# Calibration using multiple individual compounds

Question asked by kruse on Aug 22, 2019
Latest reply on Aug 22, 2019 by kruse

Hi,

I have a question regarding calibration when measuring gasses.

We use a recently purchased version of chemstation (summer 2019)

We are doing measurements of the headspace of bottles containing microorganisms producing and consuming four different gasses.

We have all four gasses available as pure gasses from gas cylinders.

My question is what the best way of creating the standards.

It seems straightforward to make serum bottle with a mixture of the four gasses in known concentrations and use that for a one level calibration, or make two bottles for a two level calibration.

This can be achieved by:

• Capping a bottle with a rubber stopper flushing it a few minutes with N2.
• Withdrawing some ml of the headspace with a syringe
• Replacing the removed N2 with same amount (in total) of the four gasses
• Using this bottle with mix gas as standard
• I was wondering if it is also possible to make calibrations based on the individual gasses? Making mix gasses containing 4-5 different gasses using syringes is not too easy to do with high accuracy.

What I would like to do is Having a set with sample 1 contains 10% gas A, sample 2 contains 25% gas A, sample 3 10% gas B, sample 4 25% gas B etc. (the remaining of the vol., will be a irrelevant gas i.e. N2)

So that a 2 level calibration curve is made for gas A based on sample 1-2 and another 2 level calibration curve is made for gas B based on sample 3-4 etc.

However it seems like the software expects to find all specified compounds in all samples.

I did work around it by labelling the samples like this:

1. Sample 1 level 1 with 10% gas A and 0% gas B
2. Sample 2 level 2 with 25% gas A and 0% gas B
3. Sample 3 level 3 with 0% gas A and 10% gas B
4. Sample 4 level 4 with 0% gas A and 25% gas B

It seems to work, but it is a bit clumsy and we get a lot of data points a 0% for the different gasses, especially when we have multiple gasses.

Is there a more correct/elegant way of doing this? Or do we need to do the calibration with mix gasses?

Any advice from more experience users are most welcome,

Thanks!

Kruse