title: A new method to assess available chlorine in small volumes of liquid.
abstract: BACKGROUND
  There is no robust and simple way to quantify available chlorine from small volumes such as human root canals. Therefore, a new method was developed and assessed.
  
  
  METHODS
  Standardized size-40 paper points were soaked in a 15% (w/v) potassium iodide solution for 1 minute. Subsequently, the paper points were placed in an incubator and dried at 110°C for 4 hours. The paper points (n = 5 per measurement) were then dipped in different concentrations of NaOCl and photographed under standardized conditions in RAW format. The pictures were imported to image processing software and adjusted to the standardized background. The red, green, and blue levels of the paper points were assessed at a predefined area. Inverse regression was used to determine NaOCl concentration from red, green, and blue values, with both explanatory and outcome variables log-transformed to base 10.
  
  
  RESULTS
  The red value measurements were chosen for further analysis based on a comparison of the coefficient of determination (R(2)) and a residual analysis. The method was applied to concentrations of NaOCl between 0.0001% and 1% (R(2) = 0.92). In this range, NaOCI concentrations could be assessed with an error not larger than 3-fold the determined concentration.
  
  
  CONCLUSIONS
  The present method proved to be robust to determine the order of magnitude of available chlorine that is present in a small volume. This should be useful for endodontic research.
authors.affiliation: Department of Preventive Dentistry, Periodontology and Cariology, University of Zürich Center for Dental Medicine, Zürich, Switzerland.
authors.forename: Dan-K
authors.initials: DK
authors.lastname: Rechenberg
authors.affiliation: Department of Preventive Dentistry, Periodontology and Cariology, University of Zürich Center for Dental Medicine, Zürich, Switzerland.
authors.forename: Kjartan T
authors.initials: KT
authors.lastname: Ragnarsson
authors.affiliation: Institute of Social and Preventive Medicine, University of Zürich, Zürich, Switzerland.
authors.forename: Sina
authors.initials: S
authors.lastname: Rüeger
authors.affiliation: Institute of Social and Preventive Medicine, University of Zürich, Zürich, Switzerland.
authors.forename: Leonhard
authors.initials: L
authors.lastname: Held
authors.affiliation: Department of Preventive Dentistry, Periodontology and Cariology, University of Zürich Center for Dental Medicine, Zürich, Switzerland; Department of Chemistry and Applied Biosciences, Institute for Chemical and Bioengineering, ETH Zürich, Zürich, Switzerland.
authors.forename: Dirk
authors.initials: D
authors.lastname: Mohn
authors.affiliation: Department of Preventive Dentistry, Periodontology and Cariology, University of Zürich Center for Dental Medicine, Zürich, Switzerland. Electronic address: matthias.zehnder@zzm.uzh.ch.
authors.forename: Matthias
authors.initials: M
authors.lastname: Zehnder
mesh_terms: D002713:Chlorine / Q000032:analysis*; D003786:Dental Pulp Cavity / Q000737:chemistry*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007202:Indicators and Reagents; D010209:Paper; D011193:Potassium Iodide; D012388:Root Canal Irrigants / Q000008:administration & dosage / Q000032:analysis*; D012973:Sodium Hypochlorite / Q000008:administration & dosage / Q000032:analysis*
chemical_list: D007202:Indicators and Reagents; D012388:Root Canal Irrigants; D011193:Potassium Iodide; D002713:Chlorine; D012973:Sodium Hypochlorite
keywords: Hypochlorite; NaOCl; method development; paper point