MLDpackings (MLD = monolayer dense) are very stable solide supports, known in the literature as\"mixed self-assembled monolayers(SAM) . They can be used both for basic and acidic compounds in a relatively wide range of pH and with high selectivity. The buffer concentration can be held less. With organic buffers one can successfully use these columns betweenpH2 11.

The applicationMLD1demonstrates a separation on UltraSep ES MLD RP18, which was performed already on UltraSep ES PHARM RP8E with 15 mM phosphate buffer as eluent (ApplicationPHARM3).

With UltraSep ES MLD RP18 already 5mM phosphoric acid is sufficient for delivering the same chromatogram quality (ApplicationMLD2). Furthermore it is important that for obtaining comparable short retention times of basic pharmaceuticals one can work with 50% acetonitrile (instead of 30%).

The applicationMLD3represents a chromatogram of basic pharmaceuticals at pH 11, which was obtained after flushing the column with 6000 ml eluent, pH 11, corresponding to a continuous use of approximay 4 weeks. Remarkable is the still very good peak shape especially of perazine dimalonate.

For working with basic eluents the usage of organic buffers and the addition of organic solvents is recommended.

MLD packing are, as already mentioned, suitable for the separation of organic acids too (ApplicationMLD4).

Using MLD packings it is possible to obtain chromatograms with good peak shapes of very different classes of compounds(ApplicationMLD5).

Examples ofAnalyzed Compounds

Analyzed inApplication

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Acetic acid

MLD4

Amitriptyline

MLD3

Chloramphenicol

MLD5

Clozapin

MLD1, MLD2, MLD3

Diphenhydramine

MLD3

Flecainide

MLD1, MLD2, MLD3

Formic acid

MLD4

Mexiletine

MLD1, MLD2

Perazine dimalonate

MLD3

Protriptyline

MLD1, MLD2

Sulfadimethoxine

MLD5

Sulfathiazole

MLD5

Size (mm)