摘要:

Selecting optimum HPLC operating conditions during the development of new analytical separations is difficult due to the high degree of process variable interaction and the lack of robust process models. Traditionally, the methods development strategy in analytical applications involves a trial-and-error grid search method that is both inefficient and costly. Several researchers have investigated more practical and efficient methods for designing optimal HPLC separations at the analytical stage. These strategies typically utilize an efficient design of experiments and response surface optimization techniques. Response or criteria functions are employed to numerically quantify chromatograms and rank them in order of desirability.

ISSN:1082-6076    

DOI:10.1081/JLC-100100475

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Three hundred and six (306) commercial samples from 19 processing plants in Florida, composed of frozen concentrated orange juice, orange juice from concentrate, and pasteurized orange juice, were analyzed for their sugars content by HPLC. In addition, the sugar profile of fresh-squeezed juice from 9 different cultivars of sweet oranges, 2 tangors, and 4 tangelos grown in Florida are included. Sucrose, fructose, glucose, total sugars, glucose/fructose ratio, and myo-inositol contents are presented.

ISSN:1082-6076    

DOI:10.1081/JLC-100100476

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The lipophilic character of a series of active anticonvulsant N-substituted amides of α-piperazine-γ-hydroxybutyric was studied. The classical RMo- values were measured by means of reversed thin layer chromatography using a mixture of methanol, TRIS buffer, and acetic acid as the solvent system and compared with the factors scores obtained by principal component analysis based also on the TLC retention data. The significant correlation between the RMo- values and slopes (the specific hydrophobic surface areas) usually indicated that this group of N-substituted amides could be considered as a homologous series of compounds independent of their structural heterogeneity. It is emphasized, once again, that this procedure can not be a rational and objective way for congeneric studies because there is always a high correlation between slope and intercept. The reliability of the factor scores values as lipophilicity indices is shown by their high correlation with the classical RMo-values. In addition, the “lipophilicity chart” described by the first two components will have the effect of separating compounds from each other most effectively from the congeneric aspect point of view.

ISSN:1082-6076    

DOI:10.1081/JLC-100100477

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An original chiral selector, namely the prop-2-enyl 3α-(N-phenylcarbamate)-7α,12α-dihydroxy-5β-cholan-24-oate, is bonded onto the silica surface by three different grafting modes. The influence of the total structure of the chiral stationary phases (CSPs) on enantioseparation is studied. These CSPs are prepared in two steps. In the first step, the silica surface is reacted with one of the following reagents: 1) (3-mercaptopropyl)trimethoxysilane, yielding a rather monomeric support, 2) chlorodimethylsilane, leading to a monomeric material, or 3) triethoxysilane, affording a polymeric packing. In the second step, the chiral selector is bonded onto the modified silica structures to provide the corresponding stationary phasesSH,CDS, andTES, respectively. The CSPSHshows the poorest column performance. CSPsCDSandTESshow similar mass transfer kinetics; this highlights the good behaviour of the polymeric packing. CSPTESdisplays globally the highest enantioselectivity and is found to be extremely stable despite its use over months. The silanization reaction with triethoxysilane provides a suitable support for chiral stationary phases.

ISSN:1082-6076    

DOI:10.1081/JLC-100100478

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Optimization procedures in Ion Chromatography require unambiguous goals. Optimization criteria express such goals in mathematical terms. If the retention factor tR, varies as a function of the parameters to be optimized, criteria should be selected that enable simultaneous optimization of retention and selectivity. The non — suppressed Ion Chromatographic method with conductometric detection is described for simultaneous determination of six inorganic anions: fluoride, chloride, nitrite, bromide, nitrate, and sulphate. It is demonstrated that the result of the optimization process depends on the optimization criterion selected. The computer-simulated chromatograms were used for the comparison of optima calculated using four different criteria. General recommendations for double criteria optimization of separation in ion chromatography are suggested.

ISSN:1082-6076    

DOI:10.1081/JLC-100100479

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Using both UV-Vis and conductivity detectors, the effects of high concentration of chloride on the determination of trace anions were studied on three different analytical columns by ion chromatography. The variations of retention behavior of these anions were caused by self-elution effect and on-column eluent change in the presence of high concentration of chloride. As the chloride concentration increased, linear ranges of the other anions became narrow. The anions separated on the column, which had higher capacity and had wider linear ranges. When their peaks overlapped with chloride, the deviations of weak acid anions were caused by anion-proton interactions within the suppressor. However, the other weak acid anions, which could not overlap with chloride and the strong acids anions, were not affected. In this paper, accurately quantitative analysis methods and their linear ranges were determined.

ISSN:1082-6076    

DOI:10.1081/JLC-100100480

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Centrifugal Partition Chromatography (CPC) was used in a generalseparation and dereplication procedure in search for new biologically activecompounds from crude plant extracts. In this procedure, the alcoholic extractwas prefractionated by CPC with the solvent system heptane/ethyl acetate/methanol/water6:1:6:1 (v/v/v/v) followed by bioactivity screening of the fractions. Theactive fractions were analyzed for the known active components for dereplication.If the activity was found in the most polar fraction, which tended to containa large group of compounds, the fraction was separated again by CPC (solventsystem ethyl acetate/methanol/water 43:22:35, v/v/v). This two-step procedurewas found to be efficient for five extracts tested for both chemical and bioactivityprofiles.

ISSN:1082-6076    

DOI:10.1081/JLC-100100481

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Turmeric powder and its main component, curcumin, have a widerange of medicinal and culinary uses. The purpose of this study was to separateand purify curcumin from demethoxycurcumin and bis-demethoxycurcumin whichare present in both turmeric powder, and commercial crude curcumin.

ISSN:1082-6076    

DOI:10.1081/JLC-100100482

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Using a multilayer helical separation column coaxially mounted on a horizontal rotary shaft, retention of the stationary phase and partition efficiency were studied at various rotation speeds ranging from 20 to 800 rpm. A binary two-phase solvent system composed of chloroform/water was used to elute the lower organic phase through the head of the rotating column. The results indicated that best retention of the stationary phase was obtained at a low rotation speed of 75 rpm yielding the highest peak resolution between caffeine and theophylline. Because of its simplicity and low rotation speed, the system has a potential to be scaled-up for an industrial-scale separation simply by increasing the capacity of the helical column.

ISSN:1082-6076    

DOI:10.1081/JLC-100100483

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An improved reverse phase high performance liquid chromatography (HPLC) procedure has been described to estimate azadirachtin-A content in crude methanolic extracts of neem seed kernels using valley-to-valley integration techniques. The present paper highlights a detailed study of extraction, estimation, and purification of azadirachtin-A present in neem seed kernels. We also present, herein, our results of Soxhlet extraction of Aza-A from the defatted neem seed cake as a function of time, which is found to be more efficient than the conventional extraction procedure.

ISSN:1082-6076    

DOI:10.1081/JLC-100100484

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor