxidase (HRP, 24.3 U) was immobilized by cross-linking with glutaraldehyde together with the mediator tetrathiafulvalene (TTF, 1 μmol), which was entrapped in the three-dimensional aggregate formed.

The amperometric biosensor allows the obtention of reproducible flow injection amperometric responses at an applied potential of 0.00 V in 0.05 mol L⁻¹ phosphate buffer, pH 7.0 (flow rate: 1.40 mL min⁻¹, injection volume: 150 μL), with a range of linearity for hydrogen peroxide within the 2.0 × 10⁻⁷–1.0 × 10⁻⁴ mol L⁻¹ concentration range (slope: (2.33 ± 0.02) × 10⁻² A mol⁻¹ L, r = 0.999). A detection limit of 6.9 × 10⁻⁸ mol L⁻¹ was obtained together with a R.S.D. (n = 50) of 2.7% for a hydrogen peroxide concentration level of 5.0 × 10⁻⁵ mol L⁻¹. The immobilization method showed a good reproducibility with a R.S.D. of 5.3% for five different electrodes. Moreover, the useful lifetime of one single biosensor was estimated in 13 days.

The SAM-based biosensor was applied for the determination of hydrogen peroxide in rainwater and in a hair dye. The results obtained were validated by comparison with those obtained with a spectrophotometric reference method. In addition, the recovery of hydrogen peroxide in sterilised milk was tested.     

Flow injection determination of selenium by successive retention of Se(IV) and tetrahydroborate(III) on an anion-exchange resin and hydride generation electrothermal atomization atomic absorption spectrometry with in-atomizer trapping: Part 1. Method development and investigation of interferences

A sample solution was passed at 20 ml min⁻¹ through a column (150×4 mm²) of Amberlite IRA-410Stron anion-exchange resin for 60 s. After washing, a solution of 0.1% sodium borohydride was passed through the column for 60 s at 5.1 ml min⁻¹. Following a second wash, a solution of 8 mol l⁻¹ hydrochloric acid was passed at 5.1 ml min⁻¹ for 45 s. The hydrogen selenide was stripped from the eluent solution by the addition of an argon flow at 150 ml min⁻¹ and the bulk phases were separated by a glass gas–liquid separator containing glass beads. The gas stream was dried by passing through a Nafion® dryer and fed, via a quartz capillary tube, into the dosing hole of a transversely heated graphite cuvette containing an integrated L’vov platform which had been pretreated with 120 μg of iridium as trapping agent. The furnace was held at a temperature of 250°C during this trapping stage and then stepped to 2000°C for atomization. The calibration was performed with aqueous standards solution of selenium (selenite, SeO₃²⁻) with quantification by peak area. A number of experimental parameters, including reagent flow rates and composition., nature of the gas–liquid separator, nature of the anion-exchange resin, column dimensions, argon flow rate and sample pH, were optimized. The effects of a number of possible interferents, both anionic and cationic were studies for a solution of 500 ng 1⁻¹ of selenium. The most severe depressions were caused by iron (III) and mercury (II) for which concentrations of 20 and 10 mg  1⁻¹ caused a 5% depression on the selenium signal. For the other cations (cadmium, cobalt, copper, lead,. magnesium, and nickel) concentrations of 50–70 mg 1⁻¹ could be tolerated. Arsenate interfered at a concentration of 3 mg⁻¹, whereas concentrations of chloride, bromide, iodide, perchlorate, and sulfate of 500–900 mg l⁻¹ could be tolerated. A linear response was obtained between the detection limit of 4 ng 1⁻¹, with a characteristic mass of 130 pg. The RSDs for solutions containing 100 and 200 ng 1⁻¹ selenium were 2.3% and 1.5%, respectively.     

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.     

Cellulose based macromolecular chelator having pyrocatechol as an anchored ligand: synthesis and applications as metal extractant prior to their determination by flame atomic absorption spectrometry

Pyrocatechol is immobilized on cellulose via ---NH---CH₂---CH₂---NH---SO₂---C₆H₄---N=N--- linker and the resulting macromolecular chelator characterized by IR, TGA, CPMAS ¹³C NMR and elemental analyses. It has been used for enrichment of Cu(II), Zn(II), Fe(III), Ni(II), Co(II), Cd(II) and Pb(II) prior to their determination by flame atomic absorption spectrometry (FAAS). The pH ranges for quantitative sorption (98.0–99.4%) are 4.0–7.0, 5.0–6.0, 3.0–4.0, 5.0–7.0, 5.0–8.0, 7.0–8.0 and 4.0–5.0, respectively. The desorption was found quantitative with 0.5 mol dm⁻³ HCl/HNO₃ (for Pb). The sorption capacity of the matrix for the seven metal ions has been found in the range 85.3–186.2 μmol g⁻¹. The optimum flow rate of metal ion solution for quantitative sorption of metal onto pyrocatechol functionalized cellulose as determined by column method, is 2–6 cm³ min⁻¹, whereas for desorption it is 2–4 cm³ min⁻¹. The tolerance limits for NaCl, NaBr, NaI, NaNO₃, Na₂SO₄, Na₃PO_4, humic acid, EDTA, ascorbic acid, citric acid, sodium tartrate, Ca(II) and Mg(II) in the sorption of all the seven metal ions are reported. Ascorbic acid is tolerable up to 0.8 mmol dm⁻³ with Cu and Pb where as sodium tartrate does not interfere up to 0.6 mmol dm⁻³ with Pb. There is no interference of NaBr, NaCl and NaNO₃ up to a concentration of 0.5 mol dm⁻³, in the sorption of Cu(II), Cd(II) and Fe(III) on to the chelating cellulose matrix The preconcentration factors are between 75 and 300 and t_1/2 values ≤5 min for all the metal ions. Simultaneous sorption of Cu, Zn, Ni and Co is possible at pH 5.0 if their total concentration does not exceed lowest sorption capacity. The present matrix coupled with FAAS has been used to enrich and determine the seven metal ions in river and tap water samples (relative standard deviation (R.S.D.) 1.05–7.20%) and synthetic certified water sample SLRS-4 (NRC, Canada) with R.S.D. 2.03%. The cobalt present in pharmaceutical vitamin tablets was also preconcentrated on the modified cellulose and determined by FAAS (R.S.D. 1.87%).     

Evaluation of selenium behavior in thermospray flame furnace atomic absorption spectrometry

The behavior of selenium in thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) was studied and the developed procedure was applied for selenium determination in biological materials after microwave-assisted sample digestion. A sample volume of 600 μL was introduced into the hot metallic Ni tube at a flow rate of 0.4 mL min⁻¹ using water as carrier. The limit of detection obtained for Se was 8.7 μg L⁻¹ (3s_blank/slope, n = 10), which is 95-fold better than that typically obtained using FAAS. The applicability of the TS-FF-AAS procedure was evaluated for selenium determination in biological materials. Certified reference materials of pig kidney (BCR 186) and mussel (GBW 08571) were analyzed and a t-test had not shown any statistically significant difference at a 95% confidence level between determined and certified values for both materials. The procedure was successfully applied for determination of Se in pig kidney and shellfish. It was demonstrated that TS-FF-AAS improved the performance of FAAS (flame atomic absorption spectrometry) for determination of Se.     

Preliminary results on the determination of ultratrace amounts of cadmium in tea samples using a flow injection on-line solid phase extraction separation and preconcentration technique to couple with a sequential injection hydride generation atomic fluorescence spectrometry

In this work, a method was developed for determination of ultra-trace levels of Cd in tea samples by atomic fluorescence spectrometry (AFS). A flow injection solid phase extraction (FI-SPE) separation and preconcentration technique, to on-line couple with a sequential injection hydride generation (SI-HG) technique is employed in this study. Cd was preconcentrated on the SPE column, which was made from a neutral extractant named Cyanex 923, while other matrix ions or interfering ions were completely or mostly separated off. Conditions for the SPE separation and preconcentration, as well as conditions for the HG technique, were studied. Due to the separation of interfering elements, Cd hydride generation efficiency could be greatly enhanced with the sole presence of Co²⁺ with a concentration of 200 μg L⁻¹, which is much lower than those in other works previously reported. Interferences on both the Cd separation and preconcentration, and Cd hydride generation (HG) were investigated; it showed that both the separation and preconcentration system, and the HG system had a strong anti-interference ability. The SPE column could be repeatedly used at least 400 times, a R.S.D. of 0.97% was obtained for 6 measurements of Cd with 0.2 μg L⁻¹ and a correlation coefficiency of 1.0000 was obtained for the measurement of a series of solutions with Cd concentrations from 0.1 to 2 μg L⁻¹. The method has a low detection limit of 10.8 ng L⁻¹ for a 25 mL solution and was successfully validated by using two tea standard reference materials (GBW08513 and GBW07605).     

The use of microemulsion for determination of sodium and potassium in biodiesel by flame atomic absorption spectrometry

A new method for F AAS determination of sodium and potassium in biodiesel using water-in-oil microemulsion as sample preparation is proposed. The method was investigated for biodiesel produced from different sources, as soybean, castor and sunflower oil and animal fat and was also applied for vegetable oils. The optimized condition for microemulsion formation was 57.6% (w/w) of n-pentanol, 20% (w/w) of biodiesel or vegetable oil, 14.4% (w/w) of Triton X-100 and 8% (w/w) of water (aqueous standard of KCl or NaCl in/or diluted HNO₃). The optimized instrumental parameters were: aspiration rate of 2 mL min⁻¹ and the flame composition of 0.131 of C₂H₂/air ratio. For comparison purpose, the determination of sodium and potassium were also carried out according to European norms (EN 14108 and EN 14109, respectively). These norms are applied for determination of sodium and potassium in fatty acid methylic ester samples and consist in the sample dilution using organic solvent and determination by F AAS. The stability of microemulsified aqueous standards and samples was investigated and it was found to be stable for at least 3 days while the organic standard diluted with xylene showed a decrease around of 15% in the analytical signal in 1 h. The limits of detection were 0.1 μg g⁻¹ and 0.06 μg g⁻¹ and the obtained characteristic concentrations were 25 μg L⁻¹ and 28 μg L⁻¹ for sodium and potassium, respectively. The proposed method presented two times better limits of detection and better precision (0.4–1.0%) when compared with the dilution technique (1.5–4.5%). The accuracy of the method was evaluated through recovery tests and comparison with the results obtained by dilution technique. The recoveries ranged from 95% to 115% for biodiesel and 90% to 115% for vegetable oil samples. Comparison between the results obtained for biodiesel by both methods showed no significant differences at the 95% confidence level according to a Student's t-test. This study shows that the proposed method based on microemulsion as sample preparation can be applied as an efficient alternative for sodium and potassium determination in biodiesel samples.     

Donnan dialysis preconcentration coupled with ion chromatography and electrocatalytic oxidation for the determination of cyanide

An electrocatalytic amperometric detector for the ion chromatographic determination of CN⁻ is described. A conducting composite that is based on a graphite-loaded sol–gel material comprises the working electrode. The composite is doped with a Ru^II metallodendrimer which is demonstrated to promote the electrochemical oxidation of CN⁻ at potentials positive of 0.5 V vs. Ag/AgCl. In 6 mM NaOH, 0.05 M NaCl flowed at 1.0 ml min⁻¹, a 5-point calibration curve with the following linear least squares parameters is obtained over the range, 1.0–30 M CN⁻: slope, 24.2±0.1 nA M⁻¹; intercept, −6±2 nA; and r, 0.9997. The detection limit, 0.7 μM CN⁻, compares favorably to that obtained by amperometry at a silver electrode, 0.5 μM CN⁻, under comparable experimental conditions. A 60-min preconcentration by Donnan dialysis increases the sensitivity by a factor of 23.6.     

Optimisation of ICPMS collision/reaction cell conditions for the simultaneous removal of argon based interferences of arsenic and selenium in water samples

The optimisation of ICPMS collision/reaction cell conditions for the simultaneous analysis of arsenic and selenium is described. A mixture of 3.8 mL min⁻¹ of H₂ and 0.5 mL min⁻¹ of He was found to be suitable for the removal of both ArAr⁺ and ArCl⁺ interferences. Detection limits down to 30 ng (element) L⁻¹ in total analysis, and between 81 and 230 ng (element) L⁻¹ in speciation analysis were achieved in chloride matrix (1 g L⁻¹ NaCl). After validation, the method was applied to commercially available mineral waters.     

Electrothermal atomic absorption spectrometric determination of lead in high-purity reagents with flow-injection on-line microcolumn preconcentration and separation using a macrocycle immobilized silica gel sorbent

A fully automated procedure for the determination of ng l⁻¹ amounts of lead has been developed using flow injection (FI) online column preconcentration coupled with electrothermal atomic absorption spectrometry (ETAAS). The proposed FI manifold and its operation make possible the introduction of the total eluate volume into the graphite atomizer, avoiding the necessity for optimization of subsampling the eluate. The interference of other heavy metal ions due to competition for active sites of the sorbent is overcome using a highly selective macrocycle immobilized on silica gel (Pb-02). Lead is adsorbed on a microcolumn (50 μl) packed with Pb-02, and after washing the column with dilute nitric acid, air is introduced to remove all solution from the column and connecting tubing. The sorbed analyte is then eluted quantitatively into the graphite tube atomizer, preheated to 100°C, with 36 μl of ETDA solution (0.035 mol l⁻¹, pH 10.5), propelled by air in order to minimize dispersion. The collection efficiency was 77% and with a sample loading flow rate of 3 ml min⁻¹ and a 60 s preconcentration time, the enhancement factor was 77 and the throughput was 17 samples per hour. The relative standard deviation (n = 10) at the 300 ng l⁻¹ level was 2.7%, and the detection limit (3σ) was 0.4 ng l⁻¹. No interference from heavy metals was observed, but ions of Ba²⁺, Sr²⁺ and K⁺ were found to interfere when the concentration ratios of interferent to lead exceeded values of 2000, 20 000 and 200 000, respectively. Quantitative recovery of lead was achieved from sodium, magnesium, aluminum, lanthanum and heavy metal salt solutions. The high selectivity and sensitivity, combined with extremely low blank values, make the proposed technique particularly attractive for the analysis of high-purity reagents, semiconductors and other high-purity materials. Results are presented for the determination of lead in some high-purity reagents.     

Simultaneous determination of three bufadienolides in rat plasma after intravenous administration of bufadienolides extract by ultra performance liquid chromatography electrospray ionization tandem mass spectrometry

A novel, rapid and specific ultra performance liquid chromatography electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) method has been developed for simultaneous determination and pharmacokinetic studies of three bufadienolides (bufalin, cinobufagin and resibufogenin) in rat plasma. The analytes, bufalin, cinobufagin, resibufogenin and the internal standard, diphenhydramine were extracted from rat plasma samples by a one-step liquid–liquid extraction and separated on an ACQUITY UPLC™ BEH C₁₈ column with gradient elution using a mobile phase composed of acetonitrile and water (containing 0.1% formic acid) at a flow rate of 0.20 mL min⁻¹. Detection was carried out on a triple-quadrupole tandem mass spectrometer in the multiple reaction monitoring (MRM) mode via an electrospray ionization (ESI) interface. The three bufadienolides could be simultaneously determined within 3.0 min. Linear calibration curves were obtained over the concentration ranges of 1.0–200 ng mL⁻¹ for all the analytes. The intra- and inter-day precisions (relative standard deviation (R.S.D.)) were less than 11.35 and 10.87%, respectively. The developed method was applied for the first time to the pharmacokinetic studies of bufadienolides in rats following a single intravenous administration of 2.10 mg kg⁻¹ bufadienolides.     

Pungency evaluation of onion cultivars from the Venezuelan West-Center region by flow injection analysis-UV-visible spectroscopy pyruvate determination

A flow injection analysis (FIA) method was developed for the determination of pyruvate in onion cultivars (Allium cepa L.) from the West-Center region of Venezuela. The reference Schwimmer and Weston (1961) (J. Agric. Food Chem. 9 (1961) 301) Batch method was modified and adapted to FIA conditions. The formation kinetic of the 2,4-dinitrophenylhydrazine (DNPH)–pyruvate complex was evaluated at room temperature and at 37 °C. It was demonstrated the suitability of the chromopher formation at room temperature. The optimal values for the FIA parameters were: sample injection volume 3 mL, flow rate 6 mL min⁻¹, reactor length 1.5 m, sodium hydroxide concentration 1.0 mol L⁻¹ and hydrochloric acid concentration 0.5 mol L⁻¹. The working calibration range was extended from 80 mg L⁻¹ (Batch method) to 700 mg L⁻¹ with the FIA set up. The sample dilution step is thus avoided, simplifying the whole analysis process. The pungency in representative samples of the cultivars Yellow granex 438, Ultra Hybrid and Red onion “Sangre de Toro” was evaluated by the flow injection analysis (FIA)–pyruvate method and the results were compared to the reference Batch pyruvate method and to the taste panel test. Non-significant differences were found at the 95% of confidence level between the FIA method and the Batch reference method. Correlation coefficient when comparing the FIA results to the taste panel test was r² = 0.8353. Significant differences (P < 0.05) were found in the pungency of the cultivars, the Ultra Hybrid having the highest pungency. The pungency order from minor to major was: Red onion, Texas Grano 438 and Ultra Hybrid.