# Get Empowered: Review Window and the Processing Method | Tip #121, Reader Question

By May 15, 2019

## Tip #121: Reader Question: How do I calculate column void volume? Welcome back to Get Empowered! In the last Empower tip-of-the-week post for Empower Chromatography Data Software, we learned how to have Empower report ‘0’ for a peak field when a peak is missing (Tip #120).

In this week’s tip, we will answer another question.

Question: How do I calculate column void volume?

One way to determine the void volume time is to inject something that will not be retained on the column and use the retention time of the unretained component. There is a way to do this mathematically and have Empower do this for us.

Let me show you how it is done.

### Step 1

The math is illustrated in ‘Help’ in the Columns Calculator v2.0. (figure 1). Figure 1

### Step 2

Create Custom Sample Fields for Column Length, Column Diameter and Porosity Factor. In this case, we use a column with a length of 15cm and internal diameter of 0.46cm with a porosity factor of 0.66 (figure 2). Figure 2

### Step 3

Create a Custom Result Field to calculate Column Volume (figure 3). Figure 3

### Step 4

Create a Custom Result Field to calculate Void Volume (figure 4). Figure 4

### Step 5

Empower calculates the Void Volume in ml and the value can be entered in to the Processing Method on the Suitability tab (figure 5). Figure 5

### Step 6

Now we have accurate calculations for K Prime and Selectivity (figure 6). Figure 6

It’s that easy!

Final notes:

• Please be sure to correct your final value for the flow rate. In this case, the flow rate was 1ml per mn.
• This procedure can be followed using the QuickStart or Pro interface.

Please rate this Empower Tip of the Week Next week in Empower Tip #122 – More answers to questions from our readers

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