Required practical 11 - Measuring concentration of glucose using a calibration curve

Outline the method for this practical:

• Create a dilution series using glucose solution and distilled water

• Then have 6 test tubes add using a syringe transfer 2 cm cubed

• Then get the 3 unknown urine samples, and add 2 cm cubed into 3 new test tubes

• To all the test tubes add Benedicts solution

• Place them in a water bath (90 degrees) for 10 minutes

• After take them out and make sure apparatus is cooled before using the colorimeter

• Place the 0.0 mmol/dm cubed concentration in the cuvette first to calibrate (should get an absorbance at 0), and record the absorbance for the rest of the dilution series

• Then plot a graph with concentration on y-axis (independent) and absorbance on x-axis (dependent)

• Then find the absorbance of the 3 urine samples and then look at the graph to find the concentration

Alternative method: using another Benedicts solution

When using another benedicts solution, this reacts with the glucose to give a white percipitate, reducing the colour blue. So first filter the solution then measure the absorbances using a cuvette.

How to increase accuracy of the estimate of the unknown glucose solution?

• Increase the number of concentrations - using smaller intervals for the calibration curve

The theory: What does high glucose concentration suggest?

• Lack of insulin to absorb the glucose from the blood, not decreasing the concentration of glucose in the blood.

• All the glucose transport proteins in the proximal convoluted tubule being saturated, preventing the reabsorbtion of glucose