The direct analysis of drugs in serum without extensive sample preparation.

Developed by Dr. Thomas Pinkerton, the result was a new phase that allows for chromatographic separations without interference by protein adsorption.

A second generation phase with an improved bonding process—bonding the GFF peptide to the silica surface through a monofunctional glycidoxypropyl linkage rather than the original trifunctional linkage.

ISPR : Internal Surface Reversed Phase.

This resulted in the following improvements:

• Increased sample retention

• Higher column efficiency

• Greater batch-to-batch reproducibility.

ISRP Selectivity

Many variables can affect the selectivity of the ISRP phase, including:

Mobile Phase Composition: The nature of ISRP analytes requires that mobile phases consist of a buffer with varying degrees of modification. Modifiers can include acetonitrile, methanol, isopropanol and tetrahydrofuran. Caution: too much modifier can result in matrix precipitation.

pH: The pH of the mobile phase can be controlled to avoid protein denaturing and to enhance selectivity. The pH range of the column is between 2.5 and 7.5; however, within the optimal pH range of 6.0 to 7.5, both the proteins and the glycine outer surface take on a negative charge. As a result, negatively charged proteins are repulsed by the outer phase and pass quickly through the column.

Temperature: Separations can also be optimized by varying column temperature. Lower temperatures have been shown to result in increased retention and selectivity.