soot formation FID

[willemdm]

hi,

about one year we are running an analysis of sugars, only since the last month we get some serious soot formation at our FID detector.

configuration of our detector is as following:

temperature: 350°C
H2 flow: 35 ml/min
air flow: 350 ml/min

the method is running on H2 as carrier gas (about 8 ml/min).
No chlorinated solvents or dirty samples are running for the moment.

any help is welcome

grtz

[CE Instruments]

Any changes that coincide with that date ? Is your column high enough in the jet ?

[dblux_]

hi,

...
air flow: 350 ml/min
...
grtz

air flow should be checked with flowmeter

seems that the air flow is not sufficient to burn solvent without soot

havn't you changed injection volume by accident ?

[Peter Apps]

Your flame is running fuel rich due to the 8 ml/min carrier gas (I presume that this is with a megabore capillary ?). This is not likely to be the sole cause of the soot, but try reducing the hydrogen to the FID to 30 ml/min. You must be derivatizing the sugars - any change to that process, new reagents etc ?

Peter

[Bigbear]

Are you running make up flow? Total flow through the FID should be 30-60 cc/min.

[willemdm]

the capillary we are using is indeed quiet wide (0.320 µm)

the sugars are indeed derivatized, otherwise GC wouldn't work i guess
we are using the same method for a couple of years so nothing has changed in that proces.

thanks for the many tips, we will check wether everything is still installed properly and check flows...

grtz

[Peter Apps]

The optimum volume flow rate for the column diameter that you have is about 3-4 ml/min. is there a reason why you are running the gas so fast ?

I doubt very much that you have been using the same bottles of reagents to 2 years (and if you have they will have deteriorated). Did a new bottle of anything come into use just before the soot problems started ?.

Peter

[willemdm]

we use a fast temperature gradient together with a fast flow to optimize the time of the analysis.

there are no new manifacturers of product or no change in grade of products.

all reagents are prepared fresh on a weekly base.

grtz

[willemdm]

Hi,

decreasing the H2 flow of the FID solved the problem.

thanks for the feedback!

[Peter Apps]

Hi,

decreasing the H2 flow of the FID solved the problem.

thanks for the feedback!

Good to hear.

Peter