INTRODUCTION AND OBJECTIVES

COMPARATIVE DETERMINATION OF ZINC IN PHARMACEUTICAL PRODUCTS

CORCIOVĂ ANDREIA, CIOBANU CONSTANTIN“Grigore T. Popa” University of Medicine and Pharmacy Iasi, Faculty of Pharmacy, Department of Drugs Analysis,

Pharmaceutical legislation and deontology, Iasi, Romania

MATERIAL AND METHODS

RESULTS

CONCLUSIONS REFERENCES

Nowadays, the use of dietary supplements based on vitamins, micro and macro elements is widespread. Zinc is the second transition metal after iron in terms of importance and its levels in the human body therefore is essential to a healthy growth and development (1). So maintaining an optimal level of zinc in the body is very important. For this purpose, continuous monitoring of the concentration of zinc in dietary supplements is of great importance. The present work describes two analytical methods (spectrophotometry and atomic absorption spectrometry) used for the quantitative determination of zinc in three pharmaceutical preparations (2).

For the UV-Vis spectrophotometric method a Jasco V 530 double beam UV-Vis spectrophotometer was used and for the FAAS method a flame high resolution continuum source atomic absorption spectrometer (ContrAA 300, Analytic Jena, Germany). The spectrophotometric method is based on the formation of a zinc-dithizone red complex (Figure 1) which is soluble in chloroform, having maximum absorbance at 516 nm. For the second proposed method (atomic absorption spectrometry) the sample was wet digested using a mixture of concentrated nitric acid and hydrogen peroxide, after which the absorbances were recorded using an atomic absorption spectrometer at 213.857 nm. The performance parameters for both methods were evaluated. Samples were labeled: sample 1 (15 mg zinc/tablet), sample 2 (10 mg zinc/tablet), sample 3 (5 mg zinc/tablet).

Linearity: for Method 1 zinc was found to be linear in the range of 0.05 - 1 mg % and for Method 2, the analytic response was linear in the range of 0.25 – 3 mg/L. Figure 2 and 3 present the obtained calibration curves .

Repetability: The precisions of the systems were studied for the concentrations of 0.5% for method 1 and for 1.6 mg/L for method 2.

The statistical analysis leads to relative standard deviations of 0.1189% (method 1) and 0.7745% (method 2) compared to the maximum of 2% set by European standards, so the systems are considered precise.

Both methods are precise, simple, however each has its advantages and disadvantages. While the used spectrophotometric method is time consuming and needs more reagents, the FAAS is faster and uses less reagents. On the other hand, the UV-Vis method is cheaper and doesn’t require sophisticated equipment. In conclusion, it has been demonstrated that the proposed methods can be successfully used for the determination of zinc in pharmaceutical preparations.

Zinc determination in pharmaceutical preparations.Both methods have been applied for the determination of zinc in 3 pharmaceutical preparations (tablets). Figure 4 presents the zinc concentrations found in the analyzed pharmaceutical products and figure 5 shows the obtained recoveries. The obtained results are in accordance with the limits imposed by the British Pharmacopoeia ed. 2013, Tablets Monography and European Pharmacopoeia, Monoghraph 0478.

Figure 1. Reaction of zinc with dithizone

Figure 2. Calibration curve for method 1

Figure 3. Calibration curve for method 2

Precision of the methods and accuracy: To determine the accuracy of the spectrophotometric method, 3 concentration levels were used and for each level 3 determinations were performed. Average recovery values were in the range of 99.00 - 101.38% with % RSD = 0.161 - 0.743 for method 1 and 100.02 – 101.18% with % RSD = 1.7091 – 2.6975 for method 2. The % RSD of the recovery values in 3 different days were in the range 0.422-0.685 for method 1 and 0.853-1.369 for method 2. As shown, the values of % RSD are less than 5, the amount proposed by European standards, which means that the methods are accurate.

Figure 4. Zinc concentrations found in the analyzed samples

Figure 5. Zinc recoveries obtained for the analyzed samples

1. Frederickson CJ, Koh JY, Bush aI. The neurobiology of zinc in health and disease. Nat Rev Neurosci. 2005;6:449-462.

2. McCall KA, Huang C, Fierke CA. Function and mechanism of zinc metalloenzymes. J Nutr.2000;130:1437S-1446S.

Zn+2 + 2 S = C

NH - NH - C6 H5

N = N - C6 H5

C6 H5 - NH - N = C

N = N - C6 H5

S

S

C6 H5 - N = N

C = N - NH - C6 H5Zn