Simultaneous determination of ultra trace amounts of lead and cadmium in food samples by adsorptive stripping voltammetry

A selective and sensitive method for simultaneous determination of lead and cadmium by adsorptive differential pulse cathodic stripping voltammetry is presented. The method is based on adsorptive accumulation of the complexes of Pb (II) and Cd (II) ions with 2-mercaptobenzothiazole onto hanging mercury drop electrode (HMDE), followed by the reduction of the adsorbed species by differential pulse cathodic stripping voltammetry. Optimal conditions were obtained at pH 8.0, 2-mercaptobenzothiazole concentration of 1.0 × 10⁻⁴ M, the accumulation potential of −0.4 V (vs. Ag/AgCl), the accumulation time of 160 s, and the scan rate of 100 mV/s. Under optimised conditions, linear calibration curves were established for the concentration of Pb (II) and Cd (II) in the range of 0.5–70 and 0.2–30 ng/ml, respectively, with detection limit of 0.017 ng/ml for Pb (II) and 0.01 ng/ml for Cd (II). The procedure was successfully applied to the simultaneous determination of both ions in food samples (rice, soya and sugar).     

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.     

Kinetic-spectrophotometry method for determination of ultra trace amounts of aluminum in food samples

A simple and sensitive kinetic-spectrophotometry method is developed for the determination of trace amounts of aluminum in food samples based on its catalytic effect on the oxidation of Nile Blue A by potassium bromate in sulfuric acid medium. The absorbance is measured at 595.5 nm with the fixed-time method. The optimization of the operating conditions regarding concentrations of the reagents, temperature and interferences are also investigated. The calibration curve is linear over the concentration range 0.07–0.9 μg ml⁻¹ of aluminum with good precision and accuracy and the detection limit was down to 0.034 μg ml⁻¹. The relative standard deviation for a standard solution of 0.4 μg ml⁻¹ of aluminum is 1.73% (n = 10). The proposed method proved highly sensitive, selective and relatively rapid for the assay of aluminum at ultra trace level without any pre-concentration and separation step. The method was applied to the determination of aluminum in food samples (rice, tea and potato). The analytical results of the real samples were in good agreement with the standard method.     

Determination of lead and cadmium in food samples by the coprecipitation method

In this study, the coprecipitation method developed using a combination of 2-mercaptobenzothiazole (MBT) as a chelating reagent and copper as coprecipitate carrier was used for the determination of trace lead and cadmium in various food samples by graphite furnace atomic absorption spectrometry (GFAAS). The method was applied for the determination of Pb(II) and Cd(II) in salami, sausage, chicken, anchovy, spinach, cabbage, onion, dill, parsley, lettuce, tea and rice samples. The matrix modifiers were added as 50 μg NH₄H₂PO₄ + 3 μg Mg(NO₃)₂ for both Pb(II) and Cd(II). The signals were measured as peak area. The concentrations of Pb(II) and Cd(II) in the food samples were found to be in the range of 6.63 ng g⁻¹ (anchovy) −3.30 μg g⁻¹ (spinach) and 2.67 ng g⁻¹ (salami) −0.51 μg g⁻¹ (lettuce), respectively.     

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.     

A highly sensitive method for simultaneous determination of ultra trace levels of copper and cadmium in food and water samples with luminol as a chelating agent by adsorptive stripping voltammetry

In the present study a selective method is presented for the simultaneous determination of copper and cadmium in food samples by adsorptive stripping voltammetry. In preliminary studies, it has been proven that the copper and cadmium react with 3-aminophthalhydrazide (luminol), giving rise to the formation of these complexes. These complexes have adsorptive characteristics on hanging mercury drop electrode (HMDE) and can be reduced in a reduction step. In this study the optimum reaction parameters and conditions studies are investigated. The calibration graphs were linear in the concentration range of 0.5–105.0 and 0.8–70.0 ng/ml for copper and cadmium, respectively. The limit of detection of the method was 0.04 ng/ml for Cu²⁺ and 0.02 ng/ml for Cd²⁺. The interference of some common ions was studied and it was concluded that application of this method for the determination of copper (II) and cadmium in food and water samples led to satisfactory results.     

Development of organic phase amperometric biosensor for measuring cholesterol in food samples

Previous works on organic phase enzyme electrodes (OPEE) applied methods that worked mostly under stirred conditions. The aim of our present work was to develop a flow-through measuring set-up for determination of cholesterol content in organic media. For determination of free cholesterol content cholesterol oxidase (COD) was used, while for measuring the total cholesterol content a bi-enzyme cell containing immobilised cholesterol esterase (CE) and cholesterol oxidase was developed. Enzyme immobilisation took place on a natural protein membrane, by a glutaraldehyde cross-linking method, in a thin-layer enzyme cell made from Teflon. The enzyme cell was connected into a stopped-flow injection system (SFIA), with a flow-through amperometric detector. The parameters of biochemical and electrochemical reactions were measured. The effect on amperometric detection of different organic salts as electron mediator or conducting salts was studied. The optimal concentration of (TBATS) was 2.4 mg L^–1 while for (FMCA) an optimal concentration was found at 0.4 mg L^–1. The minimum amount of water, necessary for enzymatic activity in the organic phase, was also determined. Changing the concentration of toluene in acetonitrile carrier solution, the peaks increased definitely in the range 10–40% toluene. Since CE and COD were immobilised together in the enzyme cell, the conversion rate was found to be about 0.7–0.8 when the toluene content was higher then 30%. The linear measuring range for cholesterol oleate and cholesterol was 0.1–0.5 mM. Total cholesterol content of lard, butter and pasta samples were determined. It is concluded that an organic phase bi-enzyme cell may be suitable for cholesterol determination in food.     

Analytical application of food dye Sunset Yellow for the rapid kinetic determination of traces of copper(II) by spectrophotometry

A sensitive and rapid kinetic method for trace determination of Cu(II) was developed and validated, based on its catalytic effect on the oxidation of disodium-6-hydroxy-5-[(4-sulphophenyl)azo]-2-naphtalenesulphonic acid (wide used, food colour “Sunset Yellow FCF”, E110, in text selected as SY) by hydrogen peroxide in borate buffer at pH 10.5. The reaction was monitored spectrophotometrically by measuring the decrease in the absorbance of SY at 478.4 nm. The optimum operating conditions regarding concentration of reagents, pH and temperature were established. The calibration curve was linear up to 318 ng mL⁻¹ of Cu(II) and the limit of detection (3σ/S) is 5.0 ng mL⁻¹, and limit of quantification (10σ/S) is 16.67 ng mL⁻¹. The proposed kinetic procedure was successfully applied to monitoring of the concentration of Cu(II) in fruit, wine and milk samples from different areas. The results obtained by the proposed kinetic procedure were compared by those obtained by ICP-OES method, and shown good agreement. The proposed kinetic method could be used for monitoring of quality of drinks or fruit depending on Cu(II) concentration, because of its important role as nutritional element.     

The use of inductively coupled plasma mass spectrometry (ICP-MS) for the determination of toxic and essential elements in different types of food samples

This paper describes a simple method for the determination of sixteen elements in food samples by using inductively coupled plasma spectrometry (ICP-MS). Prior to analysis, 100–250 mg of powdered food samples were accurately weighed into a Teflon digestion vessel. Then, 4 ml of 20% v/v concentrated nitric acid and 2 ml of hydrogen peroxide were added. Decomposition of samples was carried out in a microwave digestion system. In order to verify the accuracy and precision of the proposed method, five Standard Reference Materials from the National Institute of Standards and Technology (NIST) (Whole Egg Powder RM 8415, Rice Flour SRM 1568a, Typical Diet SRM 1548a, Wheat Flour SRM 1567a and Bovine Muscle Powder RM 8414) were analyzed. Additional validation data are provided based on the analysis of 18 different types of food samples by the proposed method and using comparative methods with AAS as the detector.     

Pyridine‐2,6‐diamine‐functionalized Fe3O4 nanoparticles as a novel sorbent for determination of lead and cadmium ions in cosmetic samples

A novel sorbent based on pyridine‐2,6‐diamine‐functionalized Fe₃O₄ nanoparticles was developed and characterized by X‐ray powder diffraction (XRD), elemental analysis, IR spectroscopy and scanning electron microscopy (SEM). The application of the sorbent was investigated for pre‐concentration and determination of lead and cadmium ions in aqueous samples. Effects of various factors such as the sample pH, eluent parameters (type, concentration and volume) and time (adsorption and desorption) were appraised. The effects of several interfering ions on method recovery were also investigated. The limit of detection (LOD) was found to be 1.3 and 0.089 μg L^?1 for lead and cadmium ions, respectively. Recovery and precision (RSD%) of the method were above 97.9% and below 0.6%, respectively. Validation of the outlined method was performed by analysing several certified reference materials. This method was successfully used for determination of lead and cadmium ions in several cosmetic samples, which are usually contaminated by lead and cadmium ions.     

钼蓝比色法测定保健食品中微量硒

建立了钼蓝比色法测定保健食品中微量硒的新方法。该方法最大吸收波长760nm,在0～100ng/mL浓度范围内浓度与吸光度呈线性关系,回归方程y=-4.142＋133.2x,相关系数r=0.9991,最低检测量1ng/mL,重复性好,RSD=3.17%,回收率95.98%～105.00%。该方法简便、快速、灵敏、准确,适合不同补硒类保健食品中的硒含量测定,该方法的建立有利于这类产品质量控制和提高。     

氢化物发生-原子荧光光谱法同时测定食品中的镉和锡

为提高食品中镉和锡的检测水平,建立了氢化物发生-原子荧光光谱法同时测定食品中的镉和锡的方法.在最佳实验条件下的检出限:镉0.002 9 ng/ml、锡0.19 ng/ml;线性范围:镉0～2ng/ml,相关系数0.999 8,锡0～100 ng/ml,相关系数0.999 9;在0.5 ng/ml时,镉测定的相对标准偏差为1.5%(RSD),2.5 ng/ml时锡的相对标准偏差为3.1%(RSD);试样加标回收率:镉93.0%～100.5%,锡91.3%～99.2%.该方法具有操作简便、快速、检出限低、灵敏度高、结果准确等优点,适合于各种食品镉、锡的联合测定.     

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%.     

分光光度计法测定食品中的微量铅

本文研究了在混合表面活性剂聚乙烯醇 (PVA)和聚乙二醇辛基苯基醚 (OP)存在下 ,铅(Ⅱ )与碘化钾、罗丹明B形成水溶性离子缔合物的条件 ,该缔合物λmax=5 60nm ,表观摩尔吸光系数ε560 =2 .7× 10 5L/mol·cm ,铅量在 0～ 6μg/ 2 5mL范围内服从比耳定律。经苯萃取分离 ,排除干扰后 ,用于大米、白酒等食品中微量铅的测定 ,结果满意。     

The determination of l-carnitine in several food samples

We designed this study to re-validate some methodological parameters of the radio-enzymatic assay, including phenomena of residual, non-carnitine radioactivity present in some assay mixtures of food samples. The second part of the paper presents l-carnitine concentrations (total-, free- and acyl-carnitine) in a wide range of food samples of animal and plant origin.     

Determination of furan in food samples using two solid phase microextraction fibers based on sol-gel technique with gas chromatography-flame ionisation detector

The headspace solid-phase microextraction (HS-SPME) method with two different coatings synthesized by sol-gel technology [such as poly(ethylene glycol) (PEG) and PEG reinforced with multi-walled carbon nanotubes (PEG/CNTs)] coupled with gas chromatography-flame ionization detector (GC-FID) was proposed for the determination of furan at trace levels in food samples. Under optimized conditions, the linear range for furan with PEG and PEG/CNTs fibers was 0.005-10 and 0.0005-10 ng/mL, the limit of detection (S/N = 3) was 0.001 and 0.00025 ng/mL and the limit of quantification (LOQ) was 0.005 and 0.0005 ng/mL, respectively. For PEG and PEG/CNTs fibers, repeatability (n = 5) was 6.2% and 4.9% and reproducibility (n = 3) was 6.6% and 5.3%, respectively. Relative recoveries for the spiked samples with 0.1 ng/mL of furan were ranged from 92% to 103%. The proposed HS-SPME-GC-FID method was successfully applied for the extraction of furan in two environmental food samples (baby food and fruit juice).     

原子吸收分光光度法测定食品中微量元素

用原子吸收法测定营养食品莲子，麦片，黑芝麻糊，豆奶粉中的Fe,Zn,Ca,Mn,Cu,K,Na等7种微量元素的含量。采用标准加入法进行回收率测定，测得回收率在95.0%-108.0%。相对标准偏差在0.3%-3.3%。     

HPLC determination of stevioside in plant material and food samples

 An HPLC method for the determination of sweet-tasting stevioside (STS) in the leaves of the plant Stevia rebaudiana and in some beverages (e.g. tea, orange juice) was developed. The pre-separation procedure consisted of extraction of STS from the plant material using boiling water and a solid-phase extraction (SPE). Recovery rates of the SPE for the analysed matrices ranged from 92.8% to 97.8% (for concentrations of STS of 105, 210 and 300 μg/ml; Relative Standard Deviation (RSD)≤3.3%). The chromatographic separations were realized using a C₁₈ column, the mobile phase consisting of methanol and water, and with UV detection at 210 nm. The limits of determination of STS were 5 μg/ml for the leaf extracts and the tea sample and 8 μg/ml for the juice sample. Received: 7 April 1998     

HPLC determination of stevioside in plant material and food samples

 An HPLC method for the determination of sweet-tasting stevioside (STS) in the leaves of the plant Stevia rebaudiana and in some beverages (e.g. tea, orange juice) was developed. The pre-separation procedure consisted of extraction of STS from the plant material using boiling water and a solid-phase extraction (SPE). Recovery rates of the SPE for the analysed matrices ranged from 92.8% to 97.8% (for concentrations of STS of 105, 210 and 300 μg/ml; Relative Standard Deviation (RSD)≤3.3%). The chromatographic separations were realized using a C₁₈ column, the mobile phase consisting of methanol and water, and with UV detection at 210 nm. The limits of determination of STS were 5 μg/ml for the leaf extracts and the tea sample and 8 μg/ml for the juice sample. Received: 7 April 1998     

分光光度法用于食品中锰含量的测定

建立用分光光度法测定食品大蒜、菠萝、茶叶中锰含量的方法,锰的含量在0.5～5 μg/mL范围内,吸收度与浓度成线性关系.线形方程为A=0.01427+0.07859c,相关系数r=0.9999.在实际样品中的回收率为90.9%～102.5%.该方法简单,准确,选择性好,不需对样品进行分离,适用于食品中微量锰含量的测定.