Capillary electrochromatography of caffeine and its metabolites in rat brain microdialysate

Abstract

A capillary electrochromatography (CEC) method has been developed for the separation of caffeine and its two metabolites 1-methylxanthine (1-MX) and 1,7-dimethylxanthine (1,7-DX). The stationary phase was 3-(1,8-naphthalimido) propyl-modified silyl silica gel (NAIP) and the best separations were achieved with 4.0 mM citrate buffer (pH 5.0) containing 80% methanol at an applied voltage of 25 kV. The compounds were completely separated in less than 3.5 min with good repeatability, which was approximately 3-times less than that in high-performance liquid chromatography (HPLC) with NAIP. The proposed method coupled with microdialysis was successfully applied to the monitoring of caffeine concentration in rat brain with detection limits of 1.11 microg/mL.

Investigation of the novel mixed‐mode stationary phase for capillary electrochromatography. II. Separation of amino acids and peptides on sulfonated naphthalimido‐modified silyl silica gel

“…6, the triply charged peptide, LysLys, could be eluted from the SNAIP stationary phase even using a moderate buffer concentration (35 mM) without deterioration of separation efficiency and EOF mobility. In our previous study [29], the bubble formation, a major problem in packed-CEC, was observed with NAIP columns at currents . 8 mA.…”

“…The interstitial EOF mobility in the CEC column, m o , is equal to the apparent EOF mobility, m o *, within the CEC column multiplied by the ratio of current in an open tube to that in a packed column [29][30][31]. For neutral analytes, k Instead of Eq.…”

“…The modification ratio of 3-aminopropyl siliyl silica gel with 4-sulfo-1,8-naphthalic anhydride was 0.523 mmol/g which was estimated from the percentage of carbon by elemental analysis. CEC columns packed with SNAIP were prepared by a slurry-packing technique as reported previously [28,29]. All columns were 37 cm long with a packed length of 9 cm.…”

Capillary electrochromatographic analysis of barbiturates in serum

“…1) was shown to be considerably useful for this purpose [18,19]. Recently, we successfully introduced NAIP as a packing material into CEC and achieved the fast separation of caffeine and its two metabolites in less than 2.5 min [20]. In this report, CEC with NAIP was employed for the separation of barbiturates.…”

“…Since the analytes are neutral within the investigated pH range, the buffer pH did not significantly affect the selectivity. Although the shortest separation time was achieved at pH 5.5, the bubble formation was experienced at higher pH (pH ,6.0) in the previous study [20]; citrate buffer (pH 5.0) was chosen as the optimal buffer. …”