Suppression effects of carbonate on the interaction between stainless steel and phosphate groups of phosphate compounds in high-performance liquid chromatography and electrospray ionization mass spectrometry.

We examined the suppression methodology of the interaction between phosphate compounds, such as nucleotides, and the stainless steel surfaces of high-performance liquid chromatography and electrospray ionization mass spectrometry (HPLC/ESI-MS) equipment in an effort to prevent the tailing of peaks seen in HPLC chromatograms of phosphate compounds. Addition of carbonate (CO(3)(2-)) to mobile phase was highly effective in suppressing the interaction of phosphate compounds derived from a complexation between phosphate groups and metal ions that exist on a stainless steel surface in a mechanism similar to Fe(III)- and Cr(III)-immobilized metal affinity chromatography (IMAC). Addition of ammonium hydrogen carbonate to mobile phase achieved a simple and reliable HPLC/ESI-MS analysis of mono-, di-, and triphosphate compounds (six nucleotides) without peak tailing due to the interaction between stainless steel surfaces and phosphate groups.

Reduction of carry-over in column-switching HPLC/MS system with automated system washing procedure for highly sensitive direct analysis of donepezil in dog plasma.

To solve the problem of carry-over--a persistent chromatographic challenge for bioanalytical assays with highly sensitive detector such as a mass spectrometry (MS)--a new on-line sample pretreatment HPLC/MS system using a column-switching technique was established. This system was designed to reduce carry-over based on a hydrophobic interaction mechanism using a washing function (multi-mobile phase flow system), as well as to remove impurities on-line in a mobile phase for the pretreatment. As a result, a washing function in this system was enabled to reduce carry-over and to remove impurities in a mobile phase by automatic operation.