Search results for "Column chromatography"

Determination of pyrethroid pesticide residues in fatty materials by solid-matrix dispersion partition, followed by mini-column size-exclusion chroma…

1999

The method studied uses a combination of a solid-matrix dispersion partition (SMDP) followed by high-performance size-exclusion chromatography on a minicolumn (HPmSEC) of 7.8 mm I.D. for the separation of pyrethroid (PYR) residues from fatty material. The solid-matrix dispersion extraction is carried out by absorbing a fat solution onto an Extrelut-3 cartridge (filled with a macroporous diatomaceous material) and extracting the PYR residues with acetonitrile. Up to 1 g of fatty material can be extracted with 15 ml acetonitrile. The small amount (mean +/- S.D. = 12.4 +/- 5.9 mg) of fatty material which is eluted into the acetonitrile is further removed by HPmSEC. PYR pesticide residues are c…

Implementation of gradients of organic solvent in micellar liquid chromatography using DryLab®: Separation of basic compounds in urine samples

2014

In micellar liquid chromatography (MLC), chromatographic peaks are more evenly distributed compared to conventional reversed-phase liquid chromatography (RPLC). This is the reason that most procedures are implemented using isocratic elution. However, gradient elution may be still useful in MLC to analyse mixtures of compounds within a wide range of polarities, decreasing the analysis time. Also, it benefits the determination of moderately to low polar compounds in physiological fluids performing direct injection: an initial micellar eluent with a low organic solvent content, or a pure micellar (without surfactant) solution, will provide better protection of the column against the proteins i…

C-28/C-30 oxidized cycloartanes from the leaves and twigs of Caloncoba dusenii Gilg

2021

Abstract Four hitherto unreported cycloartane-type triterpenes (1-4) with C-28/C-30 oxidized methyl groups together with two known compounds (5-6) have been obtained from the leaves and twigs of Caloncoba dusenii Gilg. The compounds were isolated through extraction and silica gel column chromatography. Their structures and relative stereochemistry were determined by extensive use of spectroscopic techniques including IR, 1D and 2D-NMR as well as mass spectrometry. This is the first report of C-28/C-30 oxidized positions in cycloartanes from nature.

Processing of Generator-Produced 68Ga for Medical Application

2007

The (68)Ge/(68)Ga generator provides an excellent source of positron-emitting (68)Ga. However, newly available "ionic" (68)Ge/(68)Ga radionuclide generators are not necessarily optimized for the synthesis of (68)Ga-labeled radiopharmaceuticals. The eluates have rather large volumes, a high concentration of H(+) (pH of 1), a breakthrough of (68)Ge, increasing with time or frequency of use, and impurities such as stable Zn(II) generated by the decay of (68)Ga, Ti(IV) as a constituent of the column material, and Fe(III) as a general impurity.We have developed an efficient route for the processing of generator-derived (68)Ga eluates, including the labeling and purification of biomolecules. Prec…

Determination of critical eluent composition for polyethylenglycols using on-line liquid chromatography-Fourier transform infrared spectrometry.

2008

In this work, it has been extended to methanol:water mobile phases, the use of a background correction method for on-line LC-FTIR measurements named Univariate background correction based on the use of a reference spectra matrix (UBC-RSM) and absorbance ratios. It permits to overcome the problem related to spectral changes occurring during the gradient elution, which in the past limited the on-line coupling of LC and FTIR to isocratic elutions. The combined use of the aforementioned background correction technique in on-line isocratic and gradient LC-FTIR, and partial least squares (PLS) has been applied for the search of the critical conditions for polymers. Polyethylenglycol (PEG) has bee…

Synthesis and properties of chemically modified dihydroxy-, hydroxyamino- and amino-functional silica packings in adsorption chromatography

1980

1,2-Dihydroxy-3-propoxypropyl (HPP), 1-amino-2-hydroxy-3-propoxypropyl (AHP) and 3-(2-aminoethylamino)propyl (AEAP) silica packings were synthesized by means of both a surface modification and a bulk modification procedure. In surface modification a complete monolayer of bonded groups could be achieved. The modifiers reacted with the silanol groups according to a bifunctional mechanism. Eluotropic series of solvents were established on these polar modified silicas referring to n-heptane having ɛ∘=0. The solvent parameter ratio of modified to bare silica was found to be constant over a wide range of solvent compositions as \(\varepsilon _{{\text{HPP - silica}}}^ \circ = 0.26\varepsilon _{{\t…

Determination of alinidine in human plasma by high-performance liquid chromatography.

1981

Non-porous microparticulate supports in high-performance liquid chromatography (HPLC) of biopolymers — concepts, realization and prospects

1986

On the measurement of consistent long-term retention factor values in micellar liquid chromatography

2007

Abstract In the field of the quantitative structure–retention and retention–activity relationships (QRAR and QSRR) is crucial to obtain consistent retention factors (k). For this purpose, two unbiased approaches to estimate k are used: (i) the IUPAC approach (based on the extra-column time correction) and (ii) the ‘2-references’ approach (based on the k estimation respect to two prefixed reference k values). Three reference chemicals were selected attending to their retention time, chemical stability and non-ionic character. Consistent retention factor values for these references were estimated for C18 chromatographic columns and Brij35 solutions as mobile phases after statistical analysis.…

Gel permeation Chromatography in coiled columns

1973

Whereas in gas chromatography the use of coiled columns is the usual procedure, in liquid chromatography the use of straight columns is favoured. Bent columns give an additional contribution to peak spreading which is of greater importance in liquid chromatography than in gas chromatography owing to smaller diffusion coefficients. The low linear velocities of the mobile phase used in gel permeation chromatography enable conditions to be found where the additional contribution of bending to peak spreading is small. In the separation of oligomers, columns of 2-mm tube diameter and 20-cm coil diameter were used. With total lengths of 10 and 20 m, theoretical plate counts of ca. 70,000 and 150,…