Pharmaceutical analysis electrochemical detection for

A.-L. Liu, F.-Y. He, Y.-L. Hu and X.-H. Xia, Plastified poly(ethylene ter-ephthalate) (PET)-toner microfluidic chip by direct-printing integrated with electrochemical detection for pharmaceutical analysis, Talanta, 68 (2006) 1303-1308. 

Neumayr, M. Friedrich, O. Sontag, G. Pittner, F. Flow-injection analysis with electrochemical detection for determination of salicychc acid in pharmaceutical preparations. Anal. Chim. Acta 1993, 273, 469-475. 

GC-MS is applied in some methods for the analysis of pharmaceuticals in sludge [45, 109]. However, this technique can only be successfully applied for a limited number of nonpolar and volatile pharmaceutical compounds, while analysis of polar pharmaceuticals requires a time-consuming and often irreproducible deriva-tization. Consequently, LC-MS is the preferred technique in many laboratories. Some other detection techniques are also employed, such as diode array (DAD) and electrochemical (ED) and fluorescence detection (ELD). In the case of fluoroquinolones, ELD is still the favored technique. 

UV detection, diode-array detector (DAD) and fluorescence have been the detection techniques used, coupled to HPLC for the analysis of OTC. UV detection is set at 355 nm [49-51], 350 nm [40], or at 353 nm [52], Using the diode array detector [49] offers advantages that the target peak can be identified by its retention time and absorption spectrum. Compared to UV detection, fluorescence detection is generally more specific and is less interfered by other compounds in the sample matrix [51]. A HPLC method with electrochemical detection has also been suggested recently. Zhao et al. [53] described HPLC with a coulometric electrode array system for the analysis of OTC, TC, CTC, DC, and methacycline (MC) in ovine milk. An amper-ometric detection coupled with HPLC was developed by Kazemifard and Moore [54] for the determination of tetracyclines in pharmaceutical formulations. 

The coupling of a mass spectrometer to CE and CEC provides a powerful system for the analysis of pharmaceuticals and complex biological mixtures. This can replace or complement other conventional detection methods such as UV, electrochemical, or LIE that provide less structural information. The use of mass spectrometer as a detector enhances the usefulness of the CE and CEC and allows an efficient separation and identification of complex mixtures, obtaining structure and/or molecular mass information. The choice of mass analyzers used in CE/CEC-MS depends on factors such as sensitivity, mass resolution, requirement for structural elucidation, and the type of application (Table 5). The analyzers that have been used in CEC analysis include time-of-flight (TOE), quadrupole (Q), ion-trap (IT), fourier... 

The minimum uncertainty for simple matrices is achieved with use of electrochemical sensors, especially for the assay of organic cations and organic and inorganic anions in food and clinical analysis. The selectivity and sensitivity of these sensors are adequate to detect numerous pharmaceutical products, without any prior separation. The ability of electrochemical sensors to determine continuously the activity of an ion in solution has made their use possible in in vitro and in vivo dissolution tests of drugs. 

This section will only discuss the most common detection methods used for CE analysis of pharmaceuticals, that is, UVAds absorbance, LIED, mass spectrometry, and electrochemical detection. In the tables of applications, the method of detection is indicated for each apphcation. This should aid the interested reader and provide information on detector suitability for intended applications. 

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