Another example of 2-D ion chromatography involves a technique known as AutoNeutralization ™. This technique is used when it is necessary to quantify anionic contaminants in concentrated bases. The strategy most often employed is to dilute the concentrated base prior to injection. This works to reduce the concentration of the interfering matrix ion to a level that does not affect separation, however, dilution also dilutes the concentration of trace anions and subsequently compromising their detection. AutoNeutralization ™ solves the analytical problem of achieving good detection limits of trace anions in concentrated bases by neutralizing the base using a membrane based neutralizer device. The sample anions are in a water background after neutralization and can be focused back onto a concentrator column. In the AutoNeutralization process, the concentrated base sample is loaded into the 25 ul sample loop of the sample valve as shown in the figure below. 
The sample loop is switched in-line and flushed with a stream of deionized water (also know as the carrier solution). The carrier solution transfers the concentrated base from the sample loop to the ASRN TM, where the sample is partially neutralized, then transferred to the 5000 m l loop. The recycle valve is then actuated to pass the sample through the ASRN TM again so that it is completed neutralized. The figure below shows the results of an anion analysis of a concentrated base sample without and with neutralization. As can be seen below in chromatogram A, there is a huge negative dip in the baseline due to the concentrated base within the conductivity detector. This matrix interference results in poor chromatography and detection of additional anions is virtually impossible. Conversely, chromatogram B shows the results after AutoNeutralizationTM . Note the large negative dip is completely eliminated and distinct anion peaks can be readily mined. 
|
