Multichannel Dilution Analysis Using a Single Peristaltic Pump Tube

Multi-channel dilution analysis (MCDA) is a novel, matrix-matched calibration method that automatically dilutes a standard solution using a tubing manifold to split a solution stream traveling between an autosampler and an analytical instrument. The manifold consists of separate tubing channels of various lengths, resulting in a stairstep of signal levels as different portions of the solution reach the instrument to be measured at different points in time. Multi-channel dilution analysis was initially developed on an inductively coupled plasma optical emission spectrometer (ICP-OES) equipped with a peristaltic pump with five channels, with three used to drive solution through individual tubes in the manifold and a fourth reserved for waste. The setup limited MCDA measurements from being realized on instruments that have fewer pump channels without employing an external pump. The use of a single peristaltic pump line to drive solution through the entire tubing manifold is proposed as a feasible way to overcome this hardware limitation and is applied to both ICP-OES and ICP mass spectrometry (ICP-MS). The method is validated through the analysis of certified reference materials, with recoveries for a suite of analytes ranging from 83% to 117%, with relative standard deviations on the order of 1%. The matrix matching capabilities of the method are demonstrated through the analysis of spiked matrices containing high concentrations of ethanol and calcium, and a comparison to traditional calibration techniques. In addition, the improvements in calibration statistics for ICP-MS measurements using MCDA are discussed.