Determination of benzimidazolic fungicides in fruits and vegetables by supramolecular solvent-based microextraction/liquid chromatography/fluorescence detection

A supramolecular solvent consisting of vesicles, made up of equimolecular amounts of decanoic acid (DeA) and tetrabutylammonium decanoate (Bu₄NDe), dispersed in a continuous aqueous phase, is proposed for the extraction of benzimidazolic fungicides (BFs) from fruits and vegetables. Carbendazim (CB), thiabendazole (TB) and fuberidazole (FB) were extracted in a single step and no clean-up or concentration of extracts was needed. The high extraction efficiency obtained for BFs was a result of the different types of interactions provided by the supramolecular solvent (e.g. hydrophobic and hydrogen bonds) and the high number of solubilisation sites it contains. Besides simple and efficient, the proposed extraction approach was rapid, low-cost, environment friendly and it was implemented using conventional lab equipments. The target analytes were determined in the supramolecular extract by LC/fluorescence detection. They were separated in a Kromasil C₁₈ (5 μm, 150 mm × 4.6 mm) column using isocratic elution [mobile phase: 60:40 (v/v) 50 mM phosphate buffer (pH 4)/methanol] and quantified at 286/320 nm (CB) and 300/350 nm (TB and FB) excitation/emission wavelengths, respectively. Quantitation limits provided by the supramolecular solvent-based microextraction (SUSME)/LC/fluorescence detection proposed method for the determination of CB, TB and FB in fruits and vegetables were 14.0, 1.3 and 0.03 μg kg⁻¹, respectively, values far below the current maximum residue levels (MRLs) established by the European Union, i.e. 100-2000 μg kg⁻¹ for CB, 50-5000 μg kg⁻¹ for TB and 50 μg kg⁻¹ for FB. The precision of the method, expressed as relative standard deviation, for inter-day measurements (n = 13) was 3.3% for CB (50 μg kg⁻¹), 3.5% for TB (10 μg kg⁻¹) and 2.8% for FB (0.5 μg kg⁻¹) and recoveries for fruits (oranges, tangerines, lemons, limes, grapefruits, apples, pears and bananas) and vegetables (potatoes and lettuces) fortified at the μg kg⁻¹ level were in the interval 93-102%.     

Development of a dispersive liquid–liquid microextraction method for the determination of fluoroquinolones in chicken liver by high performance liquid chromatography

A simple and cost effective sample pre-treatment method, dispersive liquid–liquid microextraction (DLLME), has been developed for the extraction of six fluoroquinolones (FQs) from chicken liver samples. Clean DLLME extracts were analyzed for fluoroquinolones using liquid chromatography with diode array detection (LC-DAD). Parameters such as type and volume of disperser solvent, type and volume of extraction solvent, concentration and composition of phosphoric acid in the disperser solvent and pH were optimized. Linearity in the concentration range of 30–500 μg kg⁻¹ was obtained with regression coefficients ranging from 0.9945 to 0.9974. Intra-day repeatability expressed as % RSD was between 4 and 7%. The recoveries determined in spiked blank chicken livers at three concentration levels (i.e. 50, 100 and 300 μg kg⁻¹) ranged from 83 to 102%. LODs were between 5 and 19 μg kg⁻¹ while LOQs ranged between 23 and 62 μg kg⁻¹. All of the eight chicken liver samples obtained from the local supermarkets were found to contain at least one type of fluoroquinolone with enrofloxacin being the most commonly detected. Only one sample had four fluoroquinolone antibiotics (ciprofloxacin, difloxacin, enrofloxacin, norfloxacin). Norfloxacin which is unlicensed for use in South Africa was also detected in three of the eight chicken liver samples analyzed. The concentration levels of all FQs antibiotics in eight samples ranged from 8.8 to 35.3 μg kg⁻¹, values which are lower than the South African stipulated maximum residue limits (MRL).     

Supramolecular solvents in solid sample microextractions: Application to the determination of residues of oxolinic acid and flumequine in fish and shellfish

Supramolecular solvents are here proposed firstly as extractants in solid sample microextractions. The approach was evaluated by extracting flumequine (FLU) and oxolinic acid (OXO), two widely used veterinary medicines, from fish and shellfish muscle using a supramolecular solvent made up of decanoic acid (DeA) reverse micelles. The antibiotics were extracted in a single step (∼15 min), at room temperature, using 400 μL of solvent. After centrifugation, an aliquot of the extract was directly analyzed by liquid chromatography and fluorescence, without the need of clean-up or solvent evaporation. Contrary to the previously reported methods, both OXO and FLU were quantitatively extracted from fish and shellfish, independently of sample composition. The high extraction efficiencies observed for these antibiotics were a consequence of their amphiphilic character which resulted in the formation of DeA-OXO and DeA-FLU mixed aggregates. The quality parameters of this quantitative method including sensitivity, linearity, selectivity, repeatability, trueness, ruggedness, stability, decision limit and detection capability were evaluated according to the 2002/657/EC Commission Decision. Quantitation limits in the different samples analyzed (salmon, sea trout, sea bass, gilt-head bream, megrim and prawns) ranged between 6.5 and 22 μg kg⁻¹ for OXO and, 5 and 15 μg kg⁻¹ for FLU. These limits were far below the current maximum residue limits (MRLs) set by the European Union (EU) (i.e. 100 and 600 μg kg⁻¹, for OXO and FLU, respectively). The trueness of the method was determined by analyzing a Certified Reference Material (CMR, BCR^®-725) consisting of a lyophilised salmon tissue material. Recoveries for fortified samples (50–100 μg kg⁻¹ of OXO and 50–600 μg kg⁻¹ of FLU) and their relative standard deviations were in the intervals 99–102% and 0.2–5%, respectively. The repeatability, expressed as relative standard deviation, was 3.6% for OXO and 2.3% for FLU ([OXO] = [FLU] = 200 μg kg⁻¹ and n = 11).     

Development, validation and application of a SDME/GC-FID methodology for the multiresidue determination of organophosphate and pyrethroid pesticides in water

A single-drop microextraction (SDME) procedure was developed for the analysis of organophosphorus and pyrethroid pesticides in water by gas chromatography (GC) with flame ionization detection (GC-FID). The significant parameters that affect SDME performance, such as the selection of microextraction solvent, solvent volume, extraction time, and stirring rate, were studied and optimized using a tool screening factorial design. The limits of detection (LODs) in water for the four investigated compounds were between 0.3 and 3.0 μg L⁻¹, with relative standard deviations ranging from 7.7 to 18.8%. Linear response data were obtained in the concentration range of 0.9-6.0 μg L⁻¹ (λ-cyhalothrin), 3.0-60.0 μg L⁻¹ (methyl parathion), 9.0-60.0 μg L⁻¹ (ethion), and 9.0-30.0 μg L⁻¹ (permethrin), with correlation coefficients ranging from 0.9337 to 0.9977. The relative recoveries for the spiked water ranged from 73.0 to 104%. Environmental water samples (n = 26) were successfully analyzed using the proposed method and methyl parathion presented concentration up to 2.74 μg L⁻¹. The SDME method, coupled with GC-FID analysis, provided good precision, accuracy, and reproducibility over a wide linear range. Other highlights of the method include its ease of use and its requirement of only small volumes of both organic solvent and sample.     

Determination of octylphenol and nonylphenol in aqueous sample using simultaneous derivatization and dispersive liquid–liquid microextraction followed by gas chromatography–mass spectrometry

A simple and fast sample preparation method for the determination of nonylphenol (NP) and octylphenol (OP) in aqueous samples by simultaneous derivatization and dispersive liquid–liquid microextraction (DLLME) was investigated using gas chromatography–mass spectrometry (GC/MS). In this method, a combined dispersant/derivatization catalyst (methanol/pyridine mixture) was firstly added to an aqueous sample, following which a derivatization reagent/extraction solvent (methyl chloroformate/chloroform) was rapidly injected to combine in situ derivatization and extraction in a single step. After centrifuging, the sedimented phase containing the analytes was injected into the GC port by autosampler for analysis. Several parameters, such as extraction solvent, dispersant solvent, amount of derivatization reagent, derivatization and extraction time, pH, and ionic strength were optimized to obtain higher sensitivity for the detection of NP and OP. Under the optimized conditions, good linearity was observed in the range of 0.1–1000 μg L⁻¹ and 0.01–100 μg L⁻¹ with the limits of detection (LOD) of 0.03 μg L⁻¹ and 0.002 μg L⁻¹ for NP and OP, respectively. Water samples collected from the Pearl River were analyzed with the proposed method, the concentrations of NP and OP were found to be 2.40 ± 0.16 μg L⁻¹ and 0.037 ± 0.001 μg L⁻¹, respectively. The relative recoveries of the water samples spiked with different concentrations of NP and OP were in the range of 88.3–106.7%. Compared with SPME and SPE, the proposed method can be successfully applied to the rapid and convenient determination of NP and OP in aqueous samples.     

Ultrasound-assisted dispersive liquid–liquid microextraction combined with high-performance liquid chromatography-fluorescence detection for sensitive determination of biogenic amines in rice wine samples

Ultrasound-assisted dispersive liquid–liquid microextraction coupled with high-performance liquid chromatography-fluorescence detection was used for the extraction and determination of three biogenic amines including octopamine, tyramine and phenethylamine in rice wine samples. Fluorescence probe 2,6-dimethyl-4-quinolinecarboxylic acid N-hydroxysuccinimide ester was applied for derivatization of biogenic amines. Acetonitrile and 1-octanol were used as disperser solvent and extraction solvent, respectively. Extraction conditions including the type of extraction solvent, the volume of extraction solvent, ultrasonication time and centrifuging time were optimized. After extraction and centrifuging, analyte was injected rapidly into high-performance liquid chromatography and then detected with fluorescence. The calibration graph of the proposed method was linear in the range of 5–500 μg mL⁻¹ (octopamine and tyramine) and 0.025–2.5 μg mL⁻¹ (phenethylamine). The relative standard deviations were 2.4–3.2% (n = 6) and the limits of detection were in the range of 0.02–5 ng mL⁻¹. The method was applied to analyze the rice wine samples and spiked recoveries in the range of 95.42–104.56% were obtained. The results showed that ultrasound-assisted dispersive liquid–liquid microextraction was a very simple, rapid, sensitive and efficient analytical method for the determination of trace amount of biogenic amines.     

Extraction of pesticides in water samples using vortex-assisted liquid–liquid microextraction

A simple solvent microextraction method termed vortex-assisted liquid–liquid microextraction (VALLME) coupled with gas chromatography micro electron-capture detector (GC-μECD) has been developed and used for the pesticide residue analysis in water samples. In the VALLME method, aliquots of 30 μL toluene used as extraction solvent were directly injected into a 25 mL volumetric flask containing the water sample. The extraction solvent was dispersed into the water phase under vigorously shaking with the vortex. The parameters affecting the extraction efficiency of the proposed VALLME such as extraction solvent, vortex time, volumes of extraction solvent and salt addition were investigated. Under the optimum condition, enrichment factors (EFs) in a range of 835–1115 and limits of detection below 0.010 μg L⁻¹ were obtained for the determination of target pesticides in water. The calculated calibration curves provide high levels of linearity yielding correlation coefficients (r²) greater than 0.9958 with the concentration level ranged from 0.05 to 2.5 μg L⁻¹. Finally, the proposed method has been successfully applied to the determination of pesticides from real water samples and acceptable recoveries over the range of 72–106.3% were obtained.     

Dispersive liquid-liquid microextraction followed by high-performance liquid chromatography as an efficient and sensitive technique for simultaneous determination of chloramphenicol and thiamphenicol in honey

Dispersive liquid-liquid microextraction (DLLME) coupled with high-performance liquid chromatography-variable wavelength detector (HPLC-VWD) was developed for extraction and determination of chloramphenicol (CAP) and thiamphenicol (THA) in honey. In this extraction method, 1.0 mL of acetonitrile (as dispersive solvent) containing 30 μL 1,1,2,2-tetrachloroethane (as extraction solution) was rapidly injected by syringe into a 5.00-mL water sample containing the analytes, thereby forming a cloudy solution. After extraction, phase separation was performed by centrifugation and the enriched analytes in the sedimented phase were determined by HPLC-VWD. Some important parameters, such as the nature and volume of extraction solvent and dispersive solvent, extraction time, sample solution pH, sample volume and salt effect were investigated and optimized. Under the optimum extraction condition, the method yields a linear calibration curve in the concentration range from 3 to 2000 μg kg⁻¹ for target analytes. The enrichment factors for CAP and THA were 68.2 and 87.9, and the limits of detection (S/N = 3) were 0.6 and 0.1 μg kg⁻¹, respectively. The relative standard deviations (RSDs) for the extraction of 10 μg kg⁻¹ of CAP and THA were 4.3% and 6.2% (n = 6). The main advantages of DLLME-HPLC method are simplicity of operation, rapidity, low cost, high enrichment factor, high recovery, good repeatability and extraction solvent volume at microliter level. Honey samples were successfully analyzed using the proposed method.     

Multi-residue method for the determination of organochlorine pesticides in fish feed based on a cleanup approach followed by gas chromatography–triple quadrupole tandem mass spectrometry

A multi-residue method for the determination of organochlorine pesticides in fish feed samples was developed and optimized. The method is based on a cleanup step of the extracted fat, carried out by liquid–liquid extraction on diatomaceous earth cartridge with n-hexane/acetonitrile (80/20, v/v) followed by solid phase extraction (SPE) with silica gel–SCX cartridge, before the identification and quantification of the residues by gas chromatography–triple quadrupole tandem spectrometry (GC–MS/MS). Performance characteristics, such as accuracy, precision, linear range, limits of detection (LOD) and quantification (LOQ), for each pesticide were determined. Instrumental LODs ranged from 0.01 to 0.11 μg L⁻¹, LOQs were in the range of 0.02–0.35 μg L⁻¹, and calibration curves were linear (r² > 0.999) in the whole range of explored concentrations (5–100 μg L⁻¹). Repeatability values were in the range of 3–15%, evaluated from the relative standard deviation of six samples spiked at 100 μg kg⁻¹ of fat, and in compliance with that derived by the Horwitz's equation. No matrix effects or interfering substances were observed in fish feed analyses. The proposed method allowed high recoveries (92–116%) of spiked extracted fat samples at 100 μg kg⁻¹, and very low LODs (between 0.02 and 0.63 μg kg⁻¹) and LOQs (between 0.05 and 2.09 μg kg⁻¹) determined in fish feed samples.     

Dispersive liquid–liquid microextraction method based on solidification of floating organic drop for extraction of organochlorine pesticides in water samples

A new simple and rapid dispersive liquid–liquid microextraction method has been developed for the extraction and analysis of organochlorine pesticides (OCPs) in water samples. The method is based on the solidification of a floating organic drop (DLLME-SFO) and is combined with gas chromatography/electron capture detection (GC/ECD). Very little solvent is required in this method. The disperser solvent (200 μL acetonitrile) containing 10 μL hexadecane (HEX) is rapidly injected by a syringe into the 5.0 mL water sample. After centrifugation, the fine HEX droplets (6 ± 0.5 μL) float at the top of the screw-cap test tube. The test tube is then cooled in an ice bath. After 5 min, the HEX solvent solidifies and is then transferred into a conical vial, where it melts quickly at room temperature, and 1 μL of it is injected into a gas chromatograph for analysis. Under optimum conditions, the enrichment factors and extraction recoveries are high and range between 37–872 and 82.9–102.5%, respectively. The linear range is wide (0.025–20 μg L⁻¹), and the limits of detection are between 0.011 and 0.11 μg L⁻¹ for most of the analytes. The relative standard deviation (RSD) for 1 μg L⁻¹ of OCPs in water was in the range of 5.8–8.8%. The performance of the method was gauged by analyzing samples of lake and tap water.     

One-step extraction and derivatization liquid-phase microextraction for the determination of chlorophenols by gas chromatography–mass spectrometry

A sample pretreatment method for the determination of 18 chlorophenols (CPs) in aqueous samples by derivatization liquid-phase microextraction (LPME) was investigated using gas chromatography–mass spectrometry. Derivatization reagent was spiked into the extraction solvent to combine derivatization and extraction into one step. High sensitivity of 18 CPs derivatives could be achieved after optimization of several parameters such as extraction solvent, percentage of derivatization reagent, extraction time, pH, and ionic strength. The results from the optimal method showed that calibration ranging from 0.5 to 500 μg L⁻¹ could be achieved with the RSDs between 1.75% and 9.39%, and the limits of detection (LOD) are ranging from 0.01 to 0.12 μg L⁻¹ for the CPs. Moreover, the proposed LPME method was compared with solid-phase microextraction (SPME) coupled with on-fiber derivatization technique. The results suggested that using both methods are quite agreeable. Furthermore, the recoveries of LPME evaluated by spiked environmental samples ranged from 87.9% (3,5-DCP) to 114.7% (2,3,5,6-TeCP), and environmental water samples collected from the Pearl River were analyzed with the optimized LPME method, the concentrations of 18 CPs ranged from 0.0237 μg L⁻¹ (3,5-DCP) to 0.3623 μg L⁻¹ (2,3,6-TCP).     

Dispersive liquid–liquid microextraction combined with high-performance liquid chromatography-UV detection as a very simple,rapid and sensitive method for the determination of bisphenol A in water samples

Dispersive liquid–liquid microextraction (DLLME) coupled with high-performance liquid chromatography (HPLC)-UV detection was applied for the extraction and determination of bisphenol A (BPA) in water samples. An appropriate mixture of acetone (disperser solvent) and chloroform (extraction solvent) was injected rapidly into a water sample containing BPA. After extraction, sedimented phase was analyzed by HPLC-UV. Under the optimum conditions (extractant solvent: 142 μL of chloroform, disperser solvent: 2.0 mL of acetone, and without salt addition), the calibration graph was linear in the range of 0.5–100 μg L⁻¹ with the detection limit of 0.07 μg L⁻¹ for BPA. The relative standard deviation (RSD, n = 5) for the extraction and determination of 100 μg L⁻¹ of BPA in the aqueous samples was 6.0%. The results showed that DLLME is a very simple, rapid, sensitive and efficient analytical method for the determination of trace amount of BPA in water samples and suitable results were obtained.     

Determination of priority pollutants in aqueous samples by dispersive liquid–liquid microextraction

A dispersive liquid–liquid microextraction (DLLME) method followed by high-performance liquid chromatography–triple quadrupole mass spectrometry has been developed for the simultaneous determination of linear alkylbenzene sulfonates (LAS C₁₀, C₁₁, C₁₂, and C₁₃), nonylphenol (NP), nonylphenol mono- and diethoxylates (NP₁EO and NP₂EO), and di-(2-ethylhexyl)phthalate (DEHP). The applicability of the method has been tested by the determination of the above mentioned organic pollutants in tap water and wastewater. Several parameters affecting DLLME, such as, the type and volume of the extraction and disperser solvents, sample pH, ionic strength and number of extractions, have been evaluated. Methanol (1.5 mL) was selected among the six disperser solvent tested. Dichlorobenzene (50 μL) was selected among the four extraction solvent tested. Enrichment factor achieved was 80. Linear ranges in samples were 0.01–3.42 μg L⁻¹ for LAS C₁₀–₁₃ and NP₂EO, 0.09–5.17 μg L⁻¹ for NP₁EO, 0.17–9.19 μg L⁻¹ for NP and 0.40–17.9 μg L⁻¹ for DEHP. Coefficients of correlation were higher than 0.997. Limits of quantitation in tap water and wastewater were in the ranges 0.009–0.019 μg L⁻¹ for LAS, 0.009–0.091 μg L⁻¹ for NP, NP₁EO and NP₂EO and 0.201–0.224 μg L⁻¹ for DEHP. Extraction recoveries were in the range from 57 to 80%, except for LAS C₁₀ (30–36%). The method was successfully applied to the determination of these pollutants in tap water and effluent wastewater from Seville (South of Spain). The DLLME method developed is fast, easy to perform, requires low solvent volumes and allows the determination of the priority hazardous substances NP and DEHP (Directive 2008/105/EC).     

Simultaneous liquid–liquid microextraction and polypropylene microporous membrane solid-phase extraction of organochlorine pesticides in water,tomato and strawberry samples

A procedure involving the simultaneous performance of liquid–liquid microextraction and polypropylene microporous membrane solid-phase extraction was carried out. The applicability of the proposed procedure was evaluated through extraction of several organochlorine pesticides from river water, tomato and strawberry samples. The parameters affecting the extraction efficiency were optimized by multivariable designs, and the analytical features were estimated. Under optimized conditions, analytes were concentrated onto 1.5 cm long microporous membranes placed directly into the sample containing 15 mL of water with 20 μL of 1-octanol. The best extraction conditions were achieved at 59 °C, with 60 min of extraction time and 2.91 g of sodium chloride. The desorption of the analytes was carried out using 30 μL of a mixture of toluene and hexane in the proportion of 60:40% (v/v) for 10 min. Detection limits in the range of 2.7–20.0 ng L⁻¹, 0.50–1.15 μg kg⁻¹, and 1.53–12.77 μg kg⁻¹ were obtained for river water, strawberry and tomato samples, respectively. Good repeatability was obtained for all three sample types. The results suggest that the proposed procedure represents a very simple and low-cost microextraction alternative rendering adequate limits of quantification for the determination of organochlorine pesticides in environmental and food samples.     

Dispersive liquid–liquid microextraction based on the solidification of floating organic drop followed by inductively coupled plasma-optical emission spectrometry as a fast technique for the simultaneous determination of heavy metals

A simple, rapid and efficient dispersive liquid–liquid microextraction based on the solidification of floating organic drop (DLLME–SFO) method, followed by inductively coupled plasma-optical emission spectrometry (ICP-OES) was developed for the simultaneous preconcentration and determination of heavy metals in water samples. One variable at a time method was applied to select the type of extraction and disperser solvents. Then, an orthogonal array design (OAD) with OA₁₆ (4⁵) matrix was employed to study the effects of different parameters on the extraction efficiency. Under the best experimental conditions (extraction solvent: 140 μL of 1-undecanol; disperser solvent: 2.0 mL of acetone; ligand to metal mole ratio: 20; pH: 6 and without salt addition), the enhancement factor ranged from 57 to 96. The calibration graphs were linear in the range of 0.5–250 μg L⁻¹ for Mn, 1.25–250 μg L⁻¹ for Cr, Co and Cu with correlation coefficient (r) better than 0.990. The detection limits were between 0.1 and 0.3 μg L⁻¹. Finally, the developed method was successfully applied to extraction and determination of the mentioned metal ions in the tap, sea and mineral water samples and satisfactory results were obtained.     

In situ derivatization hollow fibre liquid-phase microextraction for the determination of biogenic amines in food samples

Hollow fibre liquid-phase microextraction with in situ derivatization using dansyl chloride has been successfully developed for the high-performance liquid chromatography-ultraviolet (HPLC-UV) determination of the biogenic amines (tryptamine, putrescine, cadaverine, histamine, tyramine, spermidine) in food samples. Parameters affecting the performance of the in situ derivatization process such as type of extraction solvent, temperature, extraction time, stirring speed and salt addition were studied and optimized. Under the optimized conditions (extraction solvent, dihexyl ether; acceptor phase, 0.1 M HCl; extraction time, 30 min; extraction temperature, 26 °C; without addition of salt), enrichment factors varying from 47 to 456 were achieved. Good linearity of the analytes was obtained over a concentration range of 0.1–5 μg mL⁻¹ (with correlation coefficients of 0.9901–0.9974). The limits of detection and quantification based on a signal-to-noise ratio of 3–10, ranged from 0.0075 to 0.030 μg mL⁻¹ and 0.03 to 0.10 μg mL⁻¹, respectively. The relative standard deviations based on the peak areas for six replicate analysis of water spiked with 0.5 μg mL⁻¹ of each biogenic amine were lower than 7.5%. The method was successfully applied to shrimp sauce and tomato ketchup samples, offering an interesting alternative to liquid–liquid extraction and solid phase extraction for the analysis of biogenic amines in food samples.     

Hydrophilic interaction vs ion pair liquid chromatography for the determination of streptomycin and dihydrostreptomycin residues in milk based on mass spectrometric detection

Streptomycin (STR) and dihydrostreptomycin (DHSTR) are two of the most common aminoglycoside antibiotics used in veterinary medicine. The physicochemical properties of both substances, make their determination challenging. In the present study the development of methods based on ion-pair chromatography (IPC) and on hydrophilic interaction chromatography (HILIC), for the determination of the above mentioned aminoglycosides in the range of 100–1000 μg L⁻¹ is described. The two methods were validated according to EU requirements for residues in food. The recoveries for the IPC method were 69.3% and 56.5% of STR and DHSTR, respectively, and for HILIC method 85.5% and 72.3%, respectively. The intra- and inter-day precision, studied at 100, 200 and 300 μg kg⁻¹ levels in milk samples, gave %RSD ≤ 13 for both methods. LOQs for the HILIC method were 14 μg kg⁻¹ for both analytes and for the IPC method were 109 and 31 μg kg⁻¹, for STR and DHSTR, respectively. The sensitivity of the HILIC method is 80 and 210 times greater than that of the ICP method, for STR and DHSTR, respectively.     

Trace determination of sulfonamides residues in meat with a combination of solid-phase microextraction and liquid chromatography-mass spectrometry

An integrated method of combining solid-phase microextraction (SPME) with liquid chromatography-mass spectrometry (LC-MS) was evaluated for determination trace amount of sulfonamides in meat products. Eight commonly used sulfonamides, sulfadiazine (SDZ), sulfathiazole (STZ), sulfamerazine (SMR), sulfamethazine (SMT), sulfamonomethoxine (SMMX), sulfamethoxazole (SMXZ), sulfaquinoxaline (SQX) and sulfadimethoxine (SDMX), were investigated in this study. Chromatography was performed on a C₁₈ reversed-phase column using an isocratic acetonitrile in water as the mobile phase. Fiber coated with a 65 μm thickness of polydimethylsiloxane/divinylbenzene (PDMS/DVB) was used to extract sulfonamides at optimum conditions. Analytes were desorbed with static desorption in an SPME-HPLC desorbed chamber for 15 min and then determined by LC-MS. The detection limits of these sulfonamides in pork were from 16 μg kg⁻¹ (SMT) to 39 μg kg⁻¹ (SMMX). According to the analysis, the linear range was from 50 to 2000 μg kg⁻¹ with relative standard deviation (R.S.D.s) value below 15% (intra-day) and 19% (inter-day). The proposed method was tested by analyzing meats from a local market for sulfonamides residues. Some sulfonamides in our study were detected in the meat samples. The concentration of these residual sulfonamides ranged from 66 μg kg⁻¹ (SDZ) to 157 μg kg⁻¹ (SQX) in a chicken sample. The results demonstrate that the SPME-LC-MS system is highly effective in analyzing trace sulfonamides in meat products.     

Determination of naphthalene-derived compounds in apples by ultra-high performance liquid chromatography-tandem mass spectrometry

Naphthylacetic acid, naphthyloxy acetic acid and naphthylacetamide belong to a group of synthetic substances known as “auxin-like” compounds which are used as growth regulators in vegetables and fruits due to their structure similarities with the indoleacetic acid, the most important plant auxin. This paper reports a selective, sensitive and fast ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC–MS/MS) method for the determination of naphthylacetamide (NAD) and the isomers (α and β) of naphthylacetic acid (NAA) and naphthyloxy acetic (NOA) acid in apple samples. A baseline separation between the respective isomers was achieved using an RP-Amide column with gradient elution. The UHPLC-MS/MS method developed, using electrospray and selected reaction monitoring (SRM) acquisition mode led to a reliable determination of these family of compounds in apple samples at low quantitation levels, down to 1.0 μg kg⁻¹ and 0.25 μg kg⁻¹ respectively. For confirmation of NAA accurate mass measurement is proposed giving at these conditions quantitation limits of 10 μg kg⁻¹ for this compound. The UHPLC-MS/MS method developed was used for the analysis of apple samples harvested in three different apple fields from Lleida (Spain) during the blooming period. NAD and NAA were found in samples collected during 4–5 weeks after application at concentrations between the quantification limits and 43 μg kg⁻¹ and 24 μg kg⁻¹, respectively.     

Determination of ochratoxin A in wine grapes: comparison of extraction procedures and method validation

A method for determination of ochratoxin A (OTA) in wine grapes is described, using extraction with a hydrogen carbonate and polyethylene glycol (PEG) solution (5% NaHCO₃ and 1% PEG 8000), followed by immunoaffinity clean-up and liquid chromatography with fluorescence detection. Validation was made with spiked samples, in levels of 0.05 and 1 μg kg⁻¹, with average recovery rates of 76% and relative standard deviations in repeatability and intermediate precision conditions of 8 and 12%, respectively. The limit of detection and limit of quantification in grapes were established at 0.004 and 0.007 μg kg⁻¹, respectively. To evaluate further the accuracy and efficiency of this method, naturally contaminated grapes were also analysed by another method that involves extraction with acidified methanol, at levels ranging from 0.05 to 37 μg kg⁻¹, and the results compared. A good correlation (r=0.9996) was found, with better performances in terms of precision for the new method. A survey was conducted on wine grapes from 11 Portuguese vineyards, during the harvest of 2002, using the proposed method. OTA was detected in three out of the 11 samples, at levels ranging from 0.035 to 0.061 μg kg⁻¹.The new method meets all the criteria of the European Commission directive 2002/26/CE, that lays down the sampling and the analysis methods for the official control of OTA levels in foodstuffs. It is reliable for low levels of contamination (ng kg⁻¹), and avoids the use of organic solvents in the extraction step.