A Rapid Spectrophotometric Method for Trace Determination of Zinc

A simple, sensitive, and highly selective method is proposed for the determination of zinc(II) using a bis-azo dye, 2,6-bis(1-hydroxy-2-naphthylazo)pyridine as spectrophotometric reagent. At pH 7.8, in 50% (v/v) ethanol–water medium, the complex is found to obey Beer’s law up to 1.3 mg/L with an optimum concentration range between 0.19 and 1.0 mg/L. Sandell’s sensitivity of the color reaction was calculated to be 0.0011 μg cm⁻² with molar absorptivity of 6.0 × 10⁴ L mol⁻¹ cm⁻¹ at 560 nm. The optimum conditions for the determination of Zn(II) with the reagent were ascertained. The complexation at different pH was studied in water–ethanol medium. The composition of the complex is 1:2. The action of some interfering ions was verified, and the developed method applied successfully for the estimation of zinc levels in food and milk samples, and the results were then compared with those obtained by using AAS.     

Benzyloxybenzaldehydethiosemicarbazone: Extractive Spectrophotometric Reagent for the Determination of Cu(II) in Food and Water Samples

Benzyloxybenzaldehydethiosemicarbazone (BBTSC) was prepared and developed a new method for the simple, highly selective, and extractive spectrophotometric determination of copper(II) with BBTSC at wavelength 370 nm. The metal ion formed a bluish green colored complex with BBTSC in acetate buffer of pH 5.0, which was easily extractable into n-butanol with 1:1(metal/ligand) composition. The method obeys Beer’s law in the range of 0.5–5.2 ppm. The molar absorptivity and Sandell’s sensitivity were found to be 1.5 × 10⁴ l mol⁻¹ cm⁻¹ and 0.00412 g cm⁻², respectively. The correlation coefficient of the Cu(II)–BBTSC complex was 0.998, which indicated an excellent linearity between the two variables. The repeatability of the method was checked by finding the relative standard deviation (RSD; n = 10), which was 0.377% and its detection limit 0.0204 μg ml⁻¹. The interfering effect of various cations and anions were also studied. The proposed method was successfully applied to the determination of copper(II) in food and water samples. Comparing the results with those obtained using an atomic absorption spectrophotometer tested the validity of the method.     

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.     

Chemiluminescence Detection of 2,4,5-Trichlorophenoxy Acetic Acid in Apple Juice by Digital Image Analysis

An image-based detection of an enhanced chemiluminescence enzyme-linked immunosorbent assay was developed for 2,4,5-trichlorophenoxy acetic acid with an anti-rabbit secondary antibody conjugated to peroxidase (goat anti-rabbit IgG–HRP). Data acquisition on microtiter wells is performed using a low-cost charge-coupled device camera for capturing images. The standard curve was produced for 0.01–5,000 ng mL⁻¹ of 2,4,5-trichlorophenoxy acetic acid. The minimum detectable concentration was 24 pg mL⁻¹, and the relative standard deviation was 5.5% (n = 10) for a 5 ng mL⁻¹ sample concentration. Similar sensitivity was obtained with enzyme-linked immunosorbent assay using the same polyclonal antibody and data acquisition by a spectrofluorometer. This method was applied to apple juice with recoveries between 95% and 111% and relative standard deviation between 6.1% and 11.3%.     

MSPD Method to Determine Acrylamide in Food

The present work describes the development of an optimized matrix solid-phase dispersion (MSPD) procedure for the analysis of acrylamide in a variety of food matrices, namely, processed cereal products (bread, toasts, breakfast cereals, snacks, cookies, and biscuits), chocolates, and baby foods. Briefly, 1 g of sample was dispersed with 4 g of C₁₈ solid phase, the whole mixture was further packed in an empty SPE column, and acrylamide was extracted with 6 + 6 ml of water with a soak step of 5 min each. The aqueous extract was then subject to a bromination procedure and acrylamide quantified by gas chromatography–mass spectrometry (GC-MS) in SIM mode. Full validation of the method was conducted in samples representatives of each one of the food groups analyzed including a comparison of the results obtained by using the reported method with those furnished by a previously developed analytical procedure based on a liquid extraction approach. The MSPD-GC/MS method presented a limit of detection of 5.2 μg kg⁻¹ and a limit of quantification of 15.7 μg kg⁻¹, and precisions were in the range of 1–7% in all of the food matrices analyzed. Furthermore, the bias of the method was tested with a certified toasted bread sample.     

Production of Cell Membrane-Bound α- and β-Glucosidase by Lactobacillus acidophilus

Hydrolytic enzymes, viz. α- and β-glucosidase, were produced from indigenous isolate, Lactobacillus acidophilus, isolated from fermented Eleusine coracana. Production of these enzymes was enhanced by optimizing media using one factor at a time followed by response surface methodology. The optimized media resulted in a 2.5- and 2.1-fold increase in α- and β-glucosidase production compared with their production in basal MRS medium. Localization studies indicated 80% of the total activity to be present in the cell membrane-bound fraction. Lack of sufficient release of these enzymes using various physical, chemical, and enzymatic methods confirmed their unique characteristic of being tightly cell membrane bound. Enzyme characterization revealed that both α- and β-glucosidase exhibited optimum catalytic activity at 50 °C and pH 6.0 and 5.0, respectively. K _m and V _max of α-glucosidase were 4.31 mM and 149 μmol min⁻¹ mL⁻¹ for p-nitrophenyl-α-d-glucopyranoside as substrate and 3.8 mM and 120 μmol min⁻¹ mL⁻¹ for β-glucosidase using p-nitrophenyl-β-d-glucopyranoside as the substrate.     

Development of a Green Chromatographic Method for Simultaneous Determination of Food Colorants

A green chromatographic method for the successful separation and determination of eight synthetic food colorants (Tartrazine E 102, Quinoline Yellow E 104, Sunset Yellow E 110, Carmoisine E 122, Ponceau 4R E 124, Allura Red E 129, Indigo Carmine E 132 and Brilliant Blue E 133) was developed. A C8 stationary phase was used and the mobile phase was a mixture of 50 mM phosphate buffer at pH 7 containing triton X-100 (0.25% v/v). The method was validated as regards its selectivity, linearity, precision, accuracy, limit of detection (LOD) and quantification (LOQ). LOD of colorants varied between 0.17 μg mL⁻¹ in Allura Red and 1.91 μg mL⁻¹ in Quinoline Yellow. In the case of LOQ, it was ranged from 0.52 in the Allura Red to 5.79 in the Quinoline Yellow. The method applicability was verified by the determination of colorants present in 22 samples. The 15 samples were only unicolor and the color concentration in these samples varied from 18.426 ± 0.100 to 610.390 ± 4.711 ppm. The method can be used successfully to the determination of binary and ternary color food and drug samples too. This method provides substantial green benefits without using organic solvents in extraction procedure and in both liquid and paper chromatographic methods.     

Partial Purification and Characterization of Extracellular Fructofuranosidase with Transfructosylating Activity from <Emphasis Type="Italic">Candida</Emphasis> sp.

The present work was carried out with the aim to investigate some properties of an extracellular fructofuranosidase enzyme, with high transfructosylating activity, from Candida sp. LEB-I3 (Laboratory of Bioprocess Engineering, Unicamp, Brazil). The enzyme was produced through fermentation, and after cell separation from the fermented medium, the enzyme was concentrated by ethanol precipitation and than purified by anion exchange chromatography. The enzyme exhibited both fructofuranosidase (FA) and fructosyltransferase (FTA) activities on a low and high sucrose concentration. With sucrose as the substrate, the data fitted the Michaellis–Menten model for FA, showing rather a substrate inhibitory shape for fructosyltransferase activity. The K _m and v _max values were shown to be 13.4 g L⁻¹ and 21.0 μmol mL⁻¹ min⁻¹ and 25.5 g L⁻¹ and 52.5 μmol mL⁻¹ min⁻¹ for FA and FTA activities, respectively. FTA presented an inhibitory factor K _i of 729.8 g L⁻¹. The optimum conditions for FA activity were found to be pH 3.25–3.5 and temperatures around 69 °C, while for FTA, the optimum condition were 65 °C (±2 °C) and pH 4.00 (±0.25). Both activities were very stable at temperatures below 60 °C, while for FA, the best stability occurred at pH 5.0 and for FTA at pH  4.5–5.0. Despite the strong fructofuranosidase activity, causing hydrolysis of the fructooligosaccharides (FOS), the high transfructosilating activity allows a high FOS production from sucrose (44%).     

A Highly Sensitive Adsorptive Stripping Voltammetric Method for Simultaneous Determination of Lead and Vanadium in Foodstuffs

This work describes a procedure for the simultaneous determination of vanadium and lead in some food and water samples using adsorptive stripping voltammetric method. The method is based on the adsorptive accumulation of cupferron complexes of these elements onto hanging mercury drop electrode, followed by reduction of adsorbed species by voltammetric scan using differential pulse modulation. Optimal analytical conditions were found to be cupferron concentration of 8.00 × 10⁻⁵ M, pH of 4.8 (phosphate buffer), an accumulation potential at −100 mV, and a scan rate of 80 mV s⁻¹. With an accumulation time of 50 s, the peak currents proportional to the concentration of lead and vanadium over the 0.05–80.00 and 0.10–105.00 ng mL⁻¹ ranges with detection limit of 0.02 and 0.01 ng mL⁻¹, respectively. The procedure was applied to simultaneous determination of vanadium and lead in some food and water samples with satisfactory results.     

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.     

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.     

Comparison Between Systems for Synthesis of Fructooligosaccharides from Sucrose Using Free Inulinase from Kluyveromyces marxianus NRRL Y-7571

This work is focused on the synthesis of the fructooligosaccharides (FOS) from sucrose using free inulinase from Kluyveromyces marxianus NRRL Y-7571 in aqueous and aqueous–organic systems. The most significant variables for the aqueous–organic system were identified using a fractional factorial design. The evaluated variables were the temperature, pH, sucrose concentration, inulinase activity, aqueous/organic ratio, and the polyethylene glycol concentration. The use of sequential experimental design methodology was shown to be very useful in the optimization of the FOS synthesis by inulinase either in aqueous or aqueous–organic systems. For the aqueous–organic system, the maximum Y _FOS reached was 16.7 ± 1.1 wt.% with the following operational conditions: temperature of 40 °C, enzyme activity of 4 U mL⁻¹, organic solvent/total system ratio of 25/100, pH of 6.0, and sucrose concentration of 55%. In the aqueous system, the maximum conversion obtained was 12.8 ± 1.0 wt.% under the following conditions: 40 °C, pH 5.0, 55% sucrose, and inulinase activity 4 U mL⁻¹.     

Spectrophotometric Determination of Trace Nitrite with Brilliant Cresyl Blue Using β-Cyclodextrin as a Sensitizer

A simple and sensitive spectrophotometric method for determination of nitrite has been described. The method is based on the oxidation of brilliant cresyl blue (BCB) by nitrite in acidic medium, which results in the decrease in absorbance at 636 nm. The decrease in absorbance is directly proportional to nitrite concentration obeying Beer’s law. The sensitivity is largely enhanced in the presence of β-cyclodextrin (β-CD) because of inclusion complexation. It was calculated that β-CD and BCB could form 1:1 inclusion complexation with a formation constant of 546.6 L/mol. Linear calibration graphs were obtained for 0.02 × 10⁻³–0.8 × 10⁻³ g/L sodium nitrite at 636 nm. The detection limit for the analytical procedure was 4.0 × 10⁻⁶ g/L sodium nitrite. The relative standard deviation for determination of 0.1 × 10⁻³ g/L and 0.5 × 10⁻³ g/L sodium nitrite were 0.69% and 0.38%, for ten determinations, respectively. Twenty-two coexistent ions or species were examined, and no serious interference for most of ions was observed. The method has been applied to determine nitrite in water and vegetable samples with satisfactory results.     

Physicochemical and Enzymatic Properties of Five Kiwifruit Cultivars during Cold Storage

Samples of Abbot, Alison, Bruno, Monty, and Hayward cultivars of kiwifruit (Actinidia deliciosa) were obtained from the Iran Research Center of Citrus (Tonekabon, located in north of Iran) and their physicochemical properties were studied during cold storage (at T = 1 ± 1 °C, RH = 80 ± 5%) at 0-, 9-, and 18-week intervals. The mean chemical composition of the fruits were as follows: ash = 0.66–0.96%, moisture = 75.2–84.7%, starch = 0.3–7.0%, and ascorbic acid = 54.8–261.0; K = 125.0–372.0 mg 100 g⁻¹ fresh weight, Mg = 18.0–32.0 mg 100 g⁻¹ fresh weight, Na = 1.4–3.1 mg 100 g⁻¹ fresh weight, Fe = 0.17–0.52 mg 100 g⁻¹ fresh weight, Cu = 0.04–0.24 mg 100 g⁻¹ fresh weight, Zn = 0.16–0.49 mg 100 g⁻¹ fresh weight, Mn = 0.04–0.10 mg 100 g⁻¹ fresh weight, and P = 25.2–49.3 mg 100 g⁻¹ fresh weight; glucose = 0.7–2.39%, fructose = 1.20–3.13%, and sucrose = 0.0–5.8%. At the same time, the values of the parameters °Brix = 6.5–14.8% and acidity = 1.8–2.5% of the studied cultivars (mutual effects of cultivar and storage time) were investigated. The increase in peroxidase (POX = 0.0–6.65 U ml⁻¹) and the decrease in pectinesterase (PE; poor activity to 0) activities were also determined. The statistical analysis showed that the Bruno cultivar had the highest content of ascorbic acid (115.0–261.0 mg 100 g⁻¹ fresh weight), which is an important compound in fruits during storage, while Hayward had the best overall quality particularly with regards to its resistance to softening. This study confirms that long-term cold storage at 1 ± 1 °C and 80 ± 5% RH is suitable for maintaining the highest quality of Iranian grown cultivars of kiwifruit.     

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.     

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.     

Spectrophotometric Trace Determination of Iron in Food, Milk, and Tea Samples using a New Bis-azo Dye as Analytical Reagent

A newly synthesized bis-azo dye, 2,6-bis(1-hydroxy-2-naphthylazo)pyridine (PBN) was used as a sensitive reagent for iron. To determine the metal ion using a spectrophotometer in the concentration range between 0.3 and 2.76 ppm (molar absorptivity of 2.65 × 10⁴ l mol⁻¹ cm⁻¹ at 550 nm). In a phosphate-buffered medium, none of the transition metals, except Fe(II), Co(II), Ni(II), Cu(II), and Hg(II), produced color with the reagent; however, colors produced by Co(II), Ni(II), Cu(II), and Hg(II) could be masked using thiosemicarbazide, therefore, making the reagent highly selective for iron determination. The reagent was applied for the estimation of iron levels in milk, food grains, and tea samples and the results were compared with the iron levels found in those samples using AAS.     

Determination of Rosmarinic Acid by High-Performance Liquid Chromatography and Its Application to Certain Salvia Species and Rosemary

This study describes a method development for the determination of rosmarinic acid (RA) by using a gradient high-performance liquid chromatography (HPLC) and its application to certain plant materials. The analysis was performed by utilizing a two solvents system [A: methanol/water/formic acid (10:88:2; v:v:v); B: methanol/water/formic acid (90:8:2; v:v:v)] on a reverse-phase column. The flow rate and injection volume were 1 ml min⁻¹ and 10 μl, respectively. Signals were detected at 280 nm. In addition, an internal standard (IS) technique was applied for the analysis of RA to increase precision, and propylparaben was employed for this purpose. The repeatability results as RSD% were 1.66, 1.17 and 1.26 for intra-day and 1.38 was for inter-day with the employment of (3.67 × 10⁻⁵ M) RA. A limit of linearity (LOL) was observed in a wide (1.13 × 10⁻⁵–5.65 × 10⁻⁴ M) concentration range. Linearity parameters were also examined in the range of 5.95 × 10⁻⁶–7.14 × 10⁻⁵ M RA, and very good correlation was observed. The limit of detection (LOD) and limit of quantification (LOQ) (for inter-day) were 1.60 × 10⁻⁶ M (signal/noise [S/N] = 3.3) and 4.80 × 10⁻⁶ M (S/N = 10), respectively. The method was applied to the extracts of certain Lamiaceae plants (Salvia candidissima Vahl. subsp. candidissima, S. sclarea L., S. verticillata L. subsp. verticillata and R. officinalis L.), and reasonable results were obtained.     

Ultrasonically Assisted Extraction of Rutin from <Emphasis Type="Italic">Artemisia selengensis</Emphasis> Turcz: Comparison with Conventional Extraction Techniques

Ultrasonically assisted extraction (UAE) followed by high performance liquid chromatography (HPLC) analysis method for the fast extraction and determination of rutin in Artemisia selengensis Turcz has been developed. Artemisia selengensis Turcz has been used as food and herbal medicine for thousands of years in China. Rutin is one of the main active ingredients of this plant. The extraction of rutin from Artemisia selengensis Turcz was investigated by UAE. Special emphasis has been given to optimize the extraction conditions which were those with 90:10 (v/v) methanol–ethanol as solvent, 30:1 liquid–solid ratio, and 40 min extraction time. In order to show the superiority of UAE, other extractions were investigated, including microwave-assisted extraction, reflux extraction, and marinated extraction. The results showed that UAE was most suitable for the extraction of rutin in Artemisia selengensis Turcz because of its high extraction efficiency. Reversed phase-HPLC with ultraviolet detection was employed for the analysis of rutin in Artemisia selengensis Turcz. Under the optimum conditions, the calibration curve for the analyte was linear in the range of 0.34–20.7 μg mL⁻¹. The mean recovery of rutin was 100.77%, and its relative standard deviation was 0.37% (n = 5). Three kinds of Artemisia selengensis Turcz from different habitats were investigated. The total content of rutin was 9.90, 6.23, 5.56 mg g⁻¹, respectively.     

Dispersive Solid-Phase Extraction Clean-up Combined with Dispersive Liquid�CLiquid Microextraction for the Determination of Neonicotinoid Insecticides in Vegetable Samples by High-Performance Liquid Chromatography

Dispersive solid-phase extraction (DSPE) clean-up combined with dispersive liquid–liquid microextraction (DLLME) has been developed as a new approach for the extraction of neonicotinoid insecticides in vegetable samples prior to high-performance liquid chromatography with diode array detection. In the DSPE–DLLME method, neonicotinoid insecticides were first extracted with acetonitrile from vegetable samples, followed by clean-up by a DSPE with primary secondary amine and multi-walled carbonnanotubes as sorbents. A 2.5-mL aliquot of the resulting extract was then added into a centrifuge tube containing 10 mL of water, 0.8 g NaCl, and 200-μL chloroform (as the extraction solvent) for DLLME procedure. Under the optimum conditions, the enrichment factors for the compounds were in the range between 110 and 243. The linearity of the method was in the range from 5.0 to 300 ng g⁻¹ with the correlation coefficients (r) ranging from 0.9989 to 0.9998. The detection limits of the method were 0.5–1.0 ng g⁻¹. The repeatability of the method expressed as the relative standard deviations by five parallel experiments at the concentration levels of 10 and 50 ng g⁻¹ each of the neonicotinoid insecticides in tomato or cucumber samples varied from 3.6% to 5.8%. The developed method has been successfully applied for the analysis of target neonicotinoid insecticides (acetamiprid, imidacloprid, thiacloprid, and thiamethoxam) in tomato and cucumber samples. The recoveries of the method for the target neonicotinoid insecticides from the vegetable samples at spiking levels of 10.0 and 50.0 ng g⁻¹ were in the range between 84.6% and 97.5% (n = 5).