Al, B, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, Rb, Si, Sr, Ti, V and Zn are determined simultaneously by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). A 500 mg sample of dried plant material is weighed into a 20 mL high form silica crucible and dry ashed at 485°C for 10–12 hours. (Crucibles are covered during the ashing as a precaution against contamination.) The ash is equilibrated with 5 mL of 20% HCl at room temperature for ½ hour. Then 5 mL of deionized water is added, gently swirled and allowed to settle for 3 hours. The solution is decanted into 15 ml plastic disposable tubes for direct determination by ICP-OES. Upon special request the dry ash can be refluxed in 20% HCl to improve the recovery of Fe, Al, and Cr.
(See Method References No. 58 and No. 21)