Analysis of Sulfonamides by Liquid Chromatography Mass Spectrometry and Capillary Electrophoresis Combing with Voltage‐Assisted Liquid‐Phase Microextraction

The method of liquid‐phase microextraction assisted with voltage was developed and applied on determination of sulfonamides in water samples. Four analytes, such as sulfamethazine, sulfathiazole, sulfadimethoxine, and sulfamethoxazole were extracted from a sample solution at pH 4.5 through a polypropylene membrane of immobilized with 2‐octanone, and then into 25 μL of the acceptor phase of 10 mM sodium hydroxide, and applied voltage of 100 V. Subsequently, the acceptor solution was directly subjected to analysis by LC‐MS or capillary zone electrophoresis. Linearity was obtained in the range of 1.0–25.0 ng mL^?1 with R² > 0.992 in LC‐MS, and 50–1000 ng mL^?1 with R² > 0.995 in capillary zone electrophoresis. The development of VA‐LPME was also applied in analysis of sulfonamides in water samples to evaluate its practical applicability.     

An electromembrane extraction–HPLC‐UV analysis for the determination of valproic acid in human plasma

In this study, an electromembrane extraction (EME) method combined with a simple HPLC‐UV analysis was developed and validated for the determination of valproic acid in human plasma samples. The major parameters influencing EME procedure, namely the solvent composition, voltage, pH of acceptor and donor solutions, salt effect, and time of extraction, were evaluated and optimized. The drug was extracted from the donor aqueous sample solution (pH 5) to the acceptor aqueous solution (pH 13). The donor and acceptor phases were separated by a hollow fiber dipped in 1‐octanol as a supported liquid membrane. A voltage of 60 V during 25 min was applied as the driving force. The drug concentration enrichment factor obtained was >125, which enhanced the sensitivity of the method. The limit of detection and the limit of quantitation were 0.2 and 0.5 μg/mL, respectively. The proposed method was successfully applied to a human plasma sample, with a relative recovery of 75%. The method was linear over the range 0.5–10 μg/mL for valproic acid (R² > 0.9996) with a repeatability (%RSD) between 0.9 and 3.3% (n = 3). Valproic acid is an anticonvulsant drug with poor UV absorption, and EME can improve the sensitivity of HPLC‐UV for the determination of valproic acid in plasma samples.     

Stereoselective determination of hydroxychloroquine and its metabolites in human urine by liquid-phase microextraction and CE

Liquid-phase microextraction based on polypropylene hollow fibers and CE were applied for the chiral determination of hydroxychloroquine (HCQ) and its metabolites (desethylchloroquine, DCQ; desethylhydroxychloroquine, DHCQ; bisdesethylchloroquine, BDCQ) in human urine. The analytes were extracted from 3 mL of urine spiked with the internal standard (metoprolol) and alkalinized with 250 muL of 2 M NaOH. The analytes were extracted into 1-octanol impregnated in the pores of the hollow fiber, and into an acid acceptor solution inside the hollow fiber. The electrophoretic separations were carried out in 100 mmol/L Tris buffer (pH adjusted to 9.0 with phosphoric acid) containing 1% w/v S-beta-CD and 30 mg/mL HP-beta-CD with a constant voltage of +18 kV. The method was linear over the concentration range of 10-1000 ng/mL for each HCQ stereoisomer and 21-333 ng/mL for each metabolite stereoisomer. Within-day and between-day assay precision and accuracy for the analytes were studied at three concentration levels for each stereoisomer and were lower than 15%. The developed method was applied for the determination of the cumulative urinary excretion of HCQ, DCQ, and DHCQ after oral administration of rac-HCQ to a health volunteer. The results obtained are in agreement with previous literature data.     

Determination of quinolones and fluoroquinolones in hospital sewage water by off-line and on-line solid-phase extraction procedures coupled to HPLC-UV

In this work, the development of two solid-phase extraction procedures (off-line and on-line formats) for the identification and quantification of several (fluoro)quinolones in hospital sewage water by HPLC-UV is described. Both procedures are based on the use of C18 and anion exchange (SAX) sorbents for the preconcentration and clean-up steps, respectively, and all variables influencing both steps were optimised. In the off-line format, after its pH was adjusted to 2.5, sample was preconcentrated on a C18 cartridge and eluted with 4 mL of methanol/ammonia (94/6). The methanolic extract must be diluted up to 10 mL with water to allow quantitative retention of the analytes on the SAX cartridge. In the on-line format, the addition of 2.5% of NH4Cl to the sewage water sample (pH = 2.5) was necessary to increase the breakthrough volumes of the analytes in the C18 precolumn. Quantitative transfer of the (fluoro)quinolones from the C18 precolumn to the SAX precolumn was accomplished by pumping 2 mL of a mixture methanol/water (40/60, pH = 9.2) at 2 mL min(-1). Elution of the analytes from the SAX precolumn by means of the chromatographic mobile phase required the inclusion of an additional isocratic step at the beginning of the gradient program. Both off-line and on-line solid phase extraction procedures coupled to HPLC-UV were applied to the analysis of a sewage water sample collected in the sewer system at the output of the St Dimphna Hospital (Geel, Belgium). The fluoroquinolone ciprofloxacin was found in this sample and quantified at 5.8 +/- 0.4 microg L(-1) (off-line method) and 5.6 +/- 0.5 microg L(-1) (on-line method). The analysis of spiked samples containing the seven (fluoro)quinolones studied provided quantitative recoveries in all cases with low RSD values (from 6 to 12%), and all the analytes could be identified by means of their UV spectra with match factors varying from 950 to 985 depending on the (fluoro)quinolone.     

Liquid-phase microextraction of basic drugs--selection of extraction mode based on computer calculated solubility data

The extractability of 58 different basic drugs by 3-phase liquid-phase microextraction (LPME) was studied. Extraction recoveries were correlated to solubility data and log D data calculated with a commercial computer program. The basic drugs were extracted from 1.5 mL water samples (pH 13) through approximately 15 microL of dodecyl acetate immobilized within the pores of a porous polypropylene hollow fibre (organic phase), and into 15 microL of 10 mM HCl (acceptor solution) present inside the lumen of the hollow fibre. Compounds with a calculated solubility below 1 mg/mL at pH 2 were poorly recovered and remained principally in the organic phase. For these drugs, 2-phase LPME may be used as an alternative technique, where the aqueous acceptor phase is replaced by an organic solvent. In the solubility range 1-5 mg/mL, most drugs were effectively extracted (recovery >30%), whereas drugs belonging to the solubility range 5-150 mg/mL were all extracted with recoveries above 30% by 3-phase LPME. The hydrophilic nature of most drugs with solubilities above 150 mg/mL prevented them from entering the organic phase, and only those with log D >1.8 were effectively recovered by 3-phase LPME. For drugs with log D < 1.8 (and solubility >150 mg/mL), carrier-mediated LPME was found to be the preferred technique, where an ion-pair reagent (octanoic acid) was added to the sample. In the case of carrier-mediated LPME, the volume of sample was decreased to 100 microL to facilitate rapid extractions. Based on the present work, the extractability of new compounds may easily be predicted to speed up method development. Extractions were also accomplished from plasma samples, where interactions between proteins and the drugs may reduce the extraction recovery. However, dilution of the plasma samples with water and adjustment of pH into the alkaline region effectively suppressed drug-protein interactions for most of the drugs studied.     

Ion-pair liquid-liquid-liquid microextraction of nerve agent degradation products followed by capillary electrophoresis with contactless conductivity detection

The four nerve agent degradation products methylphosphonic acid (MPA), ethyl methylphosphonic acid (EMPA), isopropyl methylphosphonic acid (IMPA) and cyclohexyl methylphosphonic acid (CMPA) have been successfully extracted from aqueous sample solution by ion-pair liquid-liquid-liquid microextraction. In this procedure, the target analytes in the sample solution were converted into their ion-pair complexes with tri-n-butyl amine and then extracted by an organic solvent (1-octanol) layer on top of the sample solution. Simultaneously, the analytes were back-extracted into a drop of an aqueous acceptor solution which was suspended in the organic phase at a microsyringe needle tip. The factors influential to extraction: type of organic solvent, type of ion-pair reagent and its concentration, pH values of sample solution and acceptor aqueous phase, stirring rate and extraction time were investigated in detail. After extraction, the drop of the acceptor solution was withdrawn into the syringe and injected into a capillary electrophoresis system for analysis. Using contactless conductivity detection, direct quantification of these compounds is possible. Moreover, large-volume sample injection was employed for further preconcentration. Improvements in the limits of detection between 2.5 and 4 orders of magnitude could be achieved and concentrations at the ng/mL level can be determined. This newly established approach was successfully applied to a spiked river water sample.     

A rapid CE-potential gradient detection method for determination of quinolones

A rapid CE coupled with potential gradient detection (PGD) for the separation and detection of four quinolones, namely, enoxacin, ofloxacin (OFL), fleroxacin, and pazufloxacin, was described. Separation was performed in a fused-silica capillary (75 microm x 8.5 cm) using a buffer of 30 mM Tris and 4 mM phosphoric acid at pH 8.9. Under the separation voltage of 3 kV, the quinolones were separated within 2.8 min with good linearity (r(2) >or= 0.985). The method was successfully applied in determining OFL in a pharmaceutical formulation. Also, a liquid-liquid extraction (LLE) method was developed and coupled to CE-PGD in determining quinolones that spiked in milk samples. With dichloromethane and hexane for enrichment and purification, the LLE recoveries of the four quinolones were in the range of 77-106%. The detection limits of the quinolones with LLE-CE-PGD were from 23 to 65 ng/mL. The proposed CE-PGD method was validated with an HPLC method, and the results indicated consistency between the two methods.     

Electro membrane extraction combined with capillary electrophoresis for the determination of amlodipine enantiomers in biological samples

Electro membrane extraction as a new microextraction method was applied for the extraction of amlodipine (AM) enantiomers from biological samples. During the extraction time of 15 min, AM enantiomers migrated from a 3 mL sample solution, through a supported liquid membrane into a 20 μL acceptor solution presented inside the lumen of the hollow fiber. The driving force of the extraction was 200 V potential, with the negative electrode in the acceptor solution and the positive electrode in the sample solution. 2-Nitro phenyl octylether was used as the supported liquid membrane. Using 10 mM HCl as background electrolyte in the sample and acceptor solution, enrichment up to 124 times was achieved. Then, the extract was analyzed using CD modified CE method for separation of AM enantiomers. Best results were achieved using a phosphate running buffer (100 mM, pH 2.0) containing 5 mM hydroxypropyl-α-CD. The range of quantitation for both enantiomers was 10-500 ng/mL. Intra- and interday RSD (n=6) were less than 14%. The limits of quantitation and detection for both enantiomers were 10 and 3 ng/mL respectively. Finally, this procedure was applied to determine the concentration of AM enantiomers in plasma and urine samples.     

Polypyrrole/polyamide electrospun-based sorbent for microextraction in packed syringe of organophosphorous pesticides from aquatic samples

A novel method based on microextraction in packed syringe (MEPS) as sample preparation technique coupled off-line with gas chromatography-mass spectrometry was developed using electrospun nanofibers as sorbent. For electrospinning of polypyrrole/polyamide-based nanofiber, a homogeneous solution containing nylon 6, ferric chloride and pyrrole monomer was prepared and then was drawn into a 2.5-mL syringe. By applying a voltage of 13 kV between the needle of the syringe and an aluminum-foil collector, the nanofibers could be formed on the surface of the collector. The prepared sheet was used as the sorbent for MEPS to analyze some selected organophosphorous pesticides. Important parameters influencing the extraction and desorption processes were optimized. Limits of detection were in the range of 0.04-0.1 ng/mL using time scheduled selected ion monitoring mode, and the relative standard deviation (RSD %) values with four replicates were in the range of 3.7-11.8% at a concentration level of 5 ng/mL. The linearity of the method was in the range of 0.5-500 ng/mL for diazinon and fenithrothion and 0.5-200 ng/mL for the rest of the analytes. The developed method was successfully applied to Zayandeh-roud river water samples, whereas the matrix factors were in the range of 0.87-0.98.     

pH‐assisted homogeneous liquid–liquid microextraction using dialkylphosphoric acid as an extraction solvent for the determination of chlorophenols in water samples

In this study, a new pH‐assisted homogeneous liquid–liquid microextraction combined with HPLC with UV detection was developed for the determination of chlorophenols in water samples. In this approach, bis(2‐ethylhexyl) phosphate was used for the first time as the low‐density extraction solvent. In particular, 60 μL of bis(2‐ethylhexyl) phosphate was injected into the sample solution (5 mL) and dissolved completely in the sample solution while the pH was increased to 9. Afterwards, the pH of the sample solution was lowered to 1, and a cloudy solution was formed. At this stage, hydrophobic interactions between the analytes and the long double hydrocarbon chains of extraction solvent were expected to be the main forces driving extraction. A series of parameters that influence extraction were investigated systematically. Under the optimized conditions, the LODs and LOQs for the chlorophenols were 1.4–2.7 and 4.7–9.1 ng/mL, respectively. RSDs based on five replicate extraction of 100 ng/mL of each chlorophenols were <4.7% for intraday and 7.4% for interday precision. This method has been also successfully applied to analyze real water samples at two different spiked concentrations, and satisfactory recoveries were achieved.     

Electromembrane extraction using two separate cells: A new design for simultaneous extraction of acidic and basic compounds

Simultaneous extraction of acidic and basic analytes from a sample is seen to be a challenging task. In this work, a novel and efficient electromembrane extraction (EME) method based on two separate cells was applied to simultaneously extract and preconcentrate two acidic drugs (naproxen and ibuprofen) along with a basic drug (ketamine). Once both cells were filled with the sample solution, basic drug was extracted from one cell with the other cell used to extract acidic drugs. The employed supported liquid membranes for the extraction of acidic and basic drugs were 2‐ethyl hexanol and 1‐octanol, respectively. Under an applied potential of 250 V in the course of the extraction process, acidic, and basic drugs were extracted from a 3.0 mL aqueous sample solution into 25 μL acceptor solutions. The pH values of the donor and acceptor solutions in the cathodic cell were 5.0 and 1.5, respectively, the corresponding values in the anodic cell were, however, 8.0 and 12.5, respectively. The rates of recovery obtained within 20 min of extraction time at a stirring rate of 750 rpm ranged from 45 to 54%. With correlation coefficients ranging from 0.990 to 0.996, the proposed EME technique provided good linearity over a concentration range of 20–1000 ng/mL. The LOD for all drugs was found to be 6.7 ng/mL, while reproducibility ranged from 7 to 12% (n = 5). Finally, applying the proposed method to determine and quantify the drugs in urine and wastewater samples, satisfactory results were achieved.     

A three phase hollow fiber liquid‐phase microextraction for quantification of lamotrigine in plasma of epileptic patients by capillary electrophoresis

A three phase hollow fiber liquid‐phase microextraction technique combined with capillary electrophoresis was developed to quantify lamotrigine (LTG) in plasma samples. The analyte was extracted from 4.0 mL of a basic donor phase (composed of 0.5 mL of plasma and 3.5 mL of sodium phosphate solution pH 9.0) through a supported liquid membrane composed of 1‐octanol immobilized in the pores of the hollow fiber, and to an acidic acceptor phase (hydrochloric acid solution pH 4.0) placed in the lumen of the fiber. The extraction was carried out for 30 min at 500 rpm. The eletrophoretic analysis was carried out in 130 mmol/L MES buffer, pH 5.0 with a constant voltage of +15 kV and 20°C. Sample injections were performed for 10 s, at a pressure of 0.5 psi. The detection was performed at 214 nm for both LTG and the internal standard lidocaine. Under the optimized conditions, the method showed a limit of quantification of 1.0 μg/mL and was linear over the plasmatic concentration range of 1.0–20.0 μg/mL. Finally, the validated method was applied for the quantification of LTG in plasma samples of epileptic patients.     

Stereoselective liquid chromatographic determination of 1'-oxobufuralol and 1'-hydroxybufuralol in rat liver microsomal fraction using hollow-fiber liquid-phase microextraction for sample preparation

A three-phase hollow-fiber liquid-phase microextraction (HF-LPME) method for the stereoselective determination of bufuralol metabolites 1'-oxobufuralol (1'-Oxo-BF) and 1'-hydroxybufuralol (1'-OH-BF) in microsomal preparations is described for the first time. The HPLC analysis was carried out using a Chiralcel OD-H column with hexane/2-propanol/methanol (97.5:2.0:0.5, v/v/v) plus 0.5% diethylamine as the mobile phase, and UV detection at 248 and 273 nm. The HF-LPME optimized conditions involved: n-octanol as the organic solvent, 0.2 mol/L acetic acid as the acceptor phase, donor phase pH adjusted to 13, sample agitation at 1500 rpm and extraction for 30 min. By using this extraction procedure, the recovery rates were in the range of 63-69%. The method was linear over the concentration range of 100-5000 ng/mL for each enantiomer of 1'-Oxo-BF (r>0.9978) and of 100-2500 ng/mL for each stereoisomer of 1'-OH-BF (r>0.9957). The quantification limits were 100 ng/mL for all analytes. The validated method was used to assess the in vitro biotransformation of bufuralol using rat liver microsomal fraction that demonstrated predominant formation of (S)-1'-Oxo-BF and (R,R)-1'-OH-BF.     

Graphene oxide as a micro‐solid‐phase extraction sorbent for the enrichment of parabens from water and vinegar samples

A simple hydrophilic polyamide organic membrane protected micro‐solid‐phase extraction method with graphene oxide as the sorbent was developed for the enrichment of some parabens from water and vinegar samples prior to gas chromatography with mass spectrometry detection. The main experimental parameters affecting the extraction efficiencies, such as the type and amount of the sorbent, extraction time, stirring rate, salt addition, sample solution pH and desorption conditions, were investigated. Under the optimized experimental conditions, the method showed a good linearity in the range of 0.1–100.0 ng/mL for water samples and 0.5–100.0 ng/mL for vinegar samples, with the correlation coefficients varying from 0.9978 to 0.9997. The limits of detection (S/N = 3) of the method were in the range of 0.005–0.010 ng/mL for water samples and 0.01–0.05 ng/mL for vinegar samples, respectively. The recoveries of the method for the analytes at spiking levels of 5.0 and 70.0 ng/mL were between 84.6 and 106.4% with the relative standard deviations varying from 4.2 to 9.5%. The results indicated that the developed method could be a practical approach for the determination of paraben residues in water and vinegar samples.     

Electro‐driven extraction of inorganic anions from water samples and water miscible organic solvents and analysis by ion chromatography

A simple electromembrane extraction (EME) procedure combined with ion chromatography (IC) was developed to quantify inorganic anions in different pure water samples and water miscible organic solvents. The parameters affecting extraction performance, such as supported liquid membrane (SLM) solvent, extraction time, pH of donor and acceptor solutions, and extraction voltage were optimized. The optimized EME conditions were as follows: 1‐heptanol was used as the SLM solvent, the extraction time was 10 min, pHs of the acceptor and donor solutions were 10 and 7, respectively, and the extraction voltage was 15 V. The mobile phase used for IC was a combination of 1.8 mM sodium carbonate and 1.7 mM sodium bicarbonate. Under these optimized conditions, all anions had enrichment factors ranging from 67 to 117 with RSDs between 7.3 and 13.5% (n = 5). Good linearity values ranging from 2 to 1200 ng/mL with coefficients of determination (R²) between 0.987 and 0.999 were obtained. The LODs of the EME‐IC method ranged from 0.6 to 7.5 ng/mL. The developed method was applied to different samples to evaluate the feasibility of the method for real applications.     

Capillary electrophoretic chiral determination of mirtazapine and its main metabolites in human urine after enzymatic hydrolysis

Capillary electrophoresis and liquid-phase microextraction using porous polypropylene hollow fibers were employed for the enantioselective analyses of mirtazapine and its metabolites demethylmirtazapine and 8-hydroxymirtazapine in human urine. Before the extraction, urine samples (1.0 mL) were submitted to enzymatic hydrolysis at 37 degrees C for 16 h. Then, the enzyme was precipitated with trichloroacetic acid, the pH was adjusted to 8 with 0.5 mol/L phosphate buffer solution (pH 11) and 15% sodium chloride was further added. The analytes were transferred from the aqueous donor phase, through n-hexyl ether (organic solvent immobilized in the fiber), into 0.01 moL/L acetic acid solution (acceptor phase). The electrophoretic analyses were carried out in 50 mmol/L phosphate buffer solution (pH 2.5) containing 0.55% w/v carboxymethyl-beta-cyclodextrin. The method was linear over the concentration range of 62.5-2500 ng/mL for each mirtazapine and 8-hydroxymirtazapine enantiomer and 62.5-1250 ng/mL for each demethylmirtazapine enantiomer. The quantification limit was 62.5 ng/mL for all the enantiomers. Within-day and between-day assay precision and accuracy were lower than 15% for all the enantiomers. Finally, the method proved to be suitable for pharmacokinetic studies.     

Electromembrane extraction combined with cyclodextrin-modified capillary electrophoresis for the quantification of trimipramine enantiomers

A sensitive, simple and reproducible method was developed for preconcentration and determination of trimipramine (TPM) enantiomers in biological samples using electromembrane extraction combined with cyclodextrin‐modified capillary electrophoresis (CE). During the extraction, TPM enantiomers migrated from a 5 mL sample solution through a thin layer of 2‐nitrophenyl octyl ether NPOE immobilized in the pores of a hollow fiber, and into a 20 μL acidic aqueous acceptor phase presented inside the lumen of the fiber. A Box–Behnken design and the response surface methodology (RSM) were used for the optimization of different variables on extraction efficiency. Optimized extraction conditions were: NPOE as supported liquid membrane, inter‐electrode distance of 5 mm, stirring rate of 1000 rpm, 51 V potential difference, 34 min as the extraction time, acceptor phase pH 1.0 and donor phase pH 4.5. Then, the extract was analyzed using optimized cyclodextrin (CD)‐modified CE method for the separation of TPM enantiomers. Best results were achieved using 100 mM phosphate running buffer (pH 2.0) containing 10 mM α‐CD as the chiral selector, applied voltage of 18 kV and 20°C. The range of quantitation for both enantiomers was 20–500 ng/mL. The method was very reproducible so that intra‐ and interday RSDs (n=6) were <6%. The limits of quantitation and detection for both enantiomers were 20 and 7 ng/mL, respectively. Finally, this method was successfully applied to determine the concentration of TPM enantiomers in plasma and urine samples without any pre‐treatment.     

Optimization of some experimental parameters in the electro membrane extraction of chlorophenols from seawater

An electro membrane extraction (EME) methodology was utilized to study the isolation of some environmentally important pollutants, such as chlorophenols, from aquatic media based upon the electrokinetic migration process. The analytes were transported by application of an electrical potential difference over a supported liquid membrane (SLM). A driving force of 10 V was applied to extract the analytes through 1-octanol, used as the SLM, into a strongly alkaline solution. The alkaline acceptor solution was subsequently analyzed by high performance liquid chromatography-ultraviolet (HPLC-UV) detection. The parameters influencing electromigration, including volumes and pH of the donor and acceptor phases, the organic solvent used as the SLM, and the applied voltage and its duration, were investigated to find the most suitable extraction conditions. Since the developed method showed a rather high degree of selectivity towards pentachlorophenol (PCP), validation of the method was performed using this compound. An enrichment factor of 23 along with acceptable sample clean-up was obtained for PCP. The calibration curve showed linearity in the range of 0.5–1000 ng/mL with a coefficient of estimation corresponding to 0.999. Limits of detection and quantification, based on signal-to-noise ratios of 3 and 10, were 0.1 and 0.4 ng/mL, respectively. The relative standard deviation of the analysis at a PCP concentration of 0.5 ng/mL was found to be 6.8% (n = 6). The method was also applied to the extraction of this contaminant from seawater and an acceptable relative recovery of 74% was achieved at a concentration level of 1.0 ng/mL.     

In‐process prepared deep eutectic solvent based homogeneous liquid–liquid microextraction for the determination of irgaphos 168 and irganox 1010 in polypropylene packed drinks

In situ synthesis of a deep eutectic solvent and homogeneous liquid–liquid microextraction performed in a narrow bore tube was developed for efficient extraction of irgaphos 168 and irganox 1010 in doogh and water samples packed in polypropylene packages. First, pH of the aqueous sample solutions containing the analytes is adjusted at 9. Then a hydrogen bond acceptor (choline chloride) and a hydrogen bond donor (oleic acid) are dissolved in the solution and vortexed to obtain a homogeneous solution. The solution is filled into a narrow bore tube, in which its bottom was clogged by a septum. Then hydrochloric acid solution is injected into the solution by a syringe. The tube is placed in an ultrasonic bath. During this step, the droplets of choline chloride:oleic acid deep eutectic solvent are produced. The method indicated high enrichment factor (435 for irgaphos 168 and 488 for irganox 1010), low limits of detection (0.03 and 0.09 ng/mL for irgaphos 168 and irganox 1010, respectively) and quantification (0.13 and 0.29 ng/mL for irgaphos 168 and irganox 1010), good recovery (74 and 83% for irgaphos 168 and irganox 1010, respectively), and satisfactory repeatabilities (relative standard deviations ≤12%) can be obtained using the developed method.