Solid-Phase Extraction and LC with Fluorescence Detection for Analysis of PAHs in Rainwater

The efficiency of extraction of polycyclic aromatic hydrocarbons (PAHs) from rainwater by solid-phase extraction (SPE) with three different types of cartridge, and analysis by high-performance liquid chromatography with fluorescence detection, are discussed in this paper. Three cartridges were investigated but only one was suitable. After equilibration in a desiccator for 65–80 h or in ambient air for 90–100 h the SPE cartridges were activated with 5 mL dichloromethane then 5 mL 2-propanol. The volume of sample passed through the cartridges was 50 mL; after loading of the sample the cartridges were dried under vacuum for approximately 20 min by application of a pressure of 15 mbar to the SPE manifold. The PAHs were eluted with 5 mL dichloromethane–hexane, 50:50 (v/v). The flow rate used for conditioning, sample loading, and elution was 2.5 mL min⁻¹, achieved by application of a pressure of 6 mbar. For analysis of PAHs in rainwater, recovery was between 67 and 99%, the relative standard deviation varied between 2 and 5%, and the detection limits of the method were less than 16.9 ng L⁻¹ for several PAHs. These optimum conditions were used for analysis of rainwater collected between June 2002 and May 2003 at two sites in Alsace (eastern France) and 17 PAHs were quantitatively determined. Concentrations varied between 1.6 and 968.1 ng L⁻¹.     

Liquid chromatographic determination of aliphatic amines in water using solid support assisted derivatization with 9-fluorenylmethyl chloroformate

Summary A simple and sensitive method has been developed for the liquid chromatographic determination of short-chain aliphatic amines in water. Analytes are retained in solid-phase extraction (SPE) cartridges, and then derivatized by drawing an aliquot of the fluorogeneic reagent 9-fluorenylmethyl chloroformate (FMOC) through the cartridges. After a certain reaction time the derivatives formed are desorbed with acetonitrile. The collected extracts are then chromatographed on a LiChrospher 100 RP₁₈ 125 mm×4 mm i.d., 5 μm, column using an acetonitrile-water gradient. The influence of experimental conditions (SPE material, volume of sample, concentration of FMOC, time of reaction and pH) has been investigated. Optimal results have been obtained with C₁₈ SPE cartridges using a sample volume of 5.0 mL. For derivatization, 0.25 mL aliquots of 25 mM FMOC have been used, the reaction time being only 2 min. The method has been applied to the quantification of several aliphatic amines: methylamine, ethylamine, dimethylamine,n-butylamine,n-pentylamine andn-hexylamine. Under the proposed conditions the percentages of analytes retained plus derivatized were of about 54–107% compared to those obtained with direct solution derivatization. The method provided good reproducibility, linearity and accuracy within the 0.050–1.0 mg L⁻¹ concentration range. The limits of detection were in the 0.25–5.0 μg L⁻¹ range. The utility of the described approach has been tested by analysing tap water, river water and industrial waste water.     

Determination of paralytic shellfish poisoning toxins in cultured microalgae by high-performance liquid chromatography with fluorescence detection

A novel method for the determination of paralytic shellfish poisoning (PSP) toxins using high-performance liquid chromatography with fluorescence detection was developed. The fluorescent derivates of neosaxitoxin (neoSTX), saxitoxin (STX), gonyautoxins 1 and 4 (GTX1+4), and gonyautoxins 2 and 3 (GTX2+3) were separated on a μBondapak NH₂ column (300 mm × 3.9 mm, 10 μm) using water and acetate buffer (pH 6.5) as the mobile phase (1.00 mL min⁻¹) in gradient mode with fluorescence detection at 390 nm (excitation at 330 nm). The linear ranges of neoSTX, STX, GTX1+4 and GTX2+3 were 3.31–331, 0.952–95.2, 3.78–378 and 0.124–12.4 ng mL⁻¹, respectively. The detection limits of neoSTX, STX, GTX1+4 and GTX2+3 were 1.10, 0.32, 1.26 and 0.041 ng mL⁻¹, respectively. The method was successfully applied to the determination of PSP toxins in microalgae. The recoveries ranged from 88±2% to 107±4% and the relative standard deviations were 0.16% to 4.4%. The procedure is also environmentally friendly because no organic solvent is used in the mobile phase.     

Determination of Non-Steroidal Anti-Inflammatory Drugs in Natural Waters Using Off-Line and On-Line SPE Followed by LC Coupled with DAD-MS

Two different procedures for simultaneous determination of six NSAIDs (diflunisal, diclofenac, fenoprofen, ibuprofen, naproxen and tolmetin) in environmental waters are described. Final analysis of target compounds is performed by reversed-phase liquid chromatography – diode array detection and mass spectrometry (HPLC-DAD and LC-MS), whereas sample preparation is based on solid-phase extraction (SPE). A variety of sorbents and their respective advantages and disadvantages are discussed. For the off-line SPE of NSAIDs from water samples, a LiChrolut RP-18 was selected out of all investigated sorbents. In case of on-line coupling of SPE with chromatographic system LiChrosphere RP-18 was selected as the best one in terms of recovery of NSAIDs evaluated, RSD and availability. The applicability of the method was also evaluated. Method detection limits were in the range of 0.7−94 ng L⁻¹. Recoveries ranged from 96 to 109% and relative standard deviations were lower than 5%. The procedures were shown to be linear over a wide range of concentration, exhibited satisfactory repeatability and accuracy, and reached limits of detection in the low ng L⁻¹ range. No breakthrough volume was observed neither for off-line SPE (in the studied range of 100, 200, 300, 500, 700, 1000 and 2000 mL of tap water sample) nor for on-line SPE (in the wide range of 10 mL, 20 mL, 30 mL, 50 mL, 70 mL, 100 mL and 200 mL of tap water sample).     

Isocratic Reversed-Phase HPLC for Simultaneous Separation and Determination of Seven Antiepileptic Drugs and Two of their Active Metabolites in Human Plasma

A simple reversed-phase high-performance liquid chromatographic (HPLC) method has been developed for the simultaneous determination of the antiepileptic drugs (AEDs) zonisamide (ZNS), primidone (PRI), lamotrigine (LTG), phenobarbital (PB), phenytoin (PHT), oxcarbazepine (OXC), and carbamazepine (CBZ) and two of their active metabolites, monohydroxycarbamazepine (MHD) and carbamazepine 10,11-epoxide (CBZE) in human plasma. Plasma (100 μL) was pretreated by deproteinization with 300 μL methanol containing 20 μg mL⁻¹ propranolol hydrochloride as internal standard. HPLC was performed on a C₈ column (4.6 mm × 250 mm; particle size 5 μm) with methanol–acetonitrile–0.1% trifluoroacetic acid, 235:120:645 (v/v), as mobile phase at a flow rate of 1.5 mL min⁻¹. ZNS, OXC, and CBZ were monitored by UV detection at 235 nm, and PRI, LTG, MHD, PB, PHT, and CBZE by UV detection at 215 nm. Relationships between response and concentration were linear over the concentration ranges 1–80 μg mL⁻¹ for ZNS, 5–50 μg mL⁻¹ for PRI, 1–25 μg mL⁻¹ for LTG, 1–50 μg mL⁻¹ for MHD, 5–100 μg mL⁻¹ for PB, 1–10 μg mL⁻¹ for CBZE, 0.5–25 μg mL⁻¹ for OXC, 1–50 μg mL⁻¹ for PHT, and 1–25 μg mL⁻¹ for CBZ. Intra-day and inter-day reproducibility were adequate (coefficients of variation were ≤11.6%) and absolute recovery ranged from 95.2 ± 6.13 to 107.7 ± 7.76% for all the analytes; for the IS recovery was 98.69 ± 1.12%. The method was proved to be accurate, reproducible, convenient, and suitable for therapeutic monitoring of the nine analytes.     

Simultaneous Determination of Olanzapine and Fluoxetine by HPLC

A rapid, specific reversed phase HPLC method has been developed for simultaneous determination of olanzapine and fluoxetine in their formulations. Chromatographic separation of these two pharmaceuticals was carried out on an Inertsil C₁₈ reversed phase column (150 mm × 4.6 mm, 5 μm) with a 40:30:30 (v/v/v) mixture of 9.5 mM sodium dihydrogen phosphate (pH adjusted to 6.8 ± 0.1 with triethylamine), acetonitrile and methanol as mobile phase. The flow rate 1.2 mL min⁻¹ and the analytes are monitored at 225 nm. Paroxetine was used as internal standard. The assay results were linear from 25 to 75 μg mL⁻¹ for olanzapine (r ² ≥ 0.995) and 100–300 μg mL⁻¹ for fluoxetine (r ² ≥ 0.995), showed intra- and inter-day precision less than 1.0%, and accuracy of 97.7–99.1% and 97.9–99.0%. LOQ was 0.005 and 0.001 μg mL⁻¹ for olanzapine and fluoxetine, respectively. Separation was complete in less than 10 min. Validation of the method showed it to be robust, precise, accurate and linear over the range of analysis.     

Determination of Trihalomethanes in Drinking Water by Dispersive Liquid–Liquid Microextraction then Gas Chromatography with Electron-Capture Detection

Dispersive liquid–liquid microextraction (DLLME) has been used for preconcentration of trihalomethanes (THMs) in drinking water. In DLLME an appropriate mixture of an extraction solvent (20.0 μL carbon disulfide) and a disperser solvent (0.50 mL acetone) was used to form a cloudy solution from a 5.00-mL aqueous sample containing the analytes. After phase separation by centrifugation the enriched analytes in the settled phase (6.5 ± 0.3 μL) were determined by gas chromatography with electron-capture detection (GC–ECD). Different experimental conditions, for example type and volume of extraction solvent, type and volume of disperser solvent, extraction time, and use of salt, were investigated. After optimization of the conditions the enrichment factor ranged from 116 to 355 and the limit of detection from 0.005 to 0.040 μg L⁻¹. The linear range was 0.01–50 μg L⁻¹ (more than three orders of magnitude). Relative standard deviations (RSDs) for 2.00 μg L⁻¹ THMs in water, with internal standard, were in the range 1.3–5.9% (n = 5); without internal standard they were in the range 3.7–8.6% (n = 5). The method was successfully used for extraction and determination of THMs in drinking water. The results showed that total concentrations of THMs in drinking water from two areas of Tehran, Iran, were approximately 10.9 and 14.1 μg L⁻¹. Relative recoveries from samples of drinking water spiked at levels of 2.00 and 5.00 μg L⁻¹ were 95.0–107.8 and 92.2–100.9%, respectively. Comparison of this method with other methods indicates DLLME is a very simple and rapid (less than 2 min) method which requires a small volume of sample (5 mL).     

Determination of phenolic compounds in water samples by on-line solid-phase extraction—supercritical-fluid chromatography with diode-array detection

Summary The eleven Environmental Protection Agency (EPA) priority phenolic compounds have been determined by solid-phase extraction (SPE) coupled on-line to supercritical-fluid chromatography (SFC) with diodearray detection. The variables affecting chromatographic separation were optimized and the analytes were separated at 40 °C in two diol columns connected in series; a gradient of methanol, as modifier, and CO₂ was used as mobile phase. Under these conditions, all the compounds studied were separated to baseline in less than 13 min. PLRP-S and LiChrolut EN were tested as sorbents in a 10×3 mm i.d. laboratory-packed precolumn for solid-phase extraction. An ion-pair reagent, tetrabutylammonium bromide (TBA), was used in the extraction process to increase break-through volumes. The performance of the method was checked with tap and river waters and the pre-concentration of 20 mL of sample in a PLRP-S pre-column enabled phenolic compounds to be determined at low μg L⁻¹ levels with limits of detection ranging between 0.4 and 2 μg L⁻¹. The repeatability and reproducibility between days (n=3) for real samples spiked at 10 μg L⁻¹ were lower than 10%.     

Quantification of cis-Abienol in Oriental Tobacco Leaves by LC

A rapid and accurate method for the quantification of cis-abienol in oriental tobacco leaves by normal phase liquid chromatography was developed. Freeze-dried tobacco samples were sonicated in methylene chloride for 10 min. The supernatant was purified using a silica gel solid phase extraction cartridge. Ten milliliter of the resulting methylene chloride eluate was collected, then separated on a 250 × 4.6 mm, 5 μm particle-size CN column with n-hexane: ethyl acetate, 100:2 (v/v) at a flow rate of 1 mL min⁻¹. cis-Abienol was detected by UV absorption at 254 nm. The linear range was from 2.14 × 10⁻⁴ to 4.28 × 10⁻² mg mL⁻¹ and the correlation coefficient was 1.000. The average recovery was 98.7, 105.2 and 103.1% in five replicated sets of tobacco samples spiked with 0.2856, 0.7140 and 1.904 mg cis-abienol. The relative standard deviations (RSDs) were 1.04, 0.63 and 1.25%, respectively (n = 5). Limit of detection (S/N = 3) was 21.84 μg g⁻¹ and limit of quantification (S/N = 10) was 72.80 μg g⁻¹. The method was found to be suitable for determination of cis-abienol in oriental tobacco leaves. Furthermore, pure cis-abienol used for method validation was obtained by preparative reversed phase high-performance liquid chromatography. Identification was performed by UV detection, nuclear magnetic resonance and mass spectrometry.     

On-line determination of bipyridylium herbicides in water by HPLC

Summary Selective on-line solid phase extraction (SPE) and liquid chromatography determination (HPLC) of diquat, paraquat and difenzoquat from environmental water samples has been accomplished with Graphitized Carbon Black (GCB) as both extraction and analytical columns. The method involved passing of 50 mL of water through a cartridge filled with Carbograph. In the elution step, the herbicides were transferred from the cartridge to the analytical column (Hypercarb) by mean of a gradient of pH 3 aqueous solution of tetramethylammonium hydroxide (TMAOH) and ammonium sulphate and methanol. Hypercarb columns were found to give a low probability of false positives for bypiridylium herbicides and are very selective for polar compounds. Recovery was better than 80 %. The breakthrough volume was studied with distilled water spiked with the herbicides at various concentration levels (from 0.1 to 20 μg L⁻¹). The limits of quantification of the method were lower than 0.1 μg L⁻¹. The total analytical method was applied to surface waters from Torreblanca Nature Park (Castelló, Spain). Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996.     

Determination of five nitrobenzoic acids in groundwater by solid-phase extraction and liquid chromatography–mass spectrometry

A method involving solid-phase extraction (SPE) and reversed-phase liquid chromatography–mass spectrometry (LC–MS) has been developed for determination, in groundwater, of nitrobenzoic acids associated with 2,4,6-trinitrotoluene production. Pre-concentration on a co-polymer-based SPE cartridge enabled quantitative extraction of the analytes from water. Investigation of negative ion electrospray and atmospheric-pressure chemical ionization mass spectrometry indicated the sensitivity of APCI was more than twice that of ESI. An ¹⁵N-labeled internal standard was used to achieve more accurate quantitation and mass assignment. Recovery was better than 80% when 10 mL water was extracted with the SPE cartridge. Combination of SPE with LC–MS analysis resulted in method detection limits of less than 5 μg L⁻¹. The method has been used for analysis of groundwater samples collected from a site of a former ammunition plant. Contamination with nitrobenzoic acids was determined at μg L⁻¹ levels.     

Simultaneous RP-LC Determination of Losartan Potassium, Ramipril, and Hydrochlorothiazide in Pharmaceutical Preparations

A simple, rapid, and precise reversed-phase high-performance liquid chromatographic method has been developed for simultaneous determination of losartan potassium, ramipril, and hydrochlorothiazide. The three drugs were separated on a 150 mm × 4.6 mm i.d., 5 μm particle, Cosmosil C₁₈ column. The mobile phase was 0.025 m sodium perchlorate–acetonitrile, 62:38 (v/v), containing 0.1% heptanesulphonic acid, pH adjusted to 2.85 with orthophosphoric acid, at a flow rate of 1.0 mL min⁻¹. UV detection was performed at 215 nm. The method was validated for linearity, accuracy, precision, and limit of quantitation. Linearity, accuracy, and precision were acceptable in the ranges 35–65 μg mL⁻¹ for losartan, 1.75–3.25 μg mL⁻¹ for ramipril, and 8.75–16.25 μg mL⁻¹ for hydrochlorothiazide.     

High-performance liquid chromatographic assay for simultaneous determination of tramadol and its active metabolite in human plasma. Application to pharmacokinetic studies

Summary A sensitive liquid chromatographic assay for the quantitative determination of the opioid analgesic tramadol and its active metabolite is described. Fluconazole was used as internal standard. The assay involved a singletert-butyl methyl ether extraction and LC analysis with fluorescence detection. Chromatography was at 30°C pumping an isocratic mobile phase of acetonitrile-water (19∶81, v/v) containing 0.06M NaH₂PO₄ and 0.05M triethylamine, adjusted to pH 7.90, at 1 mL min⁻¹ through a reversed-phase, 250×4 mm base-stable column. The limit of quantitation of tramadol and its active metabolite was 1 ng mL⁻¹, only 0.5 mL plasma sample was required for the determination. The calibration curve was linear from 1–1000 ng mL⁻¹. Intra and inter-day precision (C.V.) did not exceed 10%. Mean recoveries of 96.38% for tramadol and 96.62% forO-demethyltramadol with CVs of 0.43% and 1.46% were obtained. Applicability of the method was demonstrated by a pharmacokinetic study on normal volunteers who received 100 mg tramadol intravenously.     

Development and Validation of LC–MS Method for the Determination of Hydroxyzine Hydrochloride in Human Plasma and Subsequent Application in a Bioequivalence Study

A rapid, simple and specific liquid chromatography-electrospray ionization mass spectrometry method has been developed and validated for the determination of hydroxyzine hydrochloride in human plasma. Samples were separated using a Thermo Hypersil-HyPURITYC18 reversed-phase column (150 mm × 2.1 mm i.d., 5 μm). The mobile phase consisted of 50 mM ammonium acetate (pH 4.0)–methanol–acetonitrile (45:36:19, v/v). Hydroxyzine and its internal standard were measured by electrospray ion source in positive selective ion monitoring mode. The method was validated with a linear range of 1.56–200.0 ng mL⁻¹ and the lowest limit of quantification was 1.56 ng mL⁻¹ for hydroxyzine hydrochloride (r ²= 0.9991). The extraction efficiencies were about 70% and recoveries of the method were in the range of 93.5–104.4%. The intra-day relative standard deviation (RSD) was less than 8.0% and inter-day RSD was within 7.4%. QC samples were stable when kept at ambient temperature for 12 h at −20 °C for 30 days and after four freeze–thaw cycles. The method has been successfully applied to the evaluation of pharmacokinetics and bioequivalence of two hydroxyzine hydrochloride formulations in 12 healthy Chinese volunteers after an oral dose of 25 mg.     

Determination of clozapine in human plasma by solid-phase extraction and liquid chromatography with amperometric detection

Summary A sensitive and selective high-performance liquid chromatographic method has been developed for monitoring clozapine levels in human plasma. Chromatography was performed on a reversed-phase column (C₈, 150 mm×4.6 mm i.d., 5 μm) with acetonitrile-aqueous sodium acetate solution, 88∶12 (v/v), as mobile phase; the flow rate was 1 mL min⁻¹. Clozapine oxidation at +800 mV was detected amperometrically. Response was linearly dependent on concentration over the range 50–1500 ng mL⁻¹ clozapine in plasma. Sample preparation by solid-phase extraction before HPLC analysis gave high extraction yield (94%). The accuracy and precision of the method were both very good (recovery: 97%;RSD<3.3%).     

CE Analysis of Cephalosporins in Environmental Waters

This study investigates an off-line solid phase extraction (SPE) for improving the sensitivity in the capillary electrophoretic (CE) analysis of four cephalosporins. Two sorbents—LiChrolut-C₁₈ and Oasis HLB—were used in a SPE process to detect cephalosporins in natural waters (tap, river and hospital sewage) and their performances were compared. By using Oasis HLB sorbent higher recoveries for river water were obtained (94–107% when 500 mL of sample were analyzed). The off-line SPE–CZE method was validated for river water with good detection limits (3 μg L⁻¹) and the linearity ranged between 5 and 200 μg L⁻¹.     

Direct analysis of clomipramine in human plasma by microbore high performance liquid chromatography with column-switching

Summary An automated microbore, liquid chromatographic method with column-switching was developed for the determination of clomipramine from human plasma samples. After direct injection of samples (60 μL), plasma proteins and clomipramine were separated in size-exclusion mode using 20% acetonitrile in 20 mM phosphate buffer (pH 7.0) on Capcell Pak MF Ph-1 precolumn (10×4 mm I.D.). By valve switching, a fraction containing clomipramine was directed to an intermediate column for subsequent main separation on a microbore C₁₈ column (250×1.5 mm I.D.) using 50% acetonitrile in 20 mM phosphate buffer (pH 2.5) at 0.1 mL min⁻¹. The method was advantageous for rapidity (total analysis time: 15 min), reproducibility (C.V.<4.8%), and increased sensitivity (1 ng mL⁻¹). The linearity of response was good (r ²≥0.999) over the concentration range 1–250 ng mL⁻¹.     

Validation and use of three complementary analytical methods (LC–FLS, LC–MS/MS and ICP–MS) to evaluate the pharmacokinetics, biodistribution and stability of motexafin gadolinium in plasma and tissues

Liquid chromatography–fluorescence (LC–FLS), liquid chromatography–tandem mass spectrometry (LC–MS/MS) and inductively coupled plasma–mass spectrometry (ICP-MS) methods were developed and validated for the evaluation of motexafin gadolinium (MGd, Xcytrin) pharmacokinetics and biodistribution in plasma and tissues. The LC–FLS method exhibited the greatest sensitivity (0.0057 μg mL⁻¹), and was used for pharmacokinetic, biodistribution, and protein binding studies with small sample sizes or low MGd concentrations. The LC–MS/MS method, which exhibited a short run time and excellent selectivity, was used for routine clinical plasma sample analysis. The ICP–MS method, which measured total Gd, was used in conjunction with LC methods to assess MGd stability in plasma. All three methods were validated using human plasma. The LC–FLS method was also validated using plasma, liver and kidneys from mice and rats. All three methods were shown to be accurate, precise and robust for each matrix validated. For three mice, the mean (standard deviation) concentration of MGd in plasma/tissues taken 5 hr after dosing with 23 mg kg⁻¹ MGd was determined by LC–FLS as follows: plasma (0.025±0.002 μg mL⁻¹), liver (2.89±0.45 μg g⁻¹), and kidney (6.09±1.05 μg g⁻¹). Plasma samples from a subset of patients with brain metastases from extracranial tumors were analyzed using both LC–MS/MS and ICP–MS methods. For a representative patient, ≥90% of the total Gd in plasma was accounted for as MGd over the first hour post dosing. By 24 hr post dosing, 63% of total Gd was accounted for as MGd, indicating some metabolism of MGd.     

Simultaneous HPLC Analysis of Olmesartan and Hydrochlorothiazide in Combined Tablets and in vitro Dissolution Studies

A simple, rapid and reproducible HPLC method was developed and validated for the simultaneous determination of olmesartan (OLM) medoxomil and hydrochlorothiazide (HCT) in combined tablets. Chromatography was carried out on a 4.6 mm I.D × 200 mm, 5 μm cyano column with methanol–10 mM phosphoric acid containing 0.1% triethylamine (pH 2.5, 50:50 v/v) at a flow rate of 1.0 mL min⁻¹ and UV detector was set at 260 nm. Valsartan (VAL) was used as internal standard (IS). A linear response was observed in the range of 0.2–6 μg mL⁻¹ (r ² = 0.9998) for OLM and 0.1–4 μg mL⁻¹ (r ² = 0.9999) for HCT, respectively. The method showed good recoveries (99.56% for OLM and 99.48% for HCT) and the relative standard deviation (RSD) values for intra- and inter-day precision were 0.70–1.59 and 0.80–2.00% for OLM and 1.20–1.37 and 1.63–1.93% for HCT, respectively. The developed method was applied successfully for quality control assay of OLM and HCT in combined tablets and in vitro dissolution studies.     

Determination of Abamectin Residues in Avocados by Microwave-Assisted Extraction and HPLC with Fluorescence Detection

In this article a new analytical method for the confirmation and quantification of abamectin residues in avocados is described. The method allows a fast analysis of abamectin homologues using microwave assisted extraction (MAE), solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) with fluorescence (FL) detection using trifluoroacetic anhydride (TFAA) and N-methylimidazole (NMIM) as derivatizing agents. The mobile phase consisted of water, methanol and acetonitrile (5:47.5:47.5 v/v/v) and was pumped at a rate of 1.1 mL min⁻¹ (isocratic elution). Homogenized avocado samples were extracted once with 20 mL acetonitrile:water 4:1 (v/v) in a microwave oven for 26 min at 700 W with a maximum temperature of 80 °C. MAE operational parameters were optimized by means of an experimental design. Extracts were cleaned using C₁₈ SPE cartridges. Average recoveries of the method at four spiked levels (0.005, 0.01, 0.10 and 1.0 mg kg⁻¹) were found to be in the range 90–100% with good precision (RSD < 12%). The limits of detection (LODs) and quantification (LOQs) of the whole method were 0.001 and 0.003 mg kg⁻¹, respectively, which are lower than the maximum residue limit (MRL) established by the Spanish and the European legislation in avocados (0.01 mg kg⁻¹). Several avocado samples previously treated with the pesticide were also analyzed.