Potassium, atomic emission spectrophotometry

Potassium is analyzed in chemicals that are used in the fertilizer industry and in finished fertilizers by flame photometric methods (44) or volumetric sodium tertraphenylboron methods (45) as approved by the AO AC. Gravimetric deterrnination of potassium as K2PtClg, known as the Lindo-Gladding method (46), and the wet-digestion deterrnination of potassium (47) have been declared surplus methods by the AO AC. Other methods used for control purposes and special analyses include atomic absorption spectrophotometry, inductively coupled plasma (icp) emission spectrophotometry, and a radiometric method based on measuring the radioactivity of the minute amount of the isotope present in all potassium compounds (48). 

Elemental composition As 96.12%, H 3.88%. Arsine may be absorbed in potassium permanganate solution or in bromine water and the solution may be analyzed for arsenic by atomic absorption or emission spectrophotometry (see Arsenic). Alternatively arsine may be oxidized by moist air in presence of hght to arsenic which may then be digested with nitric acid and determined as above. 

Sodium may be determined by atomic absorption spectrophotometry (AAS), flame emission spectrophotometry (FES), electrochemically with an Na -ISE, or spectrophoto-metrically. Of these methods, ISE methods are by far the most common. Excellent accuracy and coefficients of variation of less than 1.5% are readily achieved with modern equipment, reliable calibrators, and a good quality assurance program. Because sodium and potassium are routinely assayed together, methods for their analysis are described together later in this chapter. 

A.M.R. Ferreira, A.O.S.S. Rangel, J.L.F.C. Lima, Flow injection systems with stream splitting and a dialysis unit for the soil analysis of sodium and potassium by flame emission spectrometry, and calcium and magnesium by atomic absorption spectrophotometry, Commun. Soil Sci. Plant Anal. 26 (1995) 1532. 

Sulphate, chloride (Cl ), nitrate (NO ), and ammonium (NH ) in water were measured with a Technicon Autoanalyzer II system by the methylthymol blue, mercuric thiocyanate, cadmium reduction and sodium nitroprusside methods, respectively. Sulphate and Cl in highly colored samples were measured by means of ion chromatography. Cations were analyzed with an atomic-absorption spectrophotometer by means of flame-emission spectrophotometry for potassium (K ) and... 

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