Rapid Analysis of Soil Samples By Flame Atomic Absorption.

Soil nutrients are important for several applications, including agriculture, mining and construction.  A new automated procedure for soil analysis by flame atomic absorption (AA) is described.  Two grams of soil are weighed and placed in a 250 mL plastic bottle for Mehlich extraction. The sample preparation procedure involves, 1) addition of 20 mLs of Mehlich 3 extractant , 2) 5 minutes of mixing,  and 3) filtration of extractant (Whatman grade 2 filter paper).   One mL of sample filtrate is aliquoted into a vial for offline (10x) autodilution.  The undiluted sample is measured for low concentration metals (Na, Cu, Mn and Zn) by FAA while the 1 mL fraction is autodiluted for the determination of higher concentration metals (K, Ca, Mg and Fe).  After the first group of metals are analyzed, the second set of autodiluted samples are and ready.  Samples are introduced using a high throughput introduction system that utilizes an injection valve to rapidly load (vacuum) and inject (peripump) the samples into the flame.  Using this fast sample introduction system throughput is approximately 8 seconds per sample for each analyte.  Combining offline autodilution and inline fast analysis provides accurate and precise data for 8 analytes in less than 1min per sample.  This procedure offers a low-cost FAA alternative to soil analysis on the ICP for multiple elements in soil samples. The FAA methods are set up to accommodate for a wide range of concentrations in the soils.