Dear colleagues,
I am concerned with the decision of buying a new HPLC system for our lab. I have two questions to help me to decide what kind of system to choose:
As carbohydrate analysis from different biological samples is one of our most important tasks, we were thinking about buying a PEEK system in order to be able to use Dionex´ CarboPac chemistry. Now some colleagues told me that there`s no problem using 0,1M NaOH as eluent in a stainless steel system. But I think the passivated surface of the tubing might be damaged, especially if the same system is switched between different mobile phases for different applications?
My second questions aims the problem of detection: The cheapest possibility would be a RI detector but compared to a pulsed amperometric detector, the RI has shows much less sensitivity and is restricted to isocratic applications. But I fear that the amperometric detector is quite sensitive towards ageing of electrode material and we would have to take consequential costs into account. Can anybody tell me his experience with amperometric detection (and with different suppliers of detectors).
Thank You

Look at Agilent / ESA coulochem 3 carbohydrate system. Also look at the Metrohm carbohydrate IC system.
PEEK is better for alkali eluents than stainless steel esp. when changing frequently applications.
As the PAD is very much more sensitive than RI,
This can present potential problem with dilution errors, as you may have to dilute your samples by large amounts.
Some PAD will need electrode filling maintenance, so choose one which is maintenance free.

In regards to the system, PEEK would be preferred for the same reasons you've pointed out.

Regarding the detector and column, be sure to look at Alltech's ELSD. We have been using the ELSD as an allternative to both RI and PAD and it has been working great for our carbohydrate analysis. It equilibrates much faster than RI and gradients are no problem either. The prevail carbohydrate column also works well at elevated pH (we've used NH4OH) and resolves all the carbohydrates we are looking at.

Rolf,

Stainless-steel per se is not rapidly attacked by alkaline conditions although iron is soluble in hydroxide so you can expect to see some effects over time. The main point is that you need to be prepared to keep the instrument under alkaline conditions if you are going to use stainless steel components. The passivation layer will be attacked by cycling between acid and base conditions, necessitating frequent re-passivation.

Another thing to be concerned about is the injection valve. You need to make sure that the rotor does not contain Vespel as this is attacked by caustic and will seriously contaminate CarboPac columns.

Finally, the issue with electrode aging (problems are actually more often caused by electrode erosion rather than "aging") can be readily dealt with by using disposable electrodes. Disposable electrodes are typically good for several weeks and can be quickly replaced if needed. Dionex provides disposable electrodes for carbohydrate detection in order to deal with this issue.

Thank You all for your suggestions, a further question concerning electrode aging or erosion: Why do many manufacturers give five years of warranty on their products while others say it might be necessary to change electrodes at regular (short) intervals?

Rolf,

Good question! This might be depend in part upon which electrode you are talking about and how it's being used. The life of a noble metal electrode is definitely dependent on the waveform being used and it is well documented that certain waveforms commonly used for carbohydrate detection will slowly erode the electrode in the case of gold electrodes. If the customer uses a waveform which erodes the electrode, the signal will slowly decline as the electrode recesses (in the case of thin film cells, anyway) since the linear velocity of the fluid stream will decrease as the electrode surface pulls away from the flowing stream. No warranty can stop this from happening. There is a quadruple pulse waveform which Dionex pioneered which greatly minimizes this problem but even so disposable electrodes have been shown to give substantially better reproducibility from day-to-day and from instrument to instrument.