Another option is to use quartz filters instead of glass.




----- Original Message -----
From: Marja Tiirola <[log in to unmask]>
Date: Monday, December 4, 2006 1:01 pm
Subject: [ISOGEOCHEM] Problems with GF/F filters
To: [log in to unmask]

> Hello! 
> We have filtered lake water with Whatman GF/F filters, but the 
> stable 
> isotope analysis results have not been promising. When the filters 
> (1/3 of 
> the 4.5 cm diameter filter) are burned in the mass spectrometer, it 
> seems 
> that the reactor is blocked even after a few filter pieces, since 
> the 
> nitrogen values start to oscillate. Carbon values, however, seem to 
> be OK. 
> We have bought quartz inserts, since we thought that the glass 
> fiber could 
> remain there, but in our case it seems that inserts do not help us. 
> And 
> when we change the insert after 10-15 filter pieces and cool it, we 
> see 
> that the material which is remained in the insert is stone hard and 
> extremely difficult to remove, and furthermore, the insert has 
> became 
> brittle and white and is easily broken.  
> 
> The furnace of our Thermo Delta Plus is set in a temperature of 900 
> degrees Celsius. GF/F filters are said to resist 500 degrees. Those 
> who 
> measure GF/F filters, do you know the temperature of your furnace? 
> Can it 
> be that we have too high a temperature for GF/F, which makes it 
> amorphous 
> and blocks everything? Or do you have any other ideas, which can 
> make the 
> analysis of GF/F so difficult? I would be glad to hear the opinion 
> of more 
> experineced SIRMS users.
> 
> 
> Marja Tiirola 
> Researcher, Ph.D.
> University of Jyväskylä, Finland
>