Labconco RapidVap Vacuum, N2 and N2/48 Evaporation Systems 7910015 - Manual (Page 33)

29
Chapter 4: Using Your RapidVap
Product Service Domestic 1-800-522-7658, International 816-333-8811
For example, methanol (which boils at 65°C at
atmospheric pressure) boils at 5°C at pressure of 53
mBar. Under these vacuum conditions, the block
temperature should be set between 25 to 45°C. The
nomogram and equation to follow will help in this
determination.
Calculating the boiling point:
The operating pressure corresponding to the desired
boiling point temperature may be calculated for any
solvent using the following formula:
log P = 2.8811 – Ta – T
(b)(T)
Where P = Vacuum (mm Hg)
Ta = Boiling Point Temperature at Atmospheric
Pressure (°K)
T = Desired Boiling Point Temperature (°K)
b = Constant from Table
Useful conversion factors:
1 mBar = .75 mm Hg
°K = °C + 273
Using the nomogram:
To use this graph, three facts must be known about a
given solvent:
1. Boiling point at normal atmospheric pressure
(1 Bar).
2. Constant b.
3. Either operating temperature or operating pressure.
To determine the desired boiling point at a given
pressure:
1. Find the boiling point at normal atmospheric
pressure (1 Bar) on the left side of the graph (page
32).
2. Find the operating pressure on the right side of the
graph.
3. Draw a straight line linking these two points.