22 February / March 2016


Miniaturisation in GC Laboratories - the Holistic Picture


by Richard Stokes BSc MSc CCHEM MRSC, Anthias Consulting Trainer and Consultant ris@anthias.co.uk


Supply and demand issues, particularly in the last few years during the recession, have caused contract laboratories [1] to review the cost of their operations more stringently than ever; areas that provide potential financial savings include consumable rationalisation, process efficiencies, method miniaturisation, all the way to the biblical improvements e.g. lab re-arrangements and Laboratory Information Management Systems (LIMS).


Method miniaturisation is the scaling down of as many instrumental and analytical parameters as possible to optimise efficiency and it has multiple practical benefits in itself. In addition, it has the added attraction of ensuring multiple on- going financial savings or rapid paybacks for a one-off capital expenditure.


In its purest form, miniaturising a method involves looking at the sample extraction solvent, the extraction technique, the injection onto the instrument, the separation on column, the quantification via the detector and finally the general cycle time of one analytical run to the next. We are also aiming to make the method more robust which should improve quality, to give us at least the same if not better Limit of Detection (LOD), but deliver the result far more quickly and hence more cost effectively. Remember, time is money in a contract lab.


Why change the extraction solvent?


We may then be able to inject more solvent, giving better sensitivity or enabling less initial sample to be extracted, and also start the


Soxhlet 1 sample/hr Soxtherm 6 samples/hr


analytical run at a higher temperature meaning shorter cycle times. Old environmental soil methods, for example, traditionally used dichloromethane (boiling point 39.6˚C) whereas that of a mixture of hexane/acetone (90:10 v:v) will be nearer 68˚C. The latter still has some polarity, the extraction efficiency will be sufficient (and can be performance- checked by a Proficiency Testing scheme if need be), yet the starting oven temperature for solvent focussing can be increased from 35˚C to 60˚C, saving a lot of cycle time. Added benefits of the proposed solvent mixture are that it is more environmentally friendly and has less health and safety issues.


Table 1: Polarity indices Solvent


Dichloromethane Hexane


Hexane/Acetone (90:10)


Polarity index ~3.1 ~0.1


~0.56


Extraction techniques for solids have typically evolved through speed and capacity [2], as efficiency has historically been universally satisfactory. Any piece of equipment that can run more samples in parallel, per unit space, should be investigated in this process. Whilst


Sonicator 60 samples/hr


presenting a beginner’s training course in GC in late January this year, I was honestly asked about soxhlet extraction, yes it was in a research laboratory but I can almost certainly guarantee it will be in use in a contract lab somewhere, one sample at a time is NOT high throughput and there are other, quicker methods that give the same recoveries, such as soxtherm, sonication or orbital shaking.


Why change the injection technique?


For sample matrices where large volumes have traditionally been necessary, i.e. waters, something fundamentally more intelligent has been required, as laboratory space quickly becomes prohibitive in such instances. To miniaturise environmental water analysis to the same scale as soil analysis, the technique of Large Volume Injection [3] (LVI) is often used. This enables the user to get more analyte onto the column by expertly injecting a hundred times more sample dissolved in solvent but then venting almost all of the latter leaving the concentrated analytes of interest to


Orbital shaker 600 samples/hr


Diagram 2: Evolution of semi-volatile soil extraction


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