Search results for "liquid"
showing 10 items of 4351 documents
Rapid method for analysis of nicotine and nicotine-related substances in chewing gum formulations
1998
Abstract Based on environmental requirements and demands for a high throughput a rapid method for the analysis of nicotine and nicotine-related substances in chewing gum formulations was developed. The method is based on sample preparation through liquid–liquid extraction followed by reversed-phase HPLC using gradient elution. It allowed up to nine analytes to be determined within 15 min, including the sample preparation, and was considered as accurate and robust.
Description of the retention behaviour in micellar liquid chromatography as a function of pH, surfactant and modifier concentration
1997
Abstract Micellar liquid chromatography permits the elution of solutes of diverse polarity. One of the most outstanding advantages of the technique is its capability of predicting the retention with high accuracy, as a function of different experimental variables. The separation of a group of compounds is usually optimized by varying the concentrations of surfactant and modifier in the mobile phase. The pH is, however, for many solutes, a variable that should be considered in the description of their elution behaviour. A global model that takes into account, simultaneously, the concentrations of surfactant and modifier, and the pH as chromatographic variables, is proposed for ionizable solu…
Micellar liquid chromatography: suitable technique for screening analysis.
2002
The screening capability of micellar liquid chromatography (MLC) is discussed using the reported chromatographic data of several sets of compounds (amino acids, beta-blockers, diuretics, phenethylamines, phenols, polynuclear aromatic hydrocarbons, steroids and sulfonamides) and new results (sulfonamides and steroids). The chromatographic data are treated with an interpretive optimisation resolution procedure to obtain the best separation conditions. Usually, the pH and the concentration of surfactant (sodium dodecyl sulfate, SDS, or cetyltrimethylammonium bromide) for the optimal mobile phase were 2.5-3 and0.12 M, respectively. The nature and concentration of organic solvent depended on the…
An automatic multidimensional chromatography system for purification of human uterine progesterone receptor and induction of polyclonal antibodies.
1986
Abstract This paper reports on the synthesis of Org2058-bonded microparticulate silicas and their use in affinity chromatography as the first step for the purification of human progesterone receptor. The development of microprocessor-controlled instruments allows all the various steps to be performed automatically. The various steps used for the purification of human progesterone receptor were carried out with the FPLC system: (1) affinity chromatography, (2) desalting of eluate on Sephadex G-25, (3) anion-exchange chromatography using a Mono Q column. With this procedure the receptor was purified approx. 10,000-fold within 24 h. The yield of receptor was generally 85–95%. Investigations wi…
Solid-phase extraction of quaternary ammonium herbicides
2000
This paper highlights recent advances in the solid-phase extraction (SPE) of quaternary ammonium herbicides in water, soil, plant and biological samples. After a brief introduction summarizing the properties of quaternary ammonium herbicides and the difficulties involved in measuring them, attention is paid primarily to solid supports used for isolation and concentration, pre-treatments required for the different matrices, and eluents applied for quantitative desorption of these analytes. The determination techniques used after SPE and applications of the proposed SPE methodology are also briefly discussed.
Levels in the interpretive optimisation of selectivity in high-performance liquid chromatography: a magical mystery tour.
2006
Interpretive approaches for selectivity optimisation, which are those supported by retention models, are able to exploit efficiently the capabilities of the chromatographic system. The resolution of a mixture is usually faced in a first trial by looking for a unique experimental condition, able to resolve all compounds in the sample. If this is not possible, the problem can be outlined with less ambitious aims, focusing on only some compounds. In an extreme case, a single analyte can be individually optimised. Current strategies that give answer to the different goals pursued in the analysis, which are classified as total, partial and specific, are reviewed. Optimisation oriented to deconvo…
Effects of thermal processing and storage on available lysine and furfural compounds contents of infant formulas.
2000
The Maillard reaction-related effects that thermal treatments during the manufacturing process and storage (at 20 and 37 degrees C) have on powdered adapted and follow-up milk-based infant formulas were estimated by measuring the available lysine and furfural compounds contents of raw cow milk used in manufacturing, intermediate products and formulas. A fluorimetric method was used to measure the available lysine contents, and free and total furfural compounds were determined by HPLC. Statistically significant losses in available lysine (about 20%) in the infant formulas with respect to raw milk were found. The storage period did not affect the available lysine contents of adapted formulas …
Analysis of neuropeptide Y and its metabolites by high-performance liquid chromatography-electrospray ionization mass spectrometry and integrated sam…
2000
A novel restricted access cation exchanger with sulphonic acid groups at the internal surface was proven to be highly suitable in the sample clean up of peptides on-line coupled to HPLC-electrospray ionization (ESI)-MS. Neuropeptide Y (NPY) and several of its fragments in plasma were subjected to the sample clean-up procedure. The peptides were eluted by a step gradient from the restricted access column, applying 10 mM phosphate buffer pH 3.5 from 5 to 20% (v/v) of acetonitrile with 1 M NaCl and transferred to a Micra ODS II column (33x4.6 mm). The separation of the peptides and their fragments was performed by a linear gradient from 20 to 60% (v/v) acetonitrile in water with 0.1% formic ac…
Isobaric Vapor−Liquid Equilibria for 1-Propanol + Water + Calcium Nitrate
1999
Isobaric vapor−liquid equilibria for all of the binary and ternary mixtures of 1-propanol, water, and calcium nitrate have been measured at 100.00 kPa using a recirculating still. The addition of calcium nitrate to the solvent mixture produced an important salt effect; the azeotrope was removed at salt mole fractions higher than 0.08. The three experimental binary data sets were independently fitted with the electrolyte NRTL model (Mock, B.; Evans, L. B.; Chen, C. C. AIChE J. 1986, 32, 1655−1664), and the parameters of Mock's model were estimated for each binary system. No ternary parameter was required. These parameters were used to predict the ternary vapor−liquid equilibrium using the sa…
Isobaric Vapor−Liquid Equilibria for Water + Acetic Acid + Lithium Acetate
2001
Isobaric vapor−liquid equilibria for all of the binary and ternary mixtures of water, acetic acid, and lithium acetate have been measured at 100.00 kPa using a recirculating still. To take into account the association of the acetic acid in the vapor phase, Marek's chemical theory has been considered. The three experimental binary data sets have been independently correlated using Mock's electrolyte NRTL model, and the binary parameters estimated for each binary system have been used to predict the ternary vapor−liquid equilibrium using the same model. No ternary parameters were required. The ternary equilibrium values obtained in this way agreed well with the experimental values.