Monthly Archives: March 2011

Solubility of Milk of Magnesia

Milk of Magnesia, or MOM, is a suspension of Mg(OH)2.  One method for determining the amount of Mg(OH)2 in MOM is to precipitate the Mg2+ as MgNH4PO4.  Because this precipitate includes a weak acid, NH4+, and a weak base, PO43-, … Continue reading

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What is the Difference Between Repeatability, Reproducibility, Accuracy, and Precision?

In an editorial published in American Laboratory (November 2000), Ira S. Krull states that in “any science, then, one must present at the very outset evidence of repeatability, reproducibility, accuracy, and precision (emphasis added).” Suppose you are preparing a manuscript … Continue reading

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Gratzel et. al. [Anal. Chem. 1999, 71, 2751-2756] describe the use of a diffusional microburet to transfer solutions to very small droplets of solvent. The purpose of their work is to run conventional analyses, such as titrations, on an extremely … Continue reading

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Selecting an Analytical Method

As part of the study of how humans age, there is an interest in learning how the chemical composition of tissues change as we grow older or as the result of disease. Suppose you are interested in determining the concentration … Continue reading

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NIST Statistics Problem

Have you ever wondered how atomic weights are determined? The National Institute of Standards and Technology (NIST) is one of several research organizations that seeks to make accurate measurements of this sort. The most common approach is to prepare a … Continue reading

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