how to calculate Solvent Consumption for HPLC

[liltessa]

Hello

I'm Tessa, biology student. I have to perform an HPLC analysis for 20 samples with an elution (flow rate = 0.7 ml/min) in the following order:
0-10min = 100% of A
10-30 min = 0-15% of B in A
30-50 min = 15% of B in A
50-60 min = 15-25% of B in A
60-90 min = 25-100% of B in A
90-100 min = 100% of A

(Solvent A = acetonitrile/water, 1/9 v/v, pH 2.6; Solvent B = acetonitrile, 1/1 v/v, pH 2.6).

can anyone please show me how to estimate the solvent consumption?
Thank you

[Mattias]

Usually you make more mobile phase than you need, because you cannot use everything in the bottle (the filter need a few cm of solvent height to avoid air into the system). You also may want to rerun some samples and add a low flow program after the end of the sequence.

So for quick estimation: every injection is 1.7 hours, 20 injections is 34 hours. Count on some delay in the injection, so let's say 36 hours. 36 hours times 0.7 ml/min is 1500 ml of mobile phase. You will use more of A than B.

I would make 2000 ml of A and 1000 ml of B and feel safe.

If this is more an exam question, you can calculate the exact consumption by plotting the time (min) on the x-axis against the flow (ml/min) of mobile phase A on the y-axis. The consumption of A will be the area under the curve. Some instrument softwares do this calculation automatically (e.g. Chromeleon).

[Consumer Products Guy]

Out of curiosity, please post whether this is:

1. a school assignment

2. you don't want to run out of mobile phase overnight (remember, you can automatically lower the column flow after your injections on modern units)

3. your bean-counting auditors want to calculate how many cents of solvent are used per run