Use of acid-type ionization of carbazole for its quantitative determination
Abstract Generated abstract
This paper describes a spectrophotometric method for the quantitative determination of carbazole based on its acid-type ionization in alkaline dimethylformamide in the presence of o-nitroaniline. The authors establish a calibration relationship between carbazole concentration and optical density under specified reagent ratios, then examine factors affecting accuracy and reproducibility, including sampling method, temperature, and the presence of nonionizing components. Statistical treatment of analyses of purified and synthetic carbazole samples indicated relative errors generally below about 1.6 percent for mean results, while tests on artificial binary mixtures with anthracene and several 9-substituted carbazole derivatives showed errors up to several percent. The method is presented as a specific procedure suitable for determining carbazole impurities in mixtures with certain carbazole derivatives.
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USE OF ACID-TYPE IONIZATION OF CARBAZOLE FOR ITS QUANTITATIVE DETERMINATION
V. P. Lopatinskii, I. P. Zherebtsov, S. P. Yudina
(Presented by the research seminar of the Faculty of Chemical Technology)
The development of new methods for the quantitative determination of carbazole is an important practical task, although there exist a number of chemical and physicochemical methods for its analysis. A sufficiently complete review of the advantages and disadvantages of the existing methods for the analysis of carbazole is given in [1].
Many practically important substances—derivatives of carbazole, for example, 9-alkylcarbazoles and 9-vinylcarbazole—contain carbazole as an impurity, and the quantitative determination of this impurity in carbazole derivatives is difficult because some methods lack sufficient specificity and others have low accuracy.
Savitskii and co-workers made use of the acidic properties of carbazole for its detection in such mixtures [1, 2]. The presence of carbazole is judged by the character of the fluorescence of a solution of the substance in alkaline dimethylformamide, the fluorescence of the carbazole anion differing in spectrum from the fluorescence both of nonionized carbazole and of its 9-substituted derivatives. Under the conditions adopted by the authors, the carbazole anion is unstable, and the fluorescence characteristic of the carbazole anion rapidly disappears.
Using the ionization of o-nitroaniline in dimethylformamide under the action of alkalis as an example, it was shown that satisfactory reproducibility of the optical densities of such solutions, caused by absorption of the o-nitroaniline anion, can be achieved by changing the composition of the medium [3].
As a consequence of the ionization of carbazole in the presence of alkali and o-nitroaniline, at certain ratios of carbazole, indicator, and alkali there is a linear relationship between the concentration of carbazole and the optical density caused by absorption by the indicator. The latter circumstance makes it possible to use this dependence as a calibration graph for determining the content of carbazole in mixtures with nonionizing compounds.
The objective of the present work was to study certain factors determining the correctness and accuracy of the determination of carbazole by this method. The results of the experiments are presented in Tables 1 and 2.
Table 1
Results of analyses of various carbazole samples
| Results of processing the experiments | Experiment variants | Experiment variants | Experiment variants | Experiment variants | Experiment variants |
|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | |
| True content, % | – | – | 100.00 | 100.00 | 100.0 |
| Mean result, % | 97.02 | 95.03 | 100.32 | 100.16 | 99.86 |
| Number of determinations | 9 | 7 | 22 | 5 | 6 |
| Variance | 2.27 | 0.67 | 2.2 | 1.25 | 0.7 |
| Standard deviation of a single determination | 2.03 | 0.82 | 1.48 | 1.12 | 0.835 |
| Standard deviation of the mean result | 0.66 | 0.31 | 0.31 | 0.50 | 0.34 |
| Student’s criterion | 2.3 | 2.45 | 2.08 | 2.77 | 2.57 |
| with reliability 0.95 | |||||
| Presence of systematic error | – | – | no | no | no |
| Accuracy, % | 1.55 | 0.76 | 0.65 | 1.39 | 0.88 |
| Interval of the mean result | 97.02 ± 1.55 | 95.03 ± 0.76 | 100.32 ± 0.65 | 100.16 ± 1.39 | 99.86 ± 0.88 |
| Maximum possible error of the mean result | ±1.98 | ±0.93 | ±0.93 | ±1.50 | ±1.02 |
| Relative error, % | ±1.60 | ±0.8 | ±0.65 | ±1.39 | ±0.86 |
Note. I. Experiment variants. I—sample of coal-tar reactive carbazole was subjected to additional purification by recrystallization and had \(T_{\mathrm{m}}\) 244–245°C. The required weighed portion for analysis
was taken directly from the vial.
- The same carbazole sample. The required weighed portion for analysis was taken by successive quartering of 10 g of carbazole. In variants 3–5, synthetic carbazole was used, with samples taken by quartering. The temperature during conditioning of the columns with solution in variants 4–5 was 18° and 24°C, respectively; in variants 1, 2, 3 it was room temperature (within 18–22°C).
Note II. Statistical treatment of the results was carried out according to the recommendations given in the literature [4, 5, 6].
Table 2
Determination of the carbazole content in artificial binary mixtures
| Second component | Carbazole content, %, found | Carbazole content, %, taken | Relative error, % |
|---|---|---|---|
| Anthracene (synthetic, mp 216°C) | 48.85 | 48.85 | 0.0 |
| Anthracene (synthetic, mp 216°C) | 71.42 | 69.82 | 2.5 |
| Anthracene (synthetic, mp 216°C) | 85.7 | 84.13 | 1.8 |
| 9-Methylcarbazole | 57.14 | 56.07 | 1.9 |
| 9-Methylcarbazole | 71.42 | 71.82 | 0.6 |
| 9-(2-Hydroxy)ethylcarbazole | 42.85 | 44.25 | 3.3 |
| 9-Vinylcarbazole | 71.42 | 73.22 | 2.5 |
| 9-Vinylcarbazole | 42.85 | 41.05 | 4.2 |
| 9-Vinylcarbazole | 8.0 | 8.28 | 3.5 |
Note: average results from two determinations are given. Discrepancies between determinations were up to 5%.
Comparison of the variances of the results of analysis of the carbazole sample (variants 1 and 2 in Table 1) shows that the method of sampling has a significant effect on reproducibility. Indeed, the found value of the \(F\) criterion is 6.05. The tabulated value [4] is 4.15. On the other hand, comparison of the obtained analytical results by means of Student’s criterion indicates a statistically insignificant difference in the carbazole content in the sample for variants 1 and 2. Changing the temperature from 18 to 24°C does not affect
on the correctness and precision (variants 4 and 5 in Table 1). The presence of nonionizing substances also does not exert a large influence on the result of the analysis, which makes it possible to recommend the proposed procedure as a specific method for determining carbazole in mixtures with its derivatives. The results of preliminary experiments on the analysis of such mixtures are presented in Table 2.
Experimental Part
Construction of the calibration graph. Dimethylformamide (“pure”) from different bottles is mixed to obtain a homogeneous 2-liter batch. In 1 liter of dimethylformamide, 0.031125 g (to an accuracy of hundredths of a mg) of o-nitroaniline is dissolved. The resulting indicator solution is stored in the dark. The solution is suitable for analysis for one month. Into a 25-ml volumetric flask, 20.0 ml of the indicator solution, a weighed portion of pure carbazole, and 0.625 ml of a solution of caustic potash (“chemically pure for analysis”) in methanol (1.964 g in 50 ml) are introduced with a pipette. Dimethylformamide is added to the mark in the flask, and the mixture is kept at room temperature for 20 min, after which the optical density of the solution is measured twice in a 5-mm cuvette on an FEK-N-57 instrument with green filter No. 4. The mean of the two measurements is taken. Dimethylformamide is poured into the comparison cuvette. Each weighed portion of carbazole is taken in triplicate (to an accuracy of hundredths of a milligram), and from the three resulting optical-density values the mean value is calculated and plotted on the graph of optical density versus carbazole concentration. To construct the graph, 5 points are used in the range of carbazole weighed portions of 55–65 mg. For the indicated concentration ranges of carbazole, a rectilinear relationship is obtained between the carbazole concentration and optical density; moreover, the larger the carbazole weighed portion, the lower the optical density.
Procedure for determination. A weighed portion of the substance containing about 60 mg of carbazole is dissolved in the indicator solution, and the subsequent procedure is the same as in construction of the calibration graph, repeating the determination with a new weighed portion as many times as necessary, guided by Table 1. From the graph, the amount of carbazole corresponding to the found optical density of the solution is found, and the carbazole content in the weighed portion is calculated.
The authors express their sincere gratitude to Yu. P. Shekhterev for providing a sample of synthetic carbazole.
Conclusions
A new method has been developed for the quantitative determination of carbazole; its accuracy has been evaluated, and its specificity for determining carbazole in a mixture with some of its 9-derivatives has been demonstrated.
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