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# Calculations for Determining a Titer

The purpose of the experiment that took place was to determine the titer of B-D-galactosidase using the enzyme-linked immunosorbent assay. I used a formula obtained from class mates to find the titer. I want to be sure this is the correct method for determining the titer. I attached my data, including the results from the plate reader, and my graphs of the log of the inverse of the antibody dilution vs. absorbance. The formula I used to find the titer of rows C and D are below. If this is not the correct method for finding the titer, what is, and how is it performed? And what do the results of the titers mean?

Row C
y = -0.033x + 0.1864

A450 max = 0.263
½ max = 0.1315
0.1315 = -0.033x + 0.1864
-0.0549 = -0.033x
1.6636 = x
10^(1.6636) = 46.09
Titer = 46.09

Row D
y = -0.0415x + 0.2306

A450 max = 0.339
½ max = 0.1695
0.1695 = -0.0415x + 0.2306
-0.0611 = -0.0415x
1.4723 = x
10^(1.4723) = 29.67
Titer = 29.67

#### Solution Preview

It looks like your calculations are correct if your definition of titer is the concentration that is ½ your max OD450. I have seen various definitions of titer. Some say it is the inverse of the dilution at which your OD450 is 1.0. Others say use the dilution at OD450 = 0.5. In either of these cases, you would plug in the value of 1.0 or 0.5 for your y-value in each equation ...

#### Solution Summary

Calculations for determining a titer is provided.

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