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  Home > JCE Print > Journal of Chemical Education > Issues > 2002  > February  >
Information • Textbooks • Media • Resources
Nonlinear Fits of Standard Curves: A Simple Route to Uncertainties in Unknowns
Carl Salter
Department of Chemistry, Moravian College, Bethlehem, PA 18018-6650

Robert de Levie
Department of Chemistry, Bowdoin College, Brunswick, ME 04011
Cover
February 2002
Vol. 79 No. 2
p. 268
Abstract
A simple nonlinear least-squares method is described that permits direct least-squares fitting to the data of a standard curve to obtain the unknown concentration and its associated uncertainty. This procedure uses the unknown concentration as a parameter of the fit, so that it and its uncertainty are obtained immediately, bypassing the need to compute a propagation of interdependent uncertainties. Examples of the procedure, as implemented on Excel, are given for a standard additions analysis and for an analysis based on a standard calibration curve.
Supplement
A detailed mathematical presentation of the equivalence of error in standard additions using the nonlinear fit y = m(x - xsa) is available.
*  Contents JCE2002p0268W.doc (Microsoft Word)
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*  Citation
 Salter, Carl; de Levie, Robert. J. Chem. Educ. 2002 79 268.
*  Keywords
 Analytical Chemistry; Laboratory Instruction; Statistics / Data Analysis
*  History
 Created:
Last Updated:		 January 2, 2002
July 27, 2005
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