Application of <SUP>1</SUP>H-NMR for the Quantitative Analysis of Short Chain Fatty Acid Methyl Ester Mixtures: An Undergraduate Instrumental Analysis Experiment

Abstract

Nuclear magnetic resonance spectroscopy (NMR) is one of the most important instrumental techniques used to elucidate the molecular structure of organic compounds. However, there are not many good simple applications of using NMR for the quantitative assay of impure or mixtures of organic substances. The current experiment was developed as part of an ongoing effort to increase exposure to quantitative proton NMR methodology in the undergraduate chemistry laboratory curriculum. The objective of the experiment is to determine the percent composition of a two component mixture of short chain fatty acid methyl esters using chemical shift and integration values obtained from running solvent-less samples both with and without an internal reference standard. We report on the experimental methods and results obtained from examining the quantitative NMR properties of a series of mixtures of methyl acetate (M.A.) and methyl propionate (M.P.) solutions ranging from 100% MA to 100% MP. Also similar data was obtained for the MA -methyl butyrate (MB) pair. The results exhibit a linear relationship of the percent composition of the methyl acetate binary mixtures found by proton NMR with the theoretical (i.e. samples prepared based on measured weights) percent compositions. The experiment confirms the quantitative usage of 1 H NMR and serves as an educational tool for the undergraduate chemical laboratory.

Application of Quantitative Proton Nuclear Magnetic Resonance Spectroscopy for the Compositional Analysis of Short Chain Fatty Acid Benzyl Ester Mixtures

“…These calibration curves can be used to quantify, with a great degree of accuracy, the % composition of binary mixtures involving the reagents used in this study. The methodology can be quickly adopted for other experiments using other reagents as this study serves to corroborate previous experiments [5] that proton NMR can be used quantitatively to determine the composition of binary mixtures. There is a direct 1 to 1 relationship between the proton integration values and the gravimetrically determined weight %.…”

“…Proton Nuclear Magnetic Resonance Spectroscopy has been utilized for both qualitative and quantitative analyses of organic mixtures [1][2][3][4][5], however, there is a lack of reliable exercises using qNMR with the purpose of educational instruction [6][7][8][9][10][11]. In order to combat this, this experiment has been designed for simple implementation of the qNMR methodology into undergraduate chemistry laboratory curriculums.…”

Application of Quantitative Proton Nuclear Magnetic Resonance Spectroscopy for the Compositional Analysis of Short-Chain Fatty Acid Ethyl Ester Mixtures

“…% calculated from qNMR and the theoretical values determined gravimetrically. This experiment can be adapted for different reagents, has substantiated previous experiments [5,6], demonstrated the quantitative usage of proton NMR, and serves as an excellent tool for the undergraduate chemistry laboratory.…”

“…Although proton nuclear magnetic resonance ( 1 H NMR) has been used for both qualitative and quantitative analyses of organic mixtures [1][2][3][4][5][6], quantitative experiments for educational instruction are limited [7][8][9][10][11][12]. A simple solution is to develop more quantitative NMR (qNMR) experiments; hence, this straightforward experiment was designed for simple implementation of the qNMR methodology into undergraduate chemistry laboratory curriculums.…”

Modelling of the adsorption of chlorinated phenols on polyethylene and polyethylene terephthalate microplastic

“…The presence of polyethylene was also confirmed based on the similarity match >80 % with the Hummel Polymer Sample Library, which is the criterion used by other researchers. 31 Characteristic bands originating from polyethylene terephthalate (PET, Fig. 1d) were detected at 2956 (C-H stretch from -CH 2 and -CH 3 groups), 1713 (C=O stretching of the keto group), 1409 (C-O stretching and O-H group deformation), 1238 (terephthalate group -OOCC 6 H 4 -COO), 1091 (vibrations of the ester C-O bond from poly(ethylene terephthalate)) and 1016 cm -1 assigned for in-plane vibration of benzene.…”