Since the Dionex CDRS 600 is a high-capacity anion exchange device which supplies the high concentration of hydroxide for acid neutralization, the hydrolysable ions such as Mg2+ and Ca2+ in hydroxide forms may be precipitated in the Dionex CDRS 600.
In general, when standard cation in water solutions are employed for system calibration, it is possible that Mg2+ and Ca2+ may be precipitated due to the high hydroxide concentration. These cations are then “carried over” to the first acid run.
To avoid the hydrolysis of the alkaline earth metals during standard calibration, the Dionex CDRS 600 is “conditioned” by running a complete pretreatment cycle of acid (preferably 24% sulfuric acid) prior to standard runs.
Follow the Dionex CDRS 600 acid treatment procedure below prior to each standard run.
- Confirm that the system functions properly.
- Set “Sample Valve” to Load Position and load 24% sulfuric acid.
- Switch the sample valve to Inject position and flush the sample loop with deionized water.
- After the sulfuric acid passes through the neutralizer and IC injection valve (approximately 4–6 minutes with the collection coil installed or 1-2 minutes without the collection coil installed), the system is ready for standard injection.
The above steps are applied only when standard calibration is performed. However, if the standard injection is made immediately after the sample runs (acid samples) the Dionex CDRS 600 acid pretreatment is not required.
If the standard run is not started within 20 minutes after the acid calibration step, the overall process must be repeated. When multiple point calibration is performed, the Dionex CDRS 600 acid pretreatment can be made any time after the beginning of the analytical separation.