How to stack and stretch curves

Functions

You can stack and stretch curves from different runs to better visualize the differences. To achieve this you can use the following functions:

  • Normalise

  • Shift

  • Multiply.

Note: All the functions require the curves to be present in one chromatogram.

How to use the Normalise function

The Normalise function provides the simplest method to align curves with respect to the X-axis or the Y-axis for easier visualization.

The table below describes how to use the Normalise function:

Step

Action

1

  • Make sure that a chromatogram with the relevant curves is open in the Evaluation module.

  • Choose Operations:Normalise.

Result: The Normalise dialog box is displayed.

2

  • Select the curve you want to normalise in the left (Select curve to normalise) field.

  • Select the reference curve you want to normalise against in the right (Select help curve) field.Example: If you want to stack the curves, select the curve at the bottom of the stack as the reference curve.

  • Click OK.

Result: The Normalise window is displayed, where a box surrounds the curve selected to be normalised.

3

In the Normalise window, you can use the following command buttons:

Size Allows the arrow keys to be used to stretch the selected curve along its Y-axis or X-axis. This is useful for comparison of curves with, for example, different gradient lengths.

  • Click the Size button and use the arrow keys to stretch the the curve either along its Y-axis or X-axis.

Move Allows the arrow keys to be used to move the selected curve to any position on the chromatogram. Axes are automatically re-scaled to accommodate the new positioning. This function is useful for stacking curves.

  • Click the Move button and use the arrow keys to move the curve into position. The curve can also be moved with the mouse pointer. Click the mouse button when the curve is in the correct position.

Note: The curve can also be moved and sized with the mouse pointer.

Normalise The curve to be normalised will be adjusted to the help curve. Thus, the height of the highest peak on both curves will be the same and will occur at the same retention point.

  • Click the Normalise button. The curve to be normalised is automatically moved along the X-axis and stretched along the Y-axis.

  • Click OK to save the new normalised curve.

Result: The Save Curve dialog box opens.

4

Choose a curve position to save the curve in and click OK.

5

  • Choose Edit:Chromatogram Layout to open the Chromatogram Layout dialog box.

  • Select the normalised curve for viewing on the Curve tab.

  • Click OK.

6

Repeat steps 1-5 for all curves you want to stack or stretch.

How to move a curve with the Shift function

If you want to position a curve more precisely, the Shift function should be used. The function is similar to Normalise:Move but each curve is repositioned by a precise value instead of by eye and the instruction is logged in the evaluation log. The table below describes how to use the Shift function:

Step

Action

1

  • Make sure that a chromatogram with the relevant curves is open in the Evaluation module.

  • Choose Operations:Shift.

Result: The Shift dialog box is displayed.

2

  • Select the curve to be shifted in the Source chromatogram list.

  • Select a curve position in the Target chromatogram list.

  • Type a new Curve name or accept the default.

  • Select the axis/axes along which the shift is to be made:

    along the X-axis (Shift retention)

    along the Y-axis (Shift amplitude).

  • Type the shift value(s).

  • Click OK.

How to stretch and shrink a curve with the Multiply function

Curves can be stretched or shrunk on the x or y plane with the Multiply function. This function is similar to Normalise:Size, but each curve is repositioned with precise numbers instead of by eye and the instruction logged in the evaluation log. The table below describes how to use the Multiply function:

Step

Action

1

  • Make sure that a chromatogram with the relevant curves is open in the Evaluation module.

  • Choose Operations:Multiply.

Result: The Multiply dialog box is displayed.

2

  • Select the curve to be multiplied in the Source chromatogram list.

  • Select a curve position in the Target chromatogram list.

  • Type a new Curve name or accept the default.

  • Select the axis/axes along which the multiplication is to be made:

    along the X-axis (Multiply retention)

    along the Y-axis (Multiply amplitude).

  • Type the multiply value(s).

  • Click OK.

2005-06-15