Weakly absorbing chromophores

The enhancement of retention of very polar basic species is also very important for pharmaceutical applications. For example, Voglibose (VGB) is very hydrophilic therefore in RPLC even under high aqueous conditions using a mobile phase with 0.1 v/v% of phosphoric acid, it will elute before the void volume. Moreover, VGB has a weak UV chromophore and a very low absorbance at 190 nm. The dose strength for a particular formulation is very low at 0.2 mg, which presents a problem for dissolution in 900-mL vessels, which necessitates the need to either (a) derivatize VGB to produce a suitable... 

Weakly absorbing chomophores (i.e., simple ketones, sulphides etc., or n -> CT or n Jt transitions) are indicated by weak bands in the absence of strong chromophores. 

Indirect methods can also use mass spectrometers as detectors. As noted above fragmentation is a potentially severe problem that must be taken into consideration. Both continuous and pulsed beam techniques can be used. A particularly novel approach has been developed using multiphoton ionization via a favorable UV-absorbing chromophore. Neutral clusters are formed containing the readily ionizable molecule, but the weak interactions between the chromophore and the rest of cluster reduces the extent... 

Chromophores absorbing in the region between 1900 and 2600 cm-4 The absorptions listed in Table 3.3 often yield useful information because, even though some are of only weak or medium intensity, they occur in regions largely devoid of absorption by other commonly occurring chromophores. 

Lubricants are used in tablet preparation and include magnesium stearate, stearic acid and polyethylene glycol. They only comprise at most 1-2% of the tablet bulk so that their potential to interfere is slight, particularly since their chromophores are weak. The fatty acid lubricants can often be observed if analysis of a tablet extract is carried out by GC-FID. Tablet coatings are often based on modified sugar polymers such as hydroxypropylmethylcellulose. These coatings are used at about 3% of the tablet bulk, are water soluble and do not absorb UV light. 

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