Ammonium column switching technique

The simultaneous analysis of alkali and alkaline earth metals is another important ion chromatographic application in the field of drinking water and surface water analysis. Environmental samples with low levels of ammonium, in matrices with high concentration of sodium, are a typical case. Unfortunately, ammonium and sodium ions have similar selectivities for the common stationary phases. This problem can be solved by a column-switching technique or by applying appropriate columns and eluents. Owing to the strong environmental impact, trace heavy metal ion determination and speciation have received particular attention in recent years. 

Figure 10.96 Column-switching technique with cation exchangers of different selectivities for analyzing sodium and ammonium with disparate concentrations.

Figure 10.100 Trace analysis of sodium and ammonium in the presence of a large excess of monoethanolamine using a column-switching technique. Separator columns lonPac CG12A/CS12A and CS10 column-switching valve is switched after 6 min eluent 24mmol/L methanesulfonic acid flow rate 1 miymin ...

Fig. 9-27. Ammonium analysis in seawater utilizing a column-switching technique. —...

Fig. 9-49. Change in elution order of mono- and di valent cations when applying a column switching technique peaks (1) lithium, (2) sodium. (3) magnesium, (4) calcium, (5) ammonium, and (5) potassium.

Wyss pioneered use of automated column-switching techniques for analysis of retinoic acid and other polar retinoids (156-160). In general, a plasma sample is diluted with acetonitrile ethanol (95 5) containing an appropriate internal standard the supernatant is passed across a preconcentration column (such as Bonda-pak C18 Corasil, 14 mm X 4.6 mm ID), and the preconcentration column is rinsed with ammonium acetate acetonitrile. The retinoids were eluted from the preconcentration column with a gradient of ammonium acetate acetonitrile acetic acid, and analyzed on a Spherisorb ODS 1 column by gradient elution (159). 

---