Chromatography Forum

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

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).

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