Qingyu Ou

New reagents for determination of amino acids by liquid chromatography with pre-column fluorescence derivatization

A liquid-chromatography method for the determination of amino acids with fluorescence detection has been developed. The reactions of three fluorescent tagging reagents, namely acridone-N-acetyl chloride (ARC-Cl), carbazole-9-acetyl chloride (CRA-Cl) and carbazole-9-propionyl chloride (CRP-Cl), with amino acids are reported. Emission maxima for the ARC, CRA and CRP derivatives of amino acids were at 430 nm (λex=404 nm), 360 nm (λex=335 nm) and 365 nm (λex=340 nm), respectively. In all cases, the derivatives exhibited strong fluorescence, whereas the reagents themselves also exhibited fluorescence. The labeled derivatives are very stable; <4% decomposition occurs after heating at 40°C for 24 h. The fluorescence intensities of the amino-acid derivatives were higher in neutral and alkaline than in acidic solutions. This method, combining a multi-gradient program, offers baseline resolution of the common ARC, CRA and CRP amino-acid derivatives than a linear acetonitrile gradient. Separation of amino-acid derivatives was carried out on a reversed-phase C18 column. Derivatization and chromatographic conditions were optimized. The separation of amino-acid derivatives has good reproducibility and the relative standard deviations (n=6) for 5 pmol of each amino acid are <4%. The detection limit is at the fmol level.

Separation of six phenylureas and chlorsulfuron standards by micellar, mixed micellar and microemulsion electrokinetic chromatography

Abstract The usefulness of electrokinetic chromatography (EKC) for the determination of phenylureas and chlorosulfuron herbicides was investigated. Micellar, mixed micellar and microemulsion EKC were examined for this purpose and compared systematically. Micelles formed from sodium dodecyl sulfate (SDS), mixed micelles formed from SDS and polyethylene glycol 400 monolaurate and oil-in-water microemulsions formed from SDS, n-butanol and n-octane were mainly employed. Capacity factors showed that the separation of the herbicides by ECK employing SDS follows an interaction mechanism similar to that in reversed-phase HPLC. Although there was not much difference in the elution order of the herbicides among the three modes of EKC, there were differences in separation selectivity. The separation efficiencies in mixed micellar and microemulsion EKC were higher than that in micellar EKC. Under the same separation conditions, the migration window in mixed micellar EKC was narrower than that in micellar EKC, but the migration window in microemulsion EKC was wider than that in micellar EKC and was also much easier to extend by changing the SDS concentration and applied voltage. The effects of the separation conditions on the separation of the herbicides by micellar EKC and microemulsion EKC were investigated.

Fast chiral separation of amino acid derivatives and acidic drugs by co-electroosmotic flow capillary electrophoresis with vancomycin as chiral selector

Abstract A fast chiral separation method for acidic enantiomers, including 9-fluorenylmethyl chloroformate (FMOC) amino acid derivatives and ketoprofen, with vancomycin as chiral selector is presented. In this method, hexadimethrine bromide (HDB), a polycationic polymer, was added to the run buffer as electroosmotic flow (EOF) modifier. The reversed EOF migrated in the same direction as the anionic analytes. Consequently, the separation time was shortened. Another advantage of using HDB as buffer additive is that the adsorption of vancomycin onto the capillary wall was minimized, hence, the separation efficiency was improved. The effects of buffer pH and vancomycin concentration on separation were investigated. Base line chiral separation of 12 FMOC-amino acid derivatives, ketoprofen and drug intermediate 4,4′-dimethoxy-5,6,5′6′-bismethylenedioxybiphenyl-2,2′-dicarboxylic acid were obtained. The separation time for each enantiomers was not more than 4.5 min, and the average efficiency of 3.2·10 5 plates/m was obtained.

Effect of high concentrations of salts in samples on capillary electrophoresis of anions

Abstract The capillary electrophoretic separation of anions using direct UV detection was studied. The separation conditions, such as carrier electrolyte, pH and concentration of electroosmotic modifier, were optimized. The carrier electrolyte co-ion affected the peak shape because electromigration dispersion was non-negligible. An unsuitable anion form of the electroosmotic flow modifier would cause negative peaks on the separation baselines when the samples contain high concentrations of salts, and the separation could be adversely affected. In this work, sodium chloride with 2.0 mM tetradecyltrimetylammonium bromide was used as the carrier electrolyte solution, and a good separation was achieved. Taking sodium chloride to represent salts in samples, the experimental results showed that the peak height and width of a detected anion were affected by the ratio of sodium chloride concentration between the carrier electrolyte solution and sample, and correspondingly the detection limit and separation efficiency of the anion were also affected. The principle of electrostacking was used to explain this phenomenon theoretically. The reproducibility of migration time, peak height and peak area under different conditions was also examined.

Kinetic spectrophotometric determination of trace manganese (II) with dahlia violet in nonionic microemulsion medium

A new catalytic kinetic spectrophotometric method has been developed for the determination of trace amount of manganese (II) in nonionic microemulsion medium. The method is based on the catalytic effect of manganese (II) on the oxidation of dahlia violet by potassium periodate with nitrilotriacetic acid as an activitor in the presence of nonionic microemulsion. Under the optimum conditions, the calibration graph is linear in the range of 0.0004-0.0056 mug ml(-1) of manganese (II) at 580 nm. The detection limit achieved is 3.75x10(-5) mug ml(-1). Manganese (II) in foodstuff samples was determined with satisfactory results.

Determination of the petroleum tracers nitrate and thiocyanate in subterranean waters by capillary ion electrophoresis

Abstract The petroleum tracers nitrate and thiocyanate in subterranean waters were determined by capillary ion electrophoresis using direct UV detection. The high concentrations of salts in subterranean waters made the determination difficult. Taking sodium chloride to represent salts in subterranean waters, the effect of high concentrations of salts in samples on the determination was examined. Because of electrostacking and its inverse process, different concentrations of salts in samples could cause different peak heights and peak widths of constant concentration of an anion, but the peak area remained constant. The experimental results showed that the determination of the tracers was feasible using peak areas. By using 100 mM sodium chloride with 2.0 mM: cetyltrimethylammonium chloride as carrier electrolyte solution, determination of nitrate and thiocyanate was accomplished at concentrations of sodium chloride in the sample from 0 to 200 mM. Standard addition recoveries of the tracers in four subterranean water samples were between 91 and 113%.

High performance liquid chromatographic determination of N- nitrosoamines by pre-column fluorescence derivatization with acridone-N- acetyl chloride

A sensitive high performance liquid chromatographic method for the determination of N-nitrosoamines with pre-column fluorescence derivatization has been developed. N-nitrosoamines are first changed into secondary amines using denitrosation reagent, then react with acridone-N-acetyl chloride (ARC-Cl) to produce corresponding secondary amine derivatives, which exhibit a strong fluorescence. Maximum emission for ARC derivatives is 430 nm (lambda(ex) 404 nm). The labelled derivatives are very stable, less than 4% decomposition occurs after heating at 40 degrees C for 24 h. Fluorescence intensities of derivatives are higher in neutral and alkaline than in acidic solutions. This method, in conjunction with a multi-gradient program, offers a baseline resolution of the ARC derivatives from a linear acetonitrile gradient. Separation is carried out on a reverse phase C(18) column. Derivatization and chromatographic conditions are optimized. The relative standard deviation (n=6) at an analytical concentration of 10 pmol of each N-nitroamine is less than 4.5%. The detection limits at the fmol level. The method described is also suitable for analysis of other amino compounds in different biological samples.

Studies of crude chloroform extract of roots ofPodophyllum emoddii var. chinesis Sprague by micellar electrokinetic chromatography

SummaryA crude chloroform extract of the roots ofPodophyllum emoddii var. chinesis Sprague was studied by micellar electrokinetic chromatography. Four peaks belonging to podophyllotoxin, 4′-desmethyl-podophyllotoxin, kaempferol and quercetin were identified by known standards. The four substances are valuable pharmaceutical ingredients of the plant.

Separation and determination of phenylpropanoid glycosides from Pedicularis species by capillary electrophoresis

Capillary zone electrophoresis, using 30 mM borate buffer (pH 9.00) with 10% (v/v) methanol, was established for the identification and determination of four phenylpropanoid glycosides (PPGs)--echinocoside (ECH), verbascoside (VER), pedicularioside M (PED-M) and pedicularioside A (PED-A)--in extracts of Pedicularis longiflora var tubiformis, Pedicularis longiflora and Pedicularis Kansuensis. Regression equations revealed linear relationships (correlation coefficients: 0.9993-0.9999) between the peak area of each compound (ECH, VER, PED-M and PED-A) and its concentration. The relative standard deviations of the migration times and peak areas were <1.93 and 4.54%, respectively. The recoveries of four PPGs ranged between 95.6 and 108.4%. The effects of several CE parameters on the resolutions were studied systematically.

Determination of trace level anions in snow samples by capillary electrophoresis with sample stacking

Abstract Trace level Cl−, SO42− and NO3− in snow samples were determined by capillary electrophoresis with the sample stacking enrichment technique to improve the detection sensitivity. The conditions of separation of standard ions (Br−, Cl−, SO42−, NO2− and NO3−) were optimized. During stacking run, large enrichment factor and good reproducibility of migration times could be achieved with electromigration injection. However, the reproducibility of peak areas was poor, and at the same time, quantitation became difficult because the enrichment factor was influenced by the ionic strength of standard ion mixtures and the real samples. Using Br− as an internal standard, standard addition method was used for the quantitative determination of anions in snow sample by electromigration injection. The results were consistent with those of ion chromatography.