Suppose you have a set of samples to run but the instrument
is being used by another analyst. You take a look at their injection sequence
and find that it won’t be finished until the next morning. You can leave your
samples in the autosampler tray overnight and add them to the end of the
sequence, but will they be okay sitting out for hours?
Left in
ambient conditions over a significant period of time, the solvent in your
sample vials can evaporate even when capped properly. For this reason, it’s
important to know what factors affect solvent evaporation. I studied these
effects by altering different variables and calculating the percent loss of
solvents in capped autosampler vials. In doing so, I aimed to discover which
factors were most significant in contributing to evaporative loss. Does a snap
cap or a screw cap provide a better seal? Will a methanol diluent lead to
greater loss than an acetonitrile/water diluent? Do pre-slit septa have a
disadvantage in terms of allowing solvent to escape the vial more readily?
The
graphs I obtained helped answer these questions. You can compare the slopes of
each set of experimental conditions to determine which parameters had the
greatest effect on evaporation. The traces with the highest slopes had the
fastest rate of evaporation. So if two traces differ by only the solvent used
in the experimental conditions, you can conclude that the one with the faster
rate of loss was likely due to the solvent.
I averaged multiple replicates from
the same set of experimental conditions in each case in order to obtain more
reliable trends in the data. That is, I wanted to ensure that any differences
in the evaporation were in fact due to the variable under study, rather than
tolerance differences in how a particular vial and cap sealed together.
This information can aid in the
selection of suitable caps, solvents, etc. for your particular application. For example, if
you’re deciding between methanol and acetonitrile/water as a diluent for your
method, the results may provide you with information to make a more informed
choice.
