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.     

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.     

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.     

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%.     

Speciation of organic and inorganic selenium in selenium-enriched rice by graphite furnace atomic absorption spectrometry after cloud point extraction

A new method was developed for the determination of organic and inorganic selenium in selenium-enriched rice by graphite furnace atomic absorption spectrometry detection after cloud point extraction. Effective separation of organic and inorganic selenium in selenium-enriched rice was achieved by sequentially extracting with water and cyclohexane. Under the optimised conditions, the limit of detection (LOD) was 0.08 μg L⁻¹, the relative standard deviation (RSD) was 2.1% (c = 10.0 μg L⁻¹, n = 11), and the enrichment factor for selenium was 82. Recoveries of inorganic selenium in the selenium-enriched rice samples were between 90.3% and 106.0%. The proposed method was successfully applied for the determination of organic and inorganic selenium as well as total selenium in selenium-enriched rice.     

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.     

Determination of nitrite in food samples by anodic voltammetry using a modified electrode

A glassy carbon (GC) electrode modified with alternated layers of iron(III) tetra-(N-methyl-4-pyridyl)-porphyrin (FeT4MPyP) and copper tetrasulfonated phthalocyanine (CuTSPc) was employed for nitrite determination by differential pulse voltammetry (DPV). This modified electrode showed excellent catalytic activity for the nitrite oxidation. After optimizing the operational conditions, a linear response range from 0.5 to 7.5 μmol l⁻¹ with a low detection limit of 0.1 μmol l⁻¹ was obtained. The proposed sensor was stable with a sensitivity of 20.0 μA, 1 μmol⁻¹ and good repeatability, evaluated in terms of relative standard deviation (R.S.D. = 1.3%) for n = 10. Possible interferences from several common ions were evaluated. This sensor was applied for the voltammetric determination of nitrite in some food samples. The results were consistent with those obtained with the standard spectrophotometric procedure.     

Microfluidic chip based chemiluminescence detection of L-phenylalanine in pharmaceutical and soft drinks

A sensitive chemiluminescence (CL) method on chip coupled with microfluidic system has been reported for the determination of L-phenylalanine (L-PA). A microfluidic chip device with the detection chamber capable of fast sensing light emitted from the luminol and hydrogen peroxide CL reaction catalyzed by copper sulphate was fabricated for the determination of L-PA. The microfluidic chip was fabricated by a soft-lithographic procedure using polydimethyl siloxane (PDMS). The fabricated PDMS microfluidic chip had four inlet microchannels for introducing the sample, chemiluminescent reagent, Cu(II), and oxidant, and a 500 μm wide, 250 μm deep, and 82 mm long microchannel. The detection was based on the enhancement effect of L-PA on the CL signals of luminol–H₂O₂–Cu²⁺ system in an alkaline medium. The CL intensity of the system was enhanced linearly with the concentration of L-PA in the range of 1.5 × 10⁻⁹–1.2 × 10⁻⁷ mol L⁻¹. The limit of detection was found to be 2.4 × 10⁻¹⁰ mol L⁻¹ with the relative standard deviation of 1.8%. The presented method offers a simple, rapid and easy to handle analytical technique in terms of sensitivity, dynamic range and low detection limit for the determination of L-PA in diet soft drinks and pharmaceutical injection samples.     

Determination of diquat and paraquat in olive oil by ion-pair liquid chromatography–electrospray ionization mass spectrometry (MRM)

For the first time a method for determination of herbicides diquat (DQ) and paraquat (PQ) in olive oil was developed utilising liquid chromatography–electrospray ionization mass spectrometry (MRM). n-Hexane/10 mM HFBA aqueous solution partitioning was used as the extraction method. Separation was carried out in an Xterra C8 column (100 × 21 mm, 3 μm), using the gradient mode. Solvent A was a HFBA aqueous solution (5 mM, pH 2) and solvent B acetonitrile/methanol 75/25 (v/v). Peaks used for quantification were m/z = 157 (diquat) and m/z = 158 (paraquat). Detection limit found for both diquat and paraquat was 4 μg kg⁻¹. The method can also be applied for determination of chlormequat (CQ, quantification peak m/z = 58), the detection limit being 0.3 μg kg⁻¹. Such limits are clearly lower than the MCLs commonly applied to olive oil as reference criteria (5 times MCLs in olives). Good reproducibilities (day to day and run to run) were obtained.     

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.     

Spectrophotometric determination of iodate in iodised salt by flow injection analysis

A simple and sensitive flow injection (FI) method for the determination of iodate is proposed. The method is based on the reaction of iodate with hydroxylamine in acidic solution. Sulfanilamide is diazotised by the nascent nitrite and the diazonium ion produced is then coupled with N-(1-naphthyl)ethyenediamine in hydrochloric acid medium to form an azo dye which is measured spectrophotometrically. The calibration graph for iodate is linear in the range of 0.1–30 mg L⁻¹ with a correlation coefficient of 0.9992. The limit of detection and relative standard deviation are 0.02 mg L⁻¹ and 1.2% (5 mg L⁻¹, n = 8). The method has been applied to the determination of iodate in table salts and accuracy was assessed through recovery experiments and independent analysis by a conventional titrimetric method.     

Immobilization of pepsin on chitosan beads

In this study, chitosan beads were prepared by using a cross-linking agent and the resulting beads were employed in immobilization process. Studies on free and immobilized pepsin systems for determination of optimum temperature, optimum pH, thermal stability, pH stability, operational stability, storage stability and kinetic parameters were carried out. The optimum temperature interval for free pepsin and immobilized pepsin were 30–40 and 40–50 °C, respectively. Free and immobilized pepsin showed higher activity at pH 2.0–4.0. Apparent K_m = 12.0 g L⁻¹ haemoglobin (1.56 mM tyrosine) and V_max = 5220 μmol (mg protein min)⁻¹ values were obtained for free pepsin, while apparent K_m = 20.0 g L⁻¹ haemoglobin (2.16 mM tyrosine) and V_max = 2780 μmol (mg protein min)⁻¹ values were obtained for immobilized pepsin. Thermal stability and storage stability of immobilized pepsin were higher than that of free pepsin. Milk clotting activity was used for evaluation of the applicability of pepsin immobilization to industrial process. Optimum milk clotting temperature was found as 40 °C for free pepsin and 50 °C for immobilized pepsin.     

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.     

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%.     

Selective determination of copper and iron in various food samples by the solid phase extraction

The solid phase extraction method developed using N-benzoyl-N-phenylhydroxylamine as a chelating reagent and Amberlite XAD-1180 as an adsorbent was used for the determination of Cu(II) and Fe(III) in various food samples by flame atomic absorption spectrometry. The samples were digested by using nitric acid and hydrogen peroxide. The Cu concentrations ranged from 1.01 to 5.81 μg g⁻¹ in cereals, from 0.40 to 9.67 μg g⁻¹ in vegetable and fruits and from 0.37 to 0.70 μg g⁻¹ in infusions while the Fe concentrations ranged from 7.48 to 34.3 μg g⁻¹ in cereals, from 5.74 to 260 μg g⁻¹ in vegetable and fruits, from 1.63 to 5.12 μg g⁻¹ in infusions and from 0.24 to 1.56 mg L⁻¹ in beverage samples. The Cu and Fe concentrations found were compared with the results obtained from the other food studies in the world.     

Comparison of sterol composition between Tuber fermentation mycelia and natural fruiting bodies

Truffle, belonging to Tuber genera, is a nutritious and sterol-rich edible fungus, and sterol is a potential health beneficial compound. A comparison of Tuber sterol composition indicates that the total sterol contents in the fermentation mycelia (i.e., 10.5 mg g⁻¹) (n = 3) were approximately 3.2-5.6 times higher than that of the fruiting bodies (p < 0.05) with the addition of soybean flour into the basal fermentation media. Moreover, the phytosterol profile of fermentation mycelia could be significantly improved by adding soybean flour into the fermentation media. After the addition of soybean flour, stigmasterol and β-sitosterol appeared in the fermentation mycelia and the contents of total phytosterols (2279 μg g⁻¹) (n = 3), brassicasterol (943 μg g⁻¹) (n = 3), and campesterol (418 μg g⁻¹) (n = 3) were all increased significantly (p < 0.05). Moreover, the total contents of sterols and phytosterols in the fermentation mycelia cultured in the soybean media were much higher than those in the fruiting bodies (i.e., 1883-3240 and 479-1832 μg g⁻¹, respectively) (n = 3, p < 0.05). This work confirms the potentiality of Tuber fermentation mycelia as the alternative resource for its fruiting bodies from the viewpoint of sterols production.     

Utility of solid phase spectrophotometry for the modified determination of trace amounts of cadmium in food samples

A modified selective, highly sensitive and accurate procedure for the determination of trace amounts of cadmium which reacts with 1-(2-benzothiazolylazo)-2-hydroxy-3-naphthoic acid (BTAHNA) to give a deep violet complex with high molar absorptivity (7.05 × 10⁶ L mol⁻¹ cm⁻¹, 3.92 × 10⁷ L mol⁻¹ cm⁻¹, 1.78 × 10⁸ L mol⁻¹ cm⁻¹, and 4.10 × 10⁸ L mol⁻¹ cm⁻¹), fixed on a Dowex 1-X8 type anion-exchange resin for 10 mL, 100 mL, 500 mL, and 1000 mL, respectively. Calibration is linear over the range 0.2-3.5 μg L⁻¹ with RSD of ?1.14% (n = 10). The detection and quantification limits were calculated. Increasing the sample volume can enhance the sensitivity. The method has been successfully applied for the determination of Cd(II) in food samples, water samples and some salts samples without interfering effect of various cations and anions.     

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.     

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.