Sample preparation for determining ions in dark colored sodic soil extracts

Robbins, Charles W. (1989) Sample preparation for determining ions in dark colored sodic soil extracts. Soil Science Society of America Journal. 53:721-725.

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Abstract

Saturation paste extracts of sodic soils (pH >8.5 and electrical
conductivity <4.0 dS m-1) usually contain dark colored, suspended
organic matter that interferes with colorimetric, turbidimetric, potentiometric,
ion chromatographic (IC) and to a lesser extent, atomic
absorption spectrophotometry and flame emission procedures. Bicarbonate
also interferes with formate analysis by IC in those extracts.
This study was conducted to develop a simple pretreatment
method for removing those interferences without introducing new
interferences. Fifteen mL extract samples were titrated to pH 8.4,
then to 4.7 and finally to a pH range of 3.0 to 3.5 with standardized
H2S04 or HCl. The first two end points determine CO23- and
HCO3 concentrations. The third pH adjustment removed the
HCO3 interference from the formate analysis and allowed for organic
matter coagulation. The acid choice depended on whether CL-
or SO24- was to be measured later. To remove the organic matter,
the extracts were centrifuged and forced through a 0.2-µm nylon
filter following 0.08 M AlCl3 or 0.04 M Al2(SO4)3 treatments. Formate
and acetate concentrations were determined by IC. The
concentrations were determined by colorimetric, and IC procedures.
The SO24- concentrations were measured turbidimetrically and by
IC. The extracts were analyzed for Ca2+ and Mg2+ by atomic adsorption
spectrophotometry, and Na+ and K+ by flame emission. Titrating
the extracts as described provided CO23- and HCO3- data,
removed the HCO3 interference from the formate analysis, and allowed
Al3+ to coagulate the suspended organic matter, which was
then removed by centrifugation and filtration. This pretreatment did
not interfere with any of the analytical methods tested, except for
cation determination by IC and anion determination by IC when
methyl orange was used as a pH end point indicator.

Item Type:	Article
NWISRL Publication Number:	0680
Subjects:	Soil Research methodology Mass Import - autoclassified (may be erroneous)
Depositing User:	Dan Stieneke
Date Deposited:	20 Nov 2010 21:53
Last Modified:	03 Jan 2017 21:15
Item ID:	518
URI:	https://eprints.nwisrl.ars.usda.gov/id/eprint/518