Slope from absorbance help?

Question

Finding the slope of a line from a chart recorder?

I'm trying to find the gradient in order to calculate the initial velocity.

The pen moved at 10 mm/min. I need the slope to calculate the initial velocity of an enzymatic reaction.

Other recorder settings: 0-1 V, full scale deflection of 0-2 absorbance units, not sure if that is relevant.

Here is a pic: http://imgur.com/tD3zGIe

Thanks for any help

Whit · Accepted Answer

I assume you seek the slope of the last part of each line, where it moves dramatically in a roughly linear fashion before stopping?

If that is the case, I would find the "average slope" (since they all curve a bit, and thus are technically not "lines") by:

1) Determine the coordinates of the starting point (the last point on the steady state part of the graph, or the first point you can identify as part of the sharp movement).  One coordinate will be time (based on the speed the paper in the chart recorder moves).  The other will be whatever value is deflecting the pen.

2) Determine the coordinates of the final point on the chart, just before the pen is reset.

3) The slope will then be:

= (Deflection 2 - Deflection 1) / (Time 2 - Time 1)

and its units will the same units you used to measure the Deflections and Time.

I hope that answers your question... as I have never worked with a chart recorder...

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Slope from absorbance help?

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