Comparison of some extraction methods for the determination of potassium content in solid materials

Kalij spada med najpomembnejša rastlinska makrohranila in je nujno potreben za rast in razvoj rastlin in živali. Določanje kalija postaja predvsem v kmetijstvu vedno pomembnejše. Lahko dostopni kalij je tisti del celokupne vsebnosti, ki se nahaja v talni raztopini ali pa je kot koloid razpršen v tleh in je kot tak dostopen za rastline. Tekom diplomskega dela smo izvedli študijo vsebnosti kalija v štirih trdnih materialih, v travi, pepelu, blatu čistilnih naprav in v zemlji. Vsebnost kalija smo določevali s hitrimi testi, kivetnimi testi in s kalijevo ion selektivno elektrodo. Za razkroj trdnih snovi se lahko uporabljajo različna ekstrakcijska topila. Določitev kalijevih ionov v trdnih materialih smo izvedli s petimi različnimi topili in metodami za ekstrakcijo trdnih snovi. Uporabili smo sledeče metode: i) Olsenovo metodo kjer pripravimo ekstrakcijsko topilo tako, da v destilirano vodo dodamo natrijev hidrogenkarbonatii) Bray in Kurtzovo metodo 1 ter iii) Bray in Kurtzovo metodo 2, kjer je topilo mešanica amonijevega fluorida in klorovodikove kisline, redčena z destilirano vodo. Razlika med metodama ii) in iii) je v količini klorovodikove kisline, ki jo dodamo ekstrakcijskemu topiluiv) Al metoda po Egner -Riehm – Domingu, ki je največkrat uporabljena metoda za ekstrakcijo trdnih snovi. Po tej metodi je topilo mešanica amonijevega laktata in ocetne kisline, redčena v destilirani vodi ter v) Williams in Stewartova metoda, kjer je ekstrakcijsko topilo ocetna kislina, redčena v destilirani vodi. Vsebnost kalija v vzorcih smo najprej preverili s hitrimi testi, da smo ugotovili približno koncentracijsko območje. Glede na rezultate smo vzorce ustrezno redčili in vsebnost kalija določili še s kivetnimi testi. Vsebnost kalija v pepelu smo določili tudi s kalijevo ion selektivno elektrodo. Rezultati dobljeni s kivetnimi testi za metodi D1 in D2 zaradi velikega redčenja niso natančni in znatno odstopajo od ostalih. Metoda C se je izkazala kot metoda pri kateri se je iz vseh materialov izločilo dosti kalijevih ionov. Najmanj kalija se je izločilo z metodo E. Koncentracije kalija za pepel, ki so dobljene z ISE so veliko nižje od povprečnih vrednosti kalorimetričnih metod. Največ kalija se je izločilo iz pepela, najmanj pa iz zemlje.Potassium is one of the most important vegetable macronutrients that is essential for the growth and development of plants and animals. Determination of potassium is becoming increasingly important in agriculture. Easily accessible potassium is the part of the total potassium content that can be found in the soil solution or as a colloid dispersed in the soil and is as such accessible to plants. During the diploma work, the study of potassium content in 4 solid materials, in grass, ash, sewage sludge and soil was performed. Potassium content was determined with rapid tests, tube tests and with the potassium ion-selective electrode. Different extraction solvents could be used for the decomposition of solid materials. The determination of potassium ions in solid materials was performed with five different solvents and methods for solid material extraction. The following methods were used: i) the Olsen method, where the extraction solvent is prepared by adding hydrogen carbonate into distilled waterii) the Bray and Kurtz method 1 and iii) the Bray and Kurtz method 2, where the solvent is a mixture of ammonium fluoride and hydrochloric acid, which is diluted with distilled water. The difference between methods ii) and iii) is in the quantity of the hydrochloric acid added to the extraction solventiv) the Al method after Egner-Riehm-Domingo is a method often used to extract solid materials. This method uses the solvent which is a mixture of acetic acid diluted with distilled water and v) the Williams and Stewart method, where the acetic acid is the extraction solvent diluted with distilled water. Potassium content in samples was first specified with rapid tests to determine the approximate concentration range. According to obtained results, samples were diluted and the potassium content was determined with tube tests. Potassium content in ash was further determined also with the potassium ion-selective electrode. The results obtained by the tube tests for methods D1 and D2 are not accurate due to the high dilution and differ significantly from the others. Method C proved to be a method in which much potassium ions were extracted from all materials. The lowest amount of potassium was extracted by method E. Potassium concentrations in ash obtained by ISE are much lower than the average values from calorimetric methods. Most of the potassium was extracted from the ash, and the least from the soil