Head Height; Eluent Viscosity; B.4 Head Height - Waters 600e User Manual

• A difference of 16 units indicates that the two liquids possess a critical solution
temperature between 25 and 75 °C, with 50 °C as the optimal temperature.
• If the difference equals 17 or more, the two liquids are immiscible, or their critical
solution temperature is above 75 °C.
Interaction between the molecules of the two liquids can sometimes change the expected
degree of miscibility. For example, ethers or tertiary amines show unpredicted miscibility
with hydroxylic eluents due to hydrogen bonding. Unusually strong hydrogen bonding is
also responsible for the miscibility of long-chain alcohols or carboxylic acids with
standard eluents of low M-number. Conversely, long-chain alcohols and carboxylic acids
show anomalous immiscibility with aprotic eluents of low M-number.
Some eluents prove immiscible with eluents at both ends of the lipophilicity scale. These
eluents receive a dual M-number as follows:
• The first number, always lower than 16, indicates the degree of miscibility with
highly lipophilic eluents.
• The second number indicates the degree of miscibility with highly lipophobic
eluents.
A large difference between the two M-numbers of an eluent indicates a limited range of
miscibility. For example, some fluorocarbons are immiscible with all the standard eluents
and have M-numbers 0 and 32. Two liquids with dual M-numbers are usually miscible
with each other.

B.4 Head Height

The 600E system allows you flexibility in the placement of the eluent reservoirs. Ideally,
the eluent elevation should be close to that of the pump heads or higher. Avoid placing
eluents on top of the system unless the bottles are in a container that can hold the total
volume of all of the eluents in case bottle leakage occurs.
B.5 Eluent Viscosity
Generally, when you operate with a single eluent or under low pressure, viscosity is not
important. However, when you run a gradient, the viscosity changes that occur as the
eluents are mixed in different proportions can result in pressure changes during the run.

Head Height 215