The most important things to do in thoroughly managing your acetonitrile stocks are to note down the name of the user and composition/mixing date of the mobile phase on the mobile phase bottle. (This is to eliminate the problem of mobile phase that is disposed of due to unknown solution content.) Otherwise, you can reduce solvent wastage by reviewing analytical processes on a daily basis and making the following small adjustments:
(1) Switch over to methanol as the column washing solvent
(2) Reduce the amount of solvent consumed at pre-analysis conditioning and post-analysis shutdown
(3) Mix two mobile phase solutions even under isocratic conditions (for users of the gradient system)
1) Switch over to methanol as the column washing solvent
Since acetonitrile is used as the mobile phase in analysis, won't acetonitrile be used for washing the column?
To switch acetonitrile currently used for analysis over to methanol, changes in the separation pattern must be taken into consideration. However, in many cases, washing with methanol is possible; and, sometimes, methanol is more effective in washing compared with acetonitrile. The exception, however, is that with methanol/water-based solvents, liquids should be delivered first at a slightly lower flow rate while paying more attention to the pressure since the liquid pressure is higher than that of acetonitrile/water-based solvents.
(Before you use methanol, check the Column's Instruction Manual to ensure it can be used.)
2) Reduce the amount of solvent consumed at pre-analysis conditioning and post-analysis shutdown
Won't more than the necessary amount of solvent flow be used when the operator is away from the instrument for a long period of time during conditioning, when mobile phase is delivered before analysis until the baseline stabilizes, or during shutdown, when mobile phase is delivered after analysis until the column temperature drops? Automation functions driven by an LC workstation, such as Shimadzu LCsolution, or a system controller can start analysis or stop pump operation after a fixed time has elapsed. These functions can be used to limit the amount of wasted mobile phase when actual measurement is not being performed.
3) Mix two mobile phase solutions using the gradient system even under isocratic conditions
Generally, with isocratic analysis, water-based solvent and organic solvent are pre-mixed for use.
However, won't excess solvent be wasted after analysis ends?
Even with isocratic analysis, solvent can be mixed using two solvent delivery units, just as for a high-pressure gradient system, or mixed using a low-pressure gradient unit.
In isocratic analysis, more than the necessary amount of mobile phase is prepared to prevent the system from running out of mobile phase during analysis, which means that excess mobile phase is eventually discarded. (It can be retained if used within a short period; however, evaporation might alter its composition.) Also, when you review analysis conditions and attempt to continue analysis using other analysis conditions, half-used mobile phase will be discarded if it was pre-mixed, resulting in wasteful solvent consumption.
In a gradient system, since organic solvents are supplied from independent mobile phase bottles, they can be re-used even under different mobile phase conditions. In analysis requiring minute separation, comparison and study are necessary regarding separation when pre-mixed mobile phase is used. In the majority of cases, however, there is no need to change analysis conditions considerably, which enables savings in solvent.