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Dear Matthew,


We faced similar challenges when collecting and shipping subsurface water samples or samples from freshwater lochs.

Samples were collected by pulling them up into use-once sterile syringes.

Since sample volume was not a limiting factor we settled on filling 22 mL glass vials (the type typically used for head-space analysis) to the brim (actually to slight overflow) and sealing the vials with crimp seals fitted with PTFE backed silicone septa.

This approach can easily be adapted to smaller sample volumes by using e.g. 2 mL autosampler vials (amber) and correspondingly size crimp seals.

To minimize risk of sample deterioration due to microbial activity we sterile filtrated samples through 0.2 um syringe filters into the vials.

The small air volume in a vial is completely replaced by the water sample during this process.  However, if you feel even this contact with air might cause problems for your particular samples you could crimp the vials and flush them with N2 prior to use.  To do this you jury-rig a syringe needle to a N2 cylinder and insert the needle through the septum.  You need a second relieve needle through which air can escape and to prevent pressurizing the vial.


Kind regards,

Wolfram



-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Matthew DeCesare
Sent: 16 December 2014 20:43
To: [log in to unmask]
Subject: [ISOGEOCHEM] Preventing pore water d18O & DO contamination

Hello everyone,

I will be taking part in an Antarctic expedition to the Ross Sea in January and will be using Rhizon samplers to extract pore water from kasten and piston cores for pH, dissolved oxygen, salinity and d18O analysis. However I am concerned about sample contamination with regard to DO and d18O and would like your advice.

In the original proposal the extracted pore waters were going to be injected into septa capped glass vials under a Helium filled portable glove bag, however there were concerns using pressurized glass vials and needles on a ship. It was advised that we use HDPE bottles (or centrifuge vials) to store the pore water after extraction. I am unsure if the pore water will be contaminated by the atmosphere during extraction (using a syringe as a vacuum attached to a hydrophobic tube and filter placed inside of the core) and if there is a method for storing pore water that will minimize possible gas exchange.

I would imagine that unless the extraction and analysis is done under an anoxic environment, the pore water will be compromised. Is this true?

Thank you,
-Matthew DeCesare


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