A new spectrophotometric method to detect residual amounts of peroxide after reprocessing hemodialysis filters. 
Reuse of hemodialysis filters is a standard practice and the sterilizing chemical most often employed is peracetic acid.  Before starting the dialysis session, filters and lines are checked for residual levels of peracetic acid by means of a non-quantitative colorimetric test that is visually interpreted.  The objective of this study was to investigate a new quantitative spectrophotometric test for detection of peracetic acid residues.  Peracetic acid solutions were prepared in concentrations ranging from 0.01 to 10 ppm.  A reagent (potassium-titanium oxide + sulfuric acid) was added to each sample in proportions varying from 0.08 to 2.00 drops/mL of solution.  Optical densities were determined in a spectrophotometer using a 405-nm filter and subjected to visual qualitative test by different observers.  A relation between peroxide concentrations and respective optical densities was observed and it was linear with R2 > 0.90 for all reagent/substrate proportions.  The peak optical densities were obtained with the reagent/substrate ratio of 0.33 drops/mL, which was later standardized for all further experiments.  Both qualitative and quantitative tests yielded a specificity of 100%.  The quantitative test was more sensitive than the qualitative test and resulted in higher positive and negative predictive values.  There was a difference between observers in the qualitative test and some samples with significant amounts of peroxide were not detected.  A quantitative spectrophotometric test may improve detection of residues of peracetic acid when compared to the standard visual qualitative test.  This innovation may contribute to the development of safer standards for reuse of hemodialysis filters.