Determination of Polyphosphates Using Ion Chromatography with Suppressed Conductivity Detection

INTRODUCTION Polyphosphates are used for a wide variety of industrial applications due to their sequestering and dispersing properties. Polyphosphate samples are commonly characterized by various end-group titration methods that provide an estimate of average polyphosphate chain length, but no information on the relative amounts of individual polyphosphate oligomers. Manufacturers and end-users of polyphosphates need to determine the distribution of polyphosphate chain lengths because chain length is known to affect sequestering and dispersing properties. A rapid method for the separation of polyphosphates with chain lengths to about 35 phosphate units is presented in this Application Note. In this method, polyphosphates are eluted from a 2-mm IonPacAS11 anion-exchange column with a sodium hydroxide gradient. The ASRS (Anion Self-Regenerating Suppressor) is used to suppress the high hydroxide concentrations needed to elute large, multiply-charged polyphosphates. Steep hydroxide gradients can be used without a substantial increase in background conductivity because of the exceptional suppression capacity of the ASRS. As a result, suppressed conductivity detection can be used to directly generate polyphosphate chain-length distribution profiles. Popular applications of this method include: EQUIPMENT Dionex DX-500 system consisting of: GP40 Gradient Pump, high-performance microbore configuration ED40 Electrochemical Detector or CD20 Conductivity Detector DS3 Conductivity Cell LC20 Chromatography Enclosure EO1 Eluent Organizer PeakNet Chromatography Workstation