Buying a used GC w/out controller

[ajrabassa]

This is probably not the usual question about gas chromatography, but I'm running out of places to ask so I'll bug you guys.

I'm looking at purchasing a used GC/MS without a control PC attached to it. My question is this - what do I need to know about any given GC/MS in order to communicate with it? Are there resources somewhere I can find the pinouts/serial protocol for the unit? Things I need to watch out for? Is the control software standard or interoperable?

I occasionally see some older, but highly functional units come past locally, as well as the usual online sources. Based on the sources of these units and the reason for replacement, I've got a very high degree of confidence the units themselves work (especially the ones locally). I either own or have access to all the test equipment necessary to diagnose and build control electronics and software, so this part is not daunting. There's enough information available on the calibration and interpretation of the data that this portion of the task does not concern me. Likewise, the data libraries and interpretation are not an issue. I'm also looking at this as a long term project, so I do not expect the work to take less than a year to go from documentation and a physically functional unit to having software written and PC control in place.

[rb6banjo]

Wow! You're much better at this stuff than I if you think you can pull all of that off. It is my personal opinion that you're asking for big trouble trying to do all of this yourself. Interfacing to a GCMS for data collection is not as simple as hooking up a strip-chart recorder and tracking an analog detector like a flame or a TCD. If it's me, I'll leave all of that to the equipment manufacturer's. Good luck to you.

[Peter Apps]

Welcome to the forum.

You have two issues to contend with - the first is the control of the instruments, the second is the acquisition and processing of the data. Most GCs can be programmed from a front panel keypad, and then all you need is a start-stop command, but I know of no MS that has front-panel control - they are all software driven.

GC-MS data acquisition and processing is exclusively software driven - if you can replicate that you should be earning a huge salary at one of the instrument manufacturers.

Peter

[ajrabassa]

Thanks for the welcome!

My big concern/issue is purely the interface; even though I have a pile of information telling me *what* to do, there's almost no literature to tell me *how* to get instructions to or data from the instrument. Reverse engineering one of these is almost out of the question, just because of all the custom electronics inside. All I want is the data protocol, basically.

The data processing is not a task I'm daunted by, yet - I've done data processing from other sensor sources before and my primary background is in mathematics. The tools are out there in essentially a drop-in way, and there's a shocking (to me, anyway) amount of literature on exactly what to do with the data that comes off a MS. What I was really shocked by is there's even stuff on exactly how to get diagnostic information out of the mass spectrometer without having a library of spectrograms to work with. None of it has struck me as difficult from a signal processing standpoint - so far it seems like it's pretty standard stuff.

None of this is to dismiss the huge amount of signals processing and control theory that goes into building a modern GC/MS, it's just that my needs are relatively small.

I think the only hope I have is that someone knows enough about the instrument-computer interface to point me in the right direction, or who might know someone I can talk to for insight.