Selection of packing

A change in the selection of packing materials combined with a change in storage conditions or conditions during administration of the drug products may provoke stability problems. 

The selection of packing materials for SPE (Ch. 1.5.3) is especially important in multi-residue analysis. In general, nonspecific trapping on hydrophobic surfaces like Cig-bonded silica or styrene-divinylbenzene copolymers, e.g., PLRP-S, is preferred. 

A simple test mixture consisting of a to-marker and different phthalic acid esters can be used to check the performance and some basic selectivities of packed columns. 

Tables 10-12 show Kji and K22 values for HETP (in in. and mm) and surface tension (in dyn/cm) for a selection of packings.

The purification of a compound fi om a cmde extract is greatly facilitated if the identity of die compound is known. Its chemical properties can then be used to guide in the selection of appropriate isolation procedures, mcluding the selection of packing materials. In natural products isolation, the identity of the biologically active compound is rarely known, and methods of purification must be determined based on the chemical or chromatographic behavior of the biological activity of interest. 

Minimum pressure drop to flow of gases by selection of packings which can have high gas-liquid contact area as well as more void space per cubic metre of filled in volume. 

The maximum efficiency achievable through a careful selection of packed materials and electrolyte has been reported by Min et al. [2] to be at most 15 %. In contrast, Griffiths and Nilson [6] reported that the likely maximum efficiency for any electroosmotic pump would be about 10 % for operation at the condition of maximum work. 

The following characteristics for the selection of packing should be considered ... 

Resolution can be improved by increasing the column plate number, N, and/or the separation factor (selectivity of packing materials), a [a = the ratio of the capacity ratios (retention factors) of the two compounds]. N is the physical parameter and a is the chemical parameter for the separation. 

---