C18 Separation Research Articles

Reverse-phase separation of FD and C dyes using a solvent gradient

An impressive separation of FD ;dyes in aqueous solution can be demonstrated with a C18 Sep Pak and a 10-mL disposable syringe.

Molecular heterogeneity of canine cholecystokinin in portal and peripheral plasma

The release of molecular forms of cholecystokinin (CCK) into the portal and peripheral blood in response to an intraduodenal perfusion of sodium oleate (9 mmol · h −1) was studied in six conscious dogs with chronic portal vein catheters. Immunoreactive CCK as concentrated from 20 ml plasma by C18 SEP PAK cartridges and the pattern of molecular forms of CCK were studied by G50 gel filtration. CCK-like immunoreactivity (CCK-LI) was measured in the column eluates with antibody 5135, which measures gastrin and CCK equally and requires the intact carboxyl-terminus for full recognition. Gastrin was measured specifically with antibody 1611. Intraduodenal perfusion with oleate did not alter basal gastrin release. Release of CCK-LI by intraduodenal oleate was calculated by the increments of the integrated CCK-LI peaks over basal. Total CCK-like immunoreactivity (CCK-LI), calculated by integration of all CCK-LI peaks in gel filtration eluates, increased over basal by 12 fmol/ml in the portal and by 6 fmol/ml in the peripheral plasma after intraduodenal perfusion with sodium oleate. The main molecular forms eluted on gel filtration in positions of CCK33,39 and of CCK8. The pattern of CCK in the peripheral plasma was similar to that in the portal plasma except that in the peripheral plasma large molecular forms were more abundant than small forms. This finding was confirmed when CCK39 and CCK8 were infused either into the portal vein or into the peripheral vein and peripheral plasma CCK levels were measured. Elimination of CCK8 after portal vein infusion compared to peripheral vein infusion was about 3 times higher than that of CCK39. The abundance of large molecular forms of CCK in the circulating blood which are similar in potency to small forms, underlines their role in the physiology of CCK.

Differential Pulse Polarographic Determination of N-Nitrosodiethanolamine in Cosmetic Products

Abstract A differential pulse polarographic (DPP) method is described for the detection and determination of JV-nitrosodiethanolamine (NDELA) in cosmetic products. The cosmetic sample is partitioned between IN HC1 and chloroform. The aqueous extract is isolated and further purified by passing it through a cartridge containing reverse phase high pressure liquid chromatographic (HPLC) packing (C18 Sep- Pak). Samples containing proteins are cleaned up by gel permeation chromatography. Direct polarographic interferences are removed by preparative HPLC. The prepared samples are then analyzed by polarography using the method of standard additions for quantitation. The DPP method can be used to determine NDELA in cosmetic products at levels as low as 100 ppb. Analyses of a commercial lotion and a commercial cream spiked at 3 levels in the ppm range gave recoveries ranging from 73 to 91%. The average of all recoveries was 80%.

Rapid High-Performance Liquid Chromatographic Determination of Physostigmine in Plasma

Abstract A new method is described for the quantitative determination of physostigmine in human plasma. The drug is isolated from human plasma utilizing a C18 SEP PAK Cartridge, and quantified by liquid chromatography with ultraviolet detection. The average recovery is 54.3 ± 4.3% (S.D.) with a day to day coefficient of variation of 4%.