Our laboratory staff are always concerned to meet the different requirements of our customers. They are searching and developing new technologies on a daily basis.

The Uptisphere ODB and HDO, our first C18 chemistries, were created by our chemists in the mid-nineties, are meeting an ever-growing success.

A large number of analysis methods of pharmaceuticals compounds requiring the most sensitive techniques such as LC/MS, MS/MS... have been validated with one of these
2 phases.

Monofunctional bonding processes, combined with our proprietary end-capping techniques, guarantee perfect reproducibility for these C18 phases.

C18-ODB Uptisphere

Representing the C18 benchmark. Its characteristics meet the majority of analysts daily requirements. The excellent mechanical resistance of our silica-Upti-prep base combined with the perfect ODB chemistry means our silica can be used under basic pH conditions (-8), the lifetime of the column being unchanged.

The kinetic dissolution of the silica is lowered when the traditional phosphate buffers are replaced by organic buffers (tris, 1-methyl piridine, pyrrolidone..). This allows you to work under Ph 10-11 with a good lifetime (a silica-saturator upstream the injector, favours the protection of the silica of the analytic column.

We particularly recommend our C18-ODB Uptisphere for the separation of moderately polar and non-polar compounds.

The last recovering steps in its manufacturing process give it a very special selectivity. This is not a "polar linked alkyl phase " type (PLAP) and it does not have any hydrophylic end-capping.

The propietary technology developed by our chemists leads to a unique bonded-silica structure. It enables you to perform perfect separation of moderately polar and non-polar compounds, Uptisphere C18 HDO also allows you to use 100 % acqueous mobile phase.

We have very close links with the" Laboratoires des Techniques et Instruments d’Analyses Moléculaires" (LETIAM), which is part of the analytical chemistry group in Paris-Sud within the Orsay Technology and Academic Institute; this has fundamentally influenced our thoughts about developing new C18 phases.

This laboratory has made an excellent reputation in the characterization of silica in HPLC chromatography for years.

A simple and quick test has been developed in subcritic chromatography from the analysis of carotenoid pigments.

It enables the comparison of the 3 major criteria of stationnary phases :

Our C18-NEC, C18-HSC and C18-TF uptisphere phases have been synthesized to match the different areas of interests shown on the test chart.

C18-NEC Uptisphere : similar to the ODB but not end-capped, NEC keeps moderately polar and non-polar compounds away from the solvent front.

C18-HSC Uptisphere : thanks to a strong end capping process, HSC has a very good selectivity for non-polar compounds

This phase is very stable up to pH : 10

This test has been carried out in the LETIAM (Orsay techn & acad.institute), in the laboratory of the analytic chemistry group, PARIS-SUD.EA3343.

It was performed in subcritical chromatography, a fast and performing technique, offering an undeniable potential for the elaboration of this test. Great eluent strength of the modified subcritical fluid (mixture of carbon dioxide and methanol), low fluid viscosity leading both to a reduced molecular kinetic dispersion (thin peaks) and to the use of high mobile phase flows (fast analysis).

These results have been correlated with the ones obtained with hydro organic mobile phases. They provide complementary information. This test shows that we can get more than 10 classes of stationnary phases with inverted polarities phases from a carotenoid pigments analysis; their properties are sometimes very different.

• StudyS conditions

  Injection of 15 microliters of a beta-carotene diluted mixture partially isomerated and containing all-trans forms, 9-cis, 13-cis (major cis),15-cis and zeaxanthine (beta-carotene di-hydroxylated).

  The mobile phase is a carbon dioxide/methanol mixture (85/15, v/v) temperature : 25 °C, back pressure : 15 Mpa, flow rate : 3ml/min, U.V. : 440nm.

• Présentation of the results

  (see classificiation graph) : 2 selectivities are calculated and shown on the classification graph :

  One of them is shown on the X axis, between 13-cis isomer (bend shape) and the all-trans form (linear shape) of the beta-carotene.

The separation of cis/trans isomers of beta-carotene is based on form recognition, i.e. on the ability of the stationnary phase to distinguish a linear molecule and a bend molecule in space; these will not interact in the same way with the stationnary phase because of the tridimentional geometry.

Conclusions drawn from the comparison of the results with other tests (especially with NIST 869 test) with stationnary phases of identified structures show that for a cis/trans selectivity between :

• 1 and 1.1: the phase is monomeric (mono layer bonded onto the base silica) with a low bounding density

• 1.1 and 1.2 : the phase is monomeric with a high bonding density or more rarely with partial polymeric character (polymolecular layers bounded onto the base silica)

• More than 1.2 : the phase is polymeric with large pores ; polymeric phases generally show a special ability to separate polyaromatic hydrocarbons and rigid isomers from different stereochemistry.

Monomeric phases can be obtained by reaction of the base silica with mono silanes ; di or trifunctional in the absence of water ; polymeric phases can be obtained by reaction with trifunctional silanes in the presence of water traces.

• The other selectivity, on the Y-axis of the graph is calculated between the all-trans beta-carotene and the zeaxanthine ; the structure of the zeaxanthine is that of the beta-carotene with a hydroxyl group on each final cycle.

Other polar interactions can therefore be observed : silanophilic interactions which are developed between the zeaxanthine hydroxyl and the residual silanols of the stationnary phase, or, with other polar sites from the stationnary phase (i.e. siloxane for the polyfunctional phases, amide, urea, ether-oxide, quaternary ammonium or carbamate for inserted polar grouped phases called "shielded phases").

The higher this selectivity value is, the lower the interactions are ; the stationnary phase,therefore, carries fewer polar groups capable of interacting with the zeaxanthine, which has a low retention.

This selectivity varies from 0.3 for phases with an inserted polar group, to almost 20 for the most protected phases.

From 0.3 to 1 : the access to polar sites is high, from 1 to 5 it is average and from 5 to 10 it is low, above this it is very low.

The hydrophobicity values cannot be shown on the same graph, they are given separately in the form of a histogramme.

• The Y-axis shows the selectivity between the 13 cis isomer (bended shape) and the all-trans form (linear shape) of the beta-carotene.

• The X-axis shows the K log hydrophobicity, all-trans beta-carotene.