Micromass Isochroms and spin-offs

For a fair while, from the mid-1990s through 2015, the Isochroms were the real workhorses of our lab.  They were the second generation of continuous-flow machine, after the prototypical Isomass of which very few were produced.  We’re keeping the Isomass against the time when collecting old mass spectrometers becomes trendy and their values soar.  It might be a little while …

The Isochroms were specialised CF-IRMS and were nice little units.  Their electronics are essentially similar to those of the Prisms and Optimas, with the software running on PCs driven by OS/2 version 2.x.  From a modern point of view, OS/2 is rather hard to maintain and lacks certain niceties that arrived soon after, such as USB.  This makes data transfer a bit tricky and reliant on outdated technology such as the 3.5″ stiffy drives of 1.44 MB capacity.  Yup – 1.44 MB.  Thus it would be 2,800 of them on a 4 GB thumb-drive.  But for all that, 32-bit OS/2 was an excellent operating system and Windows XP moved toward being eerily similar.

We have most of three Isochroms.  Two that were used in our lab and a third acquired from Cape Town.  Typically they were used here attached either to pyrolysis furnaces for O-18 analysis of organic material and water, or they used an EA as a front end.  In the latter format they processed hundreds of thousands of d13C and d15N analyses for us and clients, right up until 2015.

90s Isochrom CF-IRMS. The near machine uses a CE EA1100 as a front end, while the rear is in the middle of being serviced and prepared for membrane-inlet work.

When Isoprime 1 started to be used more for utility work, our second Isochrom was turned into a membrane inlet machine and run by Camille Bathellier and others to examine photosynthetic processes such as carboxylation.  Camille then returned to France and the project paused for a while but he returned in 2016, the membrane inlet system was reconstructed, the mass spec moved to the new building and work continued.

An Isochrom was also used to make a system to examine the d13C and d18O of CO2 at ambient concentrations.  We purchased a Sercon source control unit (to replace the aging drawer-based electronics) and hooked this up.  A series of rotary valves, some tubing, a spare GC, a USB DAC  and other odds and ends were pieced to together (mostly by HSW with Nerea Ubierna, with substantial technical help from Peter Groeneveld) to make an automated atmospheric sampling system, driven by software written in Borland Delphi.  The gas from growth experiments passed continually through a 1/4″ stainless tube until a sample was required when the diluter switch on the Isochrom was used as a trigger to start the valve sequence.  The valves were then switched so that one tube-volume was forced through the GC by a helium carrier.  The CO2 emerged as a pulse after the nitrogen and oxygen had been dumped through another valve and was then passed to the modified Isochrom and analysed.  The precision was excellent, with the gas usually calibrated against compressed air processed identically to the sample air.  The greatest limitation was probably that the sampling interval was rather long, perhaps 7 minutes.

In August 2017 the membrane-inlet machine continues to be used but difficulties with servicing the electronics drawers have removed the other unit from service, with our bread-and-butter contract d13C and d15N work being taken over by Isoprime 1.  But when the membrane inlet work is complete … we will do more drawer juggling between the three machines …

Fisons Isochrom with GC set up.  Far right is the GC with the capillary and valve-switching to its left.  Gas flow is controlled by the MFCs on top of the black valve box.  Sercon source control is almost hidden behind the Isochrom.

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