CE coupled with amperometric detection using a boron‐doped diamond microelectrode: Validation of a method for endogenous norepinephrine analysis in tissue

Abstract

The level of endogenous norepinephrine (NE) in several tissue types was determined by CE with amperometric detection. We report herein on the method validation by HPLC using both amperometric and coulometric detection (CD). Keys to the method were the use of a diamond microelectrode for detection and off-line SPE for sample preparation. The run buffer was a 250 mM borate solution adjusted to pH 8.8 with potassium hydroxide. The diamond microelectrode exhibited a low and stable background current, and a low peak-to-peak noise < or =0.65 pA at the detection potential of +0.86 V versus Ag/AgCl. For standard solutions, the detector signal (i.e., oxidation current) changed linearly with the NE concentration (r(2) = 0.999) between 60 and 1000 nmol/L with an estimated LOD of 51 nmol/L (S/N = 3) and a response variability of 4.5% (RSD, n = 5). An Oasis MCX sorbent was used for SPE and the procedure produced an NE recovery of 95.1 +/- 5.6% (n = 6) from tissue homogenates. NE levels in the spleen, small intestine, and heart of a normotensive rat were found to be in the range of 0.77-0.97, 0.22-0.32, and 0.29-0.45 microg/g tissue (n = 3), respectively.

Capillary and microchip electrophoresis in microdialysis: Recent applications

“…Norepinephrine levels in the spleen, small intestine, and heart of a normotensive rat were determined; a typical electropherogram is shown in Fig. 6 34. The data correlated well with that obtained from an HPLC method also for norepinephrine determination.…”

“…Run buffer, 250 mM boric acid/KOH, pH 8.8. Separation voltage, 24 kV, electrokinetic: 18 kV for 8 s. Detection potential, 0.86 V versus Ag/AgCl (Quaiserova‐Mocko et al with permission 34).…”

Boron Doped Diamond Electrodes in Flow-Based Systems

“…In addition, the basic electrochemical properties of these diamond microelectrodes (low background and noise currents, reproducible responsiveness, wide linear dynamic range and low limits of detection) demonstrated the usefulness of this new electrode material for electrochemical detection in CE. Afterwards, the performance of these diamond microelectrodes was shown in the detection of dopamine and catechol; (ii) chlorinated phenols in natural waters (Muna et al, 2005), endogenous norepinephrine in sympathetic nervous system of rats (Park et al, 2006), and endogenous norepinephrine from spleen, small intestine, and heart of normotensive rats (Quaiserová-Mocko et al, 2008). Some figures of merit for the aforementioned works can be found in Table 3 (BDD electrodes and HPLC systems).…”

Recent developments in instrumentation for capillary electrophoresis and microchip‐capillary electrophoresis

“…Despite these advantages, two main challenges still affect the widespread use of ECD: 1) a limited number of commercial ECDs are available [100] and 2) (probably most importantly) there is the need to eliminate the effect of the strong electric field used in electrophoretic separation from the conditions of electrochemical detections [101]. With respect to the first point, commercial instruments from Metrohm (Switzerland), ECO Chemie (Netherlands) [102], CH Instruments (Austin, TX) [103–106], Bioanalytical Systems (West Lafayette, IN) [107], Palm Instruments BV (Netherlands) [108], Pinnacle Tech. (Lawrence, KS) [109], or ESA Biosciences (Chelmsford, MA) have been used in conjunction with CE.…”