UV/visible spectroscopy. An analyst was told to determine...

Question

An analyst was told to determine the amount of glucose in blood using a colorimetric method. The analyst prepared a series of standards containing known amounts of glucose and obtained the results given in the Table below by UV/visible spectroscopy.

Consentration of glucose/mmol ^L-1 Absorbance

^{0,0 0.11}

^{2.0 0.25}

^{4.0 0.45}

^{6.0 0.63}

^{8.0 0.87}

^{10.0 1.05}

^{12.0 1.24}

Use the data in the Table to plot a graph of absorbance against glucose concentration. a) Is Beer’s Law obeyed? b) Calculate a value for the molar absorptivity, ε. c) If the absorbance for a urine sample was 0.53, use the graph to determine the glucose concentration.

Answer 1

1. Plot the data ... x-axis for Concentration & y-axis for Absorbance ... by hand or use Excel
2. Beer's Law states: Absorbance is directly proportional to Concentration ... A = abc ... A is for Absorbance, a is for molar absorptivity (can be given for known chemical or asked to be determined for unknown), b is for length of path light (usually 1 cm for the cuvette), c is for Concentration
3. Should see linear line on plot if Beer's Law is obeyed
4. Can you see that the molar absorptivity is the slope of the line and follows the linear equation y = mx + b?
5. Now, with given Absorbance of urine sample, determine the Concentration using your linear equation