I second everything Wolfram and Stephanie say. But depending on your 
freeze-dryer set-up, poss a more immediate impact when you put the 
samples in is that the 6M solution may not stay frozen when you take the 
pressure down, leading to massive boiling over and mixing of yr samples, 
and a horrible cleaning out of the freeze-dryer. We have had that problem 
with amino acid samples. You can do it if you spin it, but not if the 
sample vials are static.
You can also take 6M HCl off pretty easily with a rotary evaporator. 
It is more actual person time consuming, as you can only do one sample at 
a time per evaporator set-up, but takes lots less time per sample than 
spin freezing, and no problems with damaging expensive equipment.

Best of luck,
Tamsin

On Thu, 7 Jul 2005, Dr W Meier-Augenstein wrote:

> I was about to say the same. Bad idea.
>
> The HCl will cause damage to your freeze dryer, and particularly the vacuum
> pump (unless you put at least 2 liquid N2 traps in the line). As you know,
> HCl itself is a gas (bp -85 C at 1013 mbar) and concentrated (or fuming) HCl
> is a 38% solution of HCl in water. Your 6 molar HCl is roughly 2/3 of that.
>
> Under vacuum, virtually the first thing to be pumped off will be gaseous
> HCl.
>
>
> Wolfram
>
>
>> -----Original Message-----
>> From: Stable Isotope Geochemistry
>> [mailto:[log in to unmask]] On Behalf Of Stephanie Ewing
>> Sent: 06 July 2005 22:41
>> To: [log in to unmask]
>> Subject: Re: siderite removal from clay/organics for d13C
>>
>>
>> The HCl will be hard on your freeze dryer unless
>> you have an effective trap.  There's been lots of
>> discussion of various alternate acids on this
>> list.  I've used 100% phosphoric, which has the
>> benefit of low vapor pressure, but makes
>> subsequent dehydration challenging.
>>
>> Stephanie
>>
>>> Folks,
>>>
>>> We're trying to separate siderite from soil/clay samples so
>> that we may
>>> analyze the organic components of the soil for d13C, d15N and CN
>>> ratios. The refs I've come across focus on 'carbonate' removal and
>>> indicate that siderite is less soluble. I found I can
>> dissolve siderite
>>> in 6 molar HCl at 50°C overnite, or soaking in 6 molar HCl
>> at 25°C for
>>> several days. To remove excess HCl I plan to freeze dry the
>> samples and
>>> not pour out any of the acid in case some of the organics have also
>>> gone into solution (I think this is the same idea as vapour removal).
>>>
>>> Any comments or suggestions regarding possible effects others have
>>> observed using this method, or better methods before I follow the
>>> tedious path of sample preparation testing? The first line
>> of testing I
>>> was going to do was to dose IAEA-C5 (wood) with siderite and see if
>>> THIS pretreatment affected its d13C values.
>>>
>>> Thanks in advance for saving me time,
>>>
>>> Toti.
>>>
>>>
>>> Toti Larson Ph.D.
>>> Los Alamos National Laboratory
>>> Earth and Environmental Sciences                505.667.9894 (lab)
>>> Los Alamos, New Mexico 87545            550.667.8006 (office)
>>

PLEASE NOTE NEW CAMBRIDGE EMAIL ADDRESS
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Dr Tamsin O'Connell
McDonald Institute for Archaeological Research
University of Cambridge
Downing Street, Cambridge CB2 3ER, UK
tel:01223-339344
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