[Show abstract][Hide abstract] ABSTRACT: Reanalysis of incurred samples showed that the bioanalytical method for the quantification of ramipril and ramiprilat was generating irreproducible results for ramiprilat.
An additional peak interfering with ramiprilat was observed in the incurred samples but not in the calibrant and quality control samples. A similar interference was detected for ramipril, but it was chromatographically separated. Interferences were produced during sample preparation, which involves strong cation exchanger cartridges. The interfering products corresponded to the methylation of ramipril and ramiprilat glucuronide.
Following this discovery, a reproducible method was developed and successfully validated for ramipril and ramiprilat. Additional stability tests were performed in the presence of glucuronide and diketopiperazine metabolites of ramipril and ramiprilat to demonstrate the method specificity.
[Show abstract][Hide abstract] ABSTRACT: The objective is to find elution conditions using different solid-phase extraction chemistries to reduce the amount of phospholipids in plasma extract, which is associated with matrix effect in LC-MS.
Phospholipids' recovery was reduced by decreasing the eluents' methanol content applied to silica-based and polymer-based reversed-phase solid-phase extraction cartridges while 100% acetonitrile applied to the silica-based cartridges drastically minimized the phospholipids' elution. Silanol interactions are involved in the increased retention of phospholipids with silica-based reversed-phase cartridges when using high percentages of ACN in eluents. The bioanalytical usefulness of these findings was confirmed by successful extraction recovery of pharmaceutical compounds.
Combinations of specific eluents and reversed-phase solid-phase extraction cartridges were found to prevent matrix effect due to phospholipids.
[Show abstract][Hide abstract] ABSTRACT: In this study, the postcolumn addition approach was used to evaluate the impact of high pH modifiers on the sensitivity of 25 compounds by LC-MS/MS under positive ESI (ESI+).
None of the compounds were significantly suppressed by the use of high pH modifiers. Most of them showed a signal enhancement by at least twofold compared with acidic modifiers. The sensitivity gained under high pH mobile phase was used to develop a bioassay for the quantification of candesartan. The use of high pH mobile phase allowed for fast sample preparation that would have been impossible under typical low pH chromatography.
We have shown that high pH modifiers are sufficient to induce a signal enhancement for the majority of compounds detected under LC-ESI+-MS/MS.