Chemometric Determination of Coloring Agents Used in Drugs

Introduction

Titanium dioxide, TiO2, is a naturally occurring, processed and refined mineral on the earth, and is also used as a pigment [1]. Indigotin is a natural origin pigment obtained from the leaves of the “Indigofera Tinctoria” plant [2]. In the literature, studies involving both color substances are as follows: Titanium dioxide is quantified by voltammetric analysis [3]; Indigotin is quantified by FTIR [4], chromatography [5, 6]. When studies are examined, a study that makes room for chemometry has not been carried out yet.

The chemometric techniques are supported by mathematical models [7]. Principal component regression (PCR) is the most frequently used chemometric methods [8]. The analyses of multicomponent pharmaceutical products using these methods are well-accepted [9]. In this study, Minitab 17 program was used as chemometric program. The Minitab 17 program (Inova, Ankara, Turkey) [10] is a statistical analysis software used not only for performing statistical analyses but for training in statistics as well. It allows statistical analysis by using the relationship between Minitab and absorbance-concentration. In this study; the quantification of titanium dioxide and indigotin in drug performed by PCR. In first step, using the available medications of these two molecules, we prepared a drug sample containing a combination of titanium dioxide and indigotin. The validation of the chemometric- spectrophotometric method used in this study is included as an appendix to this article presenting the precision, accuracy, and selectivity of the methods. PCR method successfully identified and quantified colors in the drug simultaneously without any prior separation. The data were statistically crosschecked with their respective counterparts.

Experimental

Stock solutions were prepared at 25 mg/250 ml concentration using titanium dioxide and indigotin with hot H2SO4 in analytical purity. A training set and a validation set were prepared to contain these two drugs in various proportions. Consequently, 25 distinct synthetic mixtures were prepared to be used for validation and calibration and the absorption measurement of the substance was done with s Shimadzu UV-1700 PharmaSpec Spectrophotometer. Absorption values of titanium dioxide and indigotin were recorded ƛTiO2:220 nm and ƛIndigotin: 630 nm. The calibration matrix and the training and validation sets containing two component mixtures in different proportions were used for calculating the concentrations and the concentration sets. The analysis of the drug mixtures was performed using PLS and PCR. Samples of 5.0 and 10.0 ppm of colors were placed in volumetric flasks (25 ml) and dissolved in hot H2SO4. A training set, a validation set, and 25 synthetic mixtures (for validation and calibration) containing the drugs in various proportions were prepared. They are presented in Table 1. In the last step, the coated part on the commercial tablet was prepared by stripping (in the hot) and color substances were determined and absorbance reading was done.

Results and Discussion

When the absorbance-concentration for titanium dioxide and indigotin were examined, it was observed that the absorbance value increases as the concentration increases. The linear relationship [11] between the absorbance and concentration values was confirmed by the fact that the regression coefficient [12] was close to the individual values (Table 4). The concentration values in the range of 1.0-10.00 ppm used in the study are the area where the linearity for each component was to be determined. According to Lambert- Beer [11], when the relationship between absorbance and concentration is examined, it is observed that the linear correlation coefficient [13] between the two variables is close to each other (Table 3).

Principal Component Regression (PCR)

Recovery and relative standard deviation (BSS) values calculated for each chemometric method from the contour sets in Table 1 are shown in Table 2, and Table 3.

The statistical parameters were found to produce a satisfactory validity for PCR methods. The results are presented in Table 2. The results demonstrated that the standard deviation values were sufficiently small, and the recovery values were sufficiently close to 100. This shows us that the elicited results were appropriate.

Validation of the Method

The chemometric method was validated in accordance with ICH guidelines [14, 15, 16] with respect to linearity, accuracy, intraday and interday precision, limit of detection, and limit of quantitation. For calibration, the prediction of the residual error sum-of-squares (PRESS) was calculated from the added concentration of the drug and predicted concentration. According to the actual and predicted concentrations of the samples, PRESS values of colors were calculated and listed in Table 3. It is important to emphasize that this is not a correct way to normalize the PRESS values when not all of the data sets contain the same number of samples. But the standard error of prediction (SEP) values contains the number of samples. Some statistical parameters determined the effectiveness of the calibration where n – the total number of synthetic mixtures. PRESS and SEP values were close to zero with the PCR method. The degree of accuracy showed an increasing pattern.

The observable limit (LOD) and the detection limit (LOQ) parameters are interrelated but have different definitions (equation 1-2) [17].

LOD=3Sa/3 LOD=3Sa/m (1) LOQ=10Sa/m LOQ=10Sa/m (2) m: Slope LOQ> LOD and LOQ = LOD were taken into consideration while evaluating the calculated LOD values [18].

Analysis of Drug

The experimental results of the two methods for the pharmaceutical formulation are given in Table 4 one can see that the obtained results are very close to each other.

Conclusion

The proposed principal component regression is rapid, precise and accurate for the simultaneous resolution of drug containing titanium dioxide and indigotin. In this study, PCR method is applied to the simultaneous quantitative prediction of titanium dioxide and indigotin in drug without requiring any separation step. For all values, low prediction errors and high correlation coefficients emphasized the high linear relationship between the predicted and actual concentrations.

Acknowledgements

This research work has been supported by research grants from Suleyman Demirel University Scientific Research Project FLY-2018-6858.