Computer-Aided Quantitative Analysis by Proton Magnetic Resonance of Olefinic Compounds Osamu Yamamoto,+ Masaru Yanagisawa, and Toshihiro Senba National Chemical Laboratory for Industry, 7- 7-5Honmachi, Shibuya-ku, Tokyo, Japan
In computer-aided proton magnetic resonance (PMR) quantitative analysis of a mixture of proton-containing substances which show nonseparable complex patterns, a method is presented in which only the position and the height of each PMR signal are used as input data instead of the whole observed spectrum in a digitized form. This method is successfully applied to mixtures of olefinic compounds to give results comparable to those obtained when using the whole complex pattern.
High resolution proton magnetic resonance (PMR) spectrometry has proved to be very useful as a tool for quantitative analysis of proton-containing organic compounds ( I ) . In a previous paper ( Z ) , in order to make a PMR quantitative analysis of a mixture of proton-containing substances which show nonseparable complex patterns in PMR spectra, we have presented a method in which the observed and the calculated spectra of the mixture are compared in a ccmputer, and a least squares calculation is made for residuals between the intensities of both spectra a t a number of frequency points to obtain the relative concentrations of each component in the mixture. The calculated spectrum of the mixture is generated in the computer from known PMR parameters and assumed relative concentrations. The matched filter technique is applied to avoid the difficulty arising from the disagreement in intensity due to small frequency deviation between the observed and calculated spectra. We have developed a Fortran program named QUANTNMR along this line. The general scheme of the calculation is shown in the flow diagram in Figure 1 of Ref. 2. We have successfully applied this method t o the mixtures of isomers of some benzene derivatives with a good accuracy comparable to that obtained by the usual integration technique. In benzene derivatives, the PMR patterns of the ring protons consist of a large number of signals superposed with each other forming a number of complex bands. Thus, the observed spectrum itself should be fed into the computer through a suitable input medium, e.g., punched paper tape, in a digitized form with a sufficiently large number of data points. On the other hand, it is often observed that the olefinic proton signals, which are another typical complex pattern in PMR spectra, consist of a number of lines which are sharp and considerably separated from each other. In this case, we may read the position and the height of each signal from the chart, and use them as the input data for the observed spectum. As an extension of the previous work, we attempt to make the quantitative analysis by PMR for mixtures of olefinic compounds with some expediency for data input procedure.
were of commercial sources, and, after distillation, the purity was checked by gas chromatography. The sampling was carried out as in the manner previously reported (2). Procedure. The position and the height of each PMR signal of a mixture were directly read out from the chart. When some superposition of the signals was observed, the signal band was divided into single components by assuming the Lorentzian line shape, and the height was taken after removing the tail contribution. The QUANTNMR program was modified to receive the position and the height of each PMR signal of a mixture as input data, instead of the actual observed spectrum in a digitized form. Then, an “observed spectrum” was synthesized in a computer from the input data with an appropriate Lorentzian line width, and the calculation of the relative concentrations of the components in the mixture was carried out for the “observed spectrum” in the same manner as in the previous work ( 2 ) .
RESULTS AND DISCUSSION The results are shown in Figure 1 and Table I. In Table I, the two values are shown for the relative concentrations obtained from the different calculations. Thus, “Found (1)”is the value that is obtained by use of only the position and the height of each signal as input data, while “Found (2)” means the value from the digitized observed spectrum as in the previous work. Generally close agreement was obtained for the relative concentrations in both cases, within an error of about f 3 mol %, which is an accuracy comparable t o that obtained for the benzene derivatives (2). In principle, for the calculation of the relative concentrations, it is sufficient to select a set of a small number of representative PMR signals, which belong to each particular component in the mixture. However, the accuracy obtained for the calculated relative concentrations will become higher by use of a large number of signal data, Le., by use of all the signals of the spectrum, as in the present work. In Figure 1, some superposition of the signals is observed a t the higher field side of the spectrum, Le., for cis-4-
I
EXPERIMENTAL Apparatus. The same apparatus were used as in the previous work (2). Reagent. As examples of olefinic compounds, the following five compounds were selected; acrylonitrile, methyl acrylate, divinylsulfone, and cis- and trans-4-methyl-2-pentenes. The materials
Figure 1. Observed (a) and calculated (b) spectra of a mixture of methyl acrylate and cis- and frans-4-methyl-2-pentenes (Run No. 3) ANALYTICAL CHEMISTRY, VOL. 48, NO. 3, MARCH 1976
547
Table I. Relative Concentrations Obtained for Some Olefinic Compound Mixtures 1 Taken
Acrylonitrile Divinylsulfone Methyl acrylate cis-4-Methyl-2-pentene
15.7 49.8 34.5
...
trans-4-Methyl-2-pentene
2
Found(1)a Found(2)a
18.0 48.1 33.9
...
...
15.7 48.3 35.9
... ...
Found(1)
Found(2)
Taken
Found(1)
61.9
... ...
61.9
63.0
27.6
28.1
... ...
...
28.7
... ...
9.4
10.5
8.9
38.7 16.4 44.9
38.5 15.8 45.8
41.6 15.6 42.8
...
...
4
Taken
Acrylonitrile Divinylsulfone Methyl acrylate cis-4-Methyl-2-pentene trans-4-Methyl-2-pentene a See text.
... ...
45.0 55.0
3
Taken
... ...
Found(2)
6
5
Found(1)
Found(2)
Taken
Found(1)
Found(2)
Taken
Found(1)
Found(2)
... ...
... ... ...
20.4 44.7 20.6
22.2 44.9 20.2
19.8 48.7 19.1
46.9 53.1
47.8 52.2
14.2
12.7
12.4
18.4 22.3 8.0 21.7 29.5
19.5 25.3 7.9 19.9 27.4
16.7 24.2 9.2 19.6 30.3
methyl-2-pentene. In this case, the signal heights measured from the chart are less accurate and contain some arbitrariness depending on the way of measurement. However, even if a slight superposition of the signals such as shown in Figure 1 is present, any conventional simple method for dividing the superposed band into single lines, e.g., even by visual dividing, is sufficient to give the signal height input data which provide the desired results within the experimental errors. It is an important feature of the present method that the slight frequency deviation of the observed spectrum from the calculated one can be offset by use of the broadening function. It is preferable, however, that the chemical shift values of the components in the mixture are corrected after one cycle calculation, because PMR signals of the olefinic compounds predominantly consist of well-resolved sharp lines, and a relatively large concentration dependence of the chemical shift is observed. The present method has
...
...
...
such a version, and this refinement improves the results to some extent. As described above, for the olefinic compounds which show a number of well-resolved sharp lines, only the position and the height of each PMR signal were used as input data to give the results comparable to those obtained when using the whole observed spectrum in a digitized form. Therefore, it is unnecessary to have any facility, e.g., a paper punch, that transforms the observed spectrum into a digitized form. LITERATURE C I T E D (1) F. Kasler. "Quantative Analysis by NMR Spectroscopy", Academic Press, New York, N.Y., 1973. (2) 0. Yamamoto and M. Yanagisawa, Anal. Cbem., 47, 697 (1975).
RECEIVEDfor review July 28, 1975. Accepted November 17, 1975.
Determination of Parts-per-Million Cesium in Simulated Nuclear Waste with the Cesium-Selective Electrode Elizabeth W. Baumann Savannah River Laboratory, E. 1. du Pont de Nemours and Company, Aiken,
A cesium-selective electrode with a liquid membrane of cesium tetraphenylboron dissolved in 4-ethylnitrobenzene gave near-Nernstlan response (slope of 52 mV per decade) from l o - ' to < M Cs+. Major interferences were M Cs+, the pH range was NH4+, Ag+, and Hg2+. At 6-8. For the application, cesium was first extracted from high sodium, strongly alkaline solutions with 1 M 4-secbutyl-2( a-methylbenzyl)phenol (BAMBP) in cyclohexane. Electrode measurements were then made in 0.01 M TrisHCI buffer solution at pH 7.1. By the standard addition method, cesium concentrations 2 5 X M can be determined with relative standard deviation and relative bias
