Fertilizer Analysi Methods

Element

Method

Method description

Heavy metals (arsenic, cadmium,

chromium, cobalt, lead and nickel)

Determination

of elements after digestion with acid

A suitable amount of sample is digested using weak acid. The solution is measured for concentration of various elements using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES).

Micro and Macro elements (Calcium, magnesium, potassium, sodium, phosphorus, sulphur, iron, manganese, zinc, copper, boron, molybdenum and silicon)+HM

Determination

of elements after digestion with acid

A suitable amount of sample is digested using weak acid. The solution is measured for concentration of various elements using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES).

Urea

Colorimetric

A suitable a mount is reacted with 4-Dimethylamino Benzaldehyde to yield a yellow color which is analysed at 420 nm in the UV-Vis spectrum and obeys the Beer- Lambert law

Biuret

Colorimetric

Biuret is a compound produced by heating urea at 180 ℃. Biuret test is the name of a chemical test that utilises the Biuret reagents, which contains a 1% solution of Copper II sulphate (CuSO₄). In the presence of alkaline Rochelle salt, when Biuret is reacted with dilute copper sulphate, a purple coloured substance is formed. The reason behind this colour is the formation of a chelate complex or the copper coordination complex.

Ammonium (N)

Colorimetric

Ammonia reacts with hypochlorite ions generated by the alkaline hydrolysis of sodium dichloro-isocyanurate to form monochloramine. This reacts with salicylate ions in the presence of sodium nitroprusside at around pH 12.6 to form a blue compound. The absorbance of this compound is measured spectrophotometrically at wavelength 660nm and is related to the ammonia by means of a calibration curve.

Nitrates (N)

Colorimetric

Nitrate is reduced to nitrite by hydrazine under alkaline conditions. The total nitrite ions are then reacted with sulphanilamide and N-1- naphthylethylenediamine dihydrochloride under acidic conditions to form a pink azo- dye. The absorbance is measured at 540nm and is related to the nitrate concentration by means of a calibration curve.

Fluoride

Colorimetric

Fluoride is allowed to react at a pH of 4.5 with the red chelate formed between

cerous nitrate and alizarin fluorine blue. The absorbance of the resulting blue complex is measured at wavelength 620nm.

pH

Potentiometric

pH is determined by using a high impedance voltmeter. The potential between two electrodes is measured using the voltmeter on a fertilizer suspension of 1:10

(fertilizer: water)

Moisture

Gravimetric

With oven-drying method, the loss of water on heating

fertilizer samples at a certain temperature is estimated. The temperature depends on the fertilizer type.

Particle size

Sieving

Particle size distribution is measured by conducting a screen

analysis by passing a representative sample through stacked sieves.