Quality control of dialysis fluids by micellar colorimetry and multivariate calibration

A colorimetric method for the determination of zinc, copper and manganese as a quality control criterion in dialysis fluids is discussed. The spectrophotometric reagent was an aqueous solution of 1-(2-pyridylazo)-2-naphthol (PAN) in Triton (5% v/v) in order to obtain soluble micelles of the reagent and its chelates to perform measurements in aqueous phase. Multivariate calibration by the classical least square (CLS) method was adequate to assay the analytes and to verify the presence of other contaminants. Solutions of Zn, Cu and Mn ions in borate buffer (pH 9.2) were used to obtain the spectroscopic data for the calibrations. The modelling was investigated using "one analyte" standard solutions (Zn, Cu or Mn) and also mixtures of standard solutions (Zn, Cu and Mn). The results were compared in terms of the calculated RMSEP (Root Mean Square Error of Prediction) values. Recoveries about 100% were calculated using the methodology in synthetic samples of dialysis fluids and the interference of Ca, Mg, Fe, Cd, Ni and Co ions was discussed. Concentrations of the analytes in the range of 6 . 500 mug L-1 were determined in real dialysis fluid samples using "one analyte" standard solutions for the calibrations and the results were compared with atomic absorption spectrometry. Calibrations using PCR (Principal Component Regression) and PLS (Partial Least Square) methods showed similar results as those obtained by CLS method.