摘要:

Two liquid crystal materials, 4-methoxyphenyl-4-allyloxybenzoate and cholesteryl-10-undecenoate, containing terminal olefin groups are bonded to a silica hydride surface via a metal complex catalyzed hydrosilation reaction. Bonding is confirmed by DRIFT, carbon-13 CP-MAS NMR and DSC. The effects of different catalysts, reaction temperature, catalyst to olefin ratio, and reaction time were studied to maximize the surface coverage. Chromatographic studies indicate that these bonded materials behave similarly to liquid crystal phases prepared by organosilanization. The hydrosilation method offers the possibility of bonding a wider variety of liquid crystal moieties in order to utilize the unique separation properties of these materials.

ISSN:1082-6076    

DOI:10.1080/10826079808003440

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The physically and chemically stable and batch-to-batch reproducible bonded phases of wide-pore size (300Å) were developed by using silica gels of purity over 99.99%. The chemically modified silica gels of butyl, pentyl, and octadecyl bonded phases were stable and inert for over 10,000 hours immersion in aqueous 1.0% trifluoroacetic acid (pH 1.5):CH3CN-50:50 and 20 mM sodium phosphate buffer (pH 10.0):CH3CN-50:50.

ISSN:1082-6076    

DOI:10.1080/10826079808003441

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This work evaluated the use of an alkaline phosphatase plug, slowly migrating in a polyacrylamide-coated capillary filled with buffer/soluble polymer, to convertp-nitrophenylphosphate (which was injected into the capillary as a separate plug, and migrated faster than the enzyme) top-nitrophenol under a constant applied potential. The elution of assay components was monitored on-capillary at 230 nm. The initial reaction velocity of the enzymecatalyzed reaction was estimated from the peak area ratio of the enzyme product to the internal standard. Using the Lineweaver-Burk plots, an average Michaelis constant (KM) for alkaline phosphatase was calculated to be 4.8 ± 0.3 mM (n = 4, CV = 6%). With the constant potential electrophoresis (8 kV/57 cm), the method had a detection limit of 4.4 × 10−5IU for alkaline phosphatase and a linear range up to 2.1 × 10−3IU.

ISSN:1082-6076    

DOI:10.1080/10826079808003442

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A general problem found in the analysis of samples from brain microdialysis is the existence of some substances which can interfere with the dopamine. In our chromatographic conditions, we found an interfering peak with the following mobile phases: acetic acid / sodium acetate 1M (with 5% methanol and 1mM EDTA), and citric acid / sodium phosphate (with 5% methanol and 2mM EDTA). The solution for this problem was to employ a mobile phase consisting of KH2PO4(with lmM EDTA and 5% methanol), with an ion-pair agent of sodium salt of 1-octanesulfonic acid. The interfering peak was identified as the uric acid (resulting from the cellular metabolism) based on its chromatographic properties.

ISSN:1082-6076    

DOI:10.1080/10826079808003443

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A simple and accurate reversed phase HPLC procedure is proposed for the determination of 19 phenolic compounds (flavonoids, phenolic acids, and coumarins) in seven medicinal species. The sample preparation involved extraction, alkaline and acid hydrolysis, and purification through a Bond-Elut C18 column. The chromatographic separation was achieved using a reversed phase column Spherisorb ODS2 (5μm; 25.0 × 0.46 cm). Gradient elution was carried out using water-formic acid (19:1) (A) and methanol (B). A diode-array detector monitored the effluent and chromatograms were recorded at 280, 320, and 350 nm. The optimised methodology seems to be useful for the phytochemical analysis of plant extracts. A close correlation between the phenolic compound patterns and the botanical origin of plants was found.

ISSN:1082-6076    

DOI:10.1080/10826079808003444

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

An HPLC method was developed for assay and purity control of ursodeoxycholic acid, which is separated from all related compounds. Using an evaporative light scattering mass detector (ELSD), equipped with a micronebulizer and a narrow bore column, the bile acids (ursodeoxycholic acid, ursocholic acid, cholic acid, chenodeoxycholic acid, deoxycholic acid and litocholic acid) were efficiently separated on an Hypersil ODS-RP-18 column (100 × 2.1 mm) with methanol-acetonitrile-water (60 : 22: 18), adjusted at pH 4.00 with acetic acid, as mobile phase. Linearity response, accuracy, and precision of the ELSD over the range of sample amounts of interest were established for all compounds. The method demonstrates a suitability of the detector for the assay of ursodeoxycholic and related impurities and was applied for the analysis of ten pharmaceutical preparations.

ISSN:1082-6076    

DOI:10.1080/10826079808003445

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The feasibility of simultaneous speciation of arsenic and selenium compounds after ion chromatographic separation was investigated using inductively coupled plasma mass spectrometry (ICP-MS) as multielement specific detector. Separation conditions were optimized. Under the optimized conditions, six arsenic species: arsenous acid [As (III)], methylarsonic acid (MA), dimethylarsinic acid (DMA), arsenic acid [As(V)], arsenobetaine (AsB), arsenocholine (AsC), and four selenium species: selenous acid [Se(IV)], trimethylselenonium cation (TMSe+), selenocystine (SeCys), selenomethionine (SeMet), can be separated in the same injection within 8 minutes and determined at environmental concentration levels. The detection limits are estimated in the range of 0.04–0.6 μg/L for arsenic compounds and 0.18–0.35 μg/L for selenium compounds.

ISSN:1082-6076    

DOI:10.1080/10826079808003446

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A method for the determination of impurities and degradation products in nalbuphine hydrochloride injection by gradient elution high performance liquid chromatography (HPLC) is reported. Reversed phase gradient elution chromatography was carried out using a mobile phase containing 0.05% trifluoroacetic acid, acetonitrile, and tetrahydrofuran. Validation data for linearity, accuracy, precision, robustness, detection limit, and quantitation limit are presented. The chromatographic system resolves nalbuphine from related substances with corrections made for differences in detector response at the specified wavelength.

ISSN:1082-6076    

DOI:10.1080/10826079808003447

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A liquid chromatographic method is described for the analysis of all-rac-α-tocopheryl acetate and retinyl palmitate in soy based infant formula. The vitamins are extracted from infant formula without saponification by matrix solid phase dispersion (MSPD) and quantitated by normal phase chromatography with fluorescence detection. Retinyl palmitate and all-rac-α-tocopheryl acetate are quantitated isocratically with a mobile phase of hexane containing isopropanol @ 0.125% (v/v) and 0.5% (v/v), respectively. Results compared favorably to the label declaration on a retail infant formula product.

ISSN:1082-6076    

DOI:10.1080/10826079808003448

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A high performance liquid chromatography (HPLC) method for extraction and determination of pesticides from raw milk was developed. The method involves direct injection of raw milk samples on a bovine serum albumin-dimethyl-octyl-silica gel (BSA-Si-C8) column. The mobile phase 0.05 mol.L−1phosphate buffer pH6.0 in acetonitrile (70:30 v/v) was employed for extraction and separation of bendiocarb, methylparathion, pentachlorophenol, and methomyl pesticides. The method shows good results of recovery in the pesticides studied, higher than 99.6%.

ISSN:1082-6076    

DOI:10.1080/10826079808003449

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor