Spectrophotometric Determination of Demeclocycline and Minocycline using Molybdenum (VI)

 

S.Kondaiah1*, M.S. Surendra Babu2*, V. Surya Narayana Rao1

1Department of Chemistry, Srikrishnadevaraya University, Anantapur-515001

2Department of Chemistry, GITAM University Hyderabad Campus, Hyderabad

*Corresponding Author E-mail: kondareddyseku@gmail.com  

 

ABSTRACT:

The author has developed simple, new, convenient, rapid and selective methods for determination of Demeclocycline (DMC) and Minocycline (MNC). The procedure based on the observation that, DMC or MNC forms colored complexes with molybdenum (VI), the absorbance of which is proportional to the amount of tetracycline present. The variable effecting development of the color has been investigated and the conditions are optimized. Beer’s law is obeyed in the range 0.962 to 7.36 μg/ml DMC and for 0.96 to 7.68μg/ml MNC. The proposed methods can be employed for the analytical determination of molybdenum (VI). The corresponding Beer’s law ranges are 0.005 to0.040 mg/ml with DMC and 0.004 to 0.040 mg/ml with MNC. These methods are successful applied for the determination of DMC and MNC in pharmaceutical formulations. These methods are applied where ever possible for the analysis of real samples in pharmaceutical industries.

 

KEYWORDS: Spectrophotometric determination, demeclocycline, minocycline, molybdenum (VI).

 


 

INTRODUCTION:

Drugs play an important role in human activities1,2. We use a very good number of medicinally important organic compounds for the treatment of number of diseases. Drug analysis plays an important role in marketing as well as use of these compounds for the treatment3. Tetracyclines are napthacene derivatives possessing broad spectrum antibiotic activity4-6. The napthacene unit consists of 4 partially unsaturated cyclohexane rings. Tetracyclines are antibacterial agents effective against a host of gram – positive and gram – negative aerobic and anaerobic bacteria. The important role of tetracyclines, in the treatment of sexually remitted and gonococcal diseases, urinary tract infections, bronchitis and sinusitis remains prominent. The majority of the marketed tetracyclines are tetracycline, chlorotetracycline, oxitetracycline, democlocycline, minocycline etc. The tetracyclines exhibit bacteriostatic effect on growing bacteria via the inhibition of protein synthesis. Several methods reported in the literature for the determination of tetracyclines are expensive, time consuming and are not useful for the routine analysis6-12.

 

UV – Visible spectrophotometry is still considered to be a convenient and low cost method for the determination of tetracyclines in pharmaceutical formulations. A number of spectrophotometric, colorometric and polorographic methods for determination of tetracyclines in bulk materials and dosage forms are reported in the literature. The present methods reported simple and accurate methods for the determination DMC and MNC.

 

MATERIALS AND METHODS:

Instrument: The absorbents and pH measurement are made on Elico SL UV – Visible spectrophotometer and Elico pH meter.

 

Preparation of solutions: Double distilled water is employed for the preparation of solutions. All chemicals and reagents used for these studies are analytical grade obtained from Merck. The hydrochlorides of tetracyclines obtained from Sigma. The standard solutions tetracyclines were prepared in double distilled water.

 

Recommended procedure: Known aliquots of the buffer solution of required pH, molybdenum (VI) solution and tetracycline solution were pipetted into 25 ml standard flask. The contents of the flask is made up to the mark with double distilled water and shaken well for uniform concentration. The absorption spectra are recorded against respective blank solution.

RESULTS AND DISCUSSION:

DMC and MNC form soluble yellow colored solutions with Mo (VI). The yellow is due to the complexation between DMC and MNC with Mo (VI). Results reveal that a pH of 6 and 5 is optimum for the complexation of Mo (VI) with DMC and MNC respectively. The DMC or MNC – Mo (VI) complex is found to be highly stable and reproducible in these media. The media of lower pH are not recommended as the tetracycline (DMC or MNC) is not stable in highly acidic solutions. The absorbance values found decreases with increase in pH due to the possible dissociation of the complex. Similar observations are reported by Siva et al., (1996). Therefore the selected pH is used for the determination of complexes. In order to establish stoicheiometry of the complex, the equimolar solutions of DMC or MNC and Mo (VI) are mixed in different proportions. A solution of composition 1:1 (DMC or MNC: Mo (VI) as shown the maximum absorbance indicating the formation of 1:1comlex. Several studies on tetracycline – metal systems demonstrated the formation of 1:1 complex between the tetracycline and metal ion. Parashuram et al., (2007) characterized the complexes of Co (II), Ni (II), Cd (II) and inorganic Sn (II) with tetracycline by elemental analysis, vibration spectra, electronic spectra 1H NMR spectra, magnetic susceptibility measurement , thermal studies and X – Ray diffraction studies. The above mentioned literature coupled with the Job’s method reported in the present article favor the formation of 1:1 complex between DMC or MNC and Mo (VI).

 

Effect of pH: Absorption spectral characteristics were studied in the pH range 2 to 9 and absorption spectrum of the complex recorded on the range 350 to 700 nm. The DMC-Mo (VI) complex exhibits maximum absorbance at 410nm at pH 6 (Fig. 1) and those corresponding to MNC-Mo (VI) complex are 405nm at pH 5 (Fig. 2)

 

Figure 1. Effect of pH on spectral characteristics Mo (VI) = 4 x 10-4 M; [DMC] 0.08mg/ml; λ max 410nm

 

Figure 2. Effect of pH on spectral characterstics Mo (VI) = 4 x 10-4 M; [MNC]; 0.08 mg/ml; λ max 405nm.

 

Effect of time: The absorbance values of the complex solution are recorded over a period of 90 minutes at regular intervals of time. The absorbance values are found to be approximately constant indicating that the complex is quite stable over a period of 90 minutes.

 

Composition of complex: The complex solution is yellow color in the case of DMC and an orange yellow color complex in the case MNC. The author conducted Job’s method of continuous variation to determine the stoicheiometric ratio of tetracycline to molybdenum (VI). The corresponding Job’s curves are shown in the Figs. 3 and 4 for DMC and MNC respectively.

 

Figure 3.Determination of composition of DMC-Mo(VI) complex by job’s method pH = 6; [DMC] = 1 x 10-3M;  [Mo(VI)] = 1 x 10-3M;  λmax = 410nm

 

Figure 4. Determination of composition of MNC-Mo (VI) complex by job’s method pH = 5; [MNC] = 1 x 10-3M; [Mo (VI)] = 1 x 10-3M; λmax = 405nm

 

Metal ion concentration: The concentration of the drug was maintained constant. Studies relating to the effect of metal ion concentration were carried out by varying the Mo(VI) concentration. The linear calibration plots for DMC and MNC are shown in Figs 5 and 6 respectively. The corresponding Beer’s law ranges are 0.96 to 7.36 μg/ml with DMC and 0.96 to 7.68 μg/ml with MNC.

 

Analytical determination of Mo (VI) of DMC and MNC: Under the established optimum conditions a calibration plot was constructed by varying the concentration of the metal ion. The linear calibration plots shown in the Fig’s 5 and 6 Beer’s law ranges are 0.005 to 0.40 mg/ml for DMC and 0.04 to 0.040 mg/ml for MNC.

 

Figure 5. Effect of Molybdenum (VI) on absorbance pH = 6; [DMC] = 0.08mg/ml; λmax = 410nm

 

Analytical determination of DMC and MNC: Under the established optimum conditions a calibration plot was constructed by varying the concentration of the drug. The linear calibration plots shown in Fig’s 7 and 8 indicate that Beer’s law is obeyed in the range 0.962 to 7.36 μg/ml for DMC and 0.96 to 7.68 μg/ml for MNC.

 

Figure 6. Effect of Molybdenum (VI) on absorbance pH = 5;  [MNC] = 0.06mg/ml; λmax = 405nm.

 

Figure 7. Analytical determination of DMC, pH = 6;  [Mo(VI)] = 9 x 10-5M; λmax = 410nm

 

Figure 8.Analytical determination of MNC pH = 5; [Mo (VI)] = 9 x 10-5M ;λmax = 405nm

Interference studies for molybdenum (VI) – DMC system: Interference of metals like cadmium, lead, chromium, copper, manganese and cobalt was studied. Cadmium and lead do not interfere at all concentrations. It is observed by the author that chromium and copper interfere when it is present to the extent of 10 fold molybdenum (VI).The other metal ions such as manganese and cobalt can be tolerated up to 100 fold of molybdenum (VI). The anions like fluoride, sulphate, oxalate and acetate interfere when they are present to the extent of 50 fold molybdenum (VI) concentration.

 

Interference studies for molybdenum (VI) – MNC system: Influence of various metal ions on the absorbance values has been studies by the author to know the interference of these ions on the determination of molybdenum (VI). The study reveals that aluminum, cadmium and mercury do not interfere. Palladium, cerium, tungsten, uranium seriously interfere. Tantalum and zirconium interfere when they are present to the extent of 10 fold of molybdenum (VI) concentration. Anions like chloride, bromide, nitrate and sulphate do not interfere at all concentrations.

Precision and Accuracy: The precision of the proposed methods was estimated by calculating the relative standard deviation as the average of 10 measurements.

 

Application to Pharmaceutical samples: Results of analysis of DMC and MNC in different pharmaceutical formulations using the proposed method is listed in Table 1. The percentage recoveries are calculated in each case and the results are satisfactory.

 

Table 1. Determination of DMC/MNC in pharmaceutical samples

Sample

Labeled amount mg/tab or cap

Amount found mg/tab or cap

Recovery (%)

Demeclocycline

Ledermycina

100

98

98

Ledermycinb

300

294

98

Minocycline

Cyanomycina

50

48.9

97.8

Minocyclineb

100

103.0

103.0

 

CONCLUSION:

Several methods are reported in the literature for the determination of antibiotics are expensive, time consuming and are not useful for the routine analysis. UV-Visible spectrophotometry is still considered to be a convenient and low cost method for the determination of antibiotics. The proposed methods are new, rapid, simple, and selective and can be adopted for the routine analysis. The method is successfully applied for the determination of DMC and MNC in pharmaceutical samples. This method can also be used for the determination molybdenum (VI).

 

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Received on 16.08.2011        Modified on 30.08.2011

Accepted on 11.09.2011        © AJRC All right reserved

Asian J. Research Chem. 4(10): Oct., 2011; Page1587-1590