To analyze the data you are collecting, you will need to calculate initial velocity, v0. This initial rate of reaction can be expressed simply as a change in absorbance per unit of time:ΔA410/min.
This corresponds to the slope on your absorbance vs. time graph.
An example: if I'm measuring glutathione reductase activity by decrease of NADPH at 340nm within 3 minutes, how can I calculate the slope?
Dear Arbace,
Determining the Average Rate from Change in Concentration (absorbance, OD) over a Time Period
We calculate the average rate of a reaction over a time interval by dividing the change in OD over that time period by the time interval. For the change in OD of a reactant, the equation, where the brackets mean "OD", is
Rate = - [Reactant t2] - [Reactant t1] / t2 - t1
Note: We use the minus sign before the ratio in the previous equation because a rate is a positive number. We do not need the minus sign when calculating average rates from products.
Rate = -delta [Reactant] / delta t ; Rate = delta [Product] / delta t
Determining the Instantaneous Rate from a Plot of Concentration (OD) Versus Time
An instantaneous rate is the rate at some instant in time. An instantaneous rate is a differential rate: -d[reactant]/dt or d[product]/dt.
We determine an instantaneous rate at time t:
by calculating the negative of the slope of the curve of concentration (OD) of a reactant versus time at time t.
by calculating the slope of the curve of concentration (OD) of a product versus time at time t.
For more details, please use the following link:
http://www.chem.purdue.edu/gchelp/howtosolveit/Kinetics/CalculatingRates.html
Hoping this will be helpful,
Rafik
Dear Arbace,
Determining the Average Rate from Change in Concentration (absorbance, OD) over a Time Period
We calculate the average rate of a reaction over a time interval by dividing the change in OD over that time period by the time interval. For the change in OD of a reactant, the equation, where the brackets mean "OD", is
Rate = - [Reactant t2] - [Reactant t1] / t2 - t1
Note: We use the minus sign before the ratio in the previous equation because a rate is a positive number. We do not need the minus sign when calculating average rates from products.
Rate = -delta [Reactant] / delta t ; Rate = delta [Product] / delta t
Determining the Instantaneous Rate from a Plot of Concentration (OD) Versus Time
An instantaneous rate is the rate at some instant in time. An instantaneous rate is a differential rate: -d[reactant]/dt or d[product]/dt.
We determine an instantaneous rate at time t:
by calculating the negative of the slope of the curve of concentration (OD) of a reactant versus time at time t.
by calculating the slope of the curve of concentration (OD) of a product versus time at time t.
For more details, please use the following link:
http://www.chem.purdue.edu/gchelp/howtosolveit/Kinetics/CalculatingRates.html
Hoping this will be helpful,
Rafik
If you build your 2D graph, you should have fewer difficulties, since you can then always draw a right triangle and work out yourself how to get the slope.
Try to build the graph in the example you know, then build one triangle and extract the formula you mention from it by doing opposite side over adjacent.
You know we are talking about angles, right?
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