When isothermal jackets are used, it is important not to overfill the liquid nitrogen in the Dewar. At the start of an analysis, the liquid nitrogen level should be no higher than 1/4 in. (0.64 cm) from the top of the isothermal jacket. Overfilling overrides the function of the isothermal jacket and prevents effective control of the cold zone around the sample tube throughout the analysis.
If the Dewar is filled to a level above the top of the isothermal jacket, the evaporation of the portion of LN2 above the jacket allows the emerging sample tube to warm somewhat during the run. This causes the subsequent analysis to be somewhat in error due to the small change in gas capacity of the warmed portion.
When isothermal jackets are used, it is important not to overfill the liquid nitrogen in the Dewar. At the start of an analysis, the liquid nitrogen level should be no higher than 1/4 in. (0.64 cm) from the top of the isothermal jacket. Overfilling overrides the function of the isothermal jacket and prevents effective control of the cold zone around the sample tube throughout the analysis.
If the Dewar is filled to a level above the top of the isothermal jacket, the evaporation of the portion of LN2 above the jacket allows the emerging sample tube to warm somewhat during the run. This causes the subsequent analysis to be somewhat in error due to the small change in gas capacity of the warmed portion.
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