Producing known glucose standards
A dilution series provides glucose solutions of several known concentrations. Measurements from these standards can later be used to determine the glucose concentration of an unknown urine sample, or an equivalent unknown glucose solution.
Use pipettes to combine different volumes of glucose stock solution and distilled water in labelled test tubes. Varying the proportions produces a range of known glucose concentrations.
Core apparatus
Solutions and heating
- glucose stock solution
- distilled water
- quantitative Benedict's reagent
- unknown urine sample or equivalent solution
- pipettes
- test tubes and test-tube rack
- water bath
Measurement and recording
- colorimeter
- cuvettes
- labels
- graph paper
- pen or pencil and ruler
- goggles and gloves
Treating the standards
- Prepare and label the glucose standards.
- Add the same fixed volume of quantitative Benedict's reagent to every tube.
- Heat the tubes in a water bath at a temperature of at least 70 °C for 5 minutes.
- Filter each mixture to remove the white precipitate.
- Transfer the same fixed volume of each filtrate into a separate labelled cuvette.
| Factor | How consistency is maintained |
|---|---|
| Benedict's reagent | Use the same fixed volume for every standard. |
| Heating | Keep the water-bath conditions and heating time the same. |
| Filtrate volume | Place the same fixed volume of filtered solution into each cuvette. |
Exam Tip: State that the standards have known glucose concentrations and are all subjected to the same Benedict's treatment, heating and colorimetry conditions.