We bought these "stainless steel" guides to use for SPE extraction of surface water for PFAS analysis to avoid the standard PTFE needle guides. Apparantly, they are not all stainless steel. The luer hub appears to be plated brass. EPA Method 1633 calls for WAX cartridges to be conditioned with 1% methanolic ammonium hydroxide followed by 1% aqueous formic acid. As the picture shows, the plating dissolves and the copper component of brass oxidizes. We're not sure if we can get these clean enough to avoid contamination of subsequent samples, and they are too expensive to be dispsoable.
How about some nice polypropylene replacements?
