Advances in Chemistry

Advances in Chemistry / 2014 / Article

Research Article | Open Access

Volume 2014 |Article ID 750973 | 6 pages |

A Rapid Extractive Spectrophotometric Method for the Determination of Tin with 6-Chloro-3-hydroxy-2-(2′-thienyl)-4-oxo-4H-1-benzopyran

Academic Editor: Gerd-Uwe Flechsig
Received31 May 2014
Revised03 Jul 2014
Accepted31 Jul 2014
Published14 Aug 2014


An extractive spectrophotometric method for the determination of the trace amounts of tin has been carried out by employing 6-chloro-3-hydroxy-2-(2′-thienyl)-4-oxo-4H-1-benzopyran (in acetone) (CHTB) for the complexation of the metal ion in HCl medium. The colored species thus produced is quantitatively extracted into dichloromethane and shows the maximum absorbance at 432–437 nm. The method obeys Beer’s law in the range 0.0–1.3 μg mL−1 of tin with molar absorptivity and Sandell’s sensitivity of  L mol−1 cm−1 and 0.0020 μg Sn cm−2, respectively, at 435 nm. The method is highly selective and free from the interference of a large number of elements including platinum metals. The ratio of metal to ligand in the extracted species is 1 : 2. Utilizing this method, the analysis of various synthetic and technical samples including gun metal and tin can have been carried out satisfactorily.

1. Introduction

Tin does not occur free in nature and is found almost exclusively as tin oxide known as cassiterite or tin stone. Tin although a toxic metal, still it is being widely employed in manufacturing important alloys [1] and as solders for the joining of electronic components. The excess use of tin in daily life as fungicides in crops, in food packaging, and as stabilizer for polyvinyl chloride may introduce the inorganic tin {Sn(II) and Sn(IV)} in the environment. Out of these two, Sn(II) seems to be more toxic as compared to Sn(IV) [2]. In the literature, there are numerous analytical methods for the measurement of tin which are based on sophisticated instruments [310]. These methods are highly sensitive but generally tedious and prone to serious interferences from other elements. In contrast spectrophotometric methods are preferred due to their simplicity and speed in routine analysis. The reported studies have shown that a large number of reagents such as methyl orange [11], benzopyran derivatives [1, 12, 13], 2-(5-nitro-2-pyrilazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino-phenoyl] [14], pyrocatechol violet [1518], phenylfluorone [19, 20], dibromohydroxyphenylfluorone [21], arsenazo-M [22], isoamyl xanthate [23], diacetyl-monoxime-p-hydroxybenzoyl-hydrazine [24], bromopyrogallol red [25], potassium ethylxanthate [26], ferron [27], and 5,7-dichloro-8-quinolinol [28] have been used for the spectrophotometric determination of tin(II,IV) content. Among these many reagents [18, 21, 23, 2628] are nonselective as they suffer from the interference, have low sensitivity [11, 12, 23, 24, 2628], and some of them are time consuming, as they require time for full color development [14, 18, 20]. Some of the sensitive reagents [16, 17, 21, 22, 25] are reported, but these require the use of the surfactants, plasticizer, and critical pH adjustment. Thus in the view of the above facts it reveals that there is still a lot of scope for working out new methods and effecting amendments in the existing ones especially because of their lower sensitivity and selectivity. Keeping in mind the scope of the reported facts, a chromone derivative 6-chloro-3-hydroxy-2-(2′-thienyl)-4-oxo-4H-1-benzopyran(CHTB) has been used for complexation and spectrophotometric determination of trace amount of tin(II). The reagent 6-chloro-3-hydroxy-2-(2′-thienyl)-4-oxo-4H-1-benzopyran was found to give a sensitive reaction with Sn(II). In the present communication, optimization of conditions for the quantitative extraction of Sn(II)-CHTB complex was worked out apart from the studies involving stoichiometry and Beer’s law range determination. The interference studies for diverse ions were also carried out and the extraction of Sn(II)-CHTB was made free from interference of large number of metal ions by using suitable masking agents. The extraction of the Sn(II)-CHTB complex into dichloromethane forms the basis of the proposed method, which provides the advantages particularly in respect of sensitivity, selectivity, and color development time to the existing methods. Some synthetic and technical samples including gun metal and tin can have been analyzed for tin contents with good agreement.

2. Experimental

2.1. Apparatus

A model-140-02, Shimadzu with 10 mm matched cells was used for the routine absorbance measurements and spectral studies.

2.2. Reagents and Solutions

The standard stock solution (250 mL) of Sn(II) containing 1 mg mL−1 of the metal ion was prepared by dissolving an accurately weighed amount (0.475 g) of SnCl2·2H2O (RANBAXY) in 20 mL of concentrated hydrochloric acid, diluting with deionized water up to the mark and standardized by the SnO2 method gravimetrically [29]. Lower concentration at μg mL−1 level was prepared by suitable dilution of this solution containing 0.5 mol L−1 HCl final acidity. The containers of the tin solution were wrapped with carbon paper and kept in dark place. Stock solutions of other metal ions were prepared at mg mL−1 level by dissolving their sodium or potassium salts in deionized water or dilute acid. They were suitably diluted to give μg mL−1 level concentration of the metal ions.

6-Chloro-3-hydroxy-2-(2′-thienyl)-4-oxo-4H-1-benzopyran (CHTB; m.p. 200–202°C) was synthesized by the literature method [30] and dissolved in acetone to give 0.1% (m/v) solution. The chemical composition of CHTB is C13H7O3SCl and its structure is given in Figure 4.

Dichloromethane (Ranbaxy) was used for extraction as such.

2.3. The Samples

Synthetic samples were prepared by mixing tin solution with solutions of various metal ions in suitable proportions so as to give the composition as shown in Table 1.

Sample composition
Matrix* Sn added, gSn found**, g

Zn(0.02), Pb(0.01), Cu(0.001)a10.010.03 ± 0.85
Cu(0.070), Co(0.014)b8.07.89 ± 0.71
Co(1), Ba(2), U(0.01), Mo(0.020)c7.06.83 ± 0.58
Cd(2), Fe(0.1), V(0.1)d12.011.96 ± 0.71
Cr(0.1), Sr(1), Ag(0.5), Zr(0.01)e12.011.99 ± 0.62
Pb (2), Nb(0.1), Th(0.05) f5.05.13 ± 1.63
As(2), Se(3), Ti(0.1)e8.07.92 ± 0.56
Re(0.01), Ta(0.05), Bi(1)g5.05.03 ± 0.82
Be(2), Pt(0.01), Ir(0.01)10.09.85 ± 0.41
Gun metal 4.9%h4.48% ± 0.72
Tin can0.15%i

*Amount of metal ion shown in parentheses is in mg. **Average of triplicate analyses; mean ± % RSD. a,bCorrespond to kneiss metal and argental, respectively. cIn presence of 0.5 mg dithionite. dIn presence of 100 mg ascorbic acid. eIn presence of 7 mg phosphate. fIn presence of 4 mg oxalate. gIn presence of 100 mg iodide. hCertified value. iConfirmed by SnO2 method.
2.4. Gun Metal

A weighed sample of gun metal (0.2 g) was dissolved in 10 mL of concentrated hydrochloric acid and 2–4 mL of concentrated nitric acid on heating and the volume was made up to 100 mL in a volumetric flask. 10 ML of this solution was diluted to 100 mL to get a working solution of low concentration. An aliquot (0.25 mL) of this solution was analyzed by the proposed method.

2.5. Tin Can

A weighed sample (0.6 g) of tin taken in a 10 mL beaker was heated gently with 5 mL of concentrated hydrochloric acid. The sample was dissolved completely by adding 5–10 mL of distilled water and heating until the volume was reduced to 2–5 mL. After cooling, the volume of the solution was made up to 25 mL and suitable portions of the sample solution were analyzed for tin content.

2.6. Procedure

To 1 mL aliquot of the sample solution containing ≤13 μg Sn(II) in 0.5 mol L−1 hydrochloric acid, were added 1 mL of 6-chloro-3-hydroxy-2-(2′-thienyl)-4-oxo-4H-1-benzopyran (0.1% in acetone) solution and distilled water to make the aqueous volume up to 10 mL in a short stemmed 125 mL separating funnel. The contents were mixed well and equilibrated with 10 mL of dichloromethane for 20 s. The two layers were allowed to separate and the yellow colored solvent layer was passed through Whatman filter paper (number 41, 9 cm diameter) and collected into 10 mL measuring flask. The absorbance of the yellow complex was measured at 435 nm against similarly treated reagent blank. The standard calibration curve was prepared by applying the procedure to a solution containing tin up to 13 μg per 10 mL of the aqueous volume. The tin contents were computed from this calibration curve.

Modifications of the method for V, Fe, Nb, Zr, W, Mo, Bi, and Ti: in the sample when Ti(IV), Zr(IV), and W(VI) were masked with sodium phosphate, Fe(III) and V(V) with ascorbic acid, Bi(III) with potassium iodide, Mo(VI) with sodium dithionite, and Nb(V) with sodium oxalate added prior to the addition of reagent and solvent. The respective amount of the masking agents used was mentioned in the effect of diverse ions.

3. Results and Discussion

Tin(II) reacted with 6-chloro-3-hydroxy-2-(2′-thienyl)-4-oxo-4H-1-benzopyran(CHTB) in an acid medium to form a yellow colored species, which was quantitatively extracted into dichloromethane. The absorption spectrum of the colored Sn(II)-CHTB complex in dichloromethane indicated the maximum absorbance at 432–437 nm in the visible region, where the reagent blank had hardly any absorbance (Figure 1). The effect of various parameters on the formation and absorbance of the complex are listed in Table 2.

HCla (M)0.0430.0440.0450.046–0.0600.065
CHTBb (mL)–2.22.5
Equilibration timec (sec)0.0245–300

Conditions: (a) Sn(II) = 10 g; HCl = variable; CHTB (0.1% (m/v) in acetone) = 1 mL; aqueous volume = solvent volume = 10 mL; solvent = dichloromethane; equilibration time = 20 s; = 435 nm, (b) HCl = 0.046–0.060 mol L−1; other conditions being the same as in (a) except for the variation in CHTB concentration; also b = 6-chloro-3-hydroxy-2-(2′-thienyl)-4-oxo-4H-1-benzopyran (CHTB), and (c) 0.1% CHTB in acetone = 1 mL; other conditions being the same as in (b) except for the variation in equilibration time.

The absorbance of the complex was found maximum in HCl medium, where as it was observed to be low in H2SO4, CH3COOH, and HClO4. Since the Sn(II)-CHTB complex showed maximum absorbance in 0.046–0.05 mol L−1 HCl, so 0.05 mol L−1 HCl was chosen to provide suitable acidity. Portions 0.5–2.2 mL of 0.1% CHTB solution in acetone resulting in maximum absorbance to the complex under all the conditions were stated in Table 1 and thus 1 mL was considered to be sufficient for the system. Further, the complex shows maximum absorbance when an equilibration time of up to 5 min is kept; therefore, in order to save time, 20 s is considered to be the desired contact time for the extraction of the complex from the aqueous solution.

Out of the number of the solvents studied for extraction of the Sn(II)-CHTB complex, dichloromethane was found to be most suitable because it provides a high absorbance value and stability of the complex. The absorbance showed a downward trend in the case of dichloromethane, 1,2-dichloroethane, benzene, toluene, ethyl acetate, carbon tetrachloride, isoamyl acetate, isobutyl methyl ketone, chloroform, cyclohexane, and isoamyl alcohol. So the dichloromethane was selected for the extraction of the Sn(II)-CHTB complex from the aqueous phase.

From a study of the above variables, the optimum conditions for the system have been laid down, as already stated in the procedure. The metal complex obeys Beer’s law in the range 0–1.3 μg Sn(II) mL−1. However, according to Ringbom plot [31], the optimum range for accurate determination of tin is 0.28–1.25 μg mL−1. The molar absorptivity, specific absorptivity, and Sandell’s sensitivity of the complex at 435 nm are 5.81 × 104 L mol−1 cm−1, 0.489 mL g−1 cm−1, and 0.0020 μg Sn(II) cm−2, respectively. The ratio of Sn(II) : CHTB in the extracted species is determined using their equimolar solution (8.425 × 10−4 M) at three different wavelengths, 410, 435, 450 nm, by Job’s method (Figure 2) of continuous variations as modified by Vosburgh and Cooper for a two-phase system [32, 33]. The sharp break in the curves indicates a metal-to-ligand ratio of 1 : 2 stoichiometry in the extracted species. This is further supported by the mole ratio method (Figure 3) [34] by taking the concentration of Sn(II) as 4.218 × 10−4 M and measuring the absorbance again at three wavelengths, 410, 435, 450 nm. The most probable structure of the Sn-CHTB complex is given as shown in Figure 5.

3.1. Effect of Diverse Ions

Under optimum conditions of the procedure, the effect of different anions and cations has been studied on the absorbance of the Sn(II)-CHTB complex. The amount of diverse ions which caused a ≤1% error in the absorbance was taken as the tolerance limit. The tolerance limit of foreign ions tested is given in Table 3. The reported anions and cations did not influence the absorbance of the Sn(II)-CHTB complex. However, fluoride interfered seriously even in traces. The amount of sodium or potassium salts of the various anions were taken in mg while glycerol and H2O2 (30%, m/v) were taken in mL.

IonsTolerance limit
(concentration mg/10 mL)

Thiourea, sulphite, ascorbic acid, and iodide100.0
Sulphate, nitrate 80.0
Bromide, sulfosalicylic acid 75.0
Chloride, tartrate 50.0
Acetate 40.0
Carbonate, citrate20.0
Thiocyanate 10.0
Phosphate 7.0
Oxalate 4.0
EDTA “disodium salt”2.0
Glycerol 1.0a
H2O2 (30%, m/v) 0.5a
Zn(II), Pb(II), and Se(II)10.0
Ba(II), Ni(II), Co(II), and Hg(II)5.0
Be(II), Ce(IV), As(II), Mg(II) Mn(II), Sr(II), Al(III), and Os(VIII)3.0
Ag(I), Cu(II)2.0
Ru(III), Ir(III)0.1

aValue given in mL.

Among the study of cations it was found that cations like Fe(III), Zr(IV), Nb(V), V(V), Mo(VI), W(VI), and Ti(IV) did influence the absorbance of the Sn(II)-CHTB complex. However the interference of these metals could be prevented by making use of suitable masking agents, that is, for 1 mg of Fe(III), 100 mg ascorbic acid; for 1 mg of Nb(V), 4 mg sodium oxalate; for 1 mg of V(V), 100 mg ascorbic acid; for 0.1 mg of Mo(VI), 5 mg of sodium dithionite; for 1 mg of W(VI), 7 mg sodium phosphate; for 1.5 mg Zr(IV), 7 mg sodium phosphate; for 0.3 mg of Ti(IV), 7 mg sodium phosphate; and for 5 mg of Bi(III), 100 mg iodide added prior to the addition of CHTB in 10 mL aqueous volume under optimum condition of the procedure.

4. Conclusion

For the determination of microamounts of tin, the proposed method is simple, rapid, sensitive, and selective and free from the interference of a large number of metal ions. The wide applicability of the method is tested by the analysis of several synthetic samples, tin can, and gun metal sample with satisfactory results. The high reproducibility of the method is tested by performing several sets of experiments while keeping the same amount of tin metal ions in each set; the relative standard deviation of the method is 0.98%.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.


The authors’ sincere thanks are due to Kurukshetra University, Kurukshetra, and Panjab University, Chandigarh, for providing the necessary facilities.


  1. R. Kataria, H. K. Sharma, N. Agnihotri, and J. R. Mehta, “2-(2′-Furyl)-3-hydroxy-4-oxo-4H-1-benzopyran as a highly selective and sensitive reagent for spectrophotometric determination of tin(II),” Proceedings of the National Academy of Sciences of India, vol. 78, pp. 31–35, 2008. View at: Google Scholar
  2. T. Madrakian, A. Afkhami, R. Moein, and M. Bahram, “Simultaneous spectrophotometric determination of Sn(II) and Sn(IV) by mean centering of ratio kinetic profiles and partial least squares methods,” Talanta, vol. 72, no. 5, pp. 1847–1852, 2007. View at: Publisher Site | Google Scholar
  3. C. Prior and G. S. Walker, “The use of the bismuth film electrode for the anodic stripping voltammetric determination of tin,” Electroanalysis, vol. 18, no. 8, pp. 823–829, 2006. View at: Publisher Site | Google Scholar
  4. Y. Mino, “Determination of tin in canned foods by X-ray fluorescence spectrometry,” Journal of Health Science, vol. 52, no. 1, pp. 67–72, 2006. View at: Publisher Site | Google Scholar
  5. J.-B. Liu and Y.-Z. Wu, “Rapid determination of tin in ore by atomic emission spectrometry,” Yejin Fenxi, vol. 33, no. 3, pp. 65–68, 2013. View at: Google Scholar
  6. Y. Lin, “Determination of tin in canned food with hydride-atomic fluorescence spectrometry,” Fenxi Ceshi Jishu Yu Yigi, vol. 19, pp. 149–152, 2013. View at: Google Scholar
  7. Y. Yu, Z.-Y. He, Z.-C. Mao et al., “Determination of tin in by spectral lines with different sensitivity of alternating current arc emission spectroscopy,” Yankuang Ceshi, vol. 32, pp. 44–47, 2013. View at: Google Scholar
  8. L. Pruša, J. Dědina, and J. Kratzer, “Ultratrace determination of tin by hydride generation in-atomizer trapping atomic absorption spectrometry,” Analytica Chimica Acta, vol. 804, pp. 50–58, 2013. View at: Publisher Site | Google Scholar
  9. S. V. de Azevedo, F. R. Moreira, and R. C. Campos, “Direct determination of tin in whole blood and urine by GF AAS,” Clinical Biochemistry, vol. 46, no. 1-2, pp. 123–127, 2013. View at: Publisher Site | Google Scholar
  10. I. Trandafir, V. Nour, and M. E. Ionica, “Determination of tin in canned foods by inductively coupled plasma-mass spectrometry,” Polish Journal of Environmental Studies, vol. 21, no. 3, pp. 749–754, 2012. View at: Google Scholar
  11. X.-L. Wang, P. Zhang, and Y. Chen, “Spectrophotometric determination of stannum in copper alloy based on fading reaction of methyl orange,” Yejin Fenxi, vol. 32, no. 12, pp. 73–75, 2012. View at: Google Scholar
  12. R. Kataria and H. K. Sharma, “3-Hydroxy-2-[1′-phenyl-3′-(4″-methoxyphenyl) -4′-pyrazoyl]-4-oxo-4H-1-benzopyran as a spectrophotometric reagent for the micro-determination of tin,” Journal of the Indian Chemical Society, vol. 89, no. 1, pp. 121–126, 2012. View at: Google Scholar
  13. R. Kataria and H. K. Sharma, “An extractive spectrophotometric determination of tin as Sn(II)-6-chloro-3-hydroxy-7-methyl-2-(4′-methoxyphenyl)-4-oxo-4H-1-benzopyran complex into dichloromethane,” Eurasian Journal of Analytical Chemistry, vol. 6, no. 3, pp. 140–149, 2011. View at: Google Scholar
  14. B. Chen, Q. Zhang, H. Minami, M. Uto, and S. Inoue, “Spectrophotometric determination of tin in steels with 2-(5-nitro-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol,” Analytical Letters, vol. 33, no. 14, pp. 2951–2961, 2000. View at: Publisher Site | Google Scholar
  15. J.-H. Tang, L.-H. Cheng, and X.-M. Wu, “Pyrocatechol violet-CPB spctrophotometric Determination of tin in copper alloys,” Guangpu Shiyanshi, vol. 30, pp. 1925–1928, 2013. View at: Google Scholar
  16. M. Abbasi-Tarighat, “Kinetic-spctrophotometric Determination of tin species using feed-forward neural network and radial basis function network in water and juices of canned fruits,” Analytical Chemistry, vol. 12, pp. 256–263, 2013. View at: Google Scholar
  17. T. Madrakian and F. Ghazizadeh, “Micelle-mediated extraction and determination of tin in soft drink and water samples,” Journal of the Brazilian Chemical Society, vol. 20, no. 8, pp. 1535–1540, 2009. View at: Publisher Site | Google Scholar
  18. A. C. S. Costa, L. S. G. Teixeira, and S. L. C. Ferreira, “Spectrophotometric determination of tin in copper-based alloys using pyrocatechol violet,” Talanta, vol. 42, no. 12, pp. 1973–1978, 1995. View at: Publisher Site | Google Scholar
  19. P. Huang, “Spectrophotometric determination of tin in antimony materials by using phenylflurone,” Hunan Youse Jinshu, vol. 29, pp. 68–79, 2013. View at: Google Scholar
  20. D.-X. Wang, F. Chen, and Z.-F. Liu, “Spectrophotometric determination of tin in flot glass,” The American Ceramic Society Bulletin, vol. 84, no. 12, pp. 9401–9404, 2005. View at: Google Scholar
  21. H. Yan, “Spectrophotometric determination of tin in steel with dibromo-hydroxyphenylfluorone,” Yejin Fenxi, vol. 23, no. 6, pp. 45–46, 2003. View at: Google Scholar
  22. C. Cai, Z. Zhou, S. Chen, and Y. Fang, “Research progress of tannery wastewater treatment,” Applied Mechanics and Materials, vol. 361–363, pp. 666–669, 2013. View at: Google Scholar
  23. S. P. Arya, S. C. Bhatia, A. Bansal, and M. Mahajan, “Isoamyl xanthate as a sensitive reagent for the spectrophotometric determination of tin,” Journal of the Indian Chemical Society, vol. 79, no. 4, pp. 359–360, 2002. View at: Google Scholar
  24. A. Varghese and A. M. A. Khadar, “Highly selective derivative spectrophotometric determination of tin (II) in alloy samples in the presence of cetylpyridinium chloride,” Acta Chimica Slovenica, vol. 53, no. 3, pp. 374–380, 2006. View at: Google Scholar
  25. X. Huang, W. Zhang, S. Han, and X. Wang, “Determination of tin in canned foods by UV/visible spectrophotometric technique using mixed surfactants,” Talanta, vol. 44, no. 5, pp. 817–822, 1997. View at: Publisher Site | Google Scholar
  26. S. P. Arya and A. Bansal, “Rapid and selective method for the spectrophotometric determination of tin using potassium ethylxanthate,” Mikrochimica Acta, vol. 116, no. 1–3, pp. 63–71, 1994. View at: Publisher Site | Google Scholar
  27. S. P. Arya, S. C. Bhatia, and A. Bansal, “Extractive-spectrophotometric determination of tin as Sn(II)-ferron complex,” Fresenius' Journal of Analytical Chemistry, vol. 345, no. 11, pp. 679–682, 1993. View at: Publisher Site | Google Scholar
  28. A. M. Gutierrez, M. V. Laorden, A. Sanz-Medel, and J. L. Nieto, “Spectrophotometric determination of tin(IV) by extraction of the ternary tin/iodide/5,7-dichloro-8-quinolinol complex,” Analytica Chimica Acta, vol. 184, no. C, pp. 317–322, 1986. View at: Publisher Site | Google Scholar
  29. G. H. Jeffery, J. Bassett, J. Mendham, and R. C. Denny, Vogels Textbook of Quantitative Chemical Analysis?Addison Wesley Longman, Singapore, 5th edition, 1989.
  30. S. C. Gupta, N. S. Yadev, and S. N. Dhawan, “Synthesis of 2, 3 diaryl 8 methyl 2, 3, 4, 10 tetrahydropyrano 3, 2 b, 1 benzopyran 10 ones photoisomerization of styrylchromones,” Indian Journal Of Chemistry Section B: Organic Chemistry Including Medicinal Chemistry, vol. 30, no. 2, pp. 790–792, 1991. View at: Google Scholar
  31. A. Ringbom, “Über die Genauigkeit der colorimetrischen Analysenmethoden I,” Fresenius Journal of Analytical Chemistry, vol. 115, no. 9–10, pp. 332–343, 1938. View at: Publisher Site | Google Scholar
  32. P. Job, “Formation and stability of inorganic complexes in solution,” Annali di Chimica, vol. 9, pp. 113–203, 1928. View at: Google Scholar
  33. W. C. Vosburgh and G. R. Cooper, “Complex ions. I. The identification of complex ions in solution by spectrophoto-metric measurements,” The Journal of the American Chemical Society, vol. 63, no. 2, pp. 437–442, 1941. View at: Publisher Site | Google Scholar
  34. J. H. Yoe and A. L. Jones, “Colorimetric determination of iron with disodium-1,2-dihydroxybenzene-3,5-disulfonate,” Industrial & Engineering Chemistry Analytical Edition, vol. 16, no. 2, pp. 111–115, 1944. View at: Publisher Site | Google Scholar

Copyright © 2014 Ramesh Kataria and Harish Kumar Sharma. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1442 Views | 558 Downloads | 1 Citation
 PDF  Download Citation  Citation
 Download other formatsMore
 Order printed copiesOrder

We are committed to sharing findings related to COVID-19 as quickly and safely as possible. Any author submitting a COVID-19 paper should notify us at to ensure their research is fast-tracked and made available on a preprint server as soon as possible. We will be providing unlimited waivers of publication charges for accepted articles related to COVID-19.