Bill McConnell:

Glucose
Definitive Method: Isotope Dilution Mass Spectrometry.
Reference Method: Hexokinase/G6PD after Somogyi precipitation.

Common Methods:
Glucose Biosensor (Glucose Oxidase/Glucose Dehydrogenase)
Hexokinase Enzymatic method (Endpoint or Kinetic assay)
Glucose Oxidase (Oxygen Consumption sensor)

Glucose is a Reducing Substance:
In dilute base solution the ketose version of a sugar is in equilibrium with the aldose form. The aldehyde group may be oxidised to a carboxylic acid group. This is the basis of Benedicts test. Reducing sugars may be classified in this way. All monosaccharides are reducing sugars.

Other Methods:

"Bucket Chemistry"

Traditional (Benedict's solution) for reducing substances (including glucose). Copper II reduced to copper I which then precipitates as yellow CuOH and red CuO.

Clinitest (modified Benedicts)

Dipstick tests (Clinistix etc)

Enzymatic methods:

Hexokinase (most common -see below)

Glucose Oxidase (coupled to peroxidase indicator dye, Oxygen consumption detection system or bioamperometric detector).
Glucose + O₂ ==> Glucuronic acid (Gluconolactone) + H₂ O₂

Glucose Dehydrogenase (Coupled to NAD+ or amperometric detector).
Glucose + NAD⁺ ==> Glucuronic acid (Gluconolactone) + NADH +H⁺

Many portable glucose analysers are available now. Older generations use enzymes coupled to indicator dyes with a reflectometer detection system.

Glucose Oxidase and Glucose Dehyrogenase are used in biosensors employing enzyme coupled amperometry. Important for new generation POCT analysers. Improved accuracy and precision; as well as convenience. Specific for B-D Glucose.

Non-invasive methods:

Iontophoretic sensor (enzyme coupled).

IR/NIR multi-wavelength corrected laser units- still being field tested.

Hexokinase Method for Glucose Measurement:

Glucose + ATP <==HK==> Glucose-6-phosphate + ADP

Glucose-6-phosphate + NADP⁺ <==G6PD==> 6-phosphogluconate + NADPH + H⁺

Measure increased absorbance at 340 nm (rate or end point). This is proportional to glucose concentration in original sample.

Disaccharides:
Maltose (glucose + glucose) Reducing Sugars. Anomeric carbon available for one of the glucose units to form the aldehyde that can oxidised to carboxylic acid.
Lactose (glucose + galactose) Reducing sugar for same reasons as maltose.
Sucrose (glucose + fructose) Non-reducing sugar since anomeric carbons of both glucose and fructose involved in the dissacharide bond.

Benedict's Solution:
One liter of Benedict's solution contains 173 grams sodium citrate, 100 grams sodium carbonate, and 17.3 grams cupric sulfate pentahydrate. It reacts chemically like Fehling's solution; the cupric ion (complexed with citrate ions) is reduced to cuprous ion by the aldehyde group (which is oxidized), and precipitates as cuprous oxide, Cu2O.