Pesticide analysis by micellar electrokinetic capillary chromatography

On-capillary sample concentration using sample stacking for the improvement of detection limits for various pesticides separated by micellar electrokinetic capillary chromatography was examined. The dependence of the stacking on different parameters was investigated. An approximately 30-fold preconcentration was achieved by applying sample stacking. Employing a two-step enrichment process (solid-phase extraction combined with sample stacking), detection limits were improved and the sample volume for SPE was reduced. In addition, the total time for the analysis was considerably reduced. Detection limits were between 0.01 and 0.1 ng/ml under these enrichment conditions.     

Determination of iridoid glycosides by micellar electrokinetic capillary chromatography-mass spectrometry with use of the partial filling technique

A fast and easy method was sought for determination of the iridoid glycosides catalpol, ketologanin, verbenalin, loganin, 8-epi-loganic acid, geniposidic acid and 10-cinnamoyl catalpol in plant samples. The method involved micellar electrokinetic capillary chromatography (MEKC) coupled on-line to mass spectrometry. The partial filling technique and electrospray ionization were used. Seven iridoid glycosides could be separated with use of MEKC under basic conditions. However, 8-epi-loganic acid and geniposidic acid could not be detected simultaneously with the five neutral iridoid glycosides by mass spectrometry. Therefore, only the neutral iridoid glycosides were screened from plant samples. Catalpol, verbenalin, loganin and possibly 10-cinnamoyl catalpol were found in an examination of seven plant species in the genera Plantago, Veronica, Melampyrum, Succisa, and Valeriana. Aucubin, which was not included in the sample mixture used in method development because of overlapping with catalpol in MEKC, was also detected. The limits of detection for the iridoid glycosides, both at the UV and at the mass spectrometer, are given.     

Determination of quercetin glycosides and free quercetin in buckwheat by capillary micellar electrokinetic chromatography

A simple and reliable method for determination of quercetin glycosides and free quercetin in buckwheat flower, leaves, stems and achenes was developed. The method consists of flavonoid extraction from freeze‐dried homogenous material in 50% v/v methanol solution and in presence of an antioxidant, cleaning of extract and analyte isolation using SPE. Analytical step uses capillary micellar electrokinetic chromatography. The working ranges, LOD and LOQ, recovery, precision and measurement uncertainty were calculated. The method is suitable for samples from buckwheat. The highest content of rutin was found in flowers of both kinds of buckwheat (99 400 mg/kg in F. esculentum, 108 000 mg/kg in F. tataricum). The free quercetin occurs in flowers and achenes of F. esculentum, whereas flowers and achenes of F. tataricum contained quercitrin.     

Extraction of male steroids and progesterone from water by vegetable oil gels and their determination by partial filling capillary micellar electrokinetic chromatography

Microemulsion gels were synthetized from macadamia, linseed, olive, walnut, rapeseed, sesame, and coconut oils and frying oil made from sunflower, palm, and rapeseed oils. The gels were similar as polyacrylamide–based gels with exception of replacing dodecyl sulfate with vegetable oils. The gels were modified with celluloses, cotton, or lignin to make the emulsions sustainable for water purification. They were used to compare sorption properties when they were used as solid‐phase adsorbents in isolation of steroids from water. Hydrophobicity features of the gels were compared by detecting adsorption and extraction efficiency of nonpolar androstenedione, testosterone, and progesterone, which exist in wastewater and drinking water. Quantification was done with partial filling–micellar electrokinetic chromatography with 29.5 mM sodium dodecyl sulfate–3.4 mM sodium taurocholate as the micelle and 20 mM ammonium acetate (pH 9.68) as the electrolyte. UV‐detection was used. Methanol was the best eluent for extraction of steroids from gels. The highest recoveries were from frying oil and rapeseed oil gels modified with celluloses. They also possessed the best floating properties on water surface. Lignin modified gels were too hydrophilic, when in touch with water they filled up with water. They also had the lowest capacity.     

Specific determination of cysteine in human urine by capillary micellar electrokinetic chromatography

This paper describes a method for the analysis of cysteine in human urine using capillary micellar electrokinetic chromatography and on‐column reaction with 2,2′‐dipyridyl disulfide. In this reaction cysteine is quantitatively transformed into a mixed disulfide concomitantly with formation of an equimolar amount of 2‐thiopyridone that is further separated by capillary micellar electrokinetic chromatography and determined spectrophotometrically at 343 nm. The concentration of cysteine is thus estimated indirectly from the result of 2‐thiopyridone determination. The linear detection range for concentration versus peak area for the assay is from 0.05 to 5 mM (correlation coefficient 0.989) with a detection limit of 2.5 μM and a limit of quantitation of 8.5 μM. The inter‐day reproducibility of the peak area was 2.18% and the inter‐day reproducibility of the migration time 0.51%. The method is relatively rapid, simple, and can be easily automated. Moreover, its detection limit covers the concentration range at which cysteine is present in biological samples such as human urine.     

Separation and determination of aminophenols and phenylenediamines by liquid chromatography and micellar electrokinetic capillary chromatography

The separation and determination of aminophenols and phenylenediamines were investigated by liquid chromatography (LC) and micellar electrokinetic chromatography (MEKC) in this study. Aminophenols and phenylenediamines are commonly used components in commercial hair colorants. The problem of tailing peaks in LC was improved by the technique of using mobile phase containing 15 mM triethylamine at pH 8.0. The analysis of o-aminophenol was not succeeded with LC even though the modifier of triethylamine was added. But it could be quantitative successfully by MEKC. The optimum separation condition of MEKC was achieved by employing 55 mM cetyltrimethyl ammonium chloride in 50 mM borate buffer (pH 9.2) with electric field strength of −145 V cm⁻¹. Finally, the commercial hair dyes were analyzed by developing methods of LC and MEKC. From both the results, there is no significant difference presence at 99.5% confidence level. These two methods could give the complementary results.     

Quantitative determination of glucoraphanin in Brassica vegetables by micellar electrokinetic capillary chromatography

Glucoraphanin, a glucosinolate, is found naturally in plants and is present in relatively high concentrations in broccoli. Glucosinolates have received much attention as studies have indicated that a diet rich in them may provide some protection from certain cancers. A micellar electrokinetic chromatography (MEKC) method using sodium cholate as the micellar phase has been developed to quantify for glucoraphanin in broccoli (seeds and florets) and Brussels sprouts. The glucoraphanin peak elutes just under 5 min with a theoretical plate number of 380,000 per metre of capillary. The method is suitable for crude extracts of broccoli and Brussels sprouts. Glucoraphanin in broccoli seeds (1330 mg/100 g) broccoli florets (89 mg/100 g) and Brussels sprouts (3 mg/100 g) was determined and agreed with the data obtained by high performance liquid chromatography. The LODs were 10-100 times below the levels typically found in broccoli seeds (4 mg/100 g), broccoli florets (0.9 mg/100 g) and Brussels sprouts (0.1 mg/100 g).     

Separation of coumarins by micellar electrokinetic capillary chromatography

Nine coumarins were successfully separated simultaneously using micellar electrokinetic capillary chromatography with 4-hydroxybenzoic acid as an internal standard. A carrier composed of buffer solution (20 mM sodium dodecyl sulfate-15 mM sodium borate-15 mM sodium dihydrogenphosphate)-acetonitrile (24:1) was found to be the most suitable electrolyte for this separation. The analysis time (22 min) was shorter than that using high-performance liquid chromatography (47 min). Contents of coumarins in the crude drug of Angelicae Tuhou Radix could be easily determined by the proposed method.     

Separation and determination of isoflavones in red clover by micellar electrokinetic capillary chromatography

A micellar electrokinetic capillary chromatography (MECC) method has been developed for the determination of the four isoflavones, i.e. biochanin A, formononetin, genstein and daidzein in red clover (Trifolium Pratense L.). The effect of running buffer pH and concentration were investigated. An electrolyte composed of 30 mm borate, 20 mm sodium dodecyl sulfate (SDS) and 4 mg/mL HP-beta-CD containing 5% (v/v) ethanol at pH 10.1 provides a satisfactory separation for all the analytes. The applied voltage was 25 kV, and the capillary temperature was kept constant at 25 degrees C with a UV detection at 254 nm. The relative standard deviations (RSD) of the migration time and peak area were less than 1.73 and 3.94% (intra-day), and 2.29 and 4.38% (inter-day), respectively, under the optimized separation conditions. Regression equations revealed a good linear relationship between the peak area of each compound and its concentration. The contents of the four compounds in red clover were successfully determined with satisfactory repeatability and recovery.     

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.     

Serum iohexol analysis by micellar electrokinetic capillary chromatography

A simple and rapid ( approximately 4 min) method for the measurement of iohexol in serum for assessing the glomerular filtration rate is described. It is based on direct serum injection on the capillary by MEKC. The method is linear between 8 and 260 mg/L, with an RSD of peak height of 2.9%. Several simple steps have contributed to an improved daily precision, such as choosing a high pH buffer, increasing the SDS concentration, frequent standardization, and eliminating any sample pretreatment.     

Determination of heterocyclic compounds by micellar electrokinetic capillary chromatography

Micellar electrokinetic capillary chromatography (MECC) based on sodium cholate (NaCh) and sodium dodecyl sulphate (SDS) was developed for the determination of aromatic amino acids and heterocyclic legume constituents. The influence of temperature, voltage, micellar system, pH, zwitterion and modifier concentrations in the buffer on migration times, peak areas, resolution and number of theoretical plates was investigated. This MECC method makes possible the sensitive determination of the individual compounds with detection limits in the picomole range. Up to 300 000 theoretical plates per metre of capillary were obtained together with satisfactory linearity and repeatability of the NaCh method. The applicability of MECC to samples prepared from plant material, following a fast and simple technique of isolation, purification and group separation, is illustrated by selected examples.     

Determination of plasma heparin by micellar electrokinetic capillary chromatography

The micellar electrokinetic capillary chromatography (MECC) method is reported for the separation of heparin, and for the possibility of direct determination of free heparin in plasma. The conditions for MECC were: pH 8.5, 25 mM sodium dodecyl sulfate (SDS), 25 mM borate buffer, with a 30 cmx50 mum ID fused-silica capillary. The sample was detected with a UV-detector at 270 nm with heparin as external standard. The recovery rate was 95.6-98.7%. This method was linear in the range 80-7000 U l(-1). The within-run and between-run relative standard deviations were lower than 3.1 and 4.5%, respectively. It is suggested that this MECC method may be used to determine blood samples containing high levels of heparin.     

Simultaneous determination of sweeteners and preservatives in preserved fruits by micellar electrokinetic capillary chromatography

A micellar electrokinetic capillary method for the simultaneous determination of the sweeteners dulcin, aspartame, saccharin, and acesulfame-K and the preservatives sorbic acid; benzoic acid; sodium dehydroacetate; and methyl-, ethyl-, propyl-, isopropyl-, butyl-, and isobutyl-p-hydroxybenzoate in preserved fruits is developed. These additives are ion-paired and extracted using sonication followed by solid-phase extraction from the sample. Separation is achieved using a 57-cm fused-silica capillary with a buffer comprised of 0.05 M sodium deoxycholate, 0.02 M borate-phosphate buffer (pH 8.6), and 5% acetonitrile, and the wavelength for detection is 214 nm. The average recovery rate for all sweeteners and preservatives is approximately 90% with good reproducibility, and the detection limits range from 10 to 25 microg/g. Fifty preserved fruit samples are analyzed for the content of sweeteners and preservatives. The sweeteners found in 28 samples was aspartame (0.17-11.59 g/kg) or saccharin (0.09-5.64 g/kg). Benzoic acid (0.02-1.72 g/kg) and sorbic acid (0.27-1.15 g/kg) were found as preservatives in 29 samples.     

Separation of anabolic steroids by micellar electrokinetic capillary chromatography

Summary The separation of seven analogous anabolic steroids was studied by micellar electrokinetic capillary chromatography (MECC). The retention order was found to be dependent on polarity. All of these steroids were well separated by the addition of organic modifiers to the separation buffer. Of the organic modifiers tested, 1-propanol gave the best separation, better than methanol or acetonitrile.     

Analysis of water-soluble vitamins by micellar electrokinetic capillary chromatography

Seven water-soluble vitamins were determined simultaneously by micellar electrokinetic capillary chromatography with UV detection. All these compounds were separated from each other within ca. 22 min by using a carrier containing sodium dodecyl sulphate as the surfactant. On-column detection at 254 nm with ethyl p-aminobenzoate as the internal standard allowed sensitive, accurate and reproducible determination of these compounds. Five principal constituents of a vitamin injection were determined with relative standard deviations of less than 2.1%.     

Identification and determination of active anthraquinones in Chinese teas by micellar electrokinetic capillary chromatography

The simultaneous determination of emodin, aloe-emodin and rhein, in Semen Cassiae, Qinghai Wild Dahuang tea, Ningxia Juemingzi tea, Lanzhou Juemingzi tea and Surong Juemingzi tea, has been investigated by micellar electrokinetic capillary chromatography for the fi rst time. With an electrolyte containing 15 mm borax, 30 mm SDS, 10% (v/v) ethanol, at pH 9.60 and 20 kV applied voltage, the three analytes were completely separated within 12 min. The effects of the concentration of borax, electrolyte pH, the concentrations of SDS and organic modifier and the applied voltage on electropheoretic behavior and separation were studied. The linear calibration range was 4-120 micro g/mL (r = 0.9921) for emodin, 10-200 micro g/mL (r = 0.9970) for aloe-emodin and 2-100 micro g/mL (r = 0.9971) for rhein, respectively. Under the optimum conditions, the relative standard deviation (RSD) values (n = 6) of the migration time and the peak area of each peak was 0.59-0.80% and 1.30-3.22%, respectively. The contents of the analytes in Rheum, Qinghai Wild Dahuang tea, Semen Cassiae and three other kinds of teas were easily determined with recoveries ranging from 95.3 to 104.4%.     

The separation of herbicides by micellar electrokinetic capillary chromatography

Summary A method for the separation of a number of herbicides consisting of chlorophenoxy acids by micellar electrokinetic capillary chromatography (MECC) was developed. Sodium dodecyl sulphate (SDS), Brij 35, cetyltrimethylammonium bromide (CTAB) and methanol were introduced into the buffers to investigate their effects on the separation of the herbicides. SDS combined with Brij 35 as the micellar agent was found to provide the best overall separation of these components.     

Quantitative determination of S-alk(en)ylcysteine-S-oxides by micellar electrokinetic capillary chromatography

A novel method for determination of S-alk(en)ylcysteine-S-oxides by capillary electrophoresis has been developed and validated. The method is based on extraction of these sulfur amino acids by methanol, their derivatization by fluorenylmethyl chloroformate and subsequent separation by micellar electrokinetic capillary chromatography. Main advantages of the new method are simplicity, sensitivity, high specificity and very low running costs, making it suitable for routine analysis of a large number of samples. Employing this method, the content of S-alk(en)ylcysteine-S-oxides was determined in 12 commonly consumed alliaceous and cruciferous vegetables (e.g. garlic, onion, leek, chive, cabbage, radish, cauliflower and broccoli). The total content of these amino acids in the Allium species evaluated varied between 0.59 and 12.3mg g(-1) fresh weight. Whereas alliin was found only in garlic, isoalliin was the major S-alk(en)ylcysteine-S-oxide in onion, leek, chive and shallot. On the other hand, the cruciferous species analyzed contained only methiin in the range of 0.06-2.45mg g(-1) fresh weight.