Why is deritivization (DNPH) of Formaldehyde Necessary?

[jvtruebl]

Hi Everyone,

I'm trying to find out why the most accepted method of detection of Formaldehyde via gc/ms is by derivatizing it. I know that an early method was to collect carbonyls onto DNPH coated solid sorbent and then extracting that derivate using HPLC. I also am aware of the newer method using PFPH derivatives, followed by thermal desorption and then GC/MS detection.

However, I'm unclear why these steps are necessary. All the literature states is that this is the way it has always been done. What is so special about these low weight carbonyls that they need to be derivatized?


Any info about GC/MS detection of Formaldehyde is appreciated, even if it doesn't answer this question specifically.

Thanks everyone!

[Steve Reimer]

The mass of the dnph derivative is much larger than formaldehyde. Formaldehyde mass is 30, it will be hard to pick out. It is also quite reactive while the dnph derivative is stable. It is also very water soluble.

[chromatographer1]

Formaldehyde even reacts with itself as well as almost everything else. It has almost no FID response so MS is required. It is not easy to separate from other common volatiles.

It is just very uncooperative to being measured accurately. As it is a very dangerous chemical, that is very important. Thus, the present solution.

Rod

[Jetjamnong]

Becuase Formaldehyde is not stable, less ionization efficiency and this cause of low signal with GC/MS (no signal with GC-FID).
It need to derivatize becuase,
1. Change non-stable structure to stable form.
2. Increase volatility.
3. Increase signal response.
4. Increease resolution from co-elution peaks.
5. Decrease absorbtion action to injector port.

[AICMM]

To add just a bit to Mr. Reimer's comment. Formaldehyde is 30, nitrogen is 28 and oxygen is 32 and your MS is under vacuum so you will always be pulling in a little O2/N2 (air) so you will have a very hard time with the noise level.

Best regards,

AICMM

[chrom]

Go through the below mentioned ref.
Journal of Pharmaceutical and Biomedical analysis 41(2006) 738-743
Determination of Formic acid and formaldehyde in Pharmaceutical excipiends using HSGCMS.

It really worked well for us.

[JI2002]

Go through the below mentioned ref.
Journal of Pharmaceutical and Biomedical analysis 41(2006) 738-743
Determination of Formic acid and formaldehyde in Pharmaceutical excipiends using HSGCMS.

It really worked well for us.

Could you give a brief description of the method?