Comparison of Probe with Bath Ultrasonic Leaching Procedures for Preparation to Heavy Metal Analysis of Bio-Collectors Prior to Atomic Absorption Spectrometry

Abstract

Both comparison and optimization of two sample preparation methods (probe and bath) based on leaching of lead (Pb), zinc (Zn), manganese (Mn) and nickel (Ni) from bio-collector sprouts (Pinus sylvertris L., Picea orientalis L., Thuja orientalis L.) under ultrasonic effect has been examined. The best analytical conditions influencing leaching such as sonication times, acid type, acid concentrations, ultrasound amplitude and sample position (wet, dry and grinding) were determined. Leachatants obtained upon sonication were directly nebulized into an air-acetylene flame for fast metal determination by atomic absorption spectrometry (AAS). Optimum conditions for ultrasonic metal leaching were as follows: a 15 min for probe or 30 min for bath sonication time, wet sample position, nitric acid (HNO3) solvent, 1% (w/v) for probe or 2% (w/v) for bath solvent concentration and 20% amplitude for probe. Comparable results for the ultrasonic leaching with probe (UL-P) and the ultrasonic leaching with bath (UL-B) for metals in certified reference material and bio-collectors have been obtained. Besides, UL-P reduces the time required for all treatments with UL-B approximately from 30 min to 15 min. The accuracy of methods was tested either by comparing obtained results with those of ashing method (AM) or by application on a certified reference material (CRM-7, Tea Leaves). The recoveries of metals using CRM-7 ranged from 94% to 104% for UL-P and 91% to 101% for the UL-B. The precision variance either between UL-P and UL-B or UL-P and AM was not significant at 0.05 probability for all metals. The relative standard deviation % was obtained between 3.4-7.6% (n = 3) and 4.7-9.5% (n = 3) for UL-P and UL-B, respectively, depending on the analyte.