Measurement of Potassium
in Unashed Plant Leaves 2 1
This method uses a suspension of ground plant material to directly measure the potassium concentration. It eliminates the usual steps of ashing and subsequent dissolution of the resulting ash.
The method was compared to alternative methods such as chemical analysis and spectrophotometric methods. Collaborative studies using a range of samples gave a mean of 1.74% potassium by this extraction technique as compared to 1.75% by alternative methods. The standard deviation of an analysis in the two different sample sets was ±0.0086 and ±0.0108.
Solution and Standard Preparation:
Deionised distilled water is used throughout to prepare the sample solutions. Glycerol-2-propanol Reagent was prepared by adding 200mls of 2-propanol to 125 grams of glycerol.
Sample Preparation Procedure:
The air-dried plant material was ground in a mill fitted with a 60-mesh screen and the resulting powder was thoroughly mixed by tumbling end-over-end in a jar less than ¼ full for 15 minutes.
A 1 gram sample of the air-dried plant material is weighed into an aluminium weighing container and dried for 48 hours. The container is reweighed and the loss due to moisture is calculated.
25mg sample of the air-dried plant material is weighed into a 50ml Erlenmeyer flask. 10ml of Glycerol-2-propanol Reagent is pipetted onto the plant material and the mixture is gently swirled to wet the powder.
The wetted plant material is quantitatively transferred to a 250 ml volumetric flask and made up to volume with deionised water. This is a 1:10,000 dilution.
The suspensions can be analysed by directly introducing into the flame. Prior to measurement the suspension should be thoroughly mixed and then allowed to stand for 5 minutes, to allow the particles to settle.
The resulting reading should be corrected for moisture content and dilution factor. This is done by accounting for moisture loss during the drying process and also the 1;10,000 dilution to return you to the value of potassium in your original sample.
Testing to factor in the difference in measured concentrations across a range of different parts of the plant that the tissue sample was acquired from should be accounted for into the results so that variances between samples can be accounted for when presenting data and sampling techniques.
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.
1 Mason, J.L, ‘Flame Photometric Determination of Potassium in Unashed Plant Leaves’, Anal. Chem., 35, (1963), p. 874-875.