Pico molar assay of riboflavin in human urine using voltammetry

Using a new type of DNA and carbon nano tube (CNT) mixed paste electrode using cyclic and square wave anodic stripping voltammetric (SWASV) methods, this study presents an assay of riboflavin (RF) under optimum conditions. Results of the experiment yielded a low working concentration range of nanograms with 1–10 and 10–170 ng L⁻¹ and 5–105 μg L⁻¹, at an accumulation time of 80 s in a 0.1 M H₃PO₄ electrolyte solution. A relative standard deviation of 30 μg L⁻¹ was observed at an accuracy level of 0.1164% (n = 15) under optimum conditions. The detection limit (S/N) was pegged at 0.2 ng L⁻¹ (5.31 × 10⁻¹³ mol L⁻¹ RF). The proposed method was successfully applied to an actual human urine and drug sample, and can be applied to assays of other biological samples.     

Effect of modifiers for As,Cu and Pb determinations in sugar-cane spirits by GF AAS

Palladium plus magnesium nitrates with and without Ir, Ru and W were evaluated for the simultaneous determination of As, Cu and Pb in cachaça by graphite furnace atomic absorption spectrometry. For 20 μL of sample, 5 μL Pd(NO₃)₂ and 3 μL Mg(NO₃)₂ dispensed together onto the Ir-coated platform of the THGA, analytical curves in the 0–30.0 μg L⁻¹ As, 0–1.50 mg L⁻¹ Cu and 0–60.0 μg L⁻¹ Pb were built up and typical linear correlation coefficients were always better than 0.999. The limit of detection was 1.30 μg L⁻¹ As, 140 μg L⁻¹ Cu and 0.90 μg L⁻¹ Pb. As, Cu and Pb contents in 10 cachaça samples agreed with those obtained by ICP-MS. Recoveries of spiked samples varied from 96% to 106% (As), 97% to 112% (Cu) and 92% to 108% (Pb). The relative standard deviation (n = 12) was typically 2.7%, 3.3% and 1.9%.     

Chemiluminescence microflow injection analysis system on a chip for the determination of nitrite in food

A new microflow injection analysis (μFIA) system on a chip for the determination of nitrite is described. The chip is produced by using two transparent poly(methylmethacrylate) (PMMA) slices measured 50 × 40 × 5 mm, and the microchannels etched by CO₂ laser are 200 μm wide and 100 μm deep with the volume of reaction area about 1.8 μL. Nitrite is sensed by the chemiluminescence (CL) reaction of luminol with ferricyanide that is the product of the reaction of ferrocyanide with nitrite in acidic medium. The syringe pump with an accurate timer controls all reagents, including the sample. The linear range of the nitrite concentration is 8–100 μg L⁻¹ and the detection limit is 4 μg L⁻¹ (S/N = 3). The proposed method has good reproducibility with the relative standard deviation 4.1% for 50 μg L⁻¹ of nitrite (n = 9) and is very sensitive and simple. It has been successfully applied to the determination of nitrite in food.     

Synthesis and application of a new functionalized resin for use in an on-line,solid phase extraction system for the determination of trace elements in waters and reference cereal materials by flame atomic absorption spectrometry

The synthesis and characterization of the resin Amberlite XAD-4 functionalized with 2,6-pyridinedicarboxaldehyde and its application in an on-line system for the preconcentration of cadmium, cobalt, copper, lead and manganese prior to determination using flame atomic absorption spectrometry (FAAS) is proposed. Metal ions retained on the modified resin were eluted using 1.0 mol L⁻¹ HNO₃ solution and aspirated directly to the nebulizer–burner system of a FAAS instrument using a flow injection system. Detection limits (3σ) were determined to be 0.13 μg L⁻¹ for Cd, 0.29 μg L⁻¹ for Cu, 0.23 μg L⁻¹ for Mn, 0.58 μg L⁻¹ for Co and 2.19 μg L⁻¹ for Pb using a 10 mL of water sample loading volume. The limits of detection would be 100 times higher with units of μg kg⁻¹ for the solid samples in which their dilution ratios as (volume/weight) were 100. Enrichment factors ranged from 23.6 to 28.9 (for Co and Mn, respectively). The proposed method was successfully applied to determination of the analytes in natural water samples and certified reference materials.     

Determination of aflatoxins in eggs,milk, meat and meat products using HPLC fluorescent and UV detectors

Raw and pasteurised sheep’s, cow’s and goat’s milk, eggs, and beef samples from different local markets in Jordan were collected during a period of 5 months (January through May 2007) and examined for aflatoxins B1(AFB1), B2(AFB2), G1(AFG1), G2(AFG2), M1(AFM1) and M2(AFM2). The samples were analysed with high performance liquid chromatography (HPLC) using UV and Fluorescent detectors. The analysed samples of milk collected in January were found to contain 0.56 μg L⁻¹ AFM1 and 0.1 μg L⁻¹ AFM2 whilst, the concentration of AFM1 and AFM2 was < 0.05 μg L⁻¹ for milk samples collected between March and May. The AFB1, AFB2, AFG1 and AFG2 contents in the analysed food products ranged from 1.10 to 8.32 μg L⁻¹ and 0.15 to 6.36 μg L⁻¹ in imported and fresh meat samples collected during March, respectively. The mean recovery for the HPLC method was 92% to 109% and the quantification levels were 50 ng L⁻¹ for AFM1 and AFM2. The AFM1 was found in 10% of the tested samples with concentrations between 0.08 and 1.1 μg kg⁻¹ and AFM2 was only found in 1.82% of the tested samples with a level of 0.1 μg kg⁻¹. The AFM1 levels in the examined foods were higher than the maximum level of AFM1 in liquid milk set by the European Community and Codex Alimentarius of 50 ng L⁻¹.     

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.     

Preparation of galacto-oligosaccharides using membrane reactor

Galacto-oligosaccharides (GOS) have many biological functions. They are produced from lactose by a glycosyl transfer of one or more d-galactosyl units onto the d-galactose moiety of lactose catalysed by β-galactosidase. This reaction can proceed in batch or in continuous system. Membrane reactor with ultrafiltration ceramic membrane (150 kDa) was used and batch system as well. Lactose in phosphate buffer (197.9 g L⁻¹), recombined whey (197 g L⁻¹) and evaporated ultrafiltration permeate (200.7 g L⁻¹) were used as substrates. The used concentration of enzyme Maxilact LX 5000 was 6 U mL⁻¹. The highest concentration of GOS in buffer was reached after 30 min of batch reaction and it was 25.5 g L⁻¹, for recombined whey it was 31.1 g L⁻¹ and for ultrafiltration permeate it was 32.9 g L⁻¹. For continuous process was obtained 8.8 g L⁻¹ of GOS for buffer and 21.0 g L⁻¹ for recombined whey and 16.7 g L⁻¹ of GOS for ultrafiltration permeate.     

Sensitive and rapid determination of catechol in tea samples using mesoporous Al-doped silica modified electrode

A mesoporous Al-doped silica (Al/SiO₂) was synthesised according to the published method, and then used to modify the carbon paste electrode (CPE). The electrochemical behaviour of catechol was investigated. Compared with the unmodified CPE, the resulting mesoporous Al/SiO₂ modified CPE remarkably increases the peak currents of catechol, and greatly lowers the peak potential separation. Therefore, the mesoporous Al/SiO₂ exhibits catalytic activity to catechol and significantly improves the determining sensitivity. Based on this, a sensitive, rapid and convenient electrochemical method was proposed for the determination of catechol. The linear range is between 5.0 × 10⁻⁷ and 5.0 × 10⁻⁵ mol L⁻¹ with a correlation coefficient of 0.998. The limit of detection is as low as 1.0 × 10⁻⁷ mol L⁻¹. Finally, this novel method was employed to determine catechol in tea samples, which testified by high-performance liquid chromatography.     

Speciation of organic and inorganic selenium in selenium-enriched rice by graphite furnace atomic absorption spectrometry after cloud point extraction

A new method was developed for the determination of organic and inorganic selenium in selenium-enriched rice by graphite furnace atomic absorption spectrometry detection after cloud point extraction. Effective separation of organic and inorganic selenium in selenium-enriched rice was achieved by sequentially extracting with water and cyclohexane. Under the optimised conditions, the limit of detection (LOD) was 0.08 μg L⁻¹, the relative standard deviation (RSD) was 2.1% (c = 10.0 μg L⁻¹, n = 11), and the enrichment factor for selenium was 82. Recoveries of inorganic selenium in the selenium-enriched rice samples were between 90.3% and 106.0%. The proposed method was successfully applied for the determination of organic and inorganic selenium as well as total selenium in selenium-enriched rice.     

Occurrence of patulin and its dietary intake through apple juice consumption by the Spanish population

A survey was conducted to determine levels and dietary intake of Patulin (PAT) from apple juices consumed in Spain. One hundred samples of apple juice were bought from distinct supermarkets. PAT was extracted by a liquid–liquid extraction technique and analysed with a micellar electrokinetic chromatography (MEKC) method. 66% of the samples contained PAT over the limit of detection of the method (0.7 μg L⁻¹). The PAT apple juice mean and median levels obtained were 19.4 and 4.8 μg L⁻¹, respectively, in a range between 0.7 and 118.7 μg L⁻¹. In 11% of the samples, PAT contamination exceeded the maximum permitted level of 50 μg L⁻¹ established by the EU regulation. In Spain, no significant variations were observed with respect to data published 15 years ago.     

Tungsten permanent chemical modifier with co-injection of Pd(NO3)2 + Mg(NO3)2 for direct determination of Pb in vinegar by graphite furnace atomic absorption spectrometry

A tungsten carbide coating on the integrated platform of a transversely heated graphite atomizer (THGA^®) used together with Pd(NO₃)₂ + Mg(NO₃)₂ as modifier is proposed for the direct determination of lead in vinegar by graphite furnace atomic absorption spectrometry. The optimized heating program (temperature, ramp time, hold time) of atomizer involved drying stage (110 °C, 5 s, 30 s; 130 °C, 5 s, 30 s), pyrolysis stage (1000 °C, 15 s, 30 s), atomization stage (1800 °C, 0 s, 5 s) and clean-out stage (2450 °C, 1 s, 3 s). For 10 μL of vinegar delivered into the atomizer and calibration using working standard solutions (2.5–20.0 μg L⁻¹ Pb) in 0.2% (v/v) HNO₃, analytical curve with good linear correlation (r = 0.9992) was established. The characteristic mass was 40 pg Pb and the lifetime of the tube was around 730 firings. The limit of detection (LOD) was 0.4 μg L⁻¹ and the relative standard deviations (n = 12) were typically <8% for a sample containing 25 μg L⁻¹ Pb. Accuracy of the proposed method was checked after direct analysis of 23 vinegar samples. A paired t-test showed that results were in agreement at 95% confidence level with those obtained for acid-digested vinegar samples. The Pb levels varied from 2.8 to 32.4 μg L⁻¹. Accuracy was also checked by means of addition/recovery tests and recovered values varied from 90% to 110%. Additionally, two certified reference materials were analyzed and results were in agreement with certified values at a 95% confidence level.     

Determination of patulin in fruit juices using HPLC-DAD and GC-MSD techniques

A high performance liquid chromatography with a diode-array detector (HPLC-DAD) and a gas chromatography with a mass spectrometer (GC-MSD) are described for the determination of patulin (PAT) in apple juice. The limits of detection (DL) and quantification (QL) for the HPLC-DAD and GC-MSD method were found to be (DL = 0.23 μg kg⁻¹ QL = 1.2 μg kg⁻¹) and (DL = 5.8 μg kg⁻¹ and QL = 13.8 μg kg⁻¹), respectively. The recovery factors for HPLC-DAD and GC-MSD were found to be 99.5% (RSD% = 0.73) and 41% (RSD% = 10.03), respectively. The HPLC-DAD method was used to determine the occurrence of PAT in 90 samples of fruit juices.     

Comparison of isoflavones composition in seed,embryo, cotyledon and seed coat of cooked-with-rice and vegetable soybean (Glycine max L.) varieties

In order to study the content and composition of isoflavones retained in soybean seed component, obtained each component part the embryo, cotyledon and seed coat tissues of nine different soybean varieties were analyzed for 12 isoflavones using high performance liquid chromatography with photo diode array detector (HPLC-PDA) and were compared to each other. A total average concentration of isoflavone was 2887 μg g⁻¹ in embryo, 575 μg g⁻¹ in whole seed, 325 μg g⁻¹ in cotyledon, and 33 μg g⁻¹ in seed coat. With respect to each tissue of soybean varieties, isoflavone content was highest in Geomjeongkong 2 embryo (5701 μg g⁻¹), Geomjeongolkong whole seed (1321 μg g⁻¹), Heugcheongkong cotyledon (951 μg g⁻¹), and Keunolkong seed coat (56 μg g⁻¹). Isoflavone was least present in Keunolkong embryo (341 μg g⁻¹), Hwaeomputkong whole seed (175 μg g⁻¹), Seonheukkong cotyledon (81 μg g⁻¹), and Seoklyangputkong seed coat (5 μg g⁻¹). Overall, embryo and seed coat of all nine varieties contained isoflavones at the highest and lowest level, respectively. Isoflavones accumulated in the order of malonylglycoside, glycoside, acetylglycoside, and aglycon, among which malonylglycoside was the most abundant form ranging from 66% to 79% of the total isoflavone content in all three tissues. The embryo of cooked-with-rice soybean with black seed coat appears to be the best source of isoflavone.     

Pharmacokinetics and residues of tetracycline in crucian carp muscle using capillary electrophoresis on-line coupled with electrochemiluminescence detection

A novel and sensitive determination for tetracycline (TC) in crucian carp muscle was developed by using capillary electrophoresis coupled with electrochemiluminescence (ECL) detection. The conditions affected separation and detection were examined in detail. The linearity range of TC concentration was from 0.005 to 10 μg mL⁻¹ with a correlation coefficient of 0.9992. The detection limit of TC (S/N = 3) was 1.8 ng mL⁻¹. The relative standard deviations of the ECL intensity and the migration time for eleven consecutive injections of 1.0 μg mL⁻¹ TC were 1.6% and 0.8%, respectively. The recovery of TC was 97.8% (n = 5). After administration of 75 mg kg⁻¹ TC, the maximum concentration and peak time of TC in crucian carp muscle were 7.33 mg kg⁻¹ and 8 h, respectively. After administration of TC, TC concentration demonstrated trivial variation in the period from 48 to 96 h.     

Response surface modelling of lead pre-concentration from food samples by miniaturised homogenous liquid–liquid solvent extraction: Box–Behnken design

In this study, a new method called miniaturised homogenous liquid–liquid extraction, followed by graphite furnace atomic absorption spectrometry, was developed for the extraction and determination of lead from food samples. The procedure was based on the fast extraction of lead from an acetic acid sample solution into 0.5 mL chloroform, as an extraction solvent. After adding water into the mixture, the extracting solvent phase immediately formed a distinct water-immiscible phase below the vial, which could easily be separated, evaporated and re-dissolved in 1.0 mL nitric acid 0.1 mol L⁻¹ for further analysis. The effects of various experimental parameters in extraction step were studied using two optimisation methods, one variable at a time and Box–Behnken design. The results showed that the amount of salt and extraction time did not have effect on the extraction efficiency. Therefore, a three-level Box–Behnken experimental design with three factors, which combined the response surface modelling, was used to optimise lead extraction. Three independent variables, including pH of solution (ranging from 6.5 to 10.5), concentration of dithizone as chelating agent (ranging from 0.05 to 0.5 μg L⁻¹) and extracting solvent volume (ranging from 300 to 900 μL) were respectively coded as pH, D and V at three different levels (−1, 0 and 1). In this study, the optimum condition was determined at pH 8.4, a volume of chloroform at 0.45 mL, and concentration of dithizone at 0.5 μg L⁻¹. Under the optimum condition, the limit of detection (LOD) was 0.05 μg L⁻¹. Furthermore, the relative standard deviation of the ten replicate was <5.0%. The developed procedure was applied to the extraction and determination of lead in the food samples.     

Comparison of positive and negative ion detection of tea catechins using tandem mass spectrometry and ultra high performance liquid chromatography

Tea catechins are an important group of natural compounds associated with health promoting effects and desired commodities for the growing market of dietary supplements and functional foods. Consequently these compounds attract more interest of research groups worldwide. A reliable quantitative analysis of tea catechins is essential for human intervention studies, manufacturers of dietary supplements and quality control by authorities. UHPLC–ESI-MS/MS analytical method was chosen due to rapid runtime, high sensitivity and selectivity. The chromatographic separation of eight tea catechins was achieved within 2.5 min on C₁₈ BEH analytical column (100 mm × 2.1 mm i.d.; 1.7 μm), whilst the gradient elution mode was employed using water:methanol mobile phase with addition of volatile organic acid. The concentration of organic acids in the mobile phase was optimised within the range of 0.01–0.1% (v/v). High sensitivities were achieved in positive (10.2-16.8 fmol/inj.) and negative ion detection mode (102.1-168.1 fmol/inj.), through accurate and complex tuning of MS parameters. The UHPLC-ESI-MS/MS method was validated in terms of linearity (>0.9997; >0.9990), range (0.02–2.40 mg L⁻¹; 0.15-24.00 mg L⁻¹), LOD (3.0–4.8 μg L⁻¹; 30.1–48.0 μg L⁻¹), LOQ (9.9–15.8 μg L⁻¹; 150.5-240.0 μg L⁻¹), intra-day precision (4.4-7.1% RSD; 3.3-5.1% RSD), accuracy (94.06-113.7%; 89.5-108.4%), retention time repeatability (0.0-0.5% RSD; 0.0-0.6% RSD), and peak area repeatability (1.2-4.0% RSD; 2.4-3.5% RSD) for positive and negative ion detection modes, respectively. The statistical comparison of the quantitative results obtained in positive and negative ion detection mode was performed.     

Amperometric detection of ascorbic acid in honey using ascorbate oxidase immobilised on amberlite IRA-743

A differential amperometric method for the specific determination of ascorbic acid in honey was developed by association of a flow injection analysis (FIA) system and a tubular reactor containing the ascorbate oxidase enzyme immobilised. A gold electrode modified by electrochemical deposition of palladium was employed as working electrode. Ascorbic acid was quantified in seven samples of commercial honeys using a potential of +0.60 V vs. Ag/AgCl_(sat). The linear dynamic range in ascorbic acid extends from 1 to 50 μmol L⁻¹, at pH 7.0. At flow rate of 1.5 mL min⁻¹ and injecting 250 μL sample volumes, a sampling frequency of 180 determinations per hour is afforded. The detection and quantification limit of this method are 0.14 and 0.49 μmol L⁻¹, respectively. The samples analyses were compared with the volumetric method, and showed an excellent correlation between the methods.     

Determination of total phenols in tea infusions,tomato and apple juice by terbium sensitized fluorescence method as an alternative approach to the Folin–Ciocalteu spectrophotometric method

A fast screening of total phenols in tea infusions, tomato and apple juice samples using terbium sensitized fluorescence is described. The proposed method is based on the fluorescence sensitization of terbium (Tb³⁺) by complexation with flavonols (quercein as a reference standard) (at pH 7.0), which fluoresces intensely with an emission maximum at 545 nm when excited at 310 nm. Quercetin and terbium cations (at pH 7.0) form a stable complex and the resulted emission at 545 nm can be used for the determination of the total phenols concentration expressed in terms of “quercetin equivalent”. Based on the obtained results, a sensitive, simple and rapid spectrofluorimetric method was developed for the determination of total phenols. In the optimum conditions, the calibration graph was linear from 0.01 to 2 μg mL⁻¹, with the limit of detection of 0.002 μg mL⁻¹. The relative standard deviation values were in the range of 0.75–2.3%. The total concentrations of quercetin equivalent in five tested samples were found in the range of 6.6–27.9 μg mL⁻¹ and the results compare favorably with those obtained by spectrophotometric method (r = 0.999).     

Spectrofluorimetric determination of buparvaquone in biological fluids,food samples and a pharmaceutical formulation by using terbium–deferasirox probe

A simple spectrofluorimetric method is described for the determination of buparvaquone (BPQ), based on its quenching effect on the fluorescence intensity of Tb³⁺–deferasirox (DFX) complex as a fluorescent probe. The excitation and emission wavelengths were 328 and 545 nm, respectively. The optimum conditions for determination of BPQ were investigated considering the effects of various affecting parameters. The variations in fluorescence intensity of the system showed a good linear relationship with the concentration of BPQ in the range of 10–1500 μg L⁻¹, its correlation coefficient was 0.999 with the detection and quantification limits of 1.1 and 3.4 μg L⁻¹, respectively. Linearity, reproducibility, recovery, limits of detection and quantification made the method suitable for BPQ assay in biological fluids, meat, dairy products and BPQ parenteral solutions (vials). The method was applied to real samples of serum and milk of three cows receiving BPQ.     

Effect of foliar application of selenium on its uptake and speciation in carrot

Carrot (Daucus carota) shoots were enriched by selenium using foliar application. Solutions of sodium selenite or sodium selenate at 10 and 100 μg Se ml⁻¹, were sprayed on the carrot leaves and the selenium content and uptake rate of selenium were estimated by ICP–MS analysis. Anion and cation exchange HPLC were tailored to and applied for the separation of selenium species in proteolytic extracts of the biological tissues using detection by ICP–MS or ESI–MS/MS. Foliar application of solutions of selenite or selenate at 100 μg Se ml⁻¹ resulted in a selenium concentration of up to 2 μg Se g⁻¹ (dry mass) in the carrot root whereas the selenium concentration in the controls was below the limit of detection at 0.045 μg Se g⁻¹ (dry mass). Selenate-enriched carrot leaves accumulated as much as 80 μg Se g⁻¹ (dry mass), while the selenite-enriched leaves contained approximately 50 μg Se g⁻¹ (dry mass). The speciation analyses showed that inorganic selenium was present in both roots and leaves. The predominant metabolised organic forms of selenium in the roots were selenomethionine and γ-glutamyl-selenomethyl-selenocysteine, regardless of which of the inorganic species were used for foliar application. Only selenomethionine was detected in the carrot leaves. The identity of selenomethionine contained in carrot roots and leaves was successfully confirmed by HPLC–ESI–MS/MS.