摘要:

A novel separation method for macromolecules, viz. liquid chromatography under limiting conditions of adsorption (LC LCA), is presented. LC LCA is designed for discrimination of complex polymers. It combines exclusion and adsorption mechanisms so that they mutually compensate. This results in the absence of separation of macromolecules according to their size or molar mass. In LC LCA, the eluent is a liquid moderately promoting adsorption of polymer species. The column packing attracts macromolecules and, if the sample were dissolved and injected in eluent, it would be retained within column. Therefore, the polymer is injected in a solvent that effectively suppresses adsorption. Experimental conditions can be identified with regard to the eluent, column packing, temperature as well as sample solvent, and injected sample volume under which macromolecules of various molar masses are eluted together with their initial solvent. in this way, binary polymer blends, with components exhibiting different adsorptive properties can be separated.

ISSN:1082-6076    

DOI:10.1081/JLC-100102064

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In this study, the trial of optimising modification conditions of silica gel with metal salts was undertaken. For the purposes of the study, colourful salts Cu(I), Cu(II), Co(III) were mainly chosen, which enabled the evenness of the coating and the effectiveness of their desorption.

ISSN:1082-6076    

DOI:10.1081/JLC-100102065

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A liquid chromatographic procedure for the determination of pentobarbital in urine and plasma samples is described. The proposed system uses a Spherisorb octadecyl-silane ODS-2 C18analytical column, a guard column of similar characteristics, and a 0.02 M CTAB-15% 1-propanol at pH 7.5 mobile phase.

ISSN:1082-6076    

DOI:10.1081/JLC-100102066

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A simple and sensitive LC method for the determination of amino compounds, using carbazole-N-acetyl-N-hydroxy-succinimide (CAHS) as condensation agent, has been developed.A mixture of amines is treated with CAHS, in the presence of triethylamine catalyst in non-aqueous acetonitrile or in the presence of 0.2 M borate buffer at pH 8.0–9.0 in 40% (v/v) of acetonitrile solution, to give quantitative yields of amides. Emission maximum for the derivatized amines is 365 nm (λex335 nm). Studies on derivatization conditions indicate that amines react very fast with CAHS under proposed conditions. The method, in conjunction with a multi-step gradient, offers baseline resolution of common amine derivatives on a reversed-phase C18column.

ISSN:1082-6076    

DOI:10.1081/JLC-100102067

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

An isocratic high performance liquid chromatographic (HPLC) method with run times of less than 22 min has been developed for simultaneous analysis of carotenoids and tocopherols in corn. The reverse phase system utilizes a nonaqueous mobile phase in combination with a polymeric C18column coupled to a monomeric C18column to separate lutein, zeaxanthin, β-cryptoxanthin, α-carotene, β-carotene, and the α-, δ- and γ- forms of tocopherol. The detector was a multi-channel UV-VIS. One channel was used to monitor carotenoid absorption at 450 nm while another monitored tocopherols at 290 nm.

ISSN:1082-6076    

DOI:10.1081/JLC-100102068

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Gel permeation chromatography (GPC) was utilised to control the progress of the reaction betweenN,N-dimethylpropylene-1,3-diamine (DMPDA) and triglycerides (fats). As per “ideal size exclusion mode”, the sample is separated into triglycerides (TGC), diglycerides (DGC), monoglycerides (MGC), and glycerine (GC), as the component groups with sufficiently different molecular weights. Moreover, the separation was obtained for MGC and amidoamines (AA), i.e. the reaction products, despite the fact that their molecular weights are the same in practice (Mw=348 and 358, respectively). The increased retention time for amidoamines was assumed to be accounted for by the additional adsorption effects in “adsorption mode”. Resulting from the overlapping of two types of chromatographic separation mechanisms, an analytical method was obtained which could be called “mixed mode” conditions.

ISSN:1082-6076    

DOI:10.1081/JLC-100102069

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The method uses high-speed countercurrent chromatography to retain a given concentration of the chiral selector (CS) in the liquid stationary phase. A minute amount of an enantiomeric analyte is eluted through the column to measure its retention time from which the distribution ratio of the analyte is computed. The experiment is repeated by varying the CS concentration in the stationary phase. Using a set of data thus obtained, plotting the CS concentration in the stationary phase against the relative distribution ratio of the analyte produces a straight line whose slope corresponds to the formation constant (Kf) of the CS-analyte complex. The validity of the method is demonstrated on a set of dinitrobenzoyl amino acids using N-dodecanoyl–L-proline-3,5-dimethylanilide as CS. The method will be useful for understanding the basic mechanism of enantioselectivity and designing effective chiral selectors.

ISSN:1082-6076    

DOI:10.1081/JLC-100102070

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A high performance liquid chromatographic method coupled with an electrochemical detector for the separation and quantification of putrescine and cadaverine as their electroactive derivatives has been developed. Two different solvent column systems were used to determine putrescine, cadaverine, spermidine, spermine, and 1,3-diaminopropane (IS) in rat cerebral cortex. The lower detection limit was less than 80 fmol. The electrochemical response was linear in the range 80–240 ng/mL.

ISSN:1082-6076    

DOI:10.1081/JLC-100102071

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

An automated reversed phase high performance liquid chromatographic (RP-HPLC) method, using a multi-linear gradient elution, is described for the simultaneous analysis of five methyluric acids: 7-methyluric acid (7-MU), 1-methyluric acid (1-MU), 1,3-di-methyluric acid (1,3-DMU), 1,7-di-methyluric acid (1,7-DMU), and 1,3,7-tri-methyluric acid (1,3,7-TMU).

ISSN:1082-6076    

DOI:10.1081/JLC-100102072

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The oxygen heterocyclic compounds (coumarins, psoralens, and polymethoxylated flavones (PMFs)) present in citrus essential oils (lemon, mandarin, sweet orange, bitter orange, bergamot, grapefruit, and lime) were analysed by an HPLC-MS system equipped with an APcI source. The mass spectra obtained at different voltages of the “sample cone” have been used to build a library.

ISSN:1082-6076    

DOI:10.1081/JLC-100102073

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor