A standard solution of glucose contains a known quantity of glucose in a known quantity of water. Scientists use standard glucose solutions to measure the concentration of a glucose in an unknown solution. These tests are helpful in many research experiments but also find practical medical application when testing patients for diabetes.
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Glucose is a 6-carbon sugar molecule, the most common carbohydrate in your body. People often refer to glucose as "blood sugar" as it circulates throughout your blood at a concentration of about 65 to 110 mg/mL. Classified as a monosaccharide, an aldose, a hexose and a reducing sugar, glucose chemically reduces other compounds in oxidation/reduction reactions by readily donating electrons. Glucose is also known as dextrose or D-glucose, due to its dextrorotatory property, the ability of glucose solutions to rotate plane polarized light to the right.
Standard solutions in general contain a known amount of substance dissolved in a known quantity of another substance. Usually, a standard glucose solution refers to a 1-percent glucose solution. Preparing a 1-percent standard glucose solution involves dissolving 1 g of glucose in 100 ml of water. Glucose standard solutions are used to create calibration curves against which unknown solutions are measured. These curves then help determine the concentration of the unknown solution.
Reactions of glucose with potassium permanganate generate calibration curves. Glucose readily donates electrons to permanganate ions in an oxidation-reduction reaction. The rate of this oxidation-reduction reaction depends on the concentration of glucose in solution. Solutions of permanganate ions have a distinct pinkish-purple color. When this solution is reduced, it becomes colorless. By measuring the different rates at which different known concentrations of glucose turn the pink solution colorless, you can generate a chart or "calibration curve" of concentration of glucose versus time.
Using Calibration Curves
After generating a calibration curve using a standard glucose solution and potassium permanganate, you can then determine the concentration of glucose in an unknown solution. Add the same volume of the unknown glucose-containing solution that you added of the known glucose containing solution, to the pink potassium permanganate solution. For example, if you used 2 mL of your 1 percent glucose solution when making your glucose calibration curve, use 2 mL of your unknown glucose-containing solution. Measure the rate at which the unknown solution turns the pink permanganate solution clear. Compare that rate to the rate of the known glucose solutions and you can determine the concentration of the glucose in your unknown solution. For example, if your unknown solution took the same amount of time to turn the pink solution clear as the 1-percent solution, then your unknown solution contains 1 percent glucose. If it took half as long, it contains 0.5 percent glucose.
Standard glucose solutions help measure glucose concentration in the blood of patients thought to have diabetes. Blood glucose may be measured when a person has fasted, or as part of an oral glucose tolerance test, known as OGTT. These tests measure glucose levels in blood samples taken from the patient using the principle of calibration to known standard glucose solutions. Normal fasting blood glucose levels fall between 70 and 90 mg/dL, while glucose concentrations of less than 140 mg/dL indicate normal OGTT blood glucose levels.