Prev. Article Next Article Table of Contents

Article

Two Experiments Illustrating the Importance of Sampling in a Quantitative Chemical Analysis

Your current credentials do not allow retrieval of the full text.

Purchase the full-text

PDF/HTML,
figures/images,
references and tables,
(where available)

David Harvey

Department of Chemistry, DePauw University, Greencastle, IN 46135

J. Chem. Educ., 2002, 79 (3), p 360

DOI: 10.1021/ed079p360

Publication Date (Web): March 1, 2002

Section:

History, Education, and Documentation

Abstract

With many instructors of quantitative analysis courses emphasizing the analysis of "real-world" samples, there is a need for more experiments illustrating the importance of sampling as a source of uncertainty. Unfortunately, the few available experiments are either very lengthy or use instrumentation that is not widely available. This paper describes modifications to two previously published experiments illustrating the importance of sampling. The gross sample, a mixture of the acid-base indicator erythrosin B coated on crystalline NaCl, is analyzed spectrophotometrically after diluting individual samples with distilled water. The first experiment uses a four-level nested design to determine the contribution to the total variance of sampling, sample preparation, the spectrometer, and the sample cell's positioning in the spectrometer. The second experiment investigates the relationship between sampling variance and sample size. Each experiment can be completed in less than three hours. At first glance, the sample appears to be homogeneous and students are often surprised to discover that sampling is the greatest source of variance. This discrepancy between the expectation that sampling uncertainty is insignificant and experimental evidence to the contrary helps emphasize the importance of sampling.

Keywords (Audience):

Second-Year Undergraduate

Keywords (Domain):

Analytical Chemistry

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

Quantitative Analysis

View: Hi-Res PDF | PDF w/ Links

Citing Articles

Citation data is made available by participants in CrossRef's Cited-by Linking service. For a more comprehensive list of citations to this article, users are encouraged to perform a search in SciFinder.

This article has been cited by 4 ACS Journal articles (4 most recent appear below).

A Laboratory Exercise To Demonstrate the Theory and Practice of Analytical Sampling
Brian A. Logue and Stephanie L. Youso
Journal of Chemical Education2010 87 (3), 316-319
- A Laboratory Exercise To Demonstrate the Theory and Practice of Analytical Sampling
  Brian A. Logue and Stephanie L. Youso
  Journal of Chemical Education2010 87 (3), 316-319
  In analytical chemistry classes, the importance of gathering a proper sample for analysis of bulk materials is often addressed only briefly or not at all. Although a number of classroom and laboratory exercises have been developed to illustrate factors ...
  Abstract | Full Text HTML | Hi-Res PDF | PDF w/ Links
Sampling the Soils Around a Residence Containing Lead-Based Paints: An X-ray Fluorescence Experiment
Steven J. Bachofer
Journal of Chemical Education2008 85 (7), 980
- Sampling the Soils Around a Residence Containing Lead-Based Paints: An X-ray Fluorescence Experiment
  Steven J. Bachofer
  Journal of Chemical Education2008 85 (7), 980
  Sampling experiments utilizing field portable instruments are instructional since students collect data following regulatory protocols, evaluate it, and begin to recognize their civic responsibilities upon collecting useful data. A lead-in-soil experiment ...
  Abstract | Hi-Res PDF | PDF w/ Links
Analysis of Iron in Lawn Fertilizer: A Sampling Study
Michael A. Jeannot
Journal of Chemical Education2006 83 (2), 243
- Analysis of Iron in Lawn Fertilizer: A Sampling Study
  Michael A. Jeannot
  Journal of Chemical Education2006 83 (2), 243
  A novel laboratory activity in sampling statistics, suitable for students in a quantitative analysis course, is described. In this activity, students measure the percentage of iron in a commercial lawn fertilizer by simple sorting and weighing. The pooled ...
  Abstract | Hi-Res PDF | PDF w/ Links
Statistical Comparison of Data in the Analytical Laboratory
Michael J. Samide
Journal of Chemical Education2004 81 (11), 1641
- Statistical Comparison of Data in the Analytical Laboratory
  Michael J. Samide
  Journal of Chemical Education2004 81 (11), 1641
  In this article, an experiment designed to provide students with an experience involving statistical treatment of data is described. Most courses that deal with quantitative analysis focus on methodology; students must learn how to perform specific types ...
  Abstract | Hi-Res PDF | PDF w/ Links