Micelle-Mediated Extraction and Flame Atomic Absorption Spectrometric Method for Determination of Trace Cobalt Ions in Beverage Samples

A new method has been developed for preconcentration of cobalt at trace levels in beverage samples using calcon carboxylic acid as chelating agent and cetyl pyridinium chloride as an auxiliary ligand and entrapped into Triton X-114 prior to its determination by flame atomic absorption spectrometry (FAAS). The main parameters affecting cloud point extraction (CPE) efficiency such as pH, concentration of the complexing agent, cationic and nonionic surfactant concentration, salt effect, the equilibrium time, and temperature were investigated and optimized. After optimization of the CPE conditions, a preconcentration factor of 60, an enhancement factor of 106, and a detection limit of 0.20 μg L⁻¹ by (R ² = 0.9978) were obtained from a calibration curve constructed in the range of 0.7–100 μg L⁻¹. The proposed preconcentration procedure was successfully applied to the determination of cobalt ions in some real samples including natural drinking water, tap water, and beer and wine samples. The accuracy and validity of the proposed CPE/FAAS method was tested by means of five repeated analysis of reference standard materials (TM-253, a low level fortified water standard for trace elements). A good agreement between analytical results (28.8 and 28.5 μg L⁻¹ with calibration curve and standard addition curve method, respectively) and certified value (27.9 μg L⁻¹) for Co (p < 0.05) were obtained and verified by means of calibration curve and standard addition curve method using CPE procedure.     

Optimization of Solid-Phase Microextraction Procedure Coupled to GC-ECD for Triazole Fungicides Determination in Juice Samples

A solid-phase microextraction (SPME) procedure followed by gas chromatography electron capture detection (GC/ECD) for the determination of triazole residues was developed. An experimental design with two steps was done. Firstly, a 2⁶⁻² fractional factorial design for screening several experimental variables (fiber-coating type, extraction temperature, extraction time, stirring rate, desorption temperature, and desorption time) was done. After, a two-factor central composite design for optimizing, the experimental conditions were carried out. The chosen experimental conditions were: fiber, PDMS/DVB; extraction time, 45 min; extraction temperature, 60 °C; desorption time, 3 min; desorption temperature, 260 °C, and stirring speed, 500 rpm. Using those conditions the limits of detection obtained for tetraconazole, myclobutanil, and diniconazole were in the order of few μg L⁻¹ in grape and apple liquid extracts. Recoveries were from 93.6% to 112.1%. Relative standard deviation ranged from 1.2% to 11.6% (apple) and 6.7 to 18.0% (grape). The method was applied to five grape samples and 13 apple samples collected in Navarra, Rioja, and Basque Country. Quantification was performed by the standard addition method. Three standard additions by duplicate covering adequate range concentration were used. Myclobutanil was found in three apple samples (110–122 μg L⁻¹) and diniconazole in one grape sample (9.4 μg L⁻¹).     

Simultaneous and Direct Determination of As, Bi, Pb, Sb, and Se and Co, Cr, Cu, Fe, and Mn in Milk by Electrothermal Atomic Absorption Spectrometry

Tungsten permanent modifier with coinjection of Pd(NO₃)₂ and W–Ru permanent modifiers are proposed for the direct and simultaneous determination of As, Bi, Pb, Sb, and Se (group 1) and Co, Cr, Cu, Fe, and Mn (group 2), respectively, in milk by graphite furnace atomic absorption spectrometry. The performance of modifiers was evaluated by means of thermal behavior of analytes, sensitivity, atomic signal profile, repeatability, graphite tube lifetime, and background intensity. An air-assisted pyrolysis step was necessary to quantitative elimination of the organic matter. After methods optimization, 14 commercial milk samples were analyzed. The found concentrations of As, Bi, Pb, Sb, Se, Co, and Cr were lower than their limit of detection (2.13, 2.21, 1.49, 1.63, 2.05, 1.0, and 1.2 μg L⁻¹, respectively). Concentrations of Cu, Fe, and Mn were in the 1.58–5.74 μg L⁻¹, 9.79–49.3 μg L⁻¹, and 2.25–4.08 μg L⁻¹ intervals, respectively. The limits of detection for Cu, Fe, and Mn were 1.7, 5.3, and 2.0 μg L⁻¹, respectively. The accuracy of methods was checked after analysis of two milk standard materials. Results for Cr, Cu, Fe, Mn, Pb, and Mn were in agreement with certified values of SRMs at the 95% confidence level. Accuracy was also evaluated by addition–recovery tests and recoveries in the 86–127% range were obtained for all elements. The use of pretreat platform of graphite tubes with W or W–Ru allowed enlarging the lifetime of atomizer in 750 heating cycles.     

Determination of Copper,Cobalt, Lead,and Iron in Table Salt by FAAS After Separation Using Violuric Acid and Multiwalled Carbon Nanotubes

A separation–enrichment technique for the determination of trace amounts of copper(II), cobalt(II), lead(II), and iron(III) as violuric acid chelates on multiwalled carbon nanotubes at pH 6.0 was established. Analytes were determined by flame atomic absorption spectrometry. The effects of some analytical parameters like pH, amounts of violuric acid, flow rates, eluent type, and sample volume were investigated. The influences of the matrix ions were also investigated. The relative standard deviations for analyte elements were below 10%. The quantification limits of the analyte ions were found as 0.36 μg g⁻¹ for copper, 0.43 μg g⁻¹ for lead, 0.15 μg g⁻¹ for cobalt, and 0.38 μg g⁻¹ for iron. The accuracy of presented method was checked by the analysis of TMDA 54.4 fortified lake water, NIST SRM 1515 apple leave, and HR-1 Humber river sediment certified reference materials. The method was applied to analyte contents of table salt samples from different origin. The levels of iron in the analyzed table salt samples were found in the range of 1.6–6.4 μg g⁻¹, while lead was found in only one sample as 5.0 μg g⁻¹. In all other samples, cobalt, lead, and copper were found below the quantification limits of the analytes.     

Square-Wave Adsorptive Stripping Voltammetry for Trace Determination of Dimoxystrobin and Azoxystrobin in Potatoes and Grapes

Square-wave voltammetry was used for trace determination of azoxystrobin and dimoxystrobin in potatoes, grapes, and grape juice. Experimental conditions have been optimized to achieve simultaneous determination of these analytes using the hanging mercury drop electrode. Supporting electrolyte was HCl 0.1 mol L⁻¹, and other optimized conditions were deposition potential (−300 mV), deposition time (30 s), amplitude (150 mV), frequency (150 Hz), and step height (2 mV). Azoxystrobin and dimoxystrobin redissolution peaks presented their maxima, respectively, at −928 mV and around −650 mV. Linear and homoscedastic analytical responses (r ² > 0.99) have been observed. Limits of quantification as low as 119 μg L⁻¹ (in grape juice) and 45 μg kg⁻¹ (in potatoes and grapes) were found. A previous solid-phase extraction was necessary to eliminate interferences from potato and grape samples. For grape juice, no sample treatment was required. Satisfactory recoveries (from 72.3% to 96.7% for dimoxystrobin and from 81.7% to 102.3% for azoxystrobin) were found. Interferences from other strobilurins (piraclostrobin and picoxystrobin) were evaluated.     

On-line Solid-Phase Extraction Coupled to Liquid Chromatography–Ion Trap Tandem Mass Spectrometry for Determination of Penicillins in Catfish

A highly selective method was developed for the simultaneous determination of eight penicillins in catfish using automated on-line solid-phase extraction coupled to liquid chromatography–tandem mass spectrometry (XLC–MS/MS). The type of cartridge, equilibration sample volume, volume of solvent to carry the sample into the cartridge, and elution times were studied in order to optimize the XLC operating conditions. MS/MS conditions were also adjusted for better peak resolution. The present method was validated in agreement with the criteria of Commission Decision 2002/657/EC, showing a linear range from 2 to 350 μg kg⁻¹ and regression coefficient higher than 0.995 for the studied penicillins. Decision limits, calculated in the case of substances with no permitted limit, were lower than 0.6 μg kg⁻¹, and detection capability values were lower than 2.0 μg kg⁻¹. Samples spiked at 2.0, 10.0, and 50.0 μg kg⁻¹ showed high recovery (72–92%) and precision values lower than 20% except for amoxicillin. The present method was also applied for the analysis of penicillins in 30 catfish samples bought in local markets.     

Determination of Melamine in Liquid Milk and Milk Powder by Titania-Based Ligand-Exchange Hydrophilic Interaction Liquid Chromatography

A simple and rapid high-performance liquid chromatography (HPLC) procedure for the analysis of melamine in liquid milk and milk powder has been developed. Decrease of acetonitrile percentage and phosphate buffer concentration in mobile phase, and lowering of buffer pH and column temperature would benefit the retention of melamine on titania. Taking advantage of the ligand-exchange and hydrophilic interaction mixed retention mode on bare titania column, neither complex pretreatment nor ion-pair reagent was required. The whole analysis for one sample including sample pretreatment and HPLC analysis could be accomplished within 30 min. The method presented good linearity (R ² = 0.9998) in a wide range of 0.02–10 μg mL⁻¹. The limit of detection (3σ) and limit of quantification (10σ) of the method were 6 and 20 μg L⁻¹, respectively, which were equivalent to 15 and 50 μg kg⁻¹ melamine in liquid milk, 60 and 200 μg kg⁻¹ melamine in milk powder, respectively. Such sensitivity could be compared with those obtained by HPLC with solid-phase extraction or HPLC coupled with tandem mass spectrometry and was adequate for the screening of melamine in tainted dairy products. The repeatability (RSDs) of the retention times and peak areas of 11 replicate detections of 1.0 μg mL⁻¹ melamine were 0.32% and 2.5%, respectively. The intermediate precision on three consecutive days (RSDs, n = 6) of the retention times and peak areas were 1.1% and 2.3%, respectively. The recovery of spiked melamine in dairy samples ranged from 95.2% to 105%. The simplicity, sensitivity and rapidity of the proposed method make it an effective alternative detecting technique for melamine.     

Total Mercury, Inorganic Mercury and Methyl Mercury Determination in Red Wine

This study deals with the development of a method for total Hg, inorganic Hg and methylmercury (MeHg) determination in red wine by using flow injection-cold vapour generation–inductively coupled plasma mass spectrometry (FI-CVG-ICP-MS) and gas chromatography-ICP-MS (GC-ICP-MS). For Hg speciation analysis, a derivatization step was carried out using a 1% (m/v) sodium tetraphenylborate (NaBPh₄) solution, followed by extraction of Hg species and their quantification by GC-ICP-MS. The main parameters evaluated were the make-up gas flow rate, volume of the NaBPh₄ solution, time for derivatization reaction/analyte extraction and solvent used for Hg species extraction. Accuracy was evaluated by analyte recovery, whereas recoveries ranged from 99% to 104% for Hg(II) and MeHg. The limits of detection (LODs) for Hg(II) and MeHg were 0.77 and 0.80 μg L⁻¹, respectively. Wine from Argentina, Brazil, Chile and Uruguay were analysed. The wine samples were also acid digested for total Hg determination by FI-CVG-ICP-MS. The LOD of the method used for total Hg determination was 0.01 μg L⁻¹. The concentrations of Hg species in red wine measured by GC-ICP-MS were lower than the respective LODs. Only total Hg was detected in the analysed samples, where the highest concentration of Hg found was 0.55 ± 0.02 μg L⁻¹.     

Determination and Evaluation of the Mineral Composition of Chinese Cabbage (Beta vulgaris)

Inductively coupled plasma optical emission spectrometry was used to determine the elements present in Chinese cabbage (Beta vulgaris). The accuracy of the method was confirmed by analysis of a certified reference material of spinach leaves. The study involved 57 samples that were collected in 13 Brazilian cities. Average concentrations of elements found per gram of Chinese cabbage were as follows: 3.44 mg g⁻¹ sodium, 5.09 mg g⁻¹ potassium, 1.25 mg g⁻¹ phosphorous, 0.85 mg g⁻¹ calcium, 0.49 mg g⁻¹ magnesium, 2.79 μg g⁻¹ manganese, 9.50 μg g⁻¹ iron, 0.74 μg g⁻¹ copper, 14.28 μg g⁻¹ zinc, and 6.44 μg g⁻¹ strontium. Principal component analysis and hierarchical cluster analysis demonstrated that there is no systematic difference in the mineral composition between the cabbage samples that were analyzed.     

Analytical procedure based on slurry sampling for determining selenium in organic vegetable samples by graphite furnace atomic absorption spectrometry

This paper presents a simple, fast and sensitive method to determine selenium in vegetable samples by graphite furnace atomic absorption spectrometry through the direct introduction of slurries of the samples into the spectrometer’s graphite tube. The limits of detection and quantification calculated for 20 readings of the blank of the standard slurries (5 mg mL⁻¹ of microcrystalline cellulose) were 0.33 and 1.10 μg L⁻¹. The proposed method was applied to determine selenium in samples of organically grown vegetables and its results proved compatible with those obtained from samples mineralized by acid digestion in a microwave oven.     

Effects of Maillard reaction conditions on the antigenicity of α-lactalbumin and β-lactoglobulin in whey protein conjugated with maltose

The effects of Maillard reaction conditions (weight ratio of protein to sugar, temperature and time) on the antigenicity of α-lactalbumin (α-LA) and β-lactoglobulin (β-LG) in conjugates of whey protein isolate (WPI) with maltose were investigated. Response surface methodology was used to establish models to predict the antigenicity of α-LA and β-LG and find an optimal reaction condition under which the antigenicity of α-LA and β-LG reduces to minimum value. Conjugating WPI with maltose was an effective way to reduce the antigenicity of α-LA and β-LG. The antigenicity of α-LA decreased from 32.25 μg mL⁻¹ to 10.91 μg mL⁻¹. And the antigenicity of β-LG decreased from 272.4 μg mL⁻¹ to 38.17 μg mL⁻¹. Temperature had the greatest effect on the antigenicity of α-LA, while weight ratio of WPI to maltose was the most significant factor on the antigenicity of β-LG.     

Effect of dynamic high-pressure microfluidization at different temperatures on the antigenic response of bovine β-lactoglobulin

The antigenic response of β-lactoglobulin (β-Lg), treated by dynamic high-pressure microfluidization (DHPM) at different temperatures, was determined by an indirect competitive enzyme-linked immunosorbent assay using polyclonal antibodies from rabbit serum. DHPM treatment causes changes in the protein structure and may influence the antigenicity of β-Lg. DHPM treatment of β-Lg at 90 °C showed significant effects with the antigenic response of 5.2 μg mL⁻¹ (untreated), 45 μg mL⁻¹ (40 MPa), 79 μg mL⁻¹ (80 MPa), 132 μg mL⁻¹ (120 MPa), and 158 μg mL⁻¹ (160 MPa). In combination with temperature treatment (70–90 °C), the antigenic response enhanced as the temperature increased at 160 MPa. The β-Lg antigenicities were about 14, 108, and 158 μg mL⁻¹ at 70, 80, and 90 °C, respectively. However, the influence of DHPM pressures on the antigenic response of β-Lg standards was different. DHPM modified β-Lg standards showed a remarkable increase in antigenicity when treated to 80 MPa. Above 80 MPa, the antigenic response decreased.     

Determination of copper in fish feed by graphite furnace atomic absorption spectrometry using slurry sampling

The present work develops and optimizes a method to determine copper in samples of feces and fish feed by graphite furnace atomic absorption spectrometry (GFAAS) through the direct introduction of slurries of the samples into the spectrometer’s graphite tube coated internally with metallic rhodium and tungsten carbide that acts as chemical modifiers. The limits of detection (LOD) and quantification (LOQ) calculated for 20 readings of the blank of the standard slurries (0.50% m/v of feces or feed devoid of copper) were 0.24 and 0.79 μg L⁻¹ for the standard feces slurries and 0.26 and 0.87 μg L⁻¹ for the standard feed slurries. The proposed method was applied in studies of absorption of copper in different fish feeds and their results proved compatible with that obtained from samples mineralized by acid digestion using microwave oven.     

Polycyclic aromatic hydrocarbons (PAHs) in traditional and industrial smoked beef and pork ham from Serbia

Smoked beef and pork ham samples were analysed during process of smoking (after packing and storing) for the presence of the 16 EU priority PAHs via Fast GC/HRMS method. This study showed that there are differences in PAH contents between final smoked beef ham samples from traditional smokehouse (TS) (3.9 μg kg⁻¹) and industrial smokehouse (IS), (1.9 μg kg⁻¹). Also there is a difference in PAH contents in final smoked pork ham samples (4.9 μg kg⁻¹, TS; 4.2 μg kg⁻¹, IS). In beef and pork ham samples from the same smokehouse different PAH contents were observed during smoking. The highest content of examined PAHs in all beef and pork ham samples during smoking showed benzo[c]fluorene (BcL) (beef ham: from 0.3 μg kg⁻¹ to 1.5 μg kg⁻¹; pork ham: from 0.2 μg kg⁻¹ to 2.1 μg kg⁻¹).The maximum level for benzo[a]pyrene (BaP) of 5 μg kg⁻¹ in smoked meat products was not exceeded in any samples. Correlation statistic analysis (P < 0.05) of obtained contents from samples both from TS and IS showed that BaP is a good marker both for 16 EU priority PAHs and 12 IARC probably and possibly carcinogenic PAHs (IS: R _BaP/Σ16PAHs = 0.95, R _BaP/Σ12PAHs = 0.96; TS: R _BaP/Σ16PAHs = 0.71, R _BaP/Σ12PAHs = 0.88).     

ITS-RFLP characterization of black <Emphasis Type="Italic">Aspergillus</Emphasis> isolates responsible for ochratoxin A contamination in cocoa beans

In the present study, ochratoxigenic mycobiota in cocoa beans was identified at species level by digestion of the ITS products using the endonucleases HhaI, NlaIII and RsaI. Of the 132 isolates of Aspergillus section Nigri collected from cocoa beans, 89 were identified as A. tubingensis, 27 as A. niger, 10 as A. tubingensis-like and 6 as A. carbonarius. No variation was observed between RFLP patterns (C, N, T1 and T2) described previously for grape isolates and those of the cocoa isolates analysed. With respect to OTA-producing fungi, a high percentage of black aspergilli (50.7%) was able to produce OTA. Additionally, most of the OTA-producing isolates were of moderate toxigenicity, producing amounts of OTA from 10 μg g⁻¹ to 100 μg g⁻¹. Percentages of OTA-producing isolates in the A. niger aggregate were higher than in other substrates, ranging from 30% to 51.7%. Furthermore, the detected levels of OTA production in the A. niger aggregate, particularly in A. tubingensis species was higher than in A. carbonarius, ranging from 0.7 μg g⁻¹ to 120 μg g⁻¹ (mean 24.55 μg g⁻¹). Due to the high occurrence, percentage of ocratoxigenic isolates and their ability to produce OTA, isolates belonging to the A. niger aggregate could be considered as the main cause of OTA contamination in cocoa beans used for manufacturing cocoa products.     

On-line Preconcentration and Determination of Zinc Using Zincon and Flame Atomic Absorption Spectrometry

In this work, a method for on-line preconcentration and determination of zinc was developed. A miniglass column (35 × 3 mm) containing 70 mg of Dowex 1X8 resin modified with 1% (w/w) of zincon was coupled into the FI-FAAS system. During the extraction procedure, it was verified that the metal reacts with the complexing reagent in the pH range from 9.0 to 10.0. After optimization of parameters such as type and concentration of the eluent, buffer concentration, elution time, sample and buffer flow rate, mixing coil length, and effect of foreign ions, the FI-FAAS system presented an enrichment factor of 10 and at least 200 reutilizations of the column were possible. The detection limit was 0.67 μg L⁻¹, and a relative standard deviation of 5% was obtained. The accuracy of the method was evaluated by using certified reference material, showing good accuracy. The proposed method was successfully applied for the determination of zinc in beverages.     

Speciation of Organic and Inorganic Selenium in Selenium-enriched Eggs by Hydride Generation Atomic Fluorescence Spectrometry

A new method was established for the speciation of Se by hydride generation-atomic fluorescence spectrometry. Effective separation of organic and inorganic Se in Se-enriched eggs was achieved by precipitating albumen with trichloroacetic acid. The detection limit for Se was 0.07 μg L⁻¹. The proposed method was successfully applied for the determination of organic and inorganic Se as well as total Se in Se-enriched eggs with the recovery of 90.1–112% and the relative standard deviation (n = 5) of 0.6–3.4%. Se in Se-enriched eggs presents mainly in organic forms, the content of which was three to seven times that of inorganic Se.     

Quantification of Nitrite/Nitrate in Food Stuff Samples Using 2-Aminobenzoic Acid as a New Amine in Diazocoupling Reaction

2-Aminobenzoic acid has been used as an amine in diazocoupling reaction to form an azo dye in the quantification of nitrite/nitrate at trace level. The formed azo dye has an absorption maximum at 550 nm in aqueous phase, and the resulted dye can be extracted into organic solvent to lower the detection limit. The method obeys Beer's law in the concentration range 0–10 μg of nitrite in 25 ml of aqueous solution with a molar absorptivity of 3.6 × 10³ L mol⁻¹ cm⁻¹ and 0–2 μg of nitrite in 5 ml of organic phase. The detection limit of the dye has been found to be 0.056 μg ml⁻¹. Nitrate is determined by reducing it to nitrite after passing through a copperized cadmium reductor column. The effect of interfering ions on the determination of nitrite/nitrate has been described. The developed method has been applied to determine the nitrite/nitrate trace level in vegetable, fruit juice, and milk powder samples.     

Co-production of Lactic Acid and <Emphasis Type="Italic">Lactobacillus rhamnosus</Emphasis> Cells from Whey Permeate with Nutrient Supplements

Lactic acid and cell production from whey permeate by Lactobacillus rhamnosus with different nutrient supplements were investigated in this study. Yeast extract was identified as the most effective nutrient affecting lactic acid production. Increase in inoculum size from 0.05% to 1% (v/v) resulted in a substantial increase in lactic acid productivity from 0.66 to 0.83 g L⁻¹ h⁻¹ (P < 0.001). The optimal temperature for lactic acid production was 37 °C, while the highest cell production was obtained at 42 °C. When whey permeate and yeast extract concentrations were 6.8% (w/v) and 3 g L⁻¹, respectively, lactic acid productivity reached 0.85 g L⁻¹ h⁻¹ after 48-h cultivation, which is 3.40 times of those without nutrient supplements.     

Substitution of Antibody with Molecularly Imprinted Film in Enzyme-Linked Immunosorbent Assay for Determination of Trace Ractopamine in Urine and Pork Samples

A new direct competitive enzyme-linked immunosorbent assay (ELISA) with molecularly imprinted film as artificial antibody was developed to detect ractopamine (RAC) in urine and pork samples. The imprinted film was directly synthesized on the well surface of 96-well plate by an organic–inorganic hybrid technology and evaluated by fourier transform infrared (FT-IR), static, and kinetic adsorption experiments. The imprinted film exhibited an antibody-like binding ability and rapid adsorption speed. The established ELISA method gave a good sensitivity (IC₅₀, 15.77 μg L⁻¹) and a low detection limit (IC₁₅, 0.01 μg L⁻¹) for RAC under the optimum conditions, and it was applied to the determination of RAC in urine and pork samples spiked at three levels with recoveries ranging from 77.7% to 108.9% (urine) and from 93.5% to 101.1% (pork). The obtained results, which correlated well with those gained from the traditional high performance liquid chromatography (HPLC) method, demonstrated that the developed ELISA method was reliable for RAC determination in real samples.