An improved FIA biosensor for the determination of aspartame in dietary food products

A flow injection analysis (FIA) biosensor system was developed for the determination of the artificial sweetener aspartame (l-aspartyl-l-phenylalanine methyl ester). The system consisted of an enzyme column of pronase immobilized on activated arylamine glass beads and al-amino acid oxidase electrode connected in series. The dipeptide bond of aspartame was cleaved by immobilized pronase to release phenylalanine, which was in turn monitored by the enzyme electrode that usedl-amino acid oxidase, immobilized on a preactivated nylon membrane in combination with an amperometric electrode (platinum vs silver/silver chloride, 700 mV). The response of the FIA biosensor was linear up to 1 mM aspartame with a lower detection limit of 25 μM and had good reproducibility (rsd 0.3%). The FIA biosensor was stable for at least 30 h of continuous use atT _r .Each assay takes 4 min giving a sample throughput of 15 h^?1 When applied to aspartame in dietary food products the results obtained agreed well with those reported by the product manufacturers.     

Disposable amperometric biosensor for the determination of tyramine using plasma amino oxidase

We have developed screen–printed carbon electrodes for the determination of tyramine (Tyr) via plasma amine oxidase. The enzyme was immobilized on the carbon working electrode by cross–linking it with bovine serum albumin using glutaraldehyde. The employment of the mediator hydroxymethylferrocene lowers the working potential to +260 mV (vs. a screen–printed Ag/AgCl reference electrode). The effects of pH, potential and mediator concentration were optimized and resulted in reproducibility and repeatability values of 8.6 % and 8.7 %, respectively. Response is linear in the range from 2 to 164 μM, and the limit of detection is 2.0?±?0.18 μM. The effects of potentially interfering biogenic amines such as putrescine, cadaverine, histamine, spermine, spermidine and tryptamine were also evaluated. The biosensor was successfully applied to the determination of Tyr in cheese.

Microfluidic based impedance biosensor for pathogens detection in food products

A MEMS‐based impedance biosensor was designed, fabricated, and tested to effectively detect the presence of bacterial cells including E. coli O157:H7 and Salmonella typhimurium in raw chicken products using detection region made of multiple interdigitated electrode arrays. A positive dielectrophoresis based focusing electrode was used in order to focus and concentrate the bacterial cells at the centerline of the fluidic microchannel and direct them toward the detection microchannel. The biosensor was fabricated using surface micromachining technology on a glass substrate. The results demonstrate that the device can detect Salmonella with concentrations as low as 10 cells/mL in less than 1 h. The device sensitivity was improved by the addition of the focusing electrodes, which increased the signal response by a factor between 6 and 18 times higher than without the use of the focusing electrodes. The biosensor is selective and can detect other types of pathogen by changing the type of the antibody immobilized on the detection electrodes. The device was able to differentiate live from dead bacteria.     

Simultaneous voltammetric determination of vanillin and guaiacol in food products on defect free graphene nanoflakes modified glassy carbon electrode

Microchimica Acta - Simple and robustic mediator free graphene nanoflake modified glassy carbon electrode (GNF/GCE) was used for the simultaneous determination of vanillin (VAN) and...     

Differential pulse voltammetric simultaneous determination of noradrenalin and acetaminophen using a hematoxylin biosensor

A highly efficient noradrenalin (NA) biosensor was fabricated on the basis of hematoxylin electrodeposited on a glassy carbon electrode, GCE. The cyclic voltammetric responses of the hematoxylin biosensor at various scan rates, which were obtained in a 0.25 mmol L⁻¹ NA solution, showed the characteristic shape typical of an EC_cat process. The kinetic parameters such as electron transfer coefficient, α, the catalytic electron transfer rate constant, k′, and the standard catalytic electron transfer rate constant, k⁰, for oxidation of NA at the hematoxylin biosensor surface were estimated using cyclic and RDE voltammetry. The peaks of differential pulse voltammetric (DPV) for NA and acetaminophen (AC) oxidation at the hematoxylin biosensor surface were clearly separated from each other when they co-exited in the physiological pH (pH 7.0). It was, therefore, possible to simultaneously determine NA and AC in the samples at a hematoxylin biosensor. Linear calibration curves were obtained for 5.0 × 10⁻¹ to 65.40 μmol L⁻¹ and 65.40-274.20 μmol L⁻¹ of NA, and for 12.00-59.10 μmol L⁻¹ and 59.10-261.70 μmol L⁻¹ of AC. The sensitivities of the biosensor to NA in the absence and presence of AC were found virtually the same, which indicates the fact that the electrocatalytic oxidation processes of NA are independent of AC and, therefore, simultaneous or independent measurements of the two analytes (NA and AC) are possible without any interference. The results of 16 successive measurements show an average voltammetric peak current of 1.13 ± 0.03 μA for an electrolyte solution containing 5.00 μmol L⁻¹ NA. The hematoxylin biosensor has been satisfactorily used for the determination of NA and AC in pharmaceutical formulations. The results obtained, using the biosensor, are in very good agreement with those declared in the label of pharmaceutical inhalation products.     

Chromatographic methods for the determination of mycotoxins in food products

Chromatographic methods for the determination of mycotoxins from different classes in food products of plant and animal origins are surveyed. The procedures of sample preparation and extract purification and the use of various chromatographic analysis techniques are considered.     

A novel sensitive electrochemical DNA biosensor for assaying of anticancer drug leuprolide and its adsorptive stripping voltammetric determination

The anticancer drug, leuprolide (LPR) bound to double-stranded fish sperm DNA (dsDNA) which was immobilized onto the surface of an anodically activated pencil graphite electrode (PGE), was employed for designing a sensitive biosensor. The interaction of leuprolide (LPR) with double-stranded DNA (dsDNA) immobilized onto pencil graphite electrode (PGE) have been studied by electrochemical methods. The mechanism of the interaction was investigated and confirmed by differential pulse voltammetry using two different interaction methods; at the PGE surface and in the solution phase. The decrease in the guanine oxidation peak current was used as an indicator for the interaction in acetate buffer at pH 4.80. The response was optimized with respect to accumulation time, potential, drug concentration, and reproducibility for both interaction methods. The linear response was obtained in the range of 0.20-6.00 ppm LPR concentration with a detection limit of 0.06 ppm on DNA modified PGE and between 0.20 and 1.00 ppm concentration range with detection limit of 0.04 ppm for interaction in solution phase method. LPR showed an irreversible oxidation behavior at all investigated pH values on a bare PGE. Differential pulse adsorptive stripping (AdSDPV) voltammetric method was developed for the determination of LPR. Under these conditions, the current showed a linear dependence with concentration within a range of 0.005-0.20 ppm with a detection limit of 0.0014 ppm. Each determination method was fully validated and applied for the analysis of LPR in its pharmaceutical dosage form.     

Gas-chromatographic determination of carbon-containing impurities in high-purity sulfur

A gas-chromatographic procedure was developed for the determination of carbon-containing impurities in sulfur with a detection limit of 6 x 10^-6%. Carbon-containing substances and elemental carbon can be effectively separated from sulfur samples as CO₂ and COS.     

Osteryoung square wave voltammetric determination of lactose in food samples by a derivative procedure

A method for determination of lactose in food samples by Osteryoung square wave voltammetry （OSWV） was developed. It was based on the nucleophilic addition reaction between lactose and aqua ammonia. The carbonyl group of lactose can be changed into imido group, and this increases the electrochemical activity in reduction and the sensitivity. The optimal condition for the nucleophilic addition reaction was investigated and it was found that in NH4C1-NH3 buffer of pH 10.1, the linear range between the peak current and the concentration of lactose was 0.6-8.4 mg L-l, and the detection limits was 0.44 mg L- 1. The proposed method was applied to the ＇determination of lactose in food samples and satisfactory results were obtained.     

A square-wave adsorptive stripping voltammetric method for the determination of Amaranth, a food additive dye

Square-wave adsorptive stripping voltammetric (AdSV) determinations of trace concentrations of the azo coloring agent Amaranth are described. The analytical methodology used was based on the adsorptive preconcentration of the dye on the hanging mercury drop electrode, followed by initiation of a negative sweep. In a pH 10 carbonate supporting electrolyte, Amaranth gave a well-defined and sensitive AdSV peak at -518 mV. The electroanalytical determination of this azo dye was found to be optimal in carbonate buffer (pH 10) under the following experimental conditions: accumulation time, 120 s; accumulation potential, 0.0 V; scan rate, 600 mV/s; pulse amplitude, 90 mV; and frequency, 50 Hz. Under these optimized conditions the AdSV peak current was proportional over the concentration range 1 x 10(-8)-1.1 x 10(-7) mol/L (r = 0.999) with a detection limit of 1.7 x 10(-9) mol/L (1.03 ppb). This analytical approach possessed enhanced sensitivity, compared with conventional liquid chromatography or spectrophotometry and it was simple and fast. The precision of the method, expressed as the relative standard deviation, was 0.23%, whereas the accuracy, expressed as the mean recovery, was 104%. Possible interferences by several substances usually present as food additive azo dyes (E110, E102), gelatin, natural and artificial sweeteners, preservatives, and antioxidants were also investigated. The developed electroanalyticals method was applied to the determination of Amaranth in soft drink samples, and the results were compared with those obtained by a reference spectrophotometric method. Statistical analysis (paired t-test) of these data showed that the results of the 2 methods compared favorably.     

Inhibition biosensor for determination of nicotine

An amperometric nicotine inhibition biosensor has been substantially simplified and used for determination of nicotine in tobacco sample. Besides the use of single enzyme choline oxidase to replace bienzyme, the use of 1,4-benzoquinone as an electron mediator makes it possible to avoid the use of oxygen or hydrogen peroxide sensor as the internal transducer. Choline oxidase was immobilized on the carbon paste electrode through cross-linking with bovine serum albumin (BSA) by glutaraldehyde. In the presence of choline oxidase and its endogenous cofactor flavin-ademine dinneleotide (FAD), choline was oxidized into betaine while FAD was reduced to FADH₂ which subsequently reduced 1,4-benzoquinone into hydroquinone. The later was finally oxidized at a relatively low potential of +450 mV versus saturated calomel electrode (SCE). Nicotine inhibits the activity of enzyme with an effect of decreasing of oxidation current. The experimental conditions were optimized. The electrode has a linear response to choline within 1.25×10⁻⁴ to 1.25×10⁻³ mol l⁻¹. The nicotine measurements were carried out in 0.067 mol l⁻¹phosphate buffer of pH 7.4 at an applied potential of 450 mV versus SCE. The electrode provided a linear response to nicotine over a concentration range of 2.0×10⁻⁵ to 9.2×10⁻⁴ mol l⁻¹ with a detection limit of 1.0×10⁻⁵ mol l⁻¹. The system was applied to the determination of nicotine in tobacco samples.     

催化荧光动力学法测定食品中痕量甲醛

基于在酸性条件中,甲醛催化KBrO3氧化吡口罗红B的褪色反应,使其荧光猝灭,建立了荧光动力学法测定痕量甲醛的新方法。反应在沸水浴中进行8 min,测定甲醛的线性范围为0.016~0.14 mg/L,检出限为8.6×10-6g/L。该方法用于水发食品中甲醛的测定,并进行了加标回收试验,回收率在96.0%~104.2%之间,相对标准偏差为1.7%~3.5%。     

Studies on the voltammetric behavior of azo dyes and its determination in cosmetic products1

The voltammetric behaviors of azo dyes on glassy carbon electrode were investigated in an aqueous containing various supporting electrolyte. The possible reaction mechanisms were discussed by the relations of scan rate and peak potentials and currents. The electroreduction process is applied for the quantitative determination of Lithol Rubine B azo dyes cosmetic products. Comparison with results obtained from high performance liquid chromatography shows good agreement.     

Highly selective determination of copper corrosion products by voltammetric reduction in a strongly alkaline electrolyte

Until recently, there had been two conflicting views about the order of copper oxides (Cu(2)O and CuO) in their cathodic reduction with a neutral or weak alkaline electrolyte (typically 0.1 M KCl). In 2001, we successfully employed a strongly alkaline electrolyte (SAE; i.e., 6 M KOH + 1 M LiOH) to achieve a perfect separation of the reduction peaks of the two oxides. It was then found that the oxides were reduced in SAE according to a thermodynamic order, i.e., "CuO → Cu(2)O", and also that the reduction of CuO occurred in one step. At an extremely slow scan rate of <0.2 mV s(-1), however, CuO appears to be reduced in two steps via Cu(2)O. It has also been shown that the developed method with SAE can be applied to analysis of various corrosion products, including Cu(2)S, Cu(OH)(2), and patinas. Use of the developed method has allowed researchers to clarify the mechanism of the atmospheric corrosion of copper.     

Fabrication of an amperometric tyramine biosensor based on immobilization of tyramine oxidase on AgNPs/l-Cys-modified Au electrode

An amperometric tyramine biosensor was constructed based on covalent immobilization of black gram tyramine oxidase onto citric acid-capped silver nanoparticles bound to surface of Au electrode through cysteine self-assembled monolayer. The enzyme electrode was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and cyclic voltametry. The biosensor showed optimum response within 8 s, when polarized at 0.25 V, pH 8.5, and 35 °C, with linearity from 0.017 to 0.25 mM and a detection limit of 0.01 mM. The biosensor was employed for measurement of tyramine in beer and sauce. The mean analytical recovery of added tyramine in beer at 0.36 and 0.72 mM were 97.2?±?2.7 and 95.8?±?4.1 %, respectively, and within and between batches coefficients of variation were 0.33–0.38 and 0.34–0.62 %, respectively. The enzyme electrode lost 35 % of its initial activity after its 100 uses, over a period of 2 months, when stored at 4 °C.     

Synergic effect studies of the bi-enzymatic system laccase-peroxidase in a voltammetric biosensor for catecholamines

Several bi-enzymatic carbon paste biosensors modified with enzymes laccase from Pleurotus ostreatus fungi and peroxidase from zucchini (Cucurbita pepo) were constructed for evaluating the synergic effect of the two enzymes on the voltammetric biosensor response for various catecholamines. Initially was investigated the effect of pH from 5.0 to 7.5, temperature from 25 to 50 °C, initial stirring time from 30 to 150 s, scan rate from 10 to 60 mV s⁻¹ and potential pulse amplitude from 10 to 60 mV on the biosensor response for several catecholamines such as dopamine, adrenaline, isoprenaline and l-dopa. It was observed a biosensor signal increase employing both enzymes, indicating thus there is a synergic effect between laccase and peroxidase, verified also in spectrophotometric studies, in the determination of these catecholamines.     

Extraction voltammetric determination of silicon

Summary A determination of silicon is described which utilizes the selective extraction of molybdosilicic acid with methyl-iso-butyl-ketone. The extract is mixed with iso-propanol. No additional electrolyte is necessary because sufficient sulphuric acid is coextracted and provides good conductivity. The 3s-limit of detection was found to be 4×10^–8 mol l^–1 Si. The method was applied to determine silicon in cereals.     

MWNT-modified electrodes for voltammetric determination of lipophilic vitamins

Multi-walled carbon nanotube modified graphite electrodes (MWNT-GEs) have been created for the voltammetric determination of α-tocopherol and retinol. The electrode surface was characterized by atomic force microscopy. The MWNT-GEs presented structured surfaces and a significant (26-fold) increase in roughness over unmodified graphite electrodes (8.2 vs. 0.32?nm for MWNT-GEs and GEs, respectively). Their surfaces consisted of aggregates with a highly regular “thorn-like” structure. α-Tocopherol and retinol were oxidized on the bare GEs and the MWNT-GEs in 0.1?M HClO₄ in acetonitrile. Decreases in the overpotential of 0.2 and 0.04?V for α-tocopherol and retinol, respectively, and increased oxidation currents were observed on the MWNT-GEs in comparison with the unmodified electrodes. The calibration graphs were linear in the range 0.065–2.00?mM for α-tocopherol and 0.05–1.50?mM for retinol. The detection limits were found to be 0.05 and 0.04?mM for α-tocopherol and retinol, respectively. The developed electrodes were applied to determine α-tocopherol and retinol in pharmaceuticals. The results obtained agreed well with coulometric titration data.     

Photokinetic voltammetric method for the determination of thiocyanate

Thiocyanate traces have a strong inhibitory effect on the oxidation of Neutral Red by potassium bromate under UV irradiation in diluted phosphoric acid. Neutral Red exhibits a sensitive second derivative oscillopolarographic wave at -0.6 V(vs. SCE) in diluted phosphoric acid and sodium acetate solution. The oscillopolarographic behavior of Neutral Red was selected as indicator component for its photo-activated oxidation. The photochemical reaction rate equation was determined. A detection limit of 0.3 ng mL(-1) (3sigma/k) and a linear calibration curve from 2.0-48.0 ng mL(-1) thiocyanate were obtained. The method was applied to the determination of thiocyanate in urine, saliva and serum with satisfactory results.     

Square-wave voltammetric determination of daminozide

A novel electrochemical method is described for the determination of the growth regulator, daminozide. Daminozide is hydrolyzed in alkaline aqueous media to form 1,1-dimethylhydrazine (UDMH). The UDMH is oxidized at ?0.38 V vs. Ag/AgCl at the hanging mercury drop electrode and detected by square-wave voltammetry. The sensitivity is about 2.3 nA 1 mg^?1 and the standard deviation (n = 8) for different standard solutions is 2.9 nA. Results obtained with apples after steam distillation agreed well with results obtained with a previously published method.