Measurement of Potassium and Sodium in Bread

Bread contributes about one-sixth of daily salt intake and is used to improve flavour and texture.

The amount of sodium in bread can differ significantly, depending upon brand and type
of grain used, ranging from 592mg/100g to
748mg/100g.

The level of sodium in bread is primarily due to the amount of salt added to the dough during manufacture. The amount of potassium is determined by the type of flour and the washing and bleaching operations during cereal processing.

Bread does not make a significant contribution to maximum daily requirements for potassium.

Method followed for this analysis is AOAC Official Method 990.23 (refer to BWB Method number 20).

Procedure
All solutions are prepared using deionised distilled water.

The sample was heated at 60 degrees centigrade overnight to dryness.

The dried sample is then ground and homogenised in a suitable grinder.

The test portion and crucible are weighed and dry ashed in an open inert vessel such as a crucible for 2 hours, then reweighed after ashing and placed back into the oven for 10 minutes. The sample was then reweighed and the process repeated until no change in weight was measured over the 10-minute span. This ensured that all of the combustible products present were removed.

Transfer the dried test sample to an airtight container of a capacity of about twice the test portion size.  Close the container and mix the sample thoroughly via inversion.

Weigh sample to nearest 1mg, add a 1.25g portion of the sample into 50ml polypropylene beaker.

Dissolve sample into approximately 20ml warm DI water while mixing. Quantitatively transfer contents to a volumetric flask and made up to volume. Alternatively, a steam bath can be used to aid dissolution.

Stock solutions are then made up of potassium and sodium; it is recommended that a single point calibration is carried out prior to examination to determine a rough estimated range in which the sample will fall. Once this expected sample concentration is determined, at minimum 5 standard solutions should be produced for calibration of the instrument.

After calibration the sample can then be aspirated into the flame photometer, to decrease the likelihood of random errors, multiple repeats of the same samples should be aspirated.

To obtain the concentration of sodium and potassium in the sample, it should be noted that a dilution step has been performed. The result of this experimental procedure is a value of concentration when dry ashed sample is diluted in 20ml water.

Preparation of Standard Graph

Set the flame photometer in accordance to MultiPoint/Single Ion Calibration found on page 24 of the BWB Technologies Installation and Operation Manual, to measure potassium emission. Nebulise the working standard solutions and adjust the controls until steady zero and maximum readings are obtained. Nebulise the intermediate working standard solutions and construct a graph relating raw emission data (known as RAW in BWB the flame photometer) to concentration of all the standard solutions.