Chromatography Forum

Trying to detect isovaleraldehyde in corn syrup. I have a method that sets the headspace oven at 120 degrees Celsius that gives great response. The problem is that this is above the boiling point of the sample matrix and has been shown to spray up and contaminate the instrument over time. Simply dialing down the temperature to 100 degrees makes anything under 60ppb or so pretty much undetectable.

Can give as much detail as needed.

Using FID detection. Wondering what I can change as far as oven, FID, needle, transfer line temperature, as well as timing for pressurization , injection, withdrawal. Can also adjust carrier gas pressure.

Obviously don't expect anyone to put a method together from this vague information. But as far as general principles go, what would be some ways to try to enhance response while keeping the sampler oven at 100 degrees?

Straight corn syrup? Have you thought of diluting it with salt water? The salt water might create a less hospitable environment for the isovaleraldehyde than the syrup alone. Sure you're diluting your sample but in the end you might realize a benefit in your ability to detect your analyte at a lower temperature. I did some work for someone on this forum on some soap (search soap analysis) a while back. Cutting the soap with water actually improved the detection limits of some fragrance compounds in the soap.

Sounds like you are tied to static headspace analysis. I know you could get better detection limit in straight corn syrup using SPME.

Sorry guess I should specify that the sample consists of syrup diluted in saturated KCl that is then spiked with IVA. Use .5ml bottler acid as well. Problem is that, after trying many different setups with Headspace oven less than 120, none of them have been able to detect IVA at 19ppb, which is the lowest sensitivity that could work for our purposes. As soon as I ramp it to 120 again I get great response. So I am wondering what I can change in congruence with lowering the HS oven in order to still get good response.

It seems that at 100 Celsius I should still be able to get IvA out of solution but doesn't seem to be happening.

19 ppb is pushing it for static HS - calculate how much IVA will be in the loaded loop, how much of that goes to the column, and is that a quantity that an FID could detect ?.

Is there anything in the sample that could form IVA when exposed to acid and KCl at 120C ?

We need to know all the temperatures, flows, pressures and times in order to make sensible suggestions.

Peter

I believe acidifying the sample might also increase the headspace concentration as the carboxylate form is more soluble than the protonated acid.

If spray contamination is the issue, have you considered packing the sample in with enough glass wool so that even if it boils, any spray will be suppressed?