The following is excerpted from A Comparison of Methods for Determining the Concentration of
Transition Metal Ions in Liquid Bleach, a thesis by Hung A. Pham, Miami University, Oxford, OH 1997.
This excerpt provides information that demonstrates the impact filtering can have on commercially
available bleach. The bleach samples provided for this research were produced on equipment
manufactured by Powell Fabrication and Manufacturing, Inc.
A Comparison of Methods for Determining the Concentration
Of Transition Metal Ions in Liquid Bleach
Abstract
The presence of transition metal (Cu, Fe, and Ni) ions in liquid bleach is a source of bleach
decomposition that results in the build-up of oxygen. The oxygen build-up causes two problems for a
water utility: it signifies that bleach is decomposing and more product must be used to disinfect the raw
water; and the handling of the highly caustic becomes more dangerous due to a pressure build-up in
storage containers and bleach transport piping.
Measurement of transition metal ions at low concentrations is a difficult task because liquid bleach
contains a complicated matrix where the presence of transition metals can potentially be present as
species with various ligands (e.g. Ni (OCl)+, Ni (OH) +, NiCl+, etc.).
Methods to identify and routinely measure the transition metal ion species at concentrations below
1 mg/l in liquid bleach have not been developed. The purpose of this research was to explore, optimize
and validate analytical methods that can be routinely used to measure transition metal ion
concentrations in bleach.
Five methods (Visual Spot Test, Inductively Coupled Plasma, Chemometric Analysis, Chloroform
Extraction Colorimetric and Ion Chromatography Postcolumn) have been evaluated in this study. The
Ion Chromatography Postcolumn is the best method for determination of three transition metal ions
because it has high precision, good accuracy and a low limit of detection (less than 10 µg/L).
From Chapter IV, A Comparison of Methods for Determining the Concentration of Transition Metal Ions
in Liquid Bleach, a thesis by Hung A. Pham, Miami University, Oxford, OH 1997.
CHAPTER IV -
Commercially Bleach Analysis
The presence of transition metal ions is known to catalyze the decomposition of bleach to form O2.
Build up of O2 in storage tanks and pipes has become a safety issue for suppliers and water utilities.
The presence of transition metal ions contributes to the loss of bleach strength. New specifications by
water utilities to check transition metal ion concentrations in delivered bleach have been initiated.
Therefore, suppliers and water utilities require simple and convenient transition metal ion analysis
methods.
We felt it is necessary to test a number of commercially available bleach samples. This will define a
typical transition metal (Cu, Fe and Ni) ion concentration range in bleach. Mr. Duane Powell PE, Powell
Fabrication and Manufacturing, Inc., St. Louis, Michigan, generously provided a number of bleach
samples for analysis.
Data from these representatives, commercially available bleach samples are presented in
Table 4 comparing Chloroform Extraction Colorimetric (CEC) and Ion Chromatography (IC) methods.
Table 4 illustrates similar results for each transition metal ion in the bleach samples. The difference
between the two methods ranges from 5.2 to 13.1% for Cu and from 3.7 to 13.2% for Ni. Analysis of the
data showed higher transition metal ion concentrations were found in unfiltered bleach samples.
Transition metal ion concentrations in unfiltered bleach were found for Cu (40 to 70 µg/L), Fe (230 to
1200 µg/L) and Ni (50 to 390 µg/L). For filtered bleach samples, Cu and Ni concentrations were greatly
reduced by filtration and were generally below the limits of detection. Thus, we recommend that the
bleach manufacturers filter their product prior to delivery to water utilities. Furthermore, water utilities
should purchase filtered bleach to avoid the loss of bleach strength and the generation of O2.
