A novel quantum dot-based fluoroimmunoassay method for detection of Enrofloxacin residue in chicken muscle tissue

A rapid indirect competitive fluorescence-linked immunosorbent assay (cFLISA) based on quantum dots (QDs) as the fluorescent marker has been developed for the detection of Enrofloxacin (ENR) in chicken muscle tissue. The end-point fluorescent detection system was carried out using QDs conjugated with goat anti-mouse secondary antibody. The cFLISA method allowed for ENR determination in a liner working range of 1–100 ng mL⁻¹ with the 50% inhibition value (IC₅₀) of 8.3 ng mL⁻¹ and the limit of detection (LOD) of 2.5 ng mL⁻¹. The recoveries for chicken muscle samples spiked with ENR at levels of 50–200 μg kg⁻¹ ranged from 81% to 94% with coefficients of variation (CV) of 10–13%. In real chicken tissue sample analysis, the results of cFLISA were similar to those obtained from an indirect competitive enzyme-linked immunosorbent assay (cELISA) to a high performance liquid chromatography method (HPLC), which indicated that cFLISA is suitable as screening method for the monitoring of veterinary drug residues.     

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.     

Microwave-assisted extraction and determination of cyanuric acid residue in infant formula samples by liquid chromatography–tandem mass spectrometry

In the present work, microwave-assisted extraction method in combining with liquid chromatography–tandem mass spectrometry (LC–MS/MS) was proposed for the determination of cyanuric acid (CYA) in infant formula samples. The separation was performed on a MERCK ZIC HILIC column (150 × 2.1 mm i.d., 5 μm) with gradient elution of 20 mM ammonium acetate solution – acetonitrile. The method could respond linearly with cyanuric acid at concentrations from 1.0 to 50 ng mL⁻¹ with a quantification limit of 0.25 mg kg⁻¹. The intra- and inter-day precision was less than 4% and the recovery of the assay was in the range of 86.7–93.1%. In the analysis of practical spiked infant formula samples, the new method yielded satisfactory results. Due to its simplicity and accuracy the straightforward method is particularly suitable for routine cyanuric acid detection.     

Determination of copper with 5,5-dimethylcyclohexane-1,2,3-trione 1,2-dioxime 3-thiosemicarbazone in olive oils by adsorptive stripping square wave voltammetry

In the present paper a method for the determination of Cu in olive oil samples by adsorptive stripping square wave voltammetry (Ad-SSWV) is presented. It has been proven that Cu reacts with 5,5-dimethylcyclohexane-1,2,3-trione 1,2-dioxime 3-thiosemicarbazone, DCDT, in strongly acid media giving rise to a complex. In Ad-SSWV the complex Cu–DCDT experiments an adsorptive reductive process which promotes the appearance of a peak at −0.570 V. The extraction process of Cu from olive oil is carried out with hot concentrated HCl. Calibration graph has been constructed from 0 to 35 ng mL⁻¹ and the detection limit was 0.49 ng mL⁻¹. The method has been applied to commercial olive oils samples and the amounts of Cu found are very similar to those obtained when samples are analysed by AAS.     

Determination of formaldehyde in beer based on cloud point extraction using 2,4-dinitrophenylhydrazine as derivative reagent

A cloud point extraction method was developed for extraction of formaldehyde in beer prior to high performance liquid chromatography analysis. The formaldehyde was taken into complex with 2,4-dinitrophenylhydrazine in aqueous nonionic surfactant Triton X-114 medium and concentrated in the surfactant-rich phase by bringing the solution to the temperature of 60 °C. Under optimal conditions, the limit of detection of formaldehyde is 0.7 ng mL⁻¹. The intra- and inter-day precisions expressed as relative standard deviations are 4.2% and 5.5%, respectively. The proposed method was successfully applied for determination of formaldehyde in various beer samples. The contents of formaldehyde in these samples are in the range of 172-385 ng mL⁻¹. The results were in agreement with those obtained by the state standard method (steam-distillation and spectrophotometry analysis) used in China. The developed method was demonstrated to be rapid and sensitive for extraction and determination of formaldehyde in beer.     

Development of polyclonal antibody-based indirect competitive enzyme-linked immunosorbent assay for sodium saccharin residue in food samples

A sensitive and specific polyclonal antibody (PcAb)-based indirect competitive enzyme-linked immunosorbent assay (icELISA) for sodium saccharin is described. 6-Amino saccharin was coupled to carrier protein for artificial antigen by diazotisation. New Zealand white rabbits were immunised to obtain anti-sodium saccharin PcAb and then icELISA was developed. The assay showed high sensitivity and specificity to sodium saccharin, with the 50% inhibition value (IC₅₀) of 0.243 μg mL⁻¹, workable range (IC₃₀–IC₇₀) of 0.050–12.8 μg mL⁻¹ and limit of detection (LOD, IC₂₀) of 0.021 μg mL⁻¹. The average recoveries of sodium saccharin in spiked food samples were estimated ranging from 70.7% to 98.8%. A statistically significant correlation of results was obtained between this new ELISA and previously established HPLC approaches with the food-relevant sodium saccharin concentration range 0–320 μg mL⁻¹ (R² = 0.9887–0.9975). These results indicated that the established ELISA was a potential and useful analytical tool for rapid determination of sodium saccharin residue in food samples.     

Highly selective optical nitrite sensor for food analysis based on Lauth’s violet-triacetyl cellulose membrane film

A new sensor has been developed for the determination of nitrite based on the immobilisation of Lauth’s violet on triacetyl cellulose membrane using absorption spectrophotometry. The optical sensor signal is based on the reaction of Lauth’s violet with bromate as an oxidant in the presence of nitrite to produce a colourless product. Nitrite has a strong catalytic effect on the oxidation of Lauth’s violet with bromate in acidic media. The difference in the absorbance of the optode at 617 nm between uncatalysed and catalysed reactions (ΔA) was directly proportional to the concentration of nitrite in sample solution. A linear calibration curve (r² = 0.985) was observed in the nitrite concentration range of 10.12-1012 ng mL⁻¹ and a detection limit of 8.3 ng mL⁻¹ was found.     

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.     

Chemiluminescent imaging detection of staphylococcal enterotoxin C1 in milk and water samples

A sensitive, simple and rapid technique for high throughput simultaneous detection of staphylococcal enterotoxin C₁ (SEC₁) has been developed. The proposed method has the advantage of showing the specificity of enzyme-linked immunosorbent assays (ELISA), sensitivity of luminol-based enhanced chemiluminescence (ECL) assay, and high throughput of chemiluminescence (CL) imaging assay. It was based on a standard sandwich immunoassay format; 96-well ELISA plates were used as solid phase material. A commercial high-sensitivity cooled CCD camera has been applied to image the weak CL. Under the optimum conditions, the increased CL intensity was proportional with the concentration of SEC₁ in the range of 8.0–125.0 ng ml⁻¹ and the detection limit was 0.5 ng ml⁻¹ (3σ). The relative standard deviation (RSD) for eight parallel measurements of 25.0 ng ml⁻¹ SEC₁ was 0.06. The proposed method has been successfully applied to the determination of SEC₁ in milk and water samples. The results obtained compared well with those by ELISA.     

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.     

Pyridine-functionalized mesoporous silica as an adsorbent material for the determination of nickel and lead in vegetables grown in close proximity by electrothermal atomic adsorption spectroscopy

A new, sensitive, and low cost solid-phase extraction method using pyridine-functionalized MCM-48 mesoporous silica for the extraction, pre-concentration, and electrothermal atomic absorption spectrometric determination of nickel and lead in food samples at ng mL⁻¹ levels is described herein. The levels of nickel and lead in different types of vegetables grow in Shiraz–Iran and Rafsanjan–Iran were determined by electrothermal atomic absorption spectrometry. The use of two standard reference materials and also comparing the results to a standard reference procedure ensured the accuracy of this method. Factors, such as flow rate of extraction, and the type, pH, concentration, and volume of eluent, were appraised. The effect of various ions on recovery was also investigated. Detection limits of 0.11 and 0.14 ng mL⁻¹ were obtained for lead and nickel, respectively.     

Analysis of fumonisins B1, B2 and their hydrolysed metabolites in pig liver by LC–MS/MS

A liquid chromatography–tandem mass spectrometry method for the quantitative determination of fumonisin FB1, FB2 and their respective hydrolysed metabolites HFB1 and HFB2 in pig liver has been developed and validated. The method was based on an easy extraction procedure followed by SPE purification. Chromatographic separation of the analytes was performed on a C18 column using 0.3% of formic acid in water and acetonitrile as elution solvent. The mass spectrometer operated in the positive electrospray ionisation mode (ESI+) using multiple reaction monitoring (MRM). An intralaboratory validation was carried out with fortified samples for determining precision, trueness, specificity, limit of detection (LOD) and limit of quantification (LOQ). The method showed good performance characteristics and proved to be sensitive, selective and reliable. The LOD was 0.05 ng g⁻¹ and the LOQ was 10 ng g⁻¹ for all the analytes. The developed method has been applied to seven pig liver samples in order to test its applicability to evaluate exposure of food animals to fumonisins.     

Quantitative analysis of lincomycin and narasin in poultry, milk and eggs by liquid chromatography-tandem mass spectrometry

This study presents the simultaneous extraction and determination of lincomycin (LCM) and narasin (NAR) by using liquid chromatography-electrospray ionisation tandem mass spectrometry (LC-MS/MS) on samples from poultry, milk and eggs (n = 196). The homogenised samples are extracted with acetonitrile and the extract is further cleaned using C₁₈ solid-phase extraction cartridges. The recoveries of the analytes in different matrices were found ranging from 90% to 101% and 85% to 95% for LCM and NAR, respectively. The corresponding limits of detection were 0.6 and 1.5 ng g⁻¹ for LCM and NAR, respectively. As a result of monitoring, NAR was not detected in any samples and LCM was detected in one egg with a concentration of 25 ng g⁻¹. The method was relatively simple to perform and therefore could be used for food safety surveillance activities.     

Determination of danofloxacin in milk combining second-order calibration and standard addition method using excitation–emission fluorescence data

For this paper we propound a new procedure for fast detection and determination of danofloxacin (DANO) in commercial bovine milks. For this aim, a spectrofluorimetric method coupled with chemometric (PARAFAC) tools has been optimized. This method provides valuable information about the total amount of DANO in the selected sample in a short analysis time. After a cleanup step, consisting in protein precipitation in acidic medium, excitation–emission fluorimetric scans (EMMs) were recorded and a standard addition calibration method, using second order multivariate procedures, was applied. The analytical method has been validated according to the European Community directive related to the decision limit (CCα) and detection capability (CCβ). The obtained values, 7.3 and 12 ng mL⁻¹, respectively calculated are well below the MRL for DANO in milk (30 ng mL⁻¹). This procedure has been applied to different commercial milks in order to accomplish the strength of this methodology by PARAFAC standard addition. Recoveries around 100% were observed for all the samples. The high sensitivity of the fluorimetric technique and the fast cleanup step make this method an easy and fast way for quality and antibiotic residues surveys in commercial milks.     

Determination of melamine by flow injection analysis based on chemiluminescence system

In this paper, based upon the phenomenon that melamine can obviously enhance the CL signal of the luminol–H₂O₂ system in basic medium, a simple, rapid and sensitive flow injection chemiluminescence (FI-CL) method for the determination of melamine has been developed. Under the optimum conditions, the linear range for the determination of melamine was 0.2–80 μg mL⁻¹ with a detection limit of 0.12 μg mL⁻¹ calculated as proposed by IUPAC and a relative standard deviation of 3.26% for 11 solutions of 10 μg mL⁻¹ melamine on the same day. The proposed method was satisfactorily applied to determine melamine in milk-based products and satisfactory results were obtained without interferences from the sample matrix. Moreover, one assay produce takes only 25 s and the minimum sampling rate is about 120 samples h⁻¹, which indicated that the FI-CL method was suitable for high throughput and real-time melamine analysis.     

Development and validation of a simple analytical method for the determination of 2,4,6-trichloroanisole in wine by GC–MS

A novel method for the residue analysis of wine spoilage compound 2,4,6-trichloroanisole is reported. Wine (60 ml) was extracted with 2 ml toluene in presence of 24 g MgSO₄ and 6 g NaCl. Cleanup of the toluene phase by dispersive solid phase extraction with mixture of 100 mg CaCl₂, 25 mg primary secondary amine and 50 mg MgSO₄ was effective in minimising co-extractives and matrix effects. Time-of-flight and tandem mass spectrometric parameters were optimised to achieve linearity over 0.25–500 ng ml⁻¹ and method detection limit 0.0083 ng ml⁻¹ which is well below the odour threshold of 0.04 ng ml⁻¹. Recoveries at 0.04, 0.2 and 0.8 ng ml⁻¹ were within 80–110% (±8%). The method was reproducible when tested for Argentinean wines with intra-laboratory Horwitz ratios being <0.20 in white and red wines at both the laboratories of India and Argentina. The method could be successfully applied for incurred wine samples.     

Immunoassay based on monoclonal antibody for aflatoxin detection in poultry feed

An indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) based on an anti-aflatoxin B₁ monoclonal antibody was standardised and validated for aflatoxin screening in poultry feed samples and its performance was compared to high-performance liquid chromatography (HPLC). The ic-ELISA showed good linearity (r² = 0.994) and detection limits of 1.25 ng g⁻¹ for broiler feed and 1.41 ng g⁻¹ for laying hen feed. Mean aflatoxin recovery rates by ic-ELISA were 102% (laying hen feed) and 98% (broiler feed). Aflatoxins were detected in 88.2% of the 34 broiler feed samples by ic-ELISA and HPLC at means of 10.48 ng g⁻¹ and 8.41 ng g⁻¹, respectively, while 92% of laying hen feed samples (n = 36) showed aflatoxin contamination at means of 20.83 and 19.75 ng g⁻¹. The standardised ic-ELISA showed reliability and a high correlation with HPLC of 0.97 (broiler feed) and 0.98 (laying hen feed) indicating its potential for aflatoxin screening in poultry feed samples.     

Use of a portable time-resolved fluorometer to determine oxytetracycline residue in four fruit crops

Oxytetracycline (OTC) is used worldwide to protect crops against bacterial diseases. The US Environmental Protection Agency approved its use in apple, pear, nectarine, and peach, and set residue tolerance at 350 ng g⁻¹. A europium-sensitised luminescence (ESL) method was developed for in-situ determination of OTC residue in these fruits. After extraction in Na₂EDTA-NaCl-McIlvaine buffer at pH 4 and filtration, cleanup was performed using hydrophilic-lipophilic balance cartridges. ESL was measured using a portable time-resolved fluorometer. The signal responded linearly over three orders of magnitude (10–10000 ng g⁻¹) with 17–50 ng g⁻¹ limits of quantitation and 2% averaged relative standard deviation. Recoveries were 84% and 82% at 100 and 350 ng g⁻¹, respectively. Inter-laboratory validation was performed by HPLC–MS/MS.     

Determination of ionophores in raw bovine milk using LC–MS/MS: Application to residue surveillance

Residues of four ionophores (lasalocid, monensin, narasin, and salinomycin) in raw milk samples were extracted with acetonitrile and subsequently determined using liquid chromatography–tandem mass spectrometry. Ionophores could be determined down to 0.1 ng g⁻¹ level, without additional cleanup or concentration of the resulting extract. The analysis of a series of raw milk samples fortified at analyte concentrations ranging from 1 to 20 ng g⁻¹ yielded average accuracies ranging from 60.7% to 118.3% with percent relative standard deviations below 13%. During six months of a surveillance program, 1072 raw milk samples were collected from the transport chain of dairy producers in Alberta and analysed. Monensin was detected in 736 of 1072 samples tested at concentrations ranging from 0.10 to 0.53 ng g⁻¹ which is well below the current Canadian maximum residue limit of 10 ng g⁻¹.     

Rapid determination of formaldehyde and sulfur dioxide in food products and Chinese herbals

Simple, sensitive and rapid methods for the determination of formaldehyde and sulfur dioxide were developed. The formaldehyde determination is based on the reaction between formaldehyde and acetylacetone solution, producing yellow 3,5-diacetyl-l-1,4-dihydrolutidine. Sulfur dioxide was detected as the deoxidize of sulfurous acid by zinc in acidic medium, which produces sulfureted hydrogen that make lead acetate paper blackening due to lead sulfide formation. The detection limits were 0.8 μg mL⁻¹ and 6.0 μg mL⁻¹ for formaldehyde and sulfur dioxide, respectively. The linear range were 0.8–20.0 μg mL⁻¹ for formaldehyde and 6.0–100.0 μg mL⁻¹ for sulfur dioxide determination. The main advantages of the new analytical procedure are the low background level, high selectivity, and very little sample preparation for on-site analysis of formaldehyde and sulfur dioxide in food or Chinese herbal samples with reference color card for qualitative or semi-quantitative determination. The results from these methods correlated well with those obtained from the standard methods.