Two types of quartz are used for EPR sample tubes:
1. Clear Fused Quartz (CFQ), a naturally occurring material
2. Suprasil, the trade name of Heraeus-Amersil synthetic quartz
Unique Properties of Quartz for EPR
· Quartz is pure silicon dioxide
· Quartz has a high dielectric constant
· Quartz has a low level of paramagnetic impurities
Materials of high dielectric constant alter the microwave field and concentrate the field on the sample. The low level of paramagnetic impurity in quartz prevents interferences with the samples EPR lines.
Over long periods, CFQ irradiated with UV will discolour. Synthetic quartz transmits electromagnetic radiation through the UV spectrum. Synthetic Quartz EPR tubes (Suprasil) should be used when applying ionising radiation to generate radical species and for a sample of very low signal. In most other cases, Clear Fused Quartz will provide the same results as Suprasil.
Due to technological advancements the sensitivity of EPR has increased, the direct result is that certain high Q cavities will pick up the signal from these impurities especially in tubes over 4mm OD.
Clear Fused Quartz (CFQ) is purified from naturally occurring quartz so the existence of certain material radicals from mining is inevitable.
In this instance we recommend switching to Suprasil EPR products which are made of synthetic material and suppress major impurity contents by an average of 2 orders of magnitude.
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