ALEXYS Carbohydrates Analyzer
Pulsed amperometric detection
Electrochemical detection of carbohydrates is done in the ‘pulse mode‘. This is necessary, because EC detection of carbohydrates results in oxidation products that stick to the electrode surface. This contaminates the electrode and causes a bad reproducibility. Therefore, a cleaning pulse is applied and the gold working electrode is regenerated every second by a cleaning step. This ensures stable and reproducible detection conditions.
A side effect of the applied pulse mode is that the gold electrode is slowly consumed in the process. After long term use – several months – it can be seen that a little gold has disappeared. The Antec flow cells are using a solid gold electrode, in case needed the electrode surface can be restored by using our metal polishing kit. The traditional 3-step detection pulse has more wear than the newer 4-step pulse. A FlexCell with replaceable working electrode can be used for both. A SenCell is recommended for a 4-step pulse only.
Measurement potential E1 with cleaning pulse E2 – E4. Measurement is on the second half of E1 (t-sample), when the current is stabilized.
High Performance Anion Exchange Chromatography (HPAEC) is used for HPLC analysis of carbohydrates. It is only at very high pH that carbohydrates are anions and can be separated. Therefore, only a few HPAEC columns can be used as they have to be used at pH 12 or higher.
At such high pH, carbonate from the surrounding air dissolves in the mobile phase and forms carbonate ions. The slowly rising concentration of carbonate enters the column, it occupies functional groups of the stationary phase and changes the retention times of carbohydrates. It is therefore most important to have proper carbonate removal from the mobile phase to ensure reproducible separation conditions.
The ALEXYS eluent tray has the infrastructure for keeping the solvent bottles under a helium blanket. Gas tight caps, tubing, fittings and a manometer to adjust the gas flow and to keep Helium consumption to an absolute minimum.
HPAEC separation and pulsed amperometric detection of carbohydrates.
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