Infrared Spectroscopy Determination of Lead Binding to Ethylenediaminotetraacetic Acid

Alanah Fitch and Simona Dragan
Loyola University - Chicago, Department of Chemistry, 6525 North Sheridan Road, Chicago, IL 60626
J. Chem. Educ., 1998, 75 (8), p 1018
DOI: 10.1021/ed075p1018
Publication Date (Web): August 1, 1998

Abstract

In an attempt to improve a thematic lab sequence based on lead analysis of community derived samples, we have considered infrared spectroscopy as a method of determining the lead bound to ethylenediaminotetraacetic acid (EDTA). Students get acquainted with infrared spectroscopy by interpreting the spectra of EDTA, disodium ethylenediaminotetraacetate (Na2EDTA) and of lead(II) ethylenediaminotetraacetate (PbEDTA). Spectral characterization of the above compounds in the 1800-1500 cm-1 region gives information about the structural changes that sodium and lead binding to EDTA, respectively, produce. The spectra show the carboxylic carbonyl absorption band shifted from 1697 cm-1 to 1633 cm-1 in Na2EDTA, and two distinctive absorption bands at 1697 cm-1 and 1558 cm-1 in PbEDTA, the former being attributed to the "free" carboxylic group, as in EDTA, and the latter to the coordinated carboxylate with the bond order of less than 1.5 between the carbon and oxygen atoms. These features led us to the conclusion that the divalent Pb is tetra-coordinated having two covalent metal-nitrogen bonds and two ionic metal-carboxylate bonds. Based on the spectral differences between PbEDTA and EDTA, we have developed a method to quantitate the amount of lead bound to EDTA by simply comparing the peak height of the most prominent peaks in the 1800-1550 cm-1 region. A potential application of this method could be determination of lead extracted by binding it to ethylenediaminotetraacetic acid, excess EDTA being added.

Keywords (Audience):

Second-Year Undergraduate

Keywords (Domain):

Analytical Chemistry

Keywords (Feature):

Advanced Chemistry Classroom and Laboratory

Keywords (Subject):

IR Spectroscopy
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  • Received: August 03, 2009

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