Solvent evaporation in your sample vial —How to avoid it

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.

                Click here to read the full study.