Talking value and performance in Micro and Capillary LC nostic methods, it must provide substantially higher quality information than conventional histology relying on mature sample staining techniques. The advantages of Raman imaging, which include noninvasiveness and a combination of morphological and molecular compositional information, suggest that Raman has the potential to contribute to breast cancer diagnosis.
Electrochemical detection for CE Detection methods for CE have excellent mass-based detection limits, but the concentration-sensitive detection limits have been poor because of the short pathlength. Electrochemical detection provides a possible answer to the concentration detection limits, but interfacing a CE system with an electrochemical detector has been difficult. Craig Lunte of the University of Kansas described both amperometric and voltammetric detection with a CE-electrochemistry interface that isolates the electrochemical and CE systems and decouples the two currents. He fractured the column and covered the break with Nation to prevent diffusion of the analyte away from the detector. With a simple break, the detector noise increased dramatically as the electrophoretic current increased; with the Nation coating, however, the noise did not much. Neither of these methods however was as effective as attaching a Nation channel to the end of the separation column and then using an independent detection capillary With amperometric detection the endcolumn decoupler prevented the loss of the analyte and decreased detector noise relative to the simple break Voltammetric detection has two major hurdles: the significant iR drop caused by the small column and the charging current. In voltammetry, the endcolumn decoupler eliminated the iR drop. The effect of the background charging current was diminished by using a second working electrode. Using the endcolumn decoupling method for amperometric detection, Lunte was able to use different pH levels—pH 6.1 and pH 2.5, respectively—for separation and detection. With a 2-mm decoupling joint, the detection limits were ~ 0.5 nM. Catecholamines were increasingly lost via ion exchange with longer Nation joints, but catechol detection was unaffected by the length of Nation.
Raman spectroscopy and isotachophoresis Raman spectroscopy might not be an intuitively obvious choice as a CE detection method, because without surface or resonance enhancement, detection of the concentrations found in CE is difficult. However, Michael D. Morris of the University of Michigan has been able to apply Raman to detection in a specialized type of CE called isotachophoresis (TTP), in which the analytes are sandwiched between a "leading" electrolyte with the fastest mobility and a "trailing" electrolyte with the slowest mobility. All species move at the same velocity and adopt the same concentration as the leading electrolyte so ITP be used to separate dilute solutions Morris interfaced ITP with a Raman microprobe in a system that consisted of a high-throughput single-stage spectrometer a low-noise CCD detector and an argon-ion laser operating at 532nm He illustrated the use of the technique for separation and detection of the ribonucleotides adenosine tri- di- and monophosphate and borate Comdexes of nucleo sides which can he preroncentrated as much as a thousandfold T h e use of Ra
man spectroscopy allows both detection and identification.
Sensing O2 in blood Ravi K. Meruva and Mark E. Meyerhoff of the University of Michigan described a potentiometric sensor for the measurement of PQ in flowing blood. The sensor is constructed of gas permeable silicone rubber tubing, which contains the buffer solution (25.0 mM potassium hydrogen phthalate and 1.0 mM KC1); a coball wire working electrode; and a Ag/AgCl reference electrode. The sensor measures a steady-state mixed potential that arises from the simultaneous oxidation of cobalt and reduction of oxygen at the surface of the working electrode. This corrosion potential changes as a function of P 0 . The silicone tubing protects the cobalt electrode from anionic interference in the sample solution that could enhance the corrosion rate. The oxygen sensor shows no response to C0 2 because the internal buffer solution prevents pH changes at the co~ balt electrode's surface, even at high C0 2 levels. Meruva and Meyerhoff used the cobalt wire oxygen sensor for the continuous monitoring of P during in vitro blood loop experiments
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Reproducibility (n = 8) Peak 1: 0.10% RSO, Peak 2: 0.05% RSD, Peak 3: 0.07% RSD
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