Multivariate calibration for the determination of analytes in urine using mid-infrared attenuated total reflection spectroscopy

The reagent-free multicomponent analysis of components in urine using mid-i nfrared spectroscopy possesses many attractions. A population of 67 individ ual urine samples fi om children and adults, collected over 24 h, was analy zed for urea, creatinine. uric acid, glucose, total protein, phosphate, and sulfate by using clinical reference methodology: The urine pH value was po tentiometrically measured by a glass electrode. Partial least-squares (:PLS ) calibration models mere calculated over optimized, component-specific ran ges from attenuated total reflection spectra of the urine samples measured by a micro-Circle cell, Apart from glucose and total protein, for which the spread ill urine sample concentrations was too small, calibrations were su ccessful for metabolites such as urea, creatinine, and uric acid. Additiona lly, concentrations of sulfate and phosphate anions, which shore significan t mid-infrared absorption bands, could also be quantified, The acid secrete d with the urine influences the equilibrium between di- and monobasic: phos phate in this biofluid, which is used as the spectroscopic basis for the pH assay presented here. The analytical performance of the reference methods is discussed with regard to evaluating the limitations of tile spectroscopi c assay, Additionally, aqueous solutions of individual urine components wit h a spread of concentrations similar to those found in native urine samples were analyzed by using PLS calibrations.