Mosh-Moah Free Vials and Caps
During sample preparation, all possible introductions of false-positive Mosh Moah contaminants into the LC-GC system must be avoided. We must be sure that all measured Mosh Moah results originate from the sample and not from the laboratory environment. The solvent we use for the experiment is tested for the presence of Mosh Moah. Gloves are used to avoid contact between the sample and the skin. Glassware is usually cleaned beforehand, but the vials and caps with septa are usually used straight out of the box.
The septa in particular can contain many Mosh Moah-related components and therefore pose a high risk of high noise or false-positive results.
Virgin PTFE septa are a good alternative. These are chemically very resistant to most media and do not change their properties. The white PTFE septa have a high temperature stability of approximately -250°C to approximately +250°C. There is no desorption of the Mosh Moah component. This material is therefore most suitable for this application.
Problem
Crimp caps are normally used for single-injection HPLC analysis. There are two disadvantages to this closure in combination with the desired septa:
- The inserted PTFE septa often fall out of the aluminium crimp cap when moving or closing the vial.
- The density of the material is not always sufficient due to a low elastomer content. In addition, the thickness of the septum is only 0.25 mm, which means that material may evaporate before injection.
Our solution:
- An aluminium crimp cap with a slight inward curve is used. This fixes the inserted thin PTFE septum in place. “Closure, aluminium crimp cap colourless, with hole and virgin PTFE septum 0.25 mm thick, 53° shore”
- Because a fluoroplastic O-ring is incorporated between the PTFE septum and the hole, the aluminium crimp cap can now be optimally crimped without having to readjust the crimping tool. The PTFE septum is fixed in place by the rolling process used here: “Closure: aluminium crimp cap, colourless, with hole and roller blind, virgin PTFE septum 0.25 mm thick, 53° shore D and O-ring made of fluoroplastic”.
The end result is a Mosh Moah Free Vial Cap system in which the PTFE septum is fixed so that there is no contact with the septum during crimping of the cap.
For more information and prices for 1.8 and 10mL vials, please contact us.