INTRODUCTION:

The objective of the present research was to increase the solubility of valsartan in water by hydrotropic solubilisation. Aqueous solubility of a therapeutically active substance is a key property as it governs dissolution, absorption and thus the efficacy in vivo; and also restricts use of organic solvent in method development¹. Articles^2,3are deliberately shows significance of hydrotropes in solubilisation of poorly water soluble drug. The development of eco-friendly method by avoiding organic solvent could be termed as economical green method⁴.

There is consistently pressure from environmental department to minimise hazardous and volatile solvent content in the waste which seriously affects environment. Use of hydrotropic solutions, supercritical fluids in the organic synthesis curbs use of organic solvent in view point of green chemistry⁵. Hydrotropes are capable of increasing the solubility of organic compounds up to 200 times in water. Hydrotopes are surface active, highly water soluble organic salt, which imparts solubility to insoluble or sparingly soluble organic compounds in water, which is when present at higher concentration. The potential use of hydrotopes in industry was studied in 1946 by McKee⁵. In literature review it is revealed that green FT-IR method⁶, eco-friendly methods^7,8 are suitable for analytical purpose; and green analytical methods are preferred over analytical methods using harmful organic solvent for environment⁹.

Valsartan an angiotensin II receptor antagonist; poorly water soluble was selected for this research. Valsartan chemically is N-(1-oxophenyl)-N-[[2¹-(1H-tetrazol-5-yl)(1-1¹-biphenyl) -4-yl]methyl]-L-valine^10,11. It is an angiotensin II receptor antagonist with actions similar to those of losartan. It is used in the management of hypertension to reduce cardiovascular mortality in patients with left ventricular dysfunction after myocardial infarction and in the management of heart failure¹². The drug is official in recently published British Pharmacopoeia¹³andIndian Pharmacopoeia¹⁴. Chemical structure of drug is shown in (Fig No 1).

Various analytical methods have been reported for the estimation of VST alone or in combination with other anti-hypertensive agents in pharmaceutical dosage form includes UV derivative spectroscopic method^15-18, RP-HPLC method^19-22, spectrofluorimetric method²³, titrimetric²⁴and liquid chromatographic^25,26.

Fig No 1: Chemical structure of Drug molecule Valsartan

For analytical method validation ICH Q2 (R1) has given various method performance characteristics^27,28.

MATERIALS AND METHODS:

Instrumentation:

Analysis was performed with a Shimadzu Double beam UV-Visible spectrophotometer (Shimadzu, Kyoto, Japan) with spectral bandwidth of 2nm and wavelength accuracy of ±1nm with 10mm matched Quartz cells was used. Electronic balance Afcoset balance (The Bombay Burmah Trading corpo Ltd) with accuracy ±0.1mg Model No. ER 200A was used for weighing and for degassing the solutions Digital Ultrasonic cleaner 1.8Ltr (Labman scientific Instruments Chennai) was used.

Reagents and Chemicals:

Pharmaceutically pure samples of VST from FDC Limited, Mumbai, Maharashtra was procured as a gift samples and the commercial formulation containing Valsartan80mg was procured from local market. Sodium acetate AR and distilled water were utilised for preparation of solvent.

Solvent selection:

Research article¹⁶was focused on effect of solvent on the retention time of valsartanand pH effect, drug interaction was precisely discussed in the research article^12,19. VST is freely soluble in methanol, insoluble in water and soluble in 0.1N NaOH. Solubility of the procured drug was studied in methanol, 0.1N NaOH and sodium acetate; and to understand characteristic nature of spectra each solution of known conc of analyte was scanned in UV range. The recorded spectra in NaOH solvent is shown in (Fig No2).Also solubility of drug was studied in sodium acetate solution and it was found that 1% w/v conc of sodium acetate (Fig No 3)is the well solubilising, low cost, shown more absorbance as compare to NaOH in producing result.

Fig No 2: UV-VIS spectra of Valsartan in NaOH solution

Fig No 3: UV-VIS spectra of Valsartan in sodium acetate solution

Preparation of 1 % sodium acetate solution:

Hydrotrope 1% sodium acetate solution was found suitable solvent for dissolving valsartan. Hence 1% solution of sodium acetate was used throughout the developed technique as eco-friendly solvent instead of organic solvent like methanol. Weighed 10 gm of sodium acetate and dissolved in water and volume was made up to the 1 lit to obtain 1% solution.

Preparation of stock solutions and standard solutions:

50mg of pure drug VST was accurately weighed; and transferred into separate 50ml volumetric flask. Dissolved into 1% sodium acetate solution and volume was made to 50ml with solvent. Subsequent stock solution of drug with conc 100μg/ml was prepared by diluting aliquot 5ml of stock solution to 50ml capacity volumetric flask. Standard solution of valsartan 10μg/ml was obtained by diluting aliquot of subsequent stock solution.

Selection of wavelength and conc. range:

From UV spectra it was found that VST has measurable absorbance at 247.2nm. From the nature of spectra of VST working conc. range 8 to 48mcg/ml (μg/ml) was selected in solvent 1% solution of sodium acetate. Also drug solution was prepared simulated to marketed formulation. Above discussed observations was guided to select critical parameters listed in Table No 1 and by using these; method was validated as per ICH guidelines and by analysing marketed preparations.

Table No 1: Selected critical parameter for UV-VIS analytical method of VST

Parameter	Selected variables For VST
Wavelength range	215 - 400
Wavelength	247.2nm
Solvent	1 % Sodium acetate in distilled water
Scan speed	Fast
Sampling interval	±0.2nm

Experimental Method for estimation:

Two simple methods calibration curve method and single point absorbance method were applied for estimation of the formulation/dosage form. Calibration curve method employed preparation of six standard solutions from stock solution in the working conc range and measurement of absorbance was recorded at selected wavelength; followed by plot of calibration curve i.e. absorbance against conc. Best linear relationship between conc and absorbance was ascertained after three replicates of calibration curve prepared from different stock solutions. The regression line equation Y = mX + c where m is the slope and c is the intercept was used for the calculation of sample concentration. Also instruments quantitation mode was utilised to know the conc of sample/formulation solution.

In Single point absorption method standard solution and sample solution were prepared and conc of sample solution was calculated by applying formula

C_std

C_sample = A _sample x --------

A_std

Where

A_std = absorbance of VST standard solution at nm

C_std= Conc of VST standard solution

A _sample = absorbance of sample solution

C _sample = Conc. of sample solution

Validation of the Method:

To attain analytical target profile of the method, selected critical parameters should meet the performance characteristics of the analytical method. In order to implement this an ICH guideline Q2 R1 was applied to study methods performance with critical parameters. The method was validated as per ICH guidelines.^17,18

System suitability:

System suitability is studied to demonstrate the suitability of the developed procedure under consideration for the analytical method. Six replicates of working standard solutions with conc30 mcg/ml of VST were prepared separately and absorbance was recorded; SD and %RSD of the response was calculated. Stability of the solution was also studied by bench top stability at laboratory temp.

Linearity:

The linearity of an analytical method is its ability to obtain response i.e. absorbance which is directly proportional to the conc. of analyte. series of working standard solutions were prepared in conc. range of 8 to 48mcg/ml (μg/ml) and scanned in 215 to 400nm range in spectrum mode of the spectrophotometer, absorbance of the standard solutions were recorded at 247.2nm for VST in spectrum order. Microsoft office excel software tool was used to obtain the standard regression curve and its analysis as slope, intercept, and correlation coefficient.

Assay of formulation:

Assay was carried out by proposed methods and method was validated by statistical parameters.

Method I: Estimation of formulations by calibration curve method:

Tablets were weighed, powdered and tablet powder equivalent to 40mg VST was weighed and transferred into 50ml volumetric flask. Dissolved into 1% Sodium acetate solvent and volume was made with solvent. Solution was filtered through whatman filter paper No 40 and aliquots of solution were diluted to obtain tablet solution. Solution was scanned in the range of 215 to 400nm to obtain absorbance of tablet solution at 247.2 nm in spectrum order. Obtained absorbance was utilised to estimate unknown conc. of formulation; and results are statistically validated to obtain % of nominal conc., standard deviation and % of RSD.

Method II: Estimation of formulations by single point absorbance method:

Standard solutions of conc. 10mcg/ml and 20mcg/ml were prepared separately scanned in 215 – 400nm range; and absorbance at 247.2nm was recorded. Also above prepared tablet Solution was scanned in 215 to 400nm range and absorbance was recorded. Equation was applied to determine conc. of sample solution; and obtained results are statistically validated to obtain % of nominal conc., standard deviation and % of RSD.

Accuracy and Precision:

The accuracy of an analytical method expresses the closeness of an agreement between test result and true result. Accuracy study was performed by recovery study i.e. standard addition method; diluted standard solution of VST was prepared and standard solutions added in 80, 100 and 120% proportionate to the tablet solution. Three replicates at each of these three levels were prepared and measured and % of conc., SD and RSD of replicates were calculated.

The precision study was carried out by performing assay of tablet six times; also the reproducibility in result was studied by interday and intraday precision.

Limit of Detection (LOD) and Limit of Quantitation (LOQ):

The LOD and LOQ of VST by the proposed method were determined using calibration graph method and calculated as 3.3σ/s and 10 σ/s for LOD and LOQ respectively. σ is the standard deviation of calibration curve and s is the slope of regression line.

Robustness and Ruggedness:

It is measure of capacity of analytical procedure to remain unaffected by small but deliberate variations in method parameter.

RESULTS AND DISCUSSION:

Method development comprises numerous steps of which solvent selection, method for measurement selection are significant one. Uses of eco-friendly solvents have got remarkable weightage due to low cost, readily available and environmentally sound. Drugs underlying analysis must have appreciable solubility in the selected solvent. Chemical structure of the drug and physico-chemical properties available in the literature guides about use of appropriate solvent in the method. Solubility of VST was studied in each solvent; and in 1 % Sodium acetate solution drug VST was shown maximum and consistent absorbance as compare to other solvent.

System Suitability:

The absorbance of six replicates of standard solutions (30 mcg/ml) are reported in Table No2. The SD and % RSD was found for VST and meets the system suitability requirements indicates method was suitable for analysis.

Table No 2: System suitability study of VST

Sr. No	Conc. in mcg/ml	Absorbance of VST
1	30 mcg/ml	0.7328
2	30 mcg/ml	0.7336
3	30 mcg/ml	0.7372
4	30 mcg/ml	0.7371
5	30 mcg/ml	0.7516
6	30 mcg/ml	0.7505
	SD	0.02653

Linearity:

The overlay spectra obtained in linearity study was shown in Fig No 4 and the calibration curve of drug found to be linear in the conc. range of 8-48μg/ml as shown in Fig No 5. The regression equation of line and its parameters slope, r²value and intercept are tabulated in Table No 3, which proved the linear relationship between conc and obtained response.

Fig No 4: UV-VIS overlay spectra of Valsartanin linearity study

Fig No 5: Calibration curve of Valsartan

Table No 3: Parameters of regression equation obtained in Microsoft excel

Parameters	VST
Detection wavelength	247.2
Beer’s law limit (μg/ml)	4 – 48 mcg/ml
Correlation coefficient (r²)	0.9992
Regression equation (y = mx + c)	Y = 0.0232 X – 0.0145

Assay:

The assay was carried out by both the methods. The spectra of formulation were shown in Fig No 6. The assay of formulation was carried out by proposed method and calculated % of nominal conc and RSD was found within acceptable limits are summarized in Table No 4. The results indicated applicability of the method for estimation of Formulation.

Accuracy and Precision:

The results of accuracy are summarised in Table No5, the obtained results were within acceptable limit; and methods accuracy was justified by calculating %drug content. The precision study was carried out by performing assay of solutions; further the reproducibility in result was studied by interday and intraday precision. The values obtained SD and %RSD was shown methods precision and are summarised in Table No 5.

Limit of Detection (LOD) and Limit of Quantitation (LOQ):

The LOD and LOQ of VST by the proposed method were shown in Table No6. The standard deviation of the calibration curve was obtained in Microsoft office excel word.

Robustness and Ruggedness:

Robustness was studied and capacity of analytical procedure to measure analyte was remain unaffected by small but deliberate variations in method parameter like variation in the wavelength ±1nm, variation in the solvent strength by ±0.1%. The analytical method was found rugged during development; similarity the result was produced by performing the analysis by different analyst given in Table No 6.

Table No.6: Results of LOD and LOQ, robustness and degradation study in stability

Parameters		VST
LOD mcg/ml		0.125 mcg/ml
LOQ mcg/ml		0.05 mcg/ml
Robustness	± 1 nm	0.5441 to 0.5273 (conc 25 mcg/ml)
Robustness	SD	0.017464 and 0.0372424
Ruggedness	Analyst 1	SD ± 1.4479
Ruggedness	Analyst 2	SD ± 1.8870
Degradation study	Acid (HCl Acid)	Percentage found 86.51%
	Alkali (NaOH)	Percentage found 43.37%
	Hydrogen Peroxide	Percentage found 71.63%

Stress Degradation study:

Formulation was undergone various degradation studies acid, alkali and hydrogen peroxide. The percentage degradation was found within acceptable limit and is tabulated in Table No.6.

CONCLUSION:

The method was developed with eco-friendly and easily available aqueous 1% Sodium acetate solvent. Valsartan was estimated from the formulation by both the method and satisfactory results were obtained. The calibration graph method was given reproducible results; however obtained results of both the methods were within acceptable limits given in the pharmacopoeia. The validated method is economical, precise, accurate, robust and reproducible hence can be routinely used for estimation of Valsartan from the dosage form.

CONFLICT OF INTEREST:

All Authors declared that there is no conflict of interest.

ACKNOWLEDGEMENT:

Authors are thankful to FDC Limited Mumbai for providing pure drug Valsartanas a gift sample. Authors are thankful to Management, Principal SVPM’S college of Pharmacy Malegaon BKII Baramati Dist. Pune for providing facilities for research.

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Received on 06.01.2023 Modified on 13.06.2023

Asian J. Research Chem. 2023; 16(5):313-318.

DOI: 10.52711/0974-4150.2023.00051

Formulation	Drug	Label Claim (mg/Tablet)	Amount found/mg; n=6	Drug Content %	Std Deviation	% RSD
Valent 80 By I method	VST	80 mg	80.744	100.93 %	1.8871	1.8691
Valent 80 By II method	VST	80 mg	78.336	97.92 %	1.4479	1.4786

S. No.	Parameter	Level of study	Data Title	Obtd. Data	S.D.	RSD
1	Precision study of VST	Intraday Precision	Mean of Abs n= 6	0.8312 (Abs of 30mcg/ml)	0.03507	-
1	Precision study of VST	Interday precision	Mean of Abs n= 6	0.8096 (Abs of 30mcg/ml)	0.63321	-
2	Accuracy study of VST	80%	% Purity found	102.68	1.88573	1.84731
		100%		105.10	2.55929	2.43515
		120%		103.33	3.97617	3.84792