Food Analytical Methods

This study reports an analytical method to simultaneously determine the residues of sulfonamides, dapsone, ormethoprim, and trimethoprim in fish and shrimp. The samples were extracted with acetonitrile, magnesium sulfate, and sodium acetate, followed by dispersive solid-phase extraction (C18) for cleanup. The target analytes were confirmed and quantified by liquid chromatography–tandem mass spectrometry. The developed method was validated according to the Codex guidelines (CAC/GL 71-2009). As a result, linearity was expressed between 0.25 and 200 μg kg−1 with a correlation coefficient > 0.98. The limits of quantitation were 0.01–2.8 μg kg−1 and the accuracy (expressed as average recovery) was 76.1–115%. The precision (expressed as the coefficient of variation) was <20%. The decision limits of sulfonamides, dapsone, ormethoprim, and trimethoprim were 94.2–114, 1.3–1.5, 105–111, and 53.3–54 μg kg−1 and detection capabilities of 102–129, 1.4–1.6, 109–120, and 55.6–58.2 μg kg−1, respectively. The proposed method was applied to the analysis of real samples (n = 54) obtained from domestic markets in Korea, resulting in a detection rate of 13% (seven samples). This method is applicable for the efficient determination of sulfonamides, dapsone, ormethoprim, and trimethoprim residues in fish and shrimp according to Korean MRL.

A novel method for the separation/analysis of linuron in fruit and vegetable samples is described. The work is based on the utilization of ionic liquid ([C6min][PF6])-loaded β-cyclodextrin cross-linked polymer (IL-β-CDCP) for the effective adsorption of linuron coupled with ultraviolet spectrophotometry. The inclusion interaction of IL-β-CDCP with linuron is studied with FTIR and inclusion constants. Under optimum conditions, the preconcentration factor achieved for this method is approximately 10. Linear range, limit of detection (LOD), limit of quantification (LOQ), and relative standard deviation are 0.08–15.00 μg/mL, 5.8 ng/mL, 17.5 ng/mL and 0.96 % (n = 3, c = 4.0 μg/mL), respectively. This technique is successfully applied for determination of linuron in real samples.

A method was developed for the determination of glyphosate residues in plant-derived food using a two-step solid phase extraction (SPE) combined with mixed-mode liquid chromatography-tandem mass spectrometry (LC-MS/MS). The samples were extracted with water. Then, the extracting solution was pretreated by a C18 cartridge to remove protein and weak-polar interferences and further directly extracted using a strong anion exchange (SAX) cartridge to remove neutral and basic substances. The obtained glyphosate residues from the SPE were separated on a hydrophilic interaction/weak anion-exchange (HILIC/WAX) column and detected by mass spectrometry with negative electrospray ionization (ESI-) in multiple reaction monitoring (MRM) mode. This approach was evaluated by five different kinds of plant-derived food (soybean, corn, carrot, apple, and spicy cabbage) matrices in terms of matrix effect and recovery. Results showed that two-step SPE and mixed-mode chromatography separation provided the method with a very low matrix effect, and the spiked recoveries of glyphosate were satisfied in the range of 83.1 to 100.8 % at three spiked levels. The limit of quantification (LOQ) and detection (LOD) of the method in different matrices were 0.016–0.026 and 0.005–0.008 mg kg−1, respectively. The procedure was validated and showed good accuracy and precision over a large linear range of 0.02–10 mg kg−1.

In the present work, a simple and fast sample pretreatment method based on salt-induced homogenous liquid–liquid microextraction has been proposed for the extraction and preconcentration of some widely used pesticides (diazinon, ametryn, chlorpyrifos, penconazole, oxadiazon, diniconazole, and fenazaquin) from different fruit juice samples prior to gas chromatography-flame ionization detection. Initially, a small volume (microliter level) of an extraction solvent (iso-propanol) is added into an aqueous phase containing the analytes in order to obtain a homogenous solution. Then, a phase separation agent (sodium sulfate) is added into the homogeneous solution. By this action, the extraction solvent releases from the homogenous solution in the form of tiny droplets containing the analytes and collects on the surface of the aqueous phase as a thin film. A home-made device is used to simplify the removal of the collected organic phase. Finally, an aliquot of the collected organic phase is removed and injected into the separation system for analysis. Under the optimum conditions, limits of detection and quantification were obtained at the ranges of 0.22–0.48 and 0.73–1.7 μg L−1, respectively. The enrichment factors and extraction recoveries of the selected pesticides ranged from 410 to 480 and 82 to 96%, respectively. The relative standard deviations were ≤ 7% for intra- (n = 6) and inter-day (n = 4) precisions at a concentration of 10 μg L−1 of each analyte. Finally, the proposed procedure was successfully applied to the analysis of real samples including apple, sour cherry, peach, grape, and orange juices in order to simultaneously determine the seven aforementioned pesticides. The proposed approach is simple, sensitive, rapid, and requires low solvent consumption, which, in the era of green chemistry, represents a significant advantage. This method and the obtained results can contribute in the improvement of food quality as well as monitoring level of pesticide usage in fruit juices.

In this work, a composite of polyethylene glycol (PEG) modified MoS2 (PEG-MoS2) was synthesized and used as the stationary phase of open-tubular capillary column via a chemical bonding strategy. The PEG-MoS2 exhibited a sphere-like architecture through characterization of scanning electronic microscopy. p-phenylenediboronic acid was introduced as a linker to combine the PEG-MoS2 with capillary column. A capillary electrochromatographic method was established for the determination of nine sulfonamides by using PEG-MoS2-coated capillary column. The intra-day, inter-day, and column-to-column relative standard deviations (RSDs) of migration time and peak area were in the range of 0.80–4.38% and 1.61–9.22%, respectively. The limits of detection were in the range of 20.4–64.8 ng/mL. The recoveries in environmental water and milk were from 83.26 to 116.29% and 80.86 to 118.22%. This work is the first report that PEG-MoS2 material is utilized as stationary phase for capillary electrochromatography.

Fungicides are applied from plant development to grape production, transport, and storage. Even after fruit processing, residues of these compounds can be present in grape by-products such as wine and juice. In this way, a fast and straightforward method based on solvent demulsification-dispersive liquid-liquid microextraction (SD-DLLME) sample preparation was developed, validated, and applied for the multiresidue determination of 30 fungicides in wine using ultra-high performance liquid chromatography–tandem mass spectrometry (UHPLC-MS/MS). The evaluated SD-DLLME parameters were agitation types, extraction and dispersive solvent type, extraction and dispersive solvent volume, sample pH, and salt types. Sample preparation using SD-DLLME avoids the centrifugation step. Validation was performed using spiked blank sample and satisfactory results for accuracy, with recoveries ranging from 70 to 117% and precision in terms of relative standard deviation ≤20%, except for three compounds at the lowest spiked level. For most of the compounds, the practical method limits of detection and quantification were 0.03 and 0.1 μg L−1, respectively. The method was successfully applied in commercial wine samples in which several pesticides were found at concentrations ranging from 0.109 to 10.6 μg L−1.

Alkaline phosphatase (ALP) is an active enzyme present in the raw milk. Due to its unique heat-sensitive properties, it is employed as an indicator to evaluate efficiency of the pasteurization treatment. In the present study, a method comprising of HPLC with fluorescence detector was developed for the quantification of ALP enzyme activity in the pasteurized milk. The method is based on the detection and quantification of 4-methylumbelliferone (4MU) liberated by the action of phosphatase enzyme (in the milk) on the substrate 4-methylumbelliferyl phosphate (4MUP). Extraction and purification of 4MU was done by clarification, centrifugation, and solid phase extraction processes. The target compound separation was achieved with the help of reversed-phase C18 column using gradient elution consisting of a binary mobile phase: HPLC grade water and methanol. The fluorescence detection was accomplished with the excitation and emission wavelengths being 365 and 460 nm, respectively. The method validation experiments clearly showed high specificity, good linearity (r2 > 0.9901), low limits of detection (0.349 mg/L) and quantification (LOQ, 0.432 mg/L), accuracy (> 100%), and precision (%RSD < 4.7652). Comparative evaluation against Lovibond comparator method revealed that the HPLC method has an advantage of detecting very low levels of ALP activity and raw milk contamination. This is the first report of detecting such low levels of ALP in the milk by HPLC-fluorescence detector technique. This new chromatographic method can be considered as a substitute to the existing standard methods that employ fluorometric technique for detecting ALP activity in the pasteurized milk. Our method could certainly enhance the quality assurance standards currently employed in the dairy industry.

A simple and quick (less than 5 min/pellet) method for the quantification of a series of macroelements (Na, Mg, P, Cl, K, and Ca) and trace elements (Fe, Cu and Zn) by wavelength dispersive X-ray fluorescence (WDXRF) has been established and validated for fortified milk powders, from a single production site. The calibration set of 23 samples was selected to uniformly cover the concentration ranges of each element. The validation set was composed of 32 samples. By using a high power WDXRF instrument, a counting time as short as 20 s for most of the analytes can be used to considerably decrease analysis time. Reference values obtained by inductively coupled plasma-atomic emission spectroscopy and by potentiometry for chloride were used to calibrate the WDXRF system. Subsequently, the WDXRF results were evaluated against those obtained from the reference methods. The results show good performance of the WDXRF method for routine analysis of milk powders including copper at low levels (<10 mg/kg). All the calibrations gave R 2 > 0.98, while all validation work has been done using three replicates of each sample; the results have additionally been reassessed to check that only two replicates per sample would not lead to significant differences in terms of quality of data and could be considered for routine analysis to further decrease analysis time.