Care and feeding of probes

ianm's picture

8. Care and feeding of probes.

Time for a mundane topic, and that is the Care and Feeding of probes for liquids. There are a number of probe shapes and styles, but they all have some features in common. One is an optical interface that has to be sealed to the probe and also furnish the interface with the liquid. Question 1 - is any design, including seal, preferable? Question 2 - what are the important aspects of size (length, diameter, distance of the opening from the bottom)? Question 3 - is any design easier to use than others? Question 4 - are adjustable pathlengths better or worse than fixed ones? Question 5 - how reproducible must adjustable pathlengths be? Question 6 - is there any convenient way to tell if a probe's optics are clean? Question 7 - how reproducible are results for "replacement" probes? Subquestion - if a problem with reproducibility of a replacement probe arises, how best to alleviate the problem? Question 8 - are there recommended storage practices for probes that are not in use? Question 9 - sapphire is used almost exclusively for the optical interface; I have heard only hydrofluoric acid and boiling sulfuric can harm the sapphire; are there any other agents that could harm the sapphire? Subquestion - how resistant to abrasion is sapphire?

These questions may be enough to start some good exchanges of a topic I can't remember seeing in any NIR books or articles.


From: Howard Mark

Bruce - here's what I got from manufacturer's literature (manufacturers of sapphire, that is, which, by the way, is the best place to get info about optical materials. NIR manufacturers do not generally provide this sort of info about components):

1) Sapphire is unaffected by common acids or bases below 1,000 deg C

2) It is unaffected by HF below 300 deg C

3) The only material harder than sapphire is diamond. This makes it resistant to ordinary abrasion. However, since it is a brittle material, sharp blows could conceivably make small pieces flake off, which could be equivalent to abrasion. On the other hand, a sharp enough blow would be more likely to break the entire piece.