Chromium determination in food by slurry sampling graphite furnace atomic absorption spectrometry using classical and permanent modifiers

A simple method, using permanent modifiers, has been developed for chromium (Cr) determination in food of plant origin by the slurry sampling graphite furnace atomic absorption spectrometry. In particular comparison of the action of Mg(NO₃)₂, iridium (Ir)/niobium (Nb) and iridium (Ir)/tungsten (W) was examined. Finally, for chromium determination in food, the mixture of 2 μg of Ir with 10 μg of Nb was used as permanent modifier. The analytical procedure was optimised carefully on the basis of the data from pyrolysis and atomisation temperature curves studies. The results obtained for four certified reference materials using external calibration with aqueous standards were in good agreement with the certified values. The precision and accuracy of Cr determination by the described method were also acceptable: the RSD were lower than 10% and recoveries for CRMs were in the range of 95-103%. The characteristic mass for chromium was determined to be 3.9 pg and the detection limit for the optimised procedure at the 0.75% (w/v) slurry concentration - 86.6 ng g⁻¹.     

Flow injection analysis of total curcuminoids in turmeric and total antioxidant capacity using 2,2′-diphenyl-1-picrylhydrazyl assay

A simple flow injection analysis procedure is proposed for the determination of curcuminoids content in turmeric extracts. The method is based on the formation of a coloured complex between 4-aminoantipyrine and curcuminoids, in the presence of an oxidising reagent such as potassium hexacyanoferrate (III) in alkaline media. Conditions selected as a result of these trials were implemented in a flow injection analytical system in which the influence of injection volume, flow rate, reagent concentration and mixing coil length, was evaluated. Under the optimum conditions the total amount of curcuminoids could be determined within a concentration range of 5–50 μg mL⁻¹ which can be expressed by the regression equation y = 0.003x − 0.0053 (r² = 0.9997). The limits of detection and quantitation were found to be 0.6 μg mL⁻¹ and 1.8 μg mL⁻¹, respectively. The reproducibility of analytical readings was indicative of standard deviations <2%. The sample was extracted and analysed by using the proposed method. The percentage recoveries were found to be 94.3–108.0. The proposed system was applied to the determination of curcuminoids content in turmeric. The total curcuminoid contents in turmeric extract were found to be 0.9–4.3% (w/w). The development method is simple, economic, rapid and especially suitable for quality control in pharmaceutical plants.     

Simultaneous determination of pyruvate and acetate levels in xanthan biopolymer by infrared spectroscopy: effect of spectral pre-processing for solid-state analysis

A rapid, direct, and reagent-free procedure based on solid-state Fourier transform infrared spectroscopy (FT-IR) coupled with partial least squares (PLS) data analysis has been developed for simultaneous determination of pyruvate and acetate levels in a microbial xanthan biopolymer. The influences of various spectral pre-processing procedures were studied in order to eliminate effects caused by sample preparation. It was determined that the combination of first derivative and orthogonal signal correction pre-processing contributes to a significant increase in the predictive performance of PLS-1 regression models. By employing the wavenumber region 1320–1350 cm⁻¹ for pyruvate determination and 1500–1600 cm⁻¹ for acetate determination, the root mean square error of cross-validation (RMSECV) for pyruvate and acetate contents were obtained 0.13% and 0.29% w/w, respectively. Results of the proposed procedure for different real samples and those obtained by their reference methods were compared.     

Determination of soybean proteins in soybean–wheat and soybean–rice commercial products by perfusion reversed-phase high-performance liquid chromatography

The determination of additions of soybean proteins in commercial bakery products containing soybean–wheat and soybean–rice binary mixtures has been achieved in this work by high-performance liquid chromatography using a perfusive column. Soybean proteins were solubilized in a 25:75 acetonitrile–water mixture containing 0.3% (v/v) acetic acid by ultrasonication for 10 min and centrifugation for 5 min. Soybean proteins were separated from rice and wheat proteins in less than 4 min using a linear binary gradient of acetonitrile–water containing 0.3% (v/v) acetic acid as ion-pairing agent. The proposed method was proved to be specific and sensitive making possible the detection and the quantitation of additions of about 0.10% (w/w) and 0.33% (w/w), respectively, of soybean proteins in soybean–wheat and soybean–rice products (related to 1 g of initial product). Precision and recoveries observed were also acceptable. The method was applied to the determination of soybean proteins in different commercial bakery products.     

Selective cloud point extraction for the determination of cadmium in food samples by flame atomic absorption spectrometry

A new cloud point extraction (CPE) procedure for preconcentration of cadmium prior to the determination by flame atomic absorption spectrometry (FAAS) was developed. The method is based on the fact that cadmium could form hydrophobic ion-associated complex in the presence of iodide and methyl green (MG), and the hydrophobic ion-associated complex could be extracted into surfactant-rich phase. The main factors affecting CPE procedure, such as pH, concentration of KI, MG and surfactant, equilibrium temperature and incubation time, sample volume were investigated. Potential interference from co-existing ions was largely eliminated as most of co-existing ions can not form extractable ion-associated complex with iodide and MG. Under the optimum conditions, the limit of detection (3σ) and limit of quantity (10σ) were 0.90 ng mL⁻¹ and 3.0 ng mL⁻¹ for cadmium, respectively, and relative standard deviation was 4.2% (c = 50 ng mL⁻¹, n = 7). The proposed method was successfully applied to determination of cadmium in the certified reference rice sample (GBW08510) and food samples with satisfactory results.     

Rapid micropreparation procedure for the gas chromatographic-mass spectrometric determination of BHT, BHA and TBHQ in edible oils

A rapid, accurate and organic solvent saving procedure has been developed for the GC/MS determination of three phenolic antioxidants butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA) and butyl hydroquinone (TBHQ) in vegetable oils. The method involves two-step microextraction and a centrifugal procedure in a 2 mL autosampler vial, consuming only 50 mg sample and total 1 mL acetonitrile. Recoveries of the phenolic antioxidants when spiked to soya bean oil, peanut oil and cereal cooking oil at 50, 200 and 250 mg/kg, respectively were in the ranges 95.6-104.3% for BHT, 99.7-107.5% for BHA and 93.6-103.8% for TBHQ with the relative standard deviation (RSD) were less than 3% for their independent measurements. The developed method was repeatable and could be applied to determine trace amounts of phenolic antioxidants in vegetable oils.     

Automatic determination of nickel in foods by flame atomic absorption spectrometry

A new sensitive and low cost flow injection method that combines acid extraction, preconcentration and flame atomic absorption spectrometric determination of nickel in food samples at μg/g levels is described. The dynamic acid extraction step was carried out by using a continuous ultrasound-assisted extraction system. The acid extract was preconcentrated on-line on a minicolumn packed with a chelating resin (Serdolit Che, with iminodiacetic groups) and nickel was eluted with diluted hydrochloric acid, being continuously monitored by flame atomic absorption spectrometry. An experimental design (Plackett-Burman 2⁶ × 3/16) is used to optimise the methodology proposed. The method allowed a total sampling frequency of 13–28 samples per hour. Good precision of the whole procedure (1.9–3.6% expressed as relative standard deviation) and a detection limit of 0.12 μg/g, for 60 mg of sample were achieved. The method was successfully applied to the determination of trace amounts of nickel in food samples.     

Determination of Cd,Cu, and Zn in fish and mussel by AAS after ultrasound-assisted acid leaching extraction

An ultrasound-assisted solid–liquid extraction procedure by using diluted mixed acid solution was developed for determination of cadmium, copper and zinc in fish and mussel samples. The effects of several parameters such as nitric acid concentration, hydrochloric acid concentration, hydrogen peroxide concentration, leaching solution volume, and sonication time have been investigated. A 30-min sonication, 56 °C operating temperature and 6 mL of 1:1:1 HNO₃(4 M):HCl(4 M):H₂O₂(0.5 M) were used for 0.5 g of dried sample. Cadmium and copper were determined by graphite furnace atomic absorption spectrometry, and zinc was determined by flame atomic absorption spectrometry. The results obtained from the proposed procedure were evaluated by comparison with the results obtained by microwave-assisted digestion. Ratio (%) of metal amount obtained from leaching technique to amount obtained from digestion technique for cadmium, copper and zinc ranged from 92% to 114% for fish and from 88% to 103% for mussel samples. The MDL were 0.02, 0.13 and 0.63 mg kg⁻¹ for cadmium, copper and zinc, respectively. The accuracy of the developed method was investigated by analyzing a dogfish muscle certified reference material (DORM-2). Recoveries were obtained in the order of 80.9 ± 0.3 and 87.2 ± 0.6%.     

Determination of histamine in cheese by chronopotentiometry on a thin film mercury electrode

Simple electroanalytical method for histamine determination based on its irreverse oxidation by a constant current on a thin film mercury electrode was developed in this work. Experimental parameters of chronopotentiometric analysis, such as concentration of the supporting electrolyte, initial potential and dissolution current were optimised. The optimal experimental parameters included an initial potential of −0.4 V and oxidation currents in the range from 3 to 30 μA in 0.02 mol/l sulphuric acid. After the optimisation of experimental parameters, the linear response was obtained in the range 2–90 mg/l of histamine with achieved detection limit of 1.31 mg/l of histamine. The method was applied for the determination of histamine in various types of cheese. Prior sample analysis the procedure for sample preparation was developed and included ultrasonically-assisted extraction and chromatographic separation on a thin layer. To our knowledge, histamine has never previously been determined on mercury electrodes nor by applying chronopotentiometric analysis, thus developed electroanalytical method represents an important contribution to electroanalytical practise. By applying the developed method it is possible to perform simple and fast cheese analysis. Furthermore, in comparison to competitive chromatographic techniques, chronopotentiometric method allows the analysis of foodstuffs under moderate price.     

Rapid determination of free anthocyanins in foodstuffs using high performance liquid chromatography

Anthocyanins constitute a major group of natural pigments, and they are responsible for the colours of fruits and vegetables. A rapid and feasible assay procedure for the determination of free forms of the six most abundant anthocyanins in foods is described. The 3-glucoside forms of pelargonidin, cyanidin, peonidin, delphinidin, petunidin and malvidin with the aglycone cyanidin (as internal standard) were separated by gradient elution and quantified using HPLC-DAD within 18 min. A fast sample preparation step was employed which allows direct injection of samples to the chromatograph without need of chemical extraction. Testing on 28 different vegetable, fruit and processed commercial product samples demonstrated applicability in the concentration range of about 80–420 ng/mL with an accuracy of 99.2 ± 0.2% and an average precision of 0.8%. The method was suggested as a cheap and robust alternative to the previous ones that employ multi-step sample treatment protocols.     

Development of a matrix solid-phase dispersion-sonication extraction method for the determination of fungicides residues in ginseng extract

A rapid method based on matrix solid-phase dispersion (MSPD) was developed for the determination of pentachloronitrobenzene, pentachloroaniline, methylpentachloro-phenylsulphide and procymidone in ginseng extract using gas chromatography. The optimal conditions selected for MSPD extraction were as follows: after blending 5 mL of aqueous ginseng extract (10%, w/v) with Florisil (10 g), the mixture was passed into a small chromatographic column and extracted twice with 10 mL ethyl acetate–hexane solvent mixture (70:30, v/v) for 15 min in an ultrasonic bath at room temperature. The analytical performance of this method showed MSPD to be efficient, fast, simple and had little or no matrix effect. The method detection limits varied from 0.1 to 0.4 μg/L. Mean recoveries were found in the range of 83.5–97.4% and had a good linear relationship (r² ? 0.9987) with relative standard deviations less than 10%. The proposed method has proved to be a feasible one for the analysis of fungicide residues in ginseng extract.     

Multi-element determination of Cu,Fe, Ni and Zn content in vegetable oils samples by high-resolution continuum source atomic absorption spectrometry and microemulsion sample preparation

The aim of this work was to evaluate the microemulsification as sample preparation procedure for determination of Cu, Fe, Ni and Zn in vegetable oils samples by High-Resolution Continuum Source Flame Atomic Absorption Spectrometry (HR-CS FAAS). Microemulsions were prepared by mixing samples with propan-1-ol and aqueous acid solution, which allowed the use of inorganic aqueous standards for the calibration. To a sample mass of 0.5 g, 100 μL of hydrochloric acid and propan-1-ol were added and the resulting mixture diluted to a final volume of 10 mL. The sample was manually shaken resulting in a visually homogeneous system. The main lines were selected for all studied metals and the detection limits (3σ, n = 10) were 0.12, 0.62, 0.58 and 0.12 mg kg⁻¹ for Cu, Fe, Ni and Zn, respectively. The relative standard deviation (RSD) ranged from 5% to 11 % in samples spiked with 0.25 and 1.5 μg mL⁻¹ of each metal, respectively. Recoveries varied from 89% to 102%. The proposed method was applied to the determination of Cu, Fe, Ni and Zn in soybean, olive and sunflower oils.     

Bioavailability study using an in-vitro method of iodine and bromine in edible seaweed

Raw edible seaweed harvested in the Galician coast (Northwester Spain), including two red seaweed types (Dulse and Nori), three brown seaweed (Kombu, Wakame and Sea Spaghetti), one green seaweed (Sea Lettuce) and one microalgae (Spirulina platensis) were analysed for total iodine and total bromine, as well as for iodine and bromine bioavailability by in-vitro methods (simulated gastric and intestinal digestion/dialysis). Similarly, a cooked seaweed sample (canned in brine) consisting of a mixture of two brown seaweed (Sea Spaghetti and Furbelows) and a derived product (agar–agar) from the red seaweed Gelidiumm sesquipedale, were also included in the study. All measurements were carried out by inductively coupled plasma–mass spectrometry using tellurium and yttrium as internal standards for iodine and bromine, respectively. An optimised microwave assisted alkaline (TMAH) digestion procedure was used as sample pre-treatment for total iodine and bromine determinations, as well as for the determination of both elements in the non-dialyzable fractions. PIPES buffer solution at a pH of 7.0 and dialysis membranes of 10 kDa molecular weight cut off (MWCO) were used for the intestinal digestion. Accuracy of the method (total bromine and iodine determinations) was assessed by analysing a NIES-09 certified reference material. The accuracy of the in-vitro procedure was established by a mass-balance study which led, after statistical evaluation (95% confidence interval), good accuracy of the whole in-vitro process. The highest dialyzability bromine percentages (36 ± 0.7% and 47 ± 3.0%) were obtained for red seaweed (Dulse and Nori), while higher dialyzability iodine was assessed for the brown seaweed (Kombu), around 17% ± 0.7%.     

Non-chromatographic speciation of inorganic arsenic in mushrooms by hydride generation atomic fluorescence spectrometry

A non-chromatographic speciation method has been developed for the determination of inorganic arsenic in cultivated and wild mushroom samples from different origins. The ultrasound-assisted extraction of the toxic arsenic species As (III) and As (V) was performed for 10 min with 1 mol l⁻¹ H₃PO₄ and 0.1% (m/v) Triton X-100. After phase separation the residue was washed with 0.1% (w/v) EDTA and centrifuged. As (III) and As (V) were determined by hydride generation atomic fluorescence spectrometry. Speciation was made using proportional equations corresponding to two different measurement conditions, (i) directly feeding sample extracts diluted with HCl and (ii) after reduction with KI and ascorbic acid for 30 min. The limits of detection of the method were 6.3 and 5.0 ng g⁻¹ for As (III) and As (V), respectively. Recovery percentages varied between 91% and 108% for As (III) and from 90% to 109% for As (V) indicating that As species interconversion was avoided. As (III) concentrations from 264 to 81 μg g⁻¹ and As (V) concentrations from 246 to 59 μg g⁻¹ were found in Spanish cultivated mushrooms. For Chinese wild mushrooms As (III) varied between 624 and 117 μg g⁻¹ and As (V) from 380 to less than 5 μg g⁻¹. The accuracy of the method was checked by the determination of total As (from the sum of As (III) and As (V)) in a tomato leaves reference sample, with good agreement with the certified value.     

Determination of biogenic diamines with a vaporisation derivatisation approach using solid-phase microextraction gas chromatography–mass spectrometry

A gas-phase on-fibre derivatisation method for the determination of putrescine and cadaverine by gas chromatography/mass spectrometry using trifluoroacetylacetone (TFAA) has been studied and optimised. Small amounts (2 μl) of putrescine, cadaverine and TFAA standards were vaporised at high temperature in a 20 cm³ closed SPME vial. The subsequent derivatives were recovered from the headspace of the vial using a PDMS/DVB fibre. The optimised mole ratio for [TFAA]/[Putrescine + Cadaverine] reaction was 22.3/1 with a derivatisation and extraction temperature of 120 ^oC and an extraction time of 20 min. The retention times for the derivatised putrescine and cadaverine were 20.5 and 22.2 min, respectively on a capillary column, CP-Sil 8CB; 30 m length × 0.25 mm i.d. × 0.25 μm film thickness. The correlation coefficients (R²) of calibration curves for putrescine and cadaverine were 0.999 and 0.997, respectively over a range of sample masses of 20–350 ng, using nonadecane as an internal standard. Putrescine and cadaverine recoveries were determined to be 93.9% and 103.3%, respectively. The method was found to be a straightforward single step procedure that was unaffected by complex sample matrices and was successfully tested on samples of meat, vegetables and cheese.     

Ultrasound assisted-hollow fibre liquid-phase microextraction for the determination of selenium in vegetable and fruit samples by using GF-AAS

A rapid, simple and sensitive cleanup procedure is demonstrated for the determination of selenium in vegetable and fruit samples by using ultrasound assisted-hollow fibre-liquid microextraction (UA-HF-LPME) and graphite furnace atomic-absorption spectrometry (GF-AAS). Method is based on the microextraction of selenium from sample solution into 3.5 μL of organic solvent containing an N-octyl acetamide (OAA) as an extracting agent, which is placed inside the hollow fibre followed by ultrasound irradiation. The parameters that affected the extraction efficiency of selenium from sample solution were investigated. The best optimum conditions for the extraction of selenium were achieved for 15 min of extraction time with 500 rpm of agitation rate at the pH range of 0.8–3.0. The optimised methodology exhibited good linearity between 0.2 and 5 ng mL⁻¹ selenium with relative standard deviations (RSD) from 2.5% to 4.4%. The proposed method has been successfully applied for the determination of selenium from different types of vegetable and fruit samples. The potentiality of the present (UA-HF-LPME) method was compared with ultrasound assisted-single drop microextraction (UA-SDME). Thus, this approach proves that the UA-HF-LPME technique can be applied as a simple, fast and feasible diagnosis tool for the analysis of selenium in vegetable and fruit samples.     

Determination of anionic minerals in black and kombucha tea using ion chromatography

A simple, rapid and accurate method for the determination of anionic minerals in tea brew has been developed. The quantitative determination of anions – fluoride, chloride, bromide, iodide, nitrate, phosphate and sulphate was accomplished by anion exchange chromatography with conductometric detection. A Metrosep Anion Dual 2 analytical column connected in series with a Metrosep RP guard column was used for anion separation. A solution containing a mixture of 1.3 mM Na₂CO₃ and 2 mM NaHCO₃ was used as eluent. The method requires a simple sample clean-up procedure to remove the interfering organic components from the tea brew. The limit of detection for different anionic minerals were in the range 0.01–0.05 μg mL⁻¹ and the relative standard deviation were in the range 4–6% for the overall method. The recovery of different anionic minerals added was in the range 95–106%. The method was applied to the determination of anions in black and kombucha tea.     

Headspace gas chromatography–mass spectrometry determination of alkylpyrazines in cocoa liquor samples

This paper proposes a fast, accurate, and quantitative method for alkylpyrazines determination in cocoa liquors samples using gas chromatography with ion trap mass spectrometry detection (GC/IT-MS) and on-line headspace (HS) sample introduction. The optimization of the experimental conditions of the headspace gas chromatography–mass spectrometry (HS–GC–MS) system was carried out using the univariate method, aiming to find a compromise between time of the analysis, sensitivity and pyrazine resolution in a Carbowax (AV-WAX) fused silica capillary column. The procedure was validated through accuracy and precision studies. The results showed a highly satisfactory accuracy rate for the method with a relative standard deviation (RSD) during 1 day and between days of <5.0% (n = 5). On the other hand, the recovery percentages (94–99%) were quantitative in all cases, with a RSD of <4.0% (n = 5). Finally, the use the on-line headspace extraction step simultaneously with the analytes separation and detection of the previous sample injection increased the analysis frequency to 3 samples/h. A total of 120 cocoa liquor samples were analyzed.     

Analysis of residual oxytetracycline in fresh milk using polymer reversed-phase column

A simple and rapid reversed phase high performance liquid chromatograph (HPLC) method for analysis of oxytetracycline (OTC) was developed and applied in the determination of the antibiotic in fresh milk sample. Isocratic elution was performed with acetic acid:water (pH 4.5):acetonitrile (4:68:28), using a polymer reversed-phase (PLRP) column and UV detection at 354 nm wavelength. The average recoveries of OTC spiked milk at 0.1, 0.2, 0.5 and 100 ng/mL were in excess of 92% with intraday and interday precision between 0.8% and 6.6% respectively. A good linearity was established between the range 100–1000 ng/mL with r² = 0.9995. The limit of detection and quantitation were 30 and 100 ng/mL respectively. The method demonstrated successful application for analysis of 100 milk samples. Two samples out of 70 from livestock keepers tested OTC positive while none of the 30 samples from milk centers tested positive.     

Simultaneous determination of tetracycline,oxytetracycline, and 4-epitetracycline in milk by high-performance liquid chromatography

A reversed-phase high-performance liquid chromatography with photodiode-array detection (HPLC–PAD) was optimized and validated for the simultaneous determination of tetracycline (TC), 4-epitetracycline (4-epiTC) and oxytetracycline (OTC) in milk. Milk samples were extracted and cleaned-up using solid-phase extraction Discovery SPE DSC-18 tubes. The separation were accomplished in less than 8 min in a Waters Symmetry C18 column at ambient temperature with a mobile phase consisted of 0.010 M aqueous oxalic acid:acetonitrile:methanol (150:20:20 by volume). Quantitation was carried out by the peak area method, with detection limits of 2.0 μg/l of each tetracycline. Average recoveries of TC, 4-epiTC and OTC from spiked samples at the four concentrations (0.25, 0.5, 1.0 and 1.5 μg/ml) were 91.5, 71.5 and 83.1, respectively, with their standard deviations less than 4% within a day and 7% between days. This method was applied for the simultaneous determination of TC, 4-epiTC and OTC in market milk samples purchased from local supermarkets. Oxytetracycline was found being present in all samples in a concentration range of 13–106 μg/l, 4-epiTC in most samples at 18–65 μg/l, TC in one sample at 44 μg/l.