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| Home > JCE Print > Journal of Chemical Education > Issues >
1999
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March
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Research: Science and Education
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Realistic Detection Limits from Confidence Bands
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Julia R. Burdge
The University of Akron, Department of Chemistry, Akron, OH 44325-3601
Douglas L. MacTaggart and Sherry O. Farwell
Graduate Office, South Dakota School of Mines and Technology, Rapid City, SD 57701-3995
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March 1999
Vol. 76 No. 3
p. 434
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| Abstract |
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Many methods exist for obtaining detection limits. Most analytical chemistry textbooks define the detection limit using either the 3-s method or the 2 x S/N method. These and similar methods can be grouped under the "classical" approach to estimating detection limits. This pedagogy in addition to past IUPAC and ACS approval has contributed to the common use of this approach, despite its shortcomings, by practicing analytical chemists. In the less commonly applied regression approach, which has recently received IUPAC approval, the detection limit is derived from confidence bands generated by least squares fitting of calibration data. These two approaches are compared here with the use of trace level sulfur gas data. Rigorous and easily implementable formulas are presented for the regression approach. In many typical instrumental calibration scenarios, the response variance is not constant, and is more optimally treated by weighted least squares (WLS) than by the often misused ordinary least squares (OLS). Selected data sets are used here to illustrate the impact of factors such as calibration design and scedasticity. On the basis of these comparisons, recommendations are made with regard to the preferential use of the regression approach compared to the classical approach, and the calculation and reporting of detection limits within the context of fully specified analytical methods using this approach.
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| More Information |
 Citation |
Burdge, Julia R.; MacTaggart, Douglas L.; Farwell, Sherry O. J. Chem. Educ. 1999 76 434.
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Keywords |
Laboratory Equipment / Apparatus; Analytical Chemistry; Curriculum; Statistics / Data Analysis; Teaching/Learning Theory/Practice
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History |
Created:
Last Updated: |
June 15, 1999
June 22, 2005
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| Home > JCE Print > Journal of Chemical Education > Issues >
1999
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March
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434
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