Malmstadt and Pardue developed a variable time method for the determination of
glucose based on its oxidation by the enzyme glucose oxidase. \({ }^{22}\) To
monitor the reaction's progress, iodide is added to the samples and standards.
The \(\mathrm{H}_{2} \mathrm{O}_{2}\) produced by the oxidation of glucose
reacts with \(\mathrm{I}^{-}\), forming \(\mathrm{I}_{2}\) as a product. The time
required to produce a fixed amount of \(I_{2}\) is determined
spectrophotometrically. The following data was reported for a set of
calibration standards
$$
\begin{array}{rrrr}
\text { [glucose] (ppm) } & & \text { time }(s) & \\
\hline 5.0 & 146.5 & 150.0 & 149.6 \\
10.0 & 69.2 & 67.1 & 66.0 \\
20.0 & 34.8 & 35.0 & 34.0 \\
30.0 & 22.3 & 22.7 & 22.6 \\
40.0 & 16.7 & 16.5 & 17.0 \\
50.0 & 13.3 & 13.3 & 13.8
\end{array}
$$
To verify the method a standard solution of 20.0 ppm glucose was analyzed in
the same way as the standards, requiring \(34.6 \mathrm{~s}\) to produce the
same extent of reaction. Determine the concentration of glucose in the
standard and the percent error for the analysis.