Flow injection analysis of BHA by NiHCF modified electrode

Flow injection method is described for the determination of the antioxidant tert-butylhydroxy anisole (BHA) based on its catalytic oxidation at a nickel hexacyanoferrate (NiHCF) surface modified graphite wax composite electrode fabricated using a new approach. The electrochemical characteristics of the modified electrode were studied using cyclic voltammetry. The voltammetric response of BHA at the modified electrode showed current densities remarkably higher than the bare graphite electrode and occurred at a reduced over voltage of 200 mV. Linear calibration graphs were obtained in the range of 1.2 × 10⁻⁶–1.07 × 10⁻³ M. A detection limit of 6 × 10⁻⁷ M was obtained with a correlation coefficient of 0.9983 based on S/N = 3. Reliable results were obtained by applying the proposed flow injection method to determine BHA spiked in dehydrated potato flakes. Results suggest that the developed method can be effectively employed for the determination of BHA from food samples.     

流动注射法同时检测水中挥发酚和氰化物

目的建立连续流动注射分析仪同时测定末梢水中挥发酚和氰化物的分析方法。方法末梢水经过EDTA和抗坏血酸的混合溶液(20.0 g/L)预处理,用连续流动注射分析仪同时测定挥发酚和氰化物。结果末梢水样品预处理的条件为50 ml水样中加入0.5 ml EDTA和抗坏血酸的混合溶液(20.0 g/L),加标回收率为90.0%~105.0%,相对标准偏差为0.39%~5.85%,挥发酚和氰化物的检出限分别为0.000 2和0.000 4 mg/L。结论该方法精密度好,准确度高,符合分析质控要求。     

Flow injection chemiluminescent detection of gallic acid in olive fruits

One economic and environment friendly flow injection chemiluminescent method for the determination of gallic acid was developed. It was based on the inhibited chemiluminescent emission of alkaline luminol–KMnO₄ system by gallic acid. The logarithm of the difference of chemiluminesent intensity of the alkaline luminol–KMnO₄ system in the absence of gallic acid from that in the presence of gallic acid was linear with the logarithm of the concentration of gallic acid in the range from 1.0 × 10⁻⁹ to 5.0 × 10⁻⁵ g ml⁻¹ with a detection limit of 2.2 × 10⁻¹⁰ g ml⁻¹. The relative standard deviation of eleven determinations of 1.0 × 10⁻⁶ g ml⁻¹ gallic acid was 1.7%. The method was successfully applied to the determination of gallic acid in olive fruits.     

Review: Flow injection analysis–a new technique for food and beverage analysis

Flow injection analysis affords a means of automating many traditional wet chemical methods of food and beverage analysis, and introducing new methods which have no conventional analogue. In this technique, reactions are carried out in a continuous flow mode and it is not necessary for a state of chemical equilibrium to be reached. Therefore, analyses using standard or official chemistries may be achieved in very short times (typically 30 sec). This review outlines the principles, instrumentation and techniques of flow injection analysis and considers the scope of its actual and potential applications in food and beverage analysis.     

Determination of bromate in bread additives and flours by flow injection analysis

A new, simple, rapid and sensitive spectrophotometric flow injection analysis (FIA) method was developed for the determination of bromate based on its reaction with 3,5-dibromo-PADAP and thiocyanate in a strongly acidic medium. This produced an unstable violet product with a maximum absorption at 602 nm. The calibration curve was linear in the range of 2.00×10⁻⁶–2.10×10⁻⁵ mol/l and the detection limit was 8.00×10⁻⁷ mol/l. The sampling frequency was 90 h⁻¹. The method has been successfully applied to the determination of bromate in commercial bread additives and flours.     

Flow injection analysis of nitrate-N determination in root vegetables: Study of the effects of cooking

Vegetables are the major vehicles for the entry of nitrate into the human system. Ever-increasing concern over nitrate toxicity has directed a number of countries to lay down maximum allowable threshold concentrations with regards to nitrate-N in vegetables. Fiji is an independent island nation, located in the southern Pacific Ocean, has a tropical oceanic climate and hence expected to have high nitrate-N levels in vegetables. Thus, the present study was devoted to establish a flow injection analysis (FIA) technique for nitrate-N determination in Fiji’s commonly consumed fresh and cooked root vegetables such as potato (Solanum tuberosum), dalo (Colocasia esculenta), sweet potato (Ipomoea batatas) and carrot (Daucus carota L.). Activated carbon extraction technique was applied to extract nitrate-N. FIA with colorimetric detection technique having linear dynamic range of determination 1.0–20.0 mg L⁻¹ and detection limit of 0.042 mg L⁻¹ (0.34 mg kg⁻¹), using sulphanilamide and N-(1-naphthyl)ethylenediamine dihydrochloride as colour reagents, was used to determine nitrate-N contents in selected fresh and cooked root vegetables. The samples throughput was 38 h⁻¹. The effects of various cooking (boiling, baking and frying) methods on nitrate-N contents in root vegetables have also been studied. The study shows that the nitrate content of fresh root vegetables ranges from 53.76–258.00 mg kg⁻¹ whereas boiling reduces nitrate content by 23.30–42.62%. The frying in soya bean oil elevates nitrate contents from 204.53–299.12% but after baking nitrate contents remains almost constant with slight increasing trend from 2.80–8.43%. A comparison of the nitrate obtained by standardised method and the nitrate contents in vegetables of other countries are also presented.     

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.     

An optical flow injection analysis system for measurement of glucose in tomato

An optical flow injection analysis (FIA) system for glucose measurement in tomato was constructed by using a glucose oxidase (GOD) immobilized reactor and a photodiode sensor, a peristaltic pump and a personal computer. The GOD reactor was crammed with strip-shaped of a GOD immobilized membrane to an acrylic pipe. The GOD was immobilized on polytetrafluoroethylene membrane by crosslinking with glutaraldehyde. Hydrogen peroxide generated by the GOD reaction oxidized luminol to produce chemiluminescence in the presence of horseradish peroxide. The chemiluminescence was detected by using the photodiode. The glucose measurement system was calibrated with standard glucose solutions. The calibration range of the system for glucose was 2.0–100.0 mmol L⁻¹. Measurement time for every sample was within 3 min. Glucose concentrations of a fresh and processed tomato samples measured with this glucose measurement system could be evaluated rapidly and non-laboriously.     

Determination of free fatty acids in palm oil samples using non-aqueous flow injection titrimetric method

Flow injection (FI) non-aqueous titrimetric methods for the determination of free fatty acids (FFA) in palm oil samples are described. Single-line and two-line FI manifolds using phenolphthalein (PHP) and bromothymol blue (BTB) as indicators were developed. The method is based on the monitoring of the changes of absorbance of the indicators used from basic–acidic–basic form (pink–colourless–pink for PHP, blue–yellow–blue for BTB) as a result of the neutralization of KOH that was used as carrier stream by the injected FFA sample. FI parameters such as carrier and reagent concentration, flow-rate, length of reaction coil, size of mixing chamber and injected volume were optimized. The single-line manifold with PHT as indicator is recommended for the determination of samples with acidity degree (a.d.) higher than 0.4, but the oil samples need to be diluted with 2-propanol before their injection. For lower acidities (a.d. < 0.4), a two-line manifold with BTB as indicator is recommended. The two-line manifold allows direct injection of oil samples (no off-line dilution required). The optimized FIA method is linear over the range 0.4–10.0 a.d. (based on palmitic acid) for single-line manifold and 0.11–0.50 a.d. for the two-line manifold. Sample throughput of 35–74 and 21–46 samples h⁻¹ for single-line and two-line manifolds, respectively, were achieved. Fifty different samples of palm oils were tested using the appropriate FIA manifolds, and results were compared with the standard PORIM procedure which involves manual titration. Good correlations between the two methods were obtained (r², at least 0.92) UV–VIS absorption spectra indicate that the absorption of these oil samples were minimum at the detection wavelengths (562 nm for PHP and 627 for BTB), indicating that the method is negligibly interfered from the background colour of the samples.     

Application of flow injection analysis for determining sulphites in food and beverages: A review

Sulphites have been widely used as preservatives in food and beverages. Preservative determination is essential for the purposes of legislation and consumer safety. Among the analytical methodologies available, those based on flow injection analysis (FIA) can be highlighted. FIA offers interesting advantages such as versatility, accuracy, low cost, speed and automation, among others. These advantages make FIA an important alternative to conventional methods. This review considers the present status of published FIA methodology for determining sulphites in food and beverages. A detailed analysis of the technique is done, stressing its impact on the aspects of the extraction, separation, detection and quantification procedures in different matrices.     

Flow injection spectrophotometry using natural reagent from Morinda citrifolia root for determination of aluminium in tea

A flow injection (FI) spectrophotometric method with using natural reagent extracted from Morinda citrifolia root has been developed for determination of aluminium. The extract contained anthraquinone compounds which could react with Al³⁺ to form reddish complexes which had maximum absorption wavelength at 499.0 nm. The extract could be used as a reagent in FI system without further purification to obtain pure compound. A sensitive method for determination of aluminium in concentration range of 0.1-1.0 mg L⁻¹, with detection limit of 0.05 mg L⁻¹ was achieved. Relative standard deviations of 1.2% and 1.7% were obtained for the determination of 0.1 and 0.6 mg L⁻¹ Al³⁺ (n = 11). Sample throughput of 35 h⁻¹ was achieved with the consumption of 3 mL each of carrier and reagent solutions per injection. The developed method was successfully applied to tea samples, validated by the FAAS standard method. The method is simple, fast, economical and could be classified as a greener analytical method.     

Determination of volatile basic nitrogen and trimethylamine nitrogen in fish sauce by flow injection analysis

 A combination of flow injection analysis (FIA), gas diffusion cell and a laboratory built photometer were introduced and used for monitoring trimethylamine (TMA) and total volatile bases (TVB) in fish sauce. The FIA results were compared with commonly used methods. (Dyer method for TMA, Antonacopoulos and Vynke (steam distillation) for TVB). The results for TVB-N were the same by FIA and commonly used methods. However, the results for TMA-N showed significant differences between different methods. The values given by FIA were approximately half those obtained by the method. FIA appears to be an adequate methodology for quality control in fish sauce production with the advantages of reduced sample volume, energy consumption and cost. Received: 29 March 1999 / Revised version: 28 July 1999     

Rapid antioxidant capacity screening in herbal extracts using a simple flow injection-spectrophotometric system

A simple flow injection (FI)-spectrophotometric system for the screening of antioxidant capacity in herbal extracts was developed. The analysis was based on the color disappearance due to the scavenging of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical by antioxidant compounds. DPPH and ascorbic acid were used as reagent and antioxidant standard, respectively. Effects of the DPPH concentration, DPPH flow rate, and reaction coil length on sensitivity were studied. The optimized condition provided the linear range of 0.010-0.300 mM ascorbic acid with less than 5%RSD_(n = 10). Detection limit and quantitation limit were 0.004 and 0.013 mM, respectively. Comparison of antioxidant capacity in some herbal extracts determined by the FI system and a standard method was carried out and no significant difference was obtained.     

Determination of trimethylamine nitrogen and total volatile basic nitrogen in fresh fish by flow injection analysis

There are many chemical, microbiological and sensory indices of fish quality. Of the chemical indices, TMA-N and TVB-N are probably the most used in connection with remaining shelf-life determination. This paper reports on a study of modifications to a flow injection analysis (FIA) method necessary to make it suitable for TMA-N and TVB-N determination, specifically the optimal concentrations of NaOH and formaldehyde for releasing the volatile bases from the acidic fish extract and sequestering the non-TMA volatile bases respectively. The effects of using perchloric acid (PCA) and trichloroacetic acid (TCA) as fish extractants were also investigated. The fish species used were monkfish (Lophius piscatorius), skate (Raia clavata) and cod (Gadus morrhua). It was found that 1 M NaOH was the optimal concentration for volatile base release and that 200 g l⁻¹ formaldehyde was adequate for non-TMA base sequestration. Use of PCA and TCA as fish extractants appeared to have no significant effect on TMA-N and TVB-N determinations. © 1999 Society of Chemical Industry     

Application of flow injection analysis to determine protein-bound nitrite in meat products

The development and application of a methodology based on flow injection analysis (FIA) for the determination of protein-bound nitrite (PBN) in meat products was studied. Since the FIA methodology used for measuring residual nitrite was not appropriate for determining PBN (even at a concentration of 15.9 mg of PBN/kg) in meat products, the procedure was modified and then studied for residual nitrites and PBN. Ammonium chloride (A), which is used conventionally (the original FIA method), was replaced by different carriers (the modified FIA method): B (buffer 7); C (buffer 7.5); D (buffer 8); E (NaOH 0.5 M) and F (NaOH 1 M). Carriers B and C provided the lowest limits of quantification of residual nitrite, lower than that obtained using the original FIA method. The method for determining PBN in several meat products (frankfurter and dry sausages) was validated by comparing it with the method usually used. The results obtained indicate that the modified FIA method (with carriers B and C) can be used as a simple, easy, fast, accurate and precise methodology for quantifying residual nitrite and PBN in meat products.     

A non-plasticized chitosan based solid state electrode for flow injection analysis of glutamate in food samples

This report describes the development of solid state glutamate sensor based on chitosan. The electrode has linearity range of 0.01–1 mM glutamate with detection limit of 0.008 mM. The presence of other conventional food additives at physiological level does not interfere. The interfering effect is, however, minimized through prior dilution of the sample. Recovery values of 88.9–99.2% are obtained throughout. The proposed electrode has been applied in flow injection analysis (FIA) glutamate in food samples. In the validation experiment, the proposed electrode is found to be comparable with the standard method.     

Evaluation of total antioxidant potential of selected biogenic polyamines, non-alcoholic drinks and alcoholic beverages using improved RP-HPLC assay involving fluorescence detection

Total antioxidant potential (TAP) is proportional to the sum from products of concentrations of all antioxidants in the sample and their antioxidant powers (rate constants). Due to components interaction in the sample, TAP frequently better describes the antioxidant properties of the complex biological samples, such as herbal extracts or blood plasma, than other parameters involving concentrations of all individual antioxidants, standard redox potentials, kinetics constants, etc. In the present study improved high-performance liquid chromatographic (HPLC) assay with fluorometric detection has been used to evaluate TAP values of selected low-molecular mass compounds like biogenic polyamines, especially spermidine, spermine, 1,7-diaminoheptane, putrescine and cadaverine. Moreover, optimised analytical protocol was employed for the TAP estimation of complex mixtures such as food products including number of alcoholic and non-alcoholic beverages. The results of our study revealed that proposed assay gives additional information about the OH radical scavenging performance and antioxidant properties of pure chemicals and complex food samples, in contrary to the described in the literature assays based on weaker radicals (peroxyl radical, DPPH, NO, ABTS or superoxide anion radical).     

Determination of free and total sulfites in wine using an automatic flow injection analysis system with voltammetric detection

An automated flow injection analysis (FIA) system, based on an initial analyte separation by gas-diffusion and subsequent determination by square-wave voltammetry (SWV) in a flow cell, was developed for the determination of total and free sulfur dioxide (SO₂) in wine. The proposed method was compared with two iodometric methodologies (the Ripper method and a simplified method commonly used by the wine industry). The developed method displayed good repeatability (RSD lower than 6%) and linearity (between 10 and 250 mg l^?1) as well as a suitable LOD (3 mg l^?1) and LOQ (9 mg l^?1). A major advantage of this system is that SO₂ is directly detected by flow SWV.     

Chemical,antioxidant and sensory properties of tomato‐watermelon‐pineapple blends,and changes in their total antioxidant capacity during storage

A conductometric analysis of the effect of condensate of peroxides generated during lipid oxidation in an accelerated stability test was adapted to test the hypothesis that total antioxidant capacity of tomato products would sometimes increase during processing and in storage. Tomato pulp blends made from a mixture of tomato (Lycopersicon esculentum var Roma VF), watermelon (Citrullus vulgaris var Babylack) and pineapple (Ananas comosus var Smooth cayennes) were analysed for basic quality profiles of dry matter, Brix, titratable acidity (TTA) and pH, total reducing sugars, Component antioxidants phytochemicals and total antioxidant capacity. The lowest sensory score (overall impression) of 4.80 ± 2.59 was recorded for tomato juice while, blend TWP 111p had highest score of 6.20 ± 1.99. There was significant difference (P < 0.05) in the basic quality profile of the pulp blends except for TTA values (0.37 ± 0.02 to 0.45 ± 0.05) and 2‐Furfurals (2.47 ± 0.03 to 2.71 ± 0.01). The fresh blend of 50% tomato, 25% watermelon and 25% pineapple had the highest total antioxidant capacity of 3.69 ± 0.52 mg 100 mL^?1 catechin equivalent. The total antioxidant capacity of the stored pulp increased from 2.95 ± 0.13 to 6.22 ± 0.32 mg 100 mL^?1 catechin equivalent in pasteurised TWP 211p blend by 60 days when stored at 40 °C. Total antioxidant status of tomato‐based fruit mix increased during the first 80 days.