Determination of Ge(IV) in rice in a mercury-coated glassy carbon electrode in the presence of catechol

Electrochemical adsorptive cathodic stripping voltammetry determination of Ge(IV) using the catechol complex on a mercury-coated (MC) electrode was prepared using a glassy carbon electrode (GCE), the peak potential of which was −0.5 V vs. Ag/AgCl on MCGCE. The various parameters of the catechol concentration, its pH, and others were optimized. The linear working ranges were obtained in the concentration of 2–700 μg L⁻¹ Ge(IV). The relative standard deviation at the Ge(IV) concentration of 50 μg L⁻¹ was 1.37% (n = 15) using the optimum condition, and the detection limit was found to be 0.6 μg L⁻¹ (8.26 × 10⁻⁹ M) (S/N = 3), with an adsorption time of 180 s. The Ge(IV) response was highly linear. This developed method was applied to Ge(IV) to determine the presence of rice grains.     

Effect of foliar application of selenium on its uptake and speciation in carrot

Carrot (Daucus carota) shoots were enriched by selenium using foliar application. Solutions of sodium selenite or sodium selenate at 10 and 100 μg Se ml⁻¹, were sprayed on the carrot leaves and the selenium content and uptake rate of selenium were estimated by ICP–MS analysis. Anion and cation exchange HPLC were tailored to and applied for the separation of selenium species in proteolytic extracts of the biological tissues using detection by ICP–MS or ESI–MS/MS. Foliar application of solutions of selenite or selenate at 100 μg Se ml⁻¹ resulted in a selenium concentration of up to 2 μg Se g⁻¹ (dry mass) in the carrot root whereas the selenium concentration in the controls was below the limit of detection at 0.045 μg Se g⁻¹ (dry mass). Selenate-enriched carrot leaves accumulated as much as 80 μg Se g⁻¹ (dry mass), while the selenite-enriched leaves contained approximately 50 μg Se g⁻¹ (dry mass). The speciation analyses showed that inorganic selenium was present in both roots and leaves. The predominant metabolised organic forms of selenium in the roots were selenomethionine and γ-glutamyl-selenomethyl-selenocysteine, regardless of which of the inorganic species were used for foliar application. Only selenomethionine was detected in the carrot leaves. The identity of selenomethionine contained in carrot roots and leaves was successfully confirmed by HPLC–ESI–MS/MS.     

Effect of modifiers for As,Cu and Pb determinations in sugar-cane spirits by GF AAS

Palladium plus magnesium nitrates with and without Ir, Ru and W were evaluated for the simultaneous determination of As, Cu and Pb in cachaça by graphite furnace atomic absorption spectrometry. For 20 μL of sample, 5 μL Pd(NO₃)₂ and 3 μL Mg(NO₃)₂ dispensed together onto the Ir-coated platform of the THGA, analytical curves in the 0–30.0 μg L⁻¹ As, 0–1.50 mg L⁻¹ Cu and 0–60.0 μg L⁻¹ Pb were built up and typical linear correlation coefficients were always better than 0.999. The limit of detection was 1.30 μg L⁻¹ As, 140 μg L⁻¹ Cu and 0.90 μg L⁻¹ Pb. As, Cu and Pb contents in 10 cachaça samples agreed with those obtained by ICP-MS. Recoveries of spiked samples varied from 96% to 106% (As), 97% to 112% (Cu) and 92% to 108% (Pb). The relative standard deviation (n = 12) was typically 2.7%, 3.3% and 1.9%.     

Chemiluminescence microflow injection analysis system on a chip for the determination of nitrite in food

A new microflow injection analysis (μFIA) system on a chip for the determination of nitrite is described. The chip is produced by using two transparent poly(methylmethacrylate) (PMMA) slices measured 50 × 40 × 5 mm, and the microchannels etched by CO₂ laser are 200 μm wide and 100 μm deep with the volume of reaction area about 1.8 μL. Nitrite is sensed by the chemiluminescence (CL) reaction of luminol with ferricyanide that is the product of the reaction of ferrocyanide with nitrite in acidic medium. The syringe pump with an accurate timer controls all reagents, including the sample. The linear range of the nitrite concentration is 8–100 μg L⁻¹ and the detection limit is 4 μg L⁻¹ (S/N = 3). The proposed method has good reproducibility with the relative standard deviation 4.1% for 50 μg L⁻¹ of nitrite (n = 9) and is very sensitive and simple. It has been successfully applied to the determination of nitrite in food.     

Synthesis and application of a new functionalized resin for use in an on-line,solid phase extraction system for the determination of trace elements in waters and reference cereal materials by flame atomic absorption spectrometry

The synthesis and characterization of the resin Amberlite XAD-4 functionalized with 2,6-pyridinedicarboxaldehyde and its application in an on-line system for the preconcentration of cadmium, cobalt, copper, lead and manganese prior to determination using flame atomic absorption spectrometry (FAAS) is proposed. Metal ions retained on the modified resin were eluted using 1.0 mol L⁻¹ HNO₃ solution and aspirated directly to the nebulizer–burner system of a FAAS instrument using a flow injection system. Detection limits (3σ) were determined to be 0.13 μg L⁻¹ for Cd, 0.29 μg L⁻¹ for Cu, 0.23 μg L⁻¹ for Mn, 0.58 μg L⁻¹ for Co and 2.19 μg L⁻¹ for Pb using a 10 mL of water sample loading volume. The limits of detection would be 100 times higher with units of μg kg⁻¹ for the solid samples in which their dilution ratios as (volume/weight) were 100. Enrichment factors ranged from 23.6 to 28.9 (for Co and Mn, respectively). The proposed method was successfully applied to determination of the analytes in natural water samples and certified reference materials.     

Kinetic-spectrophotometry method for determination of ultra trace amounts of aluminum in food samples

A simple and sensitive kinetic-spectrophotometry method is developed for the determination of trace amounts of aluminum in food samples based on its catalytic effect on the oxidation of Nile Blue A by potassium bromate in sulfuric acid medium. The absorbance is measured at 595.5 nm with the fixed-time method. The optimization of the operating conditions regarding concentrations of the reagents, temperature and interferences are also investigated. The calibration curve is linear over the concentration range 0.07–0.9 μg ml⁻¹ of aluminum with good precision and accuracy and the detection limit was down to 0.034 μg ml⁻¹. The relative standard deviation for a standard solution of 0.4 μg ml⁻¹ of aluminum is 1.73% (n = 10). The proposed method proved highly sensitive, selective and relatively rapid for the assay of aluminum at ultra trace level without any pre-concentration and separation step. The method was applied to the determination of aluminum in food samples (rice, tea and potato). The analytical results of the real samples were in good agreement with the standard method.     

Determination of cyclamate in artificial sweeteners and beverages using headspace single-drop microextraction and gas chromatography flame-ionisation detection

A new method for determination of cyclamate was developed using headspace single-drop microextraction (HS-SDME) and gas chromatography (GC). The method is based on the reaction of cyclamate and nitrite in the acidic media and microextraction of cyclohexene formed for subsequent determination with GC. Conditions for both derivatisation and HS-SDME have been optimised. The calibration curve for cyclamate determination showed good linearity in the range of 30–1000 μmol L⁻¹ (R² = 0.9992) and the limit of detection (S/N = 3) was estimated to be 5 μmol L⁻¹. The repeatability and reproducibility for a 200 μmol L⁻¹ of cyclamate were 4% and 4.8% (N = 5), respectively. The purposed method was successfully applied for determination of cyclamate in beverages and sweetener tablets. The average recovery of spiked samples was 97%. The results demonstrated that the developed method is simple, rapid, inexpensive, accurate and remarkably free from interference effects.     

Validation of a HPLC method for simultaneous determination of main organic acids in fruits and juices

A liquid chromatographic method for fast and simultaneous determination of tartaric, malic, ascorbic and citric acids was validated for further application to fruits and juices. Moreover, the organic acids content of commercial samples of fruits and juices were evaluated, as well as the ascorbic acid stability during the storage. Determination of organic acids was carried out using a liquid chromatograph coupled to a diode array detector, with reversed phase (C₁₈ column) and isocratic elution with 0.01 mol L⁻¹ KH₂PO₄ (pH = 2.60) mobile phase. The validation parameters showed efficiency, adequate linearity, relative standard deviation values between 0.4% and 2.3% (n = 10) for repeatability and from 1.2% to 5.0% (n = 18) for reproducibility, limits of detection (LD) were between 0.03 and 3.31 μg mL⁻¹ and quantification (LQ) were between 0.10 and 11.03 μg mL⁻¹, recovery rates were between 82% and 110%, for two levels. In addition, the method is fast (10 min) and generates low and non-toxic residues. The values found for vitamin C were about 10 times above the values declared at the package. Ready to drink juices have a composition similar to the fruit, concerning to organic acids, except for the powder juice, in which only ascorbic and citric acids were found, for all tastes. After opening the package, a decrease of 14.0% and 27.0% in ascorbic acid content was observed for orange powder and ready to drink juices, respectively.     

Molecularly imprinted solid phase extraction coupled to high-performance liquid chromatography for determination of trace dichlorvos residues in vegetables

In this paper, we prepared a highly selective imprinted polymer by a room temperature ionic liquid-mediated bulk polymerization technique, using dichlorvos as the template, methacrylic acid as the functional monomers, and trimethylolpropane trimethacrylate as the cross-linker. This functionalized material was characterized by FT-IR, static and kinetic adsorption experiments, and the results showed that this imprinted sorbent exhibited good recognition and selective ability, and offered fast kinetics for the adsorption and desorption of dichlorvos. Using the prepared material as a solid phase extraction sorbent, a novel sample pre-treatment technique that can be coupled to high-performance liquid chromatography (HPLC) had been developed for determination of trace dichlorvos residues in foods. Under the selected experimental condition, the detection limit (S/N = 3) of dichlorvos was 94.8 ng L⁻¹, and the peak area precision (RSD) for five replicate detections of 10 μg L⁻¹ dichlorvos was 4.41%. The blank samples of cucumber and lettuce spiked with dichlorvos at 0.005 and 0.02 μg g⁻¹ levels were determined with recoveries ranging from 82.1% to 94.0%.     

Tungsten permanent chemical modifier with co-injection of Pd(NO3)2 + Mg(NO3)2 for direct determination of Pb in vinegar by graphite furnace atomic absorption spectrometry

A tungsten carbide coating on the integrated platform of a transversely heated graphite atomizer (THGA^®) used together with Pd(NO₃)₂ + Mg(NO₃)₂ as modifier is proposed for the direct determination of lead in vinegar by graphite furnace atomic absorption spectrometry. The optimized heating program (temperature, ramp time, hold time) of atomizer involved drying stage (110 °C, 5 s, 30 s; 130 °C, 5 s, 30 s), pyrolysis stage (1000 °C, 15 s, 30 s), atomization stage (1800 °C, 0 s, 5 s) and clean-out stage (2450 °C, 1 s, 3 s). For 10 μL of vinegar delivered into the atomizer and calibration using working standard solutions (2.5–20.0 μg L⁻¹ Pb) in 0.2% (v/v) HNO₃, analytical curve with good linear correlation (r = 0.9992) was established. The characteristic mass was 40 pg Pb and the lifetime of the tube was around 730 firings. The limit of detection (LOD) was 0.4 μg L⁻¹ and the relative standard deviations (n = 12) were typically <8% for a sample containing 25 μg L⁻¹ Pb. Accuracy of the proposed method was checked after direct analysis of 23 vinegar samples. A paired t-test showed that results were in agreement at 95% confidence level with those obtained for acid-digested vinegar samples. The Pb levels varied from 2.8 to 32.4 μg L⁻¹. Accuracy was also checked by means of addition/recovery tests and recovered values varied from 90% to 110%. Additionally, two certified reference materials were analyzed and results were in agreement with certified values at a 95% confidence level.     

Pharmacokinetics and residues of tetracycline in crucian carp muscle using capillary electrophoresis on-line coupled with electrochemiluminescence detection

A novel and sensitive determination for tetracycline (TC) in crucian carp muscle was developed by using capillary electrophoresis coupled with electrochemiluminescence (ECL) detection. The conditions affected separation and detection were examined in detail. The linearity range of TC concentration was from 0.005 to 10 μg mL⁻¹ with a correlation coefficient of 0.9992. The detection limit of TC (S/N = 3) was 1.8 ng mL⁻¹. The relative standard deviations of the ECL intensity and the migration time for eleven consecutive injections of 1.0 μg mL⁻¹ TC were 1.6% and 0.8%, respectively. The recovery of TC was 97.8% (n = 5). After administration of 75 mg kg⁻¹ TC, the maximum concentration and peak time of TC in crucian carp muscle were 7.33 mg kg⁻¹ and 8 h, respectively. After administration of TC, TC concentration demonstrated trivial variation in the period from 48 to 96 h.     

The reduction of Cu(II)/neocuproine complexes by some polyphenols: Total polyphenols determination in wine samples

A new method is presented for spectrophotometric determination of total polyphenols content in wine. The procedure is a modified CUPRAC method based on the reduction of Cu(II), in hydroethanolic medium (pH 7.0) in the presence of neocuproine (2,9-dimethyl-1,10-phenanthroline), by polyphenols, yielding a Cu(I) complexes with maximum absorption peak at 450 nm. The absorbance values are linear (r = 0.998, n = 6) with tannic acid concentrations from 0.4 to 3.6 μmol L⁻¹. The limit of detection obtained was 0.41 μmol L⁻¹ and relative standard deviation 1.2% (1 μmol L⁻¹; n = 8). Recoveries between 80% and 110% (mean value of 95%) were calculated for total polyphenols determination in 14 commercials and 2 synthetic wine samples (with and without sulphite). The proposed procedure is about 1.5 more sensitive than the official Folin–Ciocalteu method. The sensitivities of both methods were compared by the analytical responses of several polyphenols tested in each method.     

Determination of patulin in fruit juices using HPLC-DAD and GC-MSD techniques

A high performance liquid chromatography with a diode-array detector (HPLC-DAD) and a gas chromatography with a mass spectrometer (GC-MSD) are described for the determination of patulin (PAT) in apple juice. The limits of detection (DL) and quantification (QL) for the HPLC-DAD and GC-MSD method were found to be (DL = 0.23 μg kg⁻¹ QL = 1.2 μg kg⁻¹) and (DL = 5.8 μg kg⁻¹ and QL = 13.8 μg kg⁻¹), respectively. The recovery factors for HPLC-DAD and GC-MSD were found to be 99.5% (RSD% = 0.73) and 41% (RSD% = 10.03), respectively. The HPLC-DAD method was used to determine the occurrence of PAT in 90 samples of fruit juices.     

Pico molar assay of riboflavin in human urine using voltammetry

Using a new type of DNA and carbon nano tube (CNT) mixed paste electrode using cyclic and square wave anodic stripping voltammetric (SWASV) methods, this study presents an assay of riboflavin (RF) under optimum conditions. Results of the experiment yielded a low working concentration range of nanograms with 1–10 and 10–170 ng L⁻¹ and 5–105 μg L⁻¹, at an accumulation time of 80 s in a 0.1 M H₃PO₄ electrolyte solution. A relative standard deviation of 30 μg L⁻¹ was observed at an accuracy level of 0.1164% (n = 15) under optimum conditions. The detection limit (S/N) was pegged at 0.2 ng L⁻¹ (5.31 × 10⁻¹³ mol L⁻¹ RF). The proposed method was successfully applied to an actual human urine and drug sample, and can be applied to assays of other biological samples.     

Comparison of positive and negative ion detection of tea catechins using tandem mass spectrometry and ultra high performance liquid chromatography

Tea catechins are an important group of natural compounds associated with health promoting effects and desired commodities for the growing market of dietary supplements and functional foods. Consequently these compounds attract more interest of research groups worldwide. A reliable quantitative analysis of tea catechins is essential for human intervention studies, manufacturers of dietary supplements and quality control by authorities. UHPLC–ESI-MS/MS analytical method was chosen due to rapid runtime, high sensitivity and selectivity. The chromatographic separation of eight tea catechins was achieved within 2.5 min on C₁₈ BEH analytical column (100 mm × 2.1 mm i.d.; 1.7 μm), whilst the gradient elution mode was employed using water:methanol mobile phase with addition of volatile organic acid. The concentration of organic acids in the mobile phase was optimised within the range of 0.01–0.1% (v/v). High sensitivities were achieved in positive (10.2-16.8 fmol/inj.) and negative ion detection mode (102.1-168.1 fmol/inj.), through accurate and complex tuning of MS parameters. The UHPLC-ESI-MS/MS method was validated in terms of linearity (>0.9997; >0.9990), range (0.02–2.40 mg L⁻¹; 0.15-24.00 mg L⁻¹), LOD (3.0–4.8 μg L⁻¹; 30.1–48.0 μg L⁻¹), LOQ (9.9–15.8 μg L⁻¹; 150.5-240.0 μg L⁻¹), intra-day precision (4.4-7.1% RSD; 3.3-5.1% RSD), accuracy (94.06-113.7%; 89.5-108.4%), retention time repeatability (0.0-0.5% RSD; 0.0-0.6% RSD), and peak area repeatability (1.2-4.0% RSD; 2.4-3.5% RSD) for positive and negative ion detection modes, respectively. The statistical comparison of the quantitative results obtained in positive and negative ion detection mode was performed.     

Determination of pyrethroids in porcine tissues by matrix solid-phase dispersion extraction and high-performance liquid chromatography

An effective matrix solid-phase dispersion (MSPD) extraction for determination of two pyrethroids (cypermethrin and deltamethrin) in porcine tissues (liver, muscle, heart and kidney) is described. A neutral alumina-based MPSD column was used for extraction of analytes. The high-performance liquid chromatography and ultraviolet detector was applied using a reverse-phase C₁₈ column and acetonitrile-water (85:15, v/v) was used as mobile phase. The good linear fit curve ranging from 0.05 to 50 μg mL⁻¹ for cypermethrin (CM) and deltamethrin (DM) was obtained with a regression coefficient (r) of 0.999. Recoveries at 0.2 and 0.5 μg g⁻¹ levels were between 83.5% and 109%. The limits of detection and quantification were: 0.01 and 0.026 μg g⁻¹ for CM, 0.017 and 0.056 μg g⁻¹ for DM, respectively. The proposed method was successfully applied to the determination of the pyrethroids in porcine tissues.     

Application of capillary electrophoresis to determine metal cations,anions, organic acids,and carbohydrates in some Pinot Noir red wines

Capillary electrophoresis was used for determination of inorganic alkali and alkali earth metal cations, inorganic anions, anions of organic acids, and carbohydrates in six Pinot Noir grape red wines. Spectrum analysis was applied to evaluate the possible chemical differences between the wines from different geographic origin. In addition, sensory evaluation was used to reveal differences between wines from the end user point of view. Both chemical analyses and the sensory evaluation revealed clear differences among the wine samples. The total concentrations of inorganic ions, carboxylate anions, and carbohydrates varied 1.9–3.1 g L⁻¹, 4.3–5.5 g L⁻¹, and 1.5–7.5 g L⁻¹, respectively. Although the grape was same in all samples, the results show considerable variations in chemical composition, the red wine from Tasmanian being the most different among samples.     

Determination of ultratrace levels of selenium in fruit and vegetable samples grown and consumed in Portugal

The selenium content in fruit and vegetable samples from two regions in Portugal were analysed using hydride generation atomic fluorescence spectrometry (HG-AFS) and radiochemical nuclear activation analysis (RNAA) – two analytical methods with very low limits of detection. The lower detection limits of HG-AFS, 3 μg kg⁻¹ and 8 μg kg⁻¹ (according to conditions used for digestion), and for RNAA, 10 μg kg⁻¹, meant that it was possible to determine selenium in samples previously analysed using the replicate sample instrumental nuclear activation analysis (RSINAA) with a higher detection limit associated.     

Development of polyclonal antibody-based indirect competitive enzyme-linked immunosorbent assay for sodium saccharin residue in food samples

A sensitive and specific polyclonal antibody (PcAb)-based indirect competitive enzyme-linked immunosorbent assay (icELISA) for sodium saccharin is described. 6-Amino saccharin was coupled to carrier protein for artificial antigen by diazotisation. New Zealand white rabbits were immunised to obtain anti-sodium saccharin PcAb and then icELISA was developed. The assay showed high sensitivity and specificity to sodium saccharin, with the 50% inhibition value (IC₅₀) of 0.243 μg mL⁻¹, workable range (IC₃₀–IC₇₀) of 0.050–12.8 μg mL⁻¹ and limit of detection (LOD, IC₂₀) of 0.021 μg mL⁻¹. The average recoveries of sodium saccharin in spiked food samples were estimated ranging from 70.7% to 98.8%. A statistically significant correlation of results was obtained between this new ELISA and previously established HPLC approaches with the food-relevant sodium saccharin concentration range 0–320 μg mL⁻¹ (R² = 0.9887–0.9975). These results indicated that the established ELISA was a potential and useful analytical tool for rapid determination of sodium saccharin residue in food samples.     

Occurrence of patulin and its dietary intake through apple juice consumption by the Spanish population

A survey was conducted to determine levels and dietary intake of Patulin (PAT) from apple juices consumed in Spain. One hundred samples of apple juice were bought from distinct supermarkets. PAT was extracted by a liquid–liquid extraction technique and analysed with a micellar electrokinetic chromatography (MEKC) method. 66% of the samples contained PAT over the limit of detection of the method (0.7 μg L⁻¹). The PAT apple juice mean and median levels obtained were 19.4 and 4.8 μg L⁻¹, respectively, in a range between 0.7 and 118.7 μg L⁻¹. In 11% of the samples, PAT contamination exceeded the maximum permitted level of 50 μg L⁻¹ established by the EU regulation. In Spain, no significant variations were observed with respect to data published 15 years ago.