Clinical analytes, optical measurement

Optical Measurement of Bioprocess and Clinical Analytes Using Lifetime-Based Phase Fluorimetry... 

The majoiity of the various analyte measurements made in automated clinical chemistry analyzers involve optical techniques such as absorbance, reflectance, luminescence, and turbidimetric and nephelometric detection means. Some of these ate illustrated in Figure 3. The measurement of electrolytes such as sodium and potassium have generally been accomphshed by flame photometry or ion-selective electrode sensors (qv). However, the development of chromogenic ionophores permits these measurements to be done by absorbance photometry also. 

The majority of the various analyte measurements made in automated clinical chemistry analyzers involve optical techniques such as absorbance, reflectance, luminescence, and turbidimctric and nephelometric detection means. 

The inherent features of these methods make them particularly suitable for clinical analyses, with either electrical or optical detection of the analytical signal, which is measured as such (non-kinetlc methods) or monitored as a function of time (kinetic methods). Some representative examples are commented on below. 

Although optical techniques —particularly photometry— prevailed in automatic methods of analysis for a long period, the advent of lon-selectlve electrodes (iSEs) marked the beginning of the automation of electroanalytical techniques. The variety of analysers currently available that Incorporate electro-analytical detection not only outperform those based on optical sensing (e.g. In analyses for alkali and alkaline-earth metals with ISEs as opposed to flame photometry), but also they have fostered the development of in vivo measurements, no doubt the most exciting and promising area of clinical chemistry. 

Fluorescent tical chemical sensors are (tf particular interest due to their inherent sensitivity and sinq>lidty (2). These types of sensors have many other advantages that optical sensors, in general, offer. One of the most attractive features is that they do not require a separate reference sensor, as a p( tiometric chemical sensor does. In addition, th r are not affected by electrical interferraice, sanq)le flow rate, and stir speed which can be serious problems with eledrochemical sensors. Fluorescent optical chemical sensors have been widdy used for quantitative measurements of various analytes in environmental, industrial, clinical, medical, and biological aj lications (2). 

The value of electrochemical detection following high performance liquid chromatography is compared with that of the more widely used optical methods of detection. Its advantages are illustrated by its application to three areas of clinical chemistry that had previously posed analytical problems. Its sensitivity allowed its use for the measurement of plasma catecholamines. Its selectivity was employed to produce rapid methods for the determination of urinary levels of catecholamine and tryptophan metabolites. Finally, its value for the estimation of urinary oxalic acid is shown. Future developments such as increasing the range of detectable compounds by derivatization are briefly discussed. 

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