Microdialysis, liquid chromatography

Wong, P. S. H. Yoshioka, K. Xie, F. Kissinger, P. T. 1999. In vivo microdialysis/liquid chromatography/tandem mass spectrometry for the on-line monitoring of melatonin in rat. Rapid Commun. Mass Spectrom., 13,1-5. 

PE Andren, RM Caprioli. In vivo metabolism of substance P in rat striatum utilizing microdialysis/liquid chromatography/micro-electrospray mass spectrometry. J Mass Spectrom 30 817—824, 1995. 

Shimoyama, M., Tatsuoka, H., Ohtori, S., Tanaka, K. and Shimoyama, N., Change of dorsal horn neurochemistry in a mouse model of neuropathic cancer pain. Pain, 114, 221-230 (2005). Andr6n, P.E. and Caprioli, R.M., In vivo metabolism of substance-P in rat striatum utilizing in vivo microdialysis liquid chromatography— micro-electrospray mass spectrometry. J. Mass Spectrom., 30, 814-824 (1995). 

Flentge, F, Venema, K, Koch, T and Korf, J (1997) An enz5mie-reactor for electrochemical monitoring of choline and acetylcholine. Applications in high-performance liquid chromatography, brain tissue, microdialysis and cerebral fluid. Annal. Biochem. 204 305-311. 

Chen, A. and Lunte, C. E., Microdialysis sampling coupled on-line to fast microbore liquid chromatography, /. Chromatogr. A, 691, 29, 1995. 

Liu, C. L. and Verma, S. S., Direct coupling of ionic high performance liquid chromatography with electrospray ionization mass spectrometry utilizing a microdialysis junction interface, ]. Chromatogr. A, 835, 93, 1999. 

Mei, D.A., Gross, G.J., and Nithipatikom, K., Simultaneous determination of adenosine, inosine, hypoxanthine, xanthine and uric acid in microdialysis samples using microbore column liquid chromatography with diode array detection, Analyt. Biochem., 238,34,1996. 

Kato T, Liu JK, Yamamoto K, Osborne PG, Niwa O. 1996. Detection of basal acetylcholine release in the microdialysis of rat frontal cortex by high- performance liquid chromatography using a horseradish peroxidase-osmium redox polymer electrode with pre-enzyme reactor. J Chromatogr B 682 162-166. 

Piepponen TP, Skujins A. 2001. Rapid and sensitive step gradient assays of glutamate, glycine, taurine and y-amino-butyric acid by high-performance liquid chromatography-fluorescence detection with o-phthalaldehyde-mercap-toethanol derivatization with emphasis on microdialysis samples. J Chromatogr B 757 277-283. 

Fuh MR, Tai YL, Pan WH. 2001. Determination of freeform of cocaine in rat brain by liquid chromatography-electrospray mass spectrometry with in vivo microdialysis. J Chromatogr B Biomed Sci Appl 752 107. 

Microdialysis is a sampling technique that must be coupled with an analytical method to identify and quantify chemical components of the dialysate. The samples can be analyzed immediately upon collection (i.e., online), or they can be stored (—80°C) for future analysis. Only analytical techniques sensitive enough to measure both small sample volumes and low concentrations of substances can be used to measure compounds in dialysate samples. High-performance liquid chromatography (HPLC) or capillary electrophoresis (CE) combined with ultraviolet (UV), electrochemical (EC), or laser-induced fluorescence (LIF)... 

Dialysis is the process in which small molecules diffuse across a semipermeable membrane that has pore sizes large enough to pass small molecules but not large ones. A microdialysis probe has a semipermeable membrane attached to the shaft of a hypodermic needle, which can be inserted into an animal. Fluid is pumped through the probe from the inlet to the outlet. Small molecules from the animal diffuse into the probe and are rapidly transported to the outlet. Fluid exiting the probe (dialysate) can be analyzed by liquid chromatography. 

The chromatogram and bar graph show results of a study of aspirin metabolism in a rat. Aspirin is converted into salicylic acid by enzymes in the bloodstream. To measure the conversion rate, aspirin was injected into a rat and dialysate from a microdialysis probe in a vein of the rat was monitored by liquid chromatography. If you simply withdrew blood for analysis, aspirin would continue to be metabolized by enzymes in the blood. Microdialysis separates the small aspirin molecule from large enzyme molecules. 

Cohen, E., R.J. Maxwell, and D.J. Donoghue. 1999. Automated multi-residue isolation of fluoroquinolone antimicrobials from fortified and incurred chicken liver using on-line microdialysis and high-performance liquid chromatography with programmable fluorescence detection. J. Chromatogr. B 724 137-145. 

Oertel R, Richter K, Ebert U, Kirch W (2001) Determination of scopolamine in human serum and microdialysis samples by liquid chromatography-tandem mass spectrometry. J ChromatogrB 750 121-128... 

Microdialysis has also been used as a sampling method for measuring the concentration of drugs in human subcutaneous tissues for pharmacokinetic studies [50]. The microdialysates are simpler than other biological fluids and do not contain proteins, permitting their direct injection for analysis by liquid chromatography. 

Microdialysis is, however, only a sampling technique. This means it provides an investigator with samples that must be chemically analyzed. In fact, the applicability of microdialysis to the study of a particular compound occurring in the extracellular fluid is entirely dependent on the sensitivity of the respective analytical technique. In this context, high performance liquid chromatography (HPLC) plays a key role in terms of sensitivity, reliability, and speed of... 

St Claire RL, Brouwer K (1992) Chemical analysis of bis (5-amidino-2-benzimidazolyl)-methane using microdialysis and microcolumn liquid chromatography. Presented at Second International Symposium on Microcolumn Separation Methods. 

Keski-Rahkonen, R et al. Quantitative determination of acetylcholine in microdialysis samples using liquid chromatography/atmospheric pressure spray ionization mass spectrometry. Rapid Commun. Mass Spectrom. 2007, 21, 2933-2943. 

Microdialysis coupled to high-performance liquid chromatography... 

The remainder of the chapter discusses microdialysis coupled to mass spectrometric detection to both on-line and off-line methods, with an emphasis on analysis of drugs. Applications of microdialysis/mass spectrometry to gas chro-matography (GC), liquid chromatography (LC), and flow injection into the mass spectrometer are discussed. In particular, approaches to overcome problems with introduction of high-ionic-strength dialysate into the mass spectrometer are described. 

Caprioli and Lin first described this method for the characterization of penicillin G in 1990 [19]. A diagram of the microdialysis/cfFAB experimental setup used is shown in Fig. 8. Dialysate was allowed to collect in a 20- dL sampling loop via syringe pump. After collection, the injection valve was switched and a high-performance liquid chromatography pump was used to deliver the microdialysis sample to the mass spectrometer. Mass spectra of penicillin from both a standard and an in vivo microdialysis sample (shown in Fig. 9) compare well. 

Microdialysis coupled to mass spectrometry is a powerful technique for on-and off-line analysis, providing information on pharmacokinetics, drug transport, and metabolite formation. With the widespread availability of LC/ESI/MS instruments there has been a shift toward liquid chromatography and away from gas chromatography and flow injection. Electrospray is the ionization method of choice for most applications and tandem mass spectrometry has grown in popularity. Thermospray and cfFAB applications have been used with microdialysis, but are older, obsolete techniques. 

JA Masucci, ME Ortegon, WJ Jones, RP Shank, GW Caldwell. In vivo microdialysis and liquid chromatography/thermospray mass spectrometry of the novel anticonvul-sant 2,3 4,5-bis-0-(l-methylethylidene)-beta-D-ffuctopyra-nose sulfamate (topira-mate) in rat brain fluid. J Mass Spectrom 33 85—88, 1998. 

P Michelsen, G Pettersson. An automated liquid chromatography/mass spectrometry system coupled on-line with microdialysis for the in vivo analysis of contrast agents. Rapid Commun Mass Spectrom 8 517—520, 1994. 

Steele, K.M. Lunte, C.E. Microdialysis sampling coupled to on-line microbore liquid chromatography for pharmacokinetic studies. J.Pharm.Biomed.Anal., 1995, 13, 149—154... 

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