MONITORING OF FREE CHLORINE IN DIALYSIS FLUIDS USING THE SPECTROPHOTOMETRIC N,N′-DIETHYL-p-PHENYLENEDIAMINE (DPD) METHOD AND MULTIVARIATE CALIBRATION

ABSTRACT

The spectrophotometric N,N′-diethyl-p-phenylenediamine (DPD) method for the determination of free chlorine in saline matrices used as dialysis fluids (DF) in hemodialysis treatment was investigated by multiple wavelength detection (multivariate DPD-method). This method was compared with the current standard DPD-method (univariate DPD-method) that uses single wavelength detection (515 nm). The multivariate DPD-method showed the best performance because the influence of the high ionic strengths of the saline matrices on the equilibrium among the DPD species was well modeled only by the multivariate approach. The univariate DPD-method showed biased results towards low chlorine concentrations (ca. 25%) in DF samples. Through the developed methodology it was possible to quantify free chlorine directly in dialysis fluids. The multivariate method showed to be adequate as a last quality control before a hemodialysis session. The regression by partial least squares (PLS) using two principal components and full cross-validation was applied to the absorbance values in the interval 200–600 nm. The root mean square errors of prediction (RMSEP) was 0.08 mg L⁻¹. Free chlorine concentrations ranging from 0.2 to 0.7 mg L⁻¹ were assayed in DF samples.

Keywords:

• Chlorine
• Dialysis fluids
• Multivariate calibration

ACKNOWLEDGMENTS

The authors express their grateful thanks to CNPq, PADCT (project no 62.0261/97-8), and FAPERGS for financial support.