Waxes Weak acids

WS, whole saliva P, parotid saliva SM/SL, submandibular/sublingiial saliva TFA trifluoroacetic acid UF, ultrafiltration, WAX, weak anion ACN, acetonitrile PTMs, posttranslational modifications. exchange chromatography ... 

Benzyloxycarbonyl, N-(3,5-dinitrobenzyloxy carbonyl), 9-fluorenylmethoxycarbonyl, benzoyl, acetyl and N-(2,4-dinitrophenyl) derivatized amino acids and profens WAX (weak anion-exchange) type CSP tert. -butylcarbamoylquinine as chiral selector on Hypersil silica gel), 3 pm Acetonitrile-methanol (80 20)+400 mM acetic acid+4 mM triethylamine 335 mm x 100 pm i.d. 250 mm effective length, chiral separation... 

The key consideration in the analysis of any sustained release dosage form as previously discussed (see Sections II.A, II.B, II.C.l, and II.C.2rg) is to determine what solvent or solvent system will be most appropriate to assure the dissolution of the drug and its excipients to make it amenable to HPLC analysis. Aqueous solubility of weak acids and bases is governed by the pfCa of the compound and the pFI of the medium. In an acidic or low pFI medium, weak acids will be unionized and will be more soluble in organic solvents. The reverse is the case for basic compounds as previously discussed in Section II.B. Because the formulation of sustained release dosage forms tend to rely on the use of insoluble plastics (i.e., methyl acrylate-methyl methacrylate, polyvinyl chloride, and polyethylene), hydrophilic polymers (i.e., methylcellulose, hydroxypropyl-methylcellulose, sodium carboxymethyl cellulose, and carbopol 934), and fatty compounds (i.e., waxes such carnauba wax and glyceryl tristearate), similar hydro-organic solvents and sample preparation steps that have been discussed for tablets and capsules can also used for their analysis by HPLC (see Sections II.A, II.B, II.C.l, and II.C.2). 

On the other hand, if the mbber contains paraffin wax, the surface treatment with sulfuric acid promotes its migration to the surface creating a weak boundary layer able to produce poor adhesion. Solvent wiping with petroleum ether after surface treatment removes this antiadherent moiety but a progressive migration from the bulk to the mbber surface with time occurs. 

Pentaerythritol Ester As with glycerol esters, the esters are produced by esterification of pentaerythritol with the desired fatty acids. For example, under defined reaction conditions and use of stearic acid in defined concentration, pentaerythritol distearate has been recently developed as an off-white wax with very weak odor (Cutina PES). This type of product is offered as co-emulsifier and consistency factor for cosmetic products with high sensorial elegance and can be applied in various formulations (Fig. 4.17). 

Lammerhofer and Lindner reported on the enantiomer separation of derivatized amino acids and profens on a weak-anion-exchange(WAX)-type stationary phase based on chiral quinine carbamate selectors by p-CEC [54,55]. The separations were performed either under aqueous or [54] non-aqueous conditions [55]. The efficiency obtained in the p-CEC mode was about two to three time higher than with LC using an acetonitrile/buffer flow system [54], Very high resolutions and efficiencies were found for non-aqueous p-CEC. For example, the enantiomer separation of Fmoc-leucine was achieved in less than 10 min with a resolution Rs of 6.9 at about 100 000... 

Someone in Orchem research management had conceived an idea for a better product. The weakness of spirit duplication systems was that the wax sheets inevitably leaked color onto the hands of the people who handled them. Secretaries hated them, as the intense colors in the wax matrix transferred to clothing, causing severe staining. Why not have a leucodye, i.e., a colorless precursor of a dye present in the wax layer, and moisten the receiver sheet with an alcoholic solution of an oxidant For a variety of reasons, the preferred oxidant was chlor-anil (tetrachlorobenzophenone), an inexpensive, colorless, and effective material (Scheme 4.6). Unfortunately, this compound also gave rise to hydrochloric acid... 

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