Separation and determination of acrylamide in potato chips by micellar electrokinetic capillary chromatography

A simple and rapid method using micellar electrokinetic capillary chromatography (MEKC) was developed for the separation and determination of acrylamide in potato chips at low levels for the first time. The experimental conditions for the separation and quantification of acrylamide were optimized at first. The optimized conditions were: 50 mmol/L Na₂B₄O₇ and 40 mmol/L SDS at pH 10.0, 12 kV applied voltage, 76 cm total length (67 cm effective length) and 75 μm i.d. capillary, 198 nm wavelength, 15 cm high 25 s hydrodynamics sample injection, 20 °C air-cooling. The linear response of acrylamide concentration ranges from 0.5 to 100 μg/mL with high correlation coefficient (r = 0.9986, n = 9). The LOD and LOQ were estimated to be 0.1 and 0.33 μg/mL based on S/N = 3 and 10. The precision values (expressed as R.S.D.) of intra- and inter-day were 0.86-4.35% and 2.61-9.65%, respectively. Recoveries spiked at levels 2, 20, 60 μg/mL ranged between 90.86% and 99.6% with R.S.D. less than 6.5%. Finally, the developed method has been applied to the analysis of real samples and has achieved satisfactory results. All of these indicated that it was a reliable method for the quantification of acrylamide in potato chips.     

A flow injection chemiluminescence method for the determination of fluoroquinolone derivative using the reaction of luminol and hydrogen peroxide catalyzed by gold nanoparticles

Based on the enhancement of chemiluminescence (CL) of luminol-hydrogen peroxide-gold nanoparticles system by fluoroquinolones (FQs), a novel and rapid CL method is reported for the determination of FQs derivatives. Under the optimum conditions, the CL intensity is proportional to the concentration of FQs derivative in solution. The corresponding linear regression equations are established over the range of 0.08-1.28 μg/mL for norfloxacin, 0.013-1.32 μg/mL for ciprofloxacin, 0.014-1.4 μg/mL for lomefloxacin, 0.029-1.46 μg/mL for fleroxacin, 0.02-1.0 μg/mL for ofloxacin and 0.01-1.44 μg/mL for levofloxacin, respectively. The limits of detection (S/N = 3) are 3.2, 9.5, 7.0, 9.0, 8.0, and 8.0 ng/mL with the relative standard deviation (n = 11) 4.3, 1.5, 1.9, 1.3, 1.6 and 2.1% for norfloxacin, ciprofloxacin, lomefloxacin, fleroxacin, ofloxacin and levofloxacin, respectively. This proposed method has been applied to detect FQs derivatives in human urine successfully.     

On-line solid-phase extraction-HPLC-fluorescence detection for simultaneous determination of puerarin and daidzein in human serum

Response surface methodology (RSM) was applied to the optimization of on-line solid-phase extraction (SPE) parameters, and an automated system of on-line SPE coupled with high-performance liquid chromatography (HPLC) with fluorescence detection was developed for the determination of puerarin and daidzein in human serum. The human serum sample of 50 μL was injected into a conditioned C18 SPE cartridge, and the matrix was washed out with acetonitrile-KH₂PO₄-triethylamine buffer (0.01 M, pH 7.4) (3:97, v/v) for 3 min at a flow rate of 0.25 mL/min. Then the target analytes were eluted and transferred to the analytical column. A chromatographic gradient elution was programmed with the mobile phase consisting of acetonitrile and KH₂PO₄-triethylamine buffer, and the analytes were determined with a fluorescence detector at excitation wavelength of 350 nm and emission wavelength of 472 nm, respectively. The proposed method presented good linear relations (0.85-170 μg/mL for puerarin and 0.2-40 μg/mL for daidzein), satisfactory precision (RSD < 8%), and accredited recovery (92.5-107.8%).     

Simultaneous sample preparation for high-performance liquid chromatographic determination of Vitamin A and β-carotene in emulsified nutritional supplements after solid-phase extraction

Determination of small amounts of the fat-soluble species Vitamin A (VA) (2.5 μg/g) and β-carotene (9 μg/g) from emulsified nutritional supplements containing 50 kinds of co-existing compounds and a fat content between 2000 and 8000 times higher was performed by solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) with fluorescence detection set at ex. 350 nm and em. 480 nm, and visible detection at 450 nm using an Inertsil ODS 80A (5 μm) analytical column. Mobile phases of methanol-ethanol (50:50) and acetonitrile-ethanol (70:30) were used for the both vitamins. A Bond Elut C₁₈ cartridge was chosen for SPE after comparison with eight other types of SPE cartridge. Retention time of VA and β-carotene was 7 and 8 min, respectively, giving a limit of detection of ca. 0.1 ng per injection at a signal-to-noise ratio 3:1. Recoveries of VA and β-carotene were over 90% by the standard addition method. Relative standard deviation of VA and β-carotene were ca. 2.9 (n=5) and 2.3% (n=5), respectively.     

Separation and determination of alpinetin and cardamonin in Alpinia katsumadai Hayata by flow injection-micellar electrokinetic chromatography

A simple, rapid, and accurate method for the separation and determination of alpinetin and cardamonin in Alpinia katsumadai Hayata was developed by combination of flow injection (FI)-micellar electrokinetic chromatography (MEKC) for the first time. The analysis was carried out using an unmodified fused-silica capillary (50 μm i.d.; total length 13.6 cm; effective length 10.3 cm) and direct ultraviolet (UV) detection at 214 nm. The sample throughput was 11-24 samples per hour using the background electrolyte (BGE) containing 4 mM sodium borate-8 mM NaH₂PO₄ (pH 8.1)-8 mM sodium dodecyl sulfate (SDS)-19% (v/v) ethanol. The repeatabilities (n = 4) reached relative standard deviation values (R.S.D.) of 3.0% and 2.5% for the peak areas and 2.5% and 3.1% for peak heights of alpinetin and cardamonin, respectively. Regression equations revealed linear relationships (r²: 0.9993-0.9994) between the peak area of each analyte and the concentration. Recoveries were in the range 90-92% and 99-105% for alpinetin and cardamonin, respectively.     

Sucralose screening in European surface waters using a solid-phase extraction-liquid chromatography–triple quadrupole mass spectrometry method

An analytical method was developed for the analysis of sucralose, a persistent chlorinated calorie-free sugar substitute, in surface waters. The method is based on solid-phase extraction (SPE) of 400 mL water using Oasis HLB (Waters) adsorber material, followed by negative electrospray ionization (ESI) triple quadrupole LC–MS–MS detection. Quantification was performed by external calibration, as well as by isotope dilution with deuterated sucralose d6 internal standard. Extraction with Oasis HLB, a polymeric adsorbent suited for polar compounds, was much more efficient at neutral pH than at pH 3; a recovery of 62 ± 9% (n = 6; determined at 1 μg/L) could be achieved. Strong ion suppression caused by matrix substances was observed for sucralose in the SPE extracts. The analysis of 120 river surface water samples from 27 European countries showed that sucralose, which is in use in Europe since beginning 2005, can be found in the aquatic environment, at concentrations up to 1 μg/L. Sucralose was predominately found in samples from the UK, Belgium, the Netherlands, France, Switzerland, Spain, Italy, Norway, and Sweden, suggesting an increased use of the substance in Western Europe.     

Simultaneous determination of nitrite and nitrate in dew, rain, snow and lake water samples by ion-pair high-performance liquid chromatography

A simple, fast, sensitive and accurate reversed-phase ion-pair HPLC method for simultaneous determination of nitrite and nitrate in atmospheric liquids and lake waters has been developed. Separations were accomplished in less than 10 min using a reversed-phase C₁₈ column (150 mm × 2.00 mm i.d., 5 μm particle size) with a mobile phase containing 83% 3.0 mM ion-interaction reagent tetrabutylammonium hydroxide (TBA-OH) and 2.0 mM sodium phosphate buffer at pH 3.9 and 17% acetonitrile (flow rate, 0.4 mL/min). UV light absorption responses at 205 nm were linear over a wide concentration range from 100 μg/mL to the detection limits of 10 μg/L for nitrite and 5 μg/L nitrate. Quantitation was carried out by the peak area method. The relative standard deviation for the analysis of nitrite and nitrate was less than 3.0%. This method was applied for the simultaneous determination of nitrite and nitrate in dew, rain, snow and lake water samples collected in southeast Massachusetts. Nitrate was found being present at 4.79-5.99 μg/mL in dew, 1.20-2.63 μg/mL in rain, 0.32-0.60 μg/mL in snow and 0.12-0.23 μg/mL in lake water. Nitrite was only a minor species in dew (0.62-0.83 μg/mL), rain (<0.005-0.14 μg/mL), snow (0.021-0.032 μg/mL) and lake water (0.12-0.16 μg/mL). High levels of nitrite and nitrate observed in dew water droplets may constitute an important source of hydroxyl radicals in the sunny early morning.     

Determination of nucleotides,nucleosides and their transformation products in Cordyceps by ion-pairing reversed-phase liquid chromatography–mass spectrometry

An ion-pairing reversed-phase liquid chromatography–mass spectrometry (IP-RP-LC–MS) was developed for the determination of nucleotides, nucleosides and their transformation products in Cordyceps. Perfluorinated carboxylic acid, namely pentadecafluorooctanoic acid (PDFOA, 0.25 mM), was used as volatile ion-paring agent and a reversed-phase column (Agilent ZORBAX SB-Aq column) was used for the separation of three nucleotides namely uridine-5′-monophosphate (UMP, 0.638–10.200 μg/mL), adenosine-5′-monophosphate (AMP, 0.24–7.80 μg/mL) and guanosine-5′-monophosphate (GMP, 0.42–13.50 μg/mL), seven nucleosides including adenosine (0.55–8.85 μg/mL), guanosine (0.42–6.75 μg/mL), uridine (0.33–10.50 μg/mL), inosine (0.21–6.60 μg/mL), cytidine (0.48–15.30 μg/mL), thymidine (0.20–6.30 μg/mL) and cordycepin (0.09–1.50 μg/mL), as well as six nucleobases, adenine (0.22–6.90 μg/mL), guanine (0.26–4.20 μg/mL), uracil (0.38–12.15 μg/mL), hypoxanthine (0.13–4.20 μg/mL), cytosine (0.39–12.45 μg/mL) and thymine (0.26–8.25 μg/mL) with 5-chlorocytosine arabinoside as the internal standard. The overall LODs and LOQs were between 0.01–0.16 μg/mL and 0.04–0.41 μg/mL for the 16 analytes, respectively. The contents of 16 investigated compounds in natural and cultured Cordyceps were also determined and compared after validation of the developed IP-RP-LC-MS method. The transformations of nucleotides and nucleosides in Cordyceps were evaluated based on the quantification of the investigated compounds in three extracts, including boiling water extraction (BWE), 24 h ambient temperature water immersion (ATWE) and 56 h ATWE extracts. Two transformation pathways including UMP → uridine → uracil and GMP → guanosine → guanine were proposed in both natural Cordyceps sinensis and cultured Cordyceps militaris. The pathway of AMP → adenosine → inosine → hypoxanthine was proposed in natural C. sinensis, while AMP → adenosine → adenine in cultured C. militaris. However, the transformation of nucleotides and nucleosides was not found in commercial cultured C. sinensis.     

Determination of trace bisphenol A in complex samples using selective molecularly imprinted solid-phase extraction coupled with capillary electrophoresis

The highly selective, fast and effective sample pretreatment technique molecularly imprinted solid-phase extraction (MISPE) can overcome the low sensitivity of the highly efficient capillary electrophoresis-UV method (CE-UV). In this work, narrowly dispersible bisphenol A (BPA)-imprinted polymeric microspheres with a high capacity factor of k′ = 6.8 and an imprinted factor of I = 6.53 were investigated as selective solid-phase extraction (SPE) sorbents for use in extraction of BPA from different sample matrices (tap water, wastewater, Yangtze River water, soil from the Yangtze River, shrimp and human urine). Washing and eluting protocols of MISPE were optimized. Under optimal conditions, recoveries of MISPE were investigated. Recoveries were basically constant and the relative standard deviation (RSD) was lower than 5.8% when loading volumes changed from 1 to 50 mL. Recoveries ranged from 71.20% to 86.23% for different sample matrices. Compared with C18 SPE, MISPE had higher selectivity and recovery for BPA. BPA was determined with good accuracy and precision in different complex samples using CE-UV coupled with MISPE. Spiked recoveries ranged from 95.20% to 105.40%, and the RSD was less than 7.2%. Because a large loading volume was achieved, the enrichment efficiency of pretreatment and the sensitivity of this method were improved. The limits of detection of this MISPE-CE-UV method for BPA in tap water, wastewater, Yangtze River water, soil from the Yangtze River, shrimp and human urine were 3.0 μg L^− 1, 5.4 μg L^− 1, 6.9 μg L^− 1, 2.1 μg L^− 1, 1.8 μg L^− 1 and 84 μg L^− 1, respectively.     

A new mixed micellar electrokinetic chromatography method for analysis of natural and synthetic anabolic steroids

A simple, rapid and low-costing new mixed surfactant MEKC method has been developed for the analysis of five neutral anabolic steroids in this paper. It was found that the bile salt coupling with Triton X-100 was a suitable bi-micellar surfactant for the separation of these anabolic steroids with similar structure. The separation conditions were optimized in detail. The five natural and synthetic anabolic steroids, such as androstenedione (AD), 19-norandrostenedione (NAD), 1,4-androstadiene-3,17-dione (ADD), methandrostenolone (MA) and methyltestosterone (MT) were separated and detected in an alkaline buffer system (pH 9.0) containing 15 mM Britton-Robinson (BR) buffer, 50 mM sodium cholate (SC) and 0.1% (v/v) Triton X-100 with detection wavelength at 241 nm and 18 kV of separation voltage. Under the optimal conditions, five coexistence neutral steroids were completely separated within 12 min with the detection limits ranged from 0.20 to 0.51 μg/mL. This method was successfully used for detection and confirmation of the anabolic steroid methandrostenolone in methandrostenolone tablets and in the real human urine, GC-MS method was applied to confirm the free methandrostenolone existence in the urine sample in order to validate the reliability of MEKC method.     

An accurate and precise high-performance liquid chromatography method for the rapid quantification of the novel HIV integrase inhibitor raltegravir in human blood plasma after solid phase extraction

The quantification of the HIV integrase inhibitor raltegravir in blood plasma is described using solid phase extraction (SPE) coupled with an accurate high-performance liquid chromatography assay with ultraviolet (UV) detection. The method was validated over the range of 20-10,000 ng/mL using simple sample preparation and chromatography. The SPE method was optimized to be selective and highly efficient. The buffer’s ionic strength and pH were optimized for retaining RAL and the internal standard on the column, the percentage of methanol was optimized in the cleaning step to remove unwanted plasma contaminants, and the type and amount of acid was optimized for complete elution of the compounds. This method has no interference with other potentially co-administered antiretrovirals or common drugs. Average recoveries for the extraction method were consistently high: 90% for raltegravir and 90% for the internal standard diazepam. This method was found to be accurate and precise. Within day (n = 6) and between day (n = 18) accuracies ranged from 97.5 to 104.4%. Within-day (n = 6) and between-day (n = 18) precision ranged from 1.4 to 3.8%, and from 2.4 to 7.9%, respectively. This is the first published method to use simple UV technology and reliable SPE extraction methodology for the quantification of raltegravir in human plasma. This method can be easily implemented in most bioanalytical laboratories.     

Rapid analysis of melamine in infant formula by sweeping-micellar electrokinetic chromatography

In the present study, an analytical method using capillary electrophoresis with on-line preconcentration technique was developed for rapid determination of melamine in infant formula. Both stacking and sweeping preconcentration techniques had been investigated for the comparison of their effectiveness in melamine analysis. The limit of detection of melamine standard was 0.5 ng/mL for the field amplified sample stacking (FASS) technique and 9.2 ng/mL for the sweeping technique. Although the FASS technique provided better concentration efficacy than the sweeping technique, the matrix effect was more profound with the former. Matrix effect was evaluated by comparing the enhancement factor (EF) of melamine standard and post-extraction spiked infant formula solution. The EF was changed from 429.86 ± 9.81 to the level less than 133.31 with significant peak distortion in the FASS system, and it was remained unchanged in the sweeping system. Sweeping-micellar electrokinetic chromatography (sweeping-MEKC) was demonstrated to be most suitable for real sample analysis. Under optimum sweeping-MEKC conditions, melamine content in infant formulas could be determined within 6 min. The developed solid phase extraction (SPE) procedures coupled with the sweeping-MEKC method was subjected to method validation. Run-to-run repeatability (n = 3) and day-to-day reproducibility (n = 3) of peak area were within 3.6% and 4.8% RSD, respectively. The accuracy was tested by spiking 0.5 and 2 μg/mL of melamine standard in the melamine contaminated milk powder provided by the European Commission, and the recoveries were 93.4 ± 0.5% and 98.7 ± 0.4%, respectively. Results of this study show a great potential for the sweeping-MEKC method as a tool for the fast screening of melamine in infant formulas.     

Determination of melatonin in commercial preparations by micellar electrokinetic chromatography and spectrofluorimetry

Melatonin was determined in pharmaceutical preparations by means of two simple and reliable analytical methods based on micellar electrokinetic chromatography (MEKC) and spectrofluorimetry. The fluorescence emission values were measured at λ=350 nm when exciting at λ=275 nm. The MEKC analysis was achieved using a system consisting of 40 mM SDS in phosphate buffer (20 mM, pH 7.5). The extraction of melatonin from the tablets was achieved by means of a simple one-step dissolution with methanol/water. Both methods were applied for the determination of melatonin in commercial formulations and galenic preparations. The MEKC procedure allows the quantitative determination of melatonin in all pharmaceutical preparations tested. On the contrary, the spectrofluorimetric method is not suitable for tablets which also contain tryptophan; this interference can be eliminated by a suitable liquid-liquid extraction procedure. The results obtained with the two methods are in good agreement and satisfactory in terms of precision and accuracy.     

Synthesis and application of a carbamazepine-imprinted polymer for solid-phase extraction from urine and wastewater

A molecularly imprinted polymer (MIP) designed to enable the selective extraction of carbamazepine (CBZ) from effluent wastewater and urine samples has been synthesised using a non-covalent molecular imprinting approach. The MIP was evaluated chromatographically in the first instance and its affinity for CBZ also confirmed by solid-phase extraction (SPE). The optimal conditions for SPE consisted of conditioning of the cartridge using acidified water purified from a Milli-Q system, loading of the sample under basic aqueous conditions, clean-up using acetonitrile and elution with methanol. The attractive molecular recognition properties of the MIP gave rise to good CBZ recoveries (80%) when 100 mL of effluent water spiked with 1 μg L⁻¹ was percolated through the polymer. For urine samples, 2 mL samples spiked with 2.5 μg L⁻¹ CBZ were extracted with a recovery of 65%. For urine, the linear range was 0.05-24 mg L⁻¹, the limit of detection was 25 μg L⁻¹ and precision, expressed as relative standard deviation at 0.5 mg L⁻¹ (n = 3), was 3.1% and 12.6% for repeatability and reproducibility between days, respectively.     

High performance capillary electrophoresis method for determination of ibuprofen enantiomers in human serum and urine

A direct and stereospecific capillary zone electrophoresis (CZE) method for quantification ibuprofen enantiomers in biological matrices: human serum and urine, has been developed. Chiral separation of the enantiomers of ibuprofen and (+)-S-indobufen [(+)-S-INDB, internal standard, IS] was obtained in an uncoated silica capillary filled with a background electrolyte (BGE), consisted of heptakis 2,3,6-tri-O-methyl-β-cyclodextrin (TM-β-CD) in buffer of pH 5.0. The complete enantioselective analysis of ibuprofen and its 1-hydroxy metabolite confirmed appropriate specificity of the method. The electrophoretic parameters: electroosmotic (μ_EOF) and electrophoretic (μ_ep) mobility and resolution factor (R_s) were determined. Extraction procedures with organic solvent and solid phase extraction (SPE) with C₁₈ stationary phase for isolation of enantiomers from biological fluids were compared. SPE method for further studies was chosen. Stereoselective extraction of IBP enantiomers from serum at basic pH has been discovered. Validation of the method was carried out. Calibration curves of ibuprofen enantiomers were linear in the range of 0.1-25.0 μg/ml in serum and of 0.5-250.0 μg/ml in urine. Recovery of both enantiomers from serum and urine amounted 74-86 and 90-98%, respectively. Intra- and inter-day measurement precision and accuracy were below 15%. Limits of detection for IBP enantiomers amounted 0.05 and 0.25 μg/ml in samples of serum and urine, respectively. Limit of quantitation was also estimated. IBP enantiomers proved to be stable following three freeze and thaw cycles and during storage in autosampler at ambient temperature. The validated methods enable pharmacokinetic studies of enantiomers in both media. The elaborated HPCE method can be alternative to HPLC.     

Gas chromatographic–mass spectrometric analysis of volatiles obtained by four different techniques from Salvia rosifolia Sm., and evaluation for biological activity

Four different isolation techniques, conventional hydrodistillation (HD), microwave-assisted hydrodistillation (MWHD), microdistillation (MD) and micro-steam distillation-solid-phase microextraction (MSD-SPME), have been used to analyze the volatile constituents from the aerial parts of Salvia rosifolia Sm. by gas chromatography and gas chromatography coupled to mass spectrometry. HD and MWHD techniques produced quantitatively (yield, 0.39% and 0.40%) and qualitatively (aromatic profile) similar essential oils. α-Pinene (15.7–34.8%), 1,8-cineole (16.6–25.1%), β-pinene (6.7–13.5%), β-caryophyllene (1.4–5.0%) and caryophyllene oxide (1.4–4.4%) were identified as major constituents of this Turkish endemic species. Besides, the hydrodistilled oil of S. rosifolia was evaluated for antibacterial, antifungal, anticancer, antioxidant and cytotoxic activities. The hydrodistilled oil of S. rosifolia showed antibacterial activity against Methicillin-resistant Staphylococcus aureus (MRSA) with a MIC value of 125 μg/mL. Other human pathogenic microorganisms (Escherichia coli, Pseudomonas aeruginosa, Enterobacter aerogenes, Salmonella typhimurium, Staphylococcus epidermidis, Candida albicans) were also inhibited within a moderate range (MIC = 125–1000 μg/mL). Antifungal activity of the oil was also observed against the strawberry anthracnose-causing fungal plant pathogens Colletotrichum acutatum, C. fragariae and C. gloeosporioides. No cytotoxicity was observed for S. rosifolia oil up to 25 mg/mL against malignant melanoma, epidermal, ductal and ovary carcinoma.     

Simultaneous determination of cypermethrin and permethrin in pear juice by ultrasound-assisted dispersive liquid-liquid microextraction combined with gas chromatography

A new method was developed for simultaneous determination of cypermethrin and permethrin residues in pear juice with ultrasound-assisted dispersive liquid-liquid microextraction (UA-DLLME) and gas chromatography-flame ionization detection (GC-FID). 3.5 mL of methanol (dispersant) and 30 μL of C₂Cl₄ (extractant) were injected into 5.0 mL of pear juice sample and then emulsified by ultrasound for 2.0 min to forming the cloudy solution. Under the optimum condition, the enrichment factors for cypermethrin and permethrin were 344 and 351 fold respectively. Good linearity was observed in a range of 0.009-1.52 μg g⁻¹ with the correlation coefficient (r²)≥0.9993. The limits of detection (LODs) were 3.1 and 2.2 μg kg⁻¹ for cypermethrin and permethrin, respectively (S/N = 3). The recoveries of the method evaluated at three spiked levels were in the range of 92.1%-107.1%. The repeatability evaluated as intra-day and inter-day precision (RSDs) were less than 4.0% (n = 5). The developed method was successfully applied to determine the two pesticide residues in different pear juice samples.     

On-line concentration and determination of tobacco-specific N-nitrosamines by cation-selective exhaustive injection-sweeping-micellar electrokinetic chromatography

In this paper, a micellar electrokinetic chromatography (MEKC) method combined with cation-selective exhaustive injection (CSEI) and sweeping was developed to separate and concentrate four tobacco-specific N-nitrosamines (TSNAs) including N′-nitrosoanabasine (NAB), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and 4-(methylnitrosamino)-4-(3-pyridyl)-1-butanol (iso-NNAL). Experimental parameters affecting separation efficiency and enhancement factors were investigated in detail. Under the optimum MEKC condition, NAB, NNK, NNAL and iso-NNAL were baseline separated with high separation efficiencies and good peak shapes. Furthermore, with the preconcentration by CSEI-sweeping-MEKC, the sensitivity enhancement factors for NAB, NNK, NNAL and iso-NNAL in terms of peak areas ranged from 6.0 × 10³ to 1.5 × 10⁴, and the detection limits (LOD, S/N = 3) of four TSNAs were in the range of 0.004-0.016 μg/mL. In addition, this method had fairly good repeatability, and the RSDs of retention time and peak area were less than 1% and 5%, respectively. Finally, this method showed promising capabilities in the application of detecting and analyzing TSNAs in human urine samples.     

A simple and fast method for chlorsulfuron and metsulfuron methyl determination in water samples using multiwalled carbon nanotubes (MWCNTs) and capillary electrophoresis

A new method to determine metsulfuron methyl (MSM) and chlorsulfuron (CS) in different water samples was developed. It consists in a solid phase extraction (SPE) procedure using multiwalled carbon nanotubes (MWCNTs) as sorbent material in combination with capillary zone electrophoretic determination. To carry out the pre-concentration step, a simple flow injection system was developed and optimized. Thus, 250 μL of aqueous solution containing methanol 50% (v/v) and acetonitrile 2% (v/v) as eluent, 10 mL of sample and a flow rate of 1.15 mL min⁻¹ were selected. The CE variables also were optimized. A rapid determination and good resolution of two herbicides were obtained within 9 min using a simple electrophoretic buffer (50 mmol L⁻¹ sodium tetraborate with 3% of methanol, pH = 9.0). Under the optimum conditions, the calibration curves were linear between 0.5 and 6 μg L⁻¹ for MSM and CS with R² = 0.995 and 0.997, respectively. The repeatability of the proposed method, expressed as relative standard deviation (RSD), varied between 4.1% and 5.4% (n = 10) and the detection limits for MSM and CS were 0.40 and 0.36 μg L⁻¹, respectively. Good results were achieved when the proposed method was applied to spiked real water samples. The recoveries percentages of the two analytes were over the range 86-108%.     

Analysis of capsaicin and dihydrocapsaicin in peppers and pepper sauces by solid phase microextraction–gas chromatography–mass spectrometry

A simple method for the analysis of capsaicin and dihydrocapsaicin in peppers and pepper sauces by solid phase microextraction–gas chromatography–mass spectrometry has been developed. A novel device was designed for direct extraction solid phase microextraction in order to avoid damage to the fiber. The analysis was performed without derivatization for the gas chromatography–mass spectrometry analysis. Selection fiber, extraction temperature, extraction time and pH, were optimized. The method was linear in the range 0.109–1.323 μg/mL for capsaicin and 0.107–1.713 μg/mL for dihydrocapsaicin with correlation coefficient up to r = 0.9970 for both capsaicinoids. The precision of the method was less than 10%. The method was applied to the analysis of 11 varieties of peppers and four pepper sauces. A broad range of capsaicin (55.0–25 459 μg/g) and dihydrocapsaicin (93–1 130 μg/g) was found in the pepper and pepper sauces samples (4.3–717.3 and 1.0–134.8 μg/g), respectively.