Abstract
A sensitive RP-HPLC method is presented for the simultaneous quantification of Fluorometholone (FLM) and Tetrahydrozoline hydrochloride (THZ). The method has the advantages of being rapid, accurate, reproducible, ecologically acceptable and sensitive. The separation utilized C8 Xbridge® column and mobile phase mixture of Acetonitrile/phosphate buffer pH 3 ± 0.1 (70:30, v/v) with UV detection at 230 nm. Stepwise optimization and factors affecting separation are properly discussed. Different factors were optimized such as stationary phase, selection of organic solvent and its content, buffer pH and concentration, flow rate, elution type and detection wavelength. The studied drugs were efficiently separated in 3.4 min with high resolution. Also, two univariate spectrophotometric methods have been optimized for the quantification of the studied drugs. Method 1: dual wavelength for THZ and iso-absorptive point for FLM, Method 2: ratio difference (RD) for THZ and first derivative FLM utilizing methanol as a solvent. These methods are accurate, precise with minimal data manipulation. Greenness of the methods was estimated using eco-scale tool where the presented methods were found to be excellent green with eco-score of 83 for HPLC and 80 for spectrophotometry. The methods are validated in conformance with ICH guidelines, with acceptable accuracy, precision, and selectivity. The suggested methods can be employed for the economic analysis of THZ and FLM in their pure form and binary ophthalmic formulation, that can be employed by quality control laboratories.
1 Introduction
Fluorometholone (FLM); [9a-fluoro-11b,17a-dihydroxy-6a-methylpregna-1,4-diene-3,20- dione] [1] (Fig. 1A) is a corticosteroid used for its glucocorticoid activity, usually as eye drops containing 0.1%, in the treatment of allergic and inflammatory conditions of the eye. Tetrahydrozoline HCl (THZ); [1H-Imidazole, 4,5-dihydro-2-(1,2,3,4-tetrahydro-1-naphthalenyl) onohydrochloride] [1] (Fig. 1B) is a sympathomimetic with effects similar to those of naphazoline. It is used as hydrochloride salt for its vasoconstrictor effect in the symptomatic relief of nasal congestion. When present together in an ophthalmic formulation they are used to treat conjunctival irritation [2]. Few methods were reported for the assay of FLM/THZ mixture, these methods include one spectrophotometric method [3] and three HPLC methods [3–5]. Thorough investigation of literature revealed that no pharmacopeial methods have been described for the simultaneous assay of FLM/THZ. Also, the reported methods suffer from lack of sensitivity and consume large amounts of organic solvents that harm the environment and increase the cost.
Chemical structure of (A) Fluorometholone and (B) Tetrahydrozoline HCl
Citation: Acta Chromatographica AChrom 33, 3; 10.1556/1326.2020.00783
HPLC is the most frequently used and well-developed method for both qualitative and quantitative analysis. HPLC method development can be implemented for various goals including improving selectivity, sensitivity, minimizing runtime, improving efficiency of separation, improving method robustness and transferability and improvement of greenness. However, most of the chromatographic applications apply hazardous solvents and produce large amounts of toxic waste that damage the environment. Recently the Society of Analytical Chemistry has been growingly seeking implementation of eco-friendly methods that eliminate or decrease toxic and corrosive waste [6]. Evaluation of analytical methods greenness is profoundly important and attention grasping for most method developers. One of the latest used greenness valuation tools for analytical techniques is the analytical eco-scale [7], which is a semi-quantitative tool to evaluate and compare analytical methods based on their conformity with green chemistry principles [8]. The eco-scale tool reflects many factors that can have adverse impacts on the environment, such as the class and amount of any chemical used in the procedure, the mass of generated waste, occupational exposure, and energy consumption [9].
UV spectrophotometry has wide applications in the field of pharmaceutical analysis either for identification or for quantitative analysis of different drugs. Many drugs are formulated as mixtures, and the ability to resolve these combination mixtures without prior separation is an extremely important issue in pharmaceutical analysis. Therefore, many univariate spectrophotometric methods were introduced for the analysis of different drugs containing mixtures. The commonly reported dual wavelength technique (DW) [10–13], Iso-absorptive point (ISO) [14], Derivative spectrophotometry (DS) [15–18] and Ratio difference (RD) [19, 20] are well established techniques with minimal data manipulations. These methods can be utilized for their simplicity to improve the sensitivity and allow the application of the drugs in a wide linearity range which are the main drawbacks of the only developed spectrophotometric method for the cited drugs [3].
The aim of this work is to develop a sensitive, rapid and eco-friendly HPLC method as well as two simple univariate spectrophotometric methods for the simultaneous quantification of FLM/THZ combination in pure form and their binary ophthalmic formulation. In this manuscript the greenness assessment was implemented using the ecoscale tool.
2 Experimental
2.1 Materials
- –Pure samples
Pure fluorometholone micronized (FLM) and tetrahydrozoline HCl (THZ); were kindly supplied by Orchidia Pharmaceutical Company, Cairo, Egypt, their purity was certified and found to be 99.81 ± 0.521 % [1] and 99.91 ± 0.112% [1], respectively.
- –Market samples
Efemyo® eye drops (1 mg mL−1 FLM and 0.25 mg mL−1 THZ, batch number 1018201) was manufactured by Orchidia Pharmaceutical Company (Egypt). Efemyo® was purchased from the Egyptian market.
- –Chemicals and reagents
Acetonitrile, methanol, Ortho-phosphoric acid 85% and sodium dihydrogen phosphate (all of HPLC grade), were purchased from Sigma-Aldrich (Germany). A water purification system (New Human Power I, Korea) was used to obtain ultra-pure water for buffer preparation.
2.2 Instruments
2.3 Chromatographic conditions
Chromatographic separations were carried out using Xbridge® C8 column (5 µm, 250 mm x 4.6 mm I.D) using a mobile phase of acetonitrile/sodium dihydrogen phosphate buffer pH 3.0 ± 0.1 (70:30, v/v) through isocratic elution with flow rate 1 mL min−1. Phosphate buffer 0.02 M was prepared according to British Pharmacopoeia [1], pH was adjusted to 3.0 ± 0.1 using orthophosphoric acid. Separation was implemented in an air-conditioned room kept at 22 ± 2 °C and UV detection at 230 nm.
2.4 Stock and working solutions
Standard stock solutions of THZ and FLM 1 mg mL−1 were prepared in separate flasks using methanol as solvent. Working standard solutions 100 μg mL−1 of THZ and FLM were prepared from their respective stock solutions by appropriate dilution with the mobile phase for the HPLC method while dilution with methanol was done for the spectrophotometric methods.
2.5 Procedures
2.5.1 Spectral characteristics of THZ and FLM
Aliquots equivalent to 5 µg of THZ and 20 µg FLM were accurately transferred from their respective working standard solutions into two separate 10-mL volumetric flasks and the volumes were completed to the mark with methanol. Zero-order absorption spectrum of each solution was then recorded over a wavelength range of 200–400 nm using methanol as a blank. The recorded spectra were further employed to determine the optimum parameters for each spectrophotometric procedure.
2.5.2 Construction of calibration curves
2.5.3 Analysis of Laboratory Prepared Mixtures
To assess the specificity of the proposed methods, different aliquots of THZ and FLM were transferred from their corresponding standard working solutions into a series of 10-mL volumetric flasks. The volumes were completed with the mobile phase for HPLC and with methanol for spectrophotometry to prepare different ratios of the two drugs including the ratio of the dosage form.
2.5.4 Application of the suggested methods on pharmaceutical formulations
3 Results and discussion
3.1 Method optimization
3.2 Method validation
Validation of the proposed univariate spectrophotometric and HPLC methods was performed according to ICH guidelines [21] by assessment of linearity, range, accuracy, precision. Obtained results are represented in Table 2. The specificity of the developed methods was assessed by analyzing laboratory prepared mixtures containing different ratios of THZ and FLM. Satisfactory results were obtained and listed in Table 3. The proposed methods were applied for the determination of THZ and FLM in pharmaceutical formulations and good results were obtained where no impurities were detected as represented in Table 4.
- –Range and LinearityTable 3.
Determination of pure THZ and FLM in laboratory prepared mixtures by the proposed spectrophotometric methods
Ratio of the studied mixtures THZ FLM HPLC DW RD HPLC ISO 1D THZ FLM Found µg mL−1 Recovery % Found µg mL−1 Recovery % Found µg mL−1 Recovery % Found µg mL−1 Recovery % Found µg mL−1 Recovery % Found µg mL−1 Recovery % 5a 20a 5.02 100.40 5.06 101.31 5.04 100.87 20.23 101.15 20.15 100.76 19.79 98.93 5 30 4.96 99.20 4.94 98.78 5.09 101.8 29.77 99.23 30.17 100.57 29.89 99.63 20 10 20.24 101.20 20.00 100.00 20.33 101.69 9.95 99.50 9.89 98.93 9.89 98.89 10 25 10.13 101.30 9.88 98.80 9.96 99.65 25.42 101.68 24.52 98.08 24.84 99.35 8a 32a 7.95 99.38 7.98 99.71 8.02 100.31 32.36 101.13 31.92 99.74 31.95 99.84 15 15 15.11 100.73 15.06 100.43 14.89 99.25 14.88 99.20 14.94 99.58 15.04 100.29 15 25 14.88 99.20 14.94 99.95 15.01 100.08 24.26 97.04 24.67 98.68 24.63 98.52 Mean ± RSD 100.2 ± 0.93 99.80 ± 0.90 100.52 ± 0.97 99.85 ± 1.61 99.48 ± 0.98 99.35 ± 0.61 Ratio of the dosage form.
Table 4.Quantitative determination of THZ and FLM in Efemyo® eye drops by the proposed methods and standard addition technique
Pharmaceutical formulation Efemyo® eyedrops (Labeled to contain 250 μg mL−1THZ and 1 mg mL−1FLM)
Batch number 1018201Drug THZ FLM Method HPLC DW RD HPLC ISO 1D Mean ±%RSDa 99.93 ± 0.97 99.37 ± 0.99 99.73 ±1.25 100.28 ± 0.90 99.67 ± 0.88 99.70 ± 0.66 Recovery of standard added ±%RSDa 101.39 ± 0.45 100.05 ± 1.28 100.00 ± 0.23 100.53 ± 1.07 101.20 ± 0.87 98.81 ± 0.41 Average of three determinations.
The linearity of the presented methods was examined by managing variable concentrations of the different calibration curves on 3 different days. The calibration curves were built within concentration ranges that are related to drugs concentration in the dosage forms.
- –Accuracy
The suggested methods were applied for measuring three concentrations of THZ and FLM within their linearity ranges – each repeated three times - and the concentrations were calculated from their corresponding regression equations. The percentage recovery for each drug was calculated Table 2. The accuracy of the proposed methods was further assessed by applying the standard addition technique for the analysis of Efemyo® eyedrops.
- –Precision
The precision of the methods expressed as %RSD was calculated by the determination of three different concentrations of pure drugs chosen along the linearity range. The intra-day precision was obtained from the throughout results of three replicate determinations of three pure drugs samples throughout a single day. To determine the inter-day (intermediate) precision, the same samples were analyzed on 3 consecutive days. The %RSD of the results of both inter and intraday precisions were less than 2.00% indicating the good precision [41]. The results are illustrated in Table 2.
- –Limits of detection and quantification
The limit of detection and quantification for the HPLC and 1D method were calculated using signal to noise ratio method [21] while LOD and LOQ for the remaining methods were determined via calculations, LOD = 3.3 (SD of the response/slope), LOQ = 10 (SD of the response/slope).
- –Specificity
The specificity of the spectrophotometric methods was assessed by analyzing different laboratory prepared mixtures of THZ and FLM within the linearity range Table 3, where good results were obtained. Moreover, the specificity of the HPLC method is presented by resolution of the investigated drugs, Table 1 [21], also with the peak purity and 3D figures imported from Chemstation software, Figs. S1 and S2.
- –Robustness
The robustness was examined by testing the samples under a minor variety of experimental conditions. For RP-HPLC methods, small changes in the pH (±0.2), small changes in percentage of acetonitrile by up to ±2% were introduced to the mobile phase, small changes in the detection wavelength (±5 nm) and small changes in flow rate (±0.1 mL min−1). A slight modification in the elution time and peak symmetry was observed, however, the system suitability parameters are still within the acceptable values, Table 5.
- –System suitabilityTable 5.
System suitability parameters for robustness of the proposed HPLC method for THZ and FLM
Parameters Symmetry Retention factor Number of theoretical plates Selectivity Resolution THZ FLM THZ FLM THZ FLM FLM FLM Wavelength nm 230+5 0.97 1.05 2.16 2.85 2,004 7,284 1.59 4.20 230–5 1.10 1.05 2.16 2.85 2,217 6,607 1.59 4.25 Flow rate mL min−1 1.10 0.92 1.05 2.16 2.93 2,217 7,744 1.67 4.89 0.90 0.94 1.05 2.14 2.79 2,165 7,009 1.58 3.42 Mobile phase ratio v/v 72–28 0.88 1.13 2.40 3.16 2,692 7,093 1.54 3.96 68–32 1.13 1.20 2.04 2.59 2,704 6,021 1.67 4.49 pH 3.30 0.92 1.10 2.08 3.10 2,212 6,087 1.20 4.27 2.70 1.00 1.20 2.15 2.86 2,072 9,056 1.61 4.38 According to the ICH [21] system suitability is a crucial part of many analytical methods, particularly liquid chromatographic methods. They are applied to authenticate that the resolution and reproducibility of the proposed methods are suitable for the real-life quality control analysis to take place. Different parameters, namely retention factor (k’), symmetry factor, selectivity factor (α) and resolution (Rs), were calculated and proved to be within the accepted values Table 1.
3.3 Application to pharmaceutical formulation and standard addition technique
The suggested HPLC method is valid for the determination of THZ and FLM in pure form and in Efemyo® eye drops. The validity of the proposed method and interference of added excipients in the pharmaceutical products was further investigated by implementing the standard addition technique, which produced acceptable results, Table 4. Good accuracy confirmed that the excipients in pharmaceutical products did not interfere in the determination of these drugs. The results support the suitability of the suggested method for the regular analysis of these compounds in their combined formulations.
3.4 Greenness Assessment: Analytical eco-scale
Appling the eco-scale metric to determine the proposed methods greenness is based on giving penalty points to any aspect that doesn't conform with perfect green technique, where the ideal green analysis has its eco-scale value of 100, excellent green analysis should score >75 eco-scale, acceptable green analysis scores >50, while if the method scores <50, it will be considered as inadequate green analysis [7]. Penalty points' calculations for the proposed methods are shown in Table 6, where both methods were found to be excellent green method. HPLC has comparable score to spectrophotometry. The calculation of the penalty point for each used chemical is based on the calculation of (amount penalty points × hazard penalty points). Hazard penalty points is the number of pictograms in material safety data sheet of the chemical × the score for the signal word (safe = 1, danger = 2). Amount penalty points are assigned based on the rule that (less than 10 mL = 1, 10–100 mL = 2, more than 100 mL = 3). So, for acetonitrile (2 pictograms, signal word is danger, amount is between 10 and 100 mL) the penalty point score is [2 pictograms × 2 (danger) × 2 (amount 10–100 mL)] = 8 penalty points. Methanol penalty points calculated as follows [3 pictograms × 2 (danger) × 2 (amount 10–100 mL)] = 12 penalty points. Sodium dihydrogen phosphate has no pictograms, so zero penalty points. The instrumental energy consumption also has penalty points as following (0 for methods using less than 0.1 kWh per sample, 1 for methods using 0.1–1.5 kWh per sample, 2 for methods using more than 1.5 kWh per sample). Spectrophotometry is assigned zero while HPLC is assigned one penalty point. Waste penalty points is calculated as follows (None = 0, <1 mL (g) = 1, 1–10 mL (g) = 3, >10 mL (g) = 5) then processing points are added where (recycling 0, degradation = 1, passivation = 2, no treatment = 3). The waste penalty points for both developed methods is [(1–10 mL (g) = 3) + (no treatment = 3)] = 8.
Penalty points for greenness assessment of the proposed methods
Hazard | Penalty Points | |
HPLC | Spectrophotometry | |
Reagents | ||
Acetonitrile | 8 | |
Phosphate buffer | 0 | |
Methanol | 12 | |
Instruments energy | 1b | 0b |
Occupational hazard | 0 | 0 |
Waste | 8 | 8 |
Total penalty points | 17 | 20 |
Analytical eco-scale total score | 83a | 80a |
>75 represents excellent green analysis, >50 represents acceptable green analysis, <50 represents inadequate green analysis.
Energy consumed by instrument per sample (0 for methods using less than 0.1 kWh per sample, 1 for methods using 0.1–1.5 kWh per sample, 2 for methods using more than 1.5 kWh per sample).
4 Conclusion
The proposed spectrophotometric and HPLC methods have the advancements of being green, simple with no excessive data manipulation, reproducible, fast and accurate according to the study in hands. Under optimized chromatographic conditions, excellent separation of THZ and FLM was obtained. The chosen buffer and flow rate had shown superior performance and selectivity regarding system suitability parameters, analysis time, analysis cost, conditioning time, backpressure. Spectrophotometric methods have the advantages of minimal data manipulation and being eco-friendly. The developed methods have advantages over the reported method in being greener, with lower cost, lower volumes consumption and most importantly better sensitivity. The proposed approaches can be used for the routine analysis of THZ and FLM, in their binary pharmaceutical preparation or in bulk powder form. The methods are characterized by broad applicability, short analysis time and adequate robustness. The suggested methods are validated utilizing ICH guidelines. they could be implemented in QC laboratories for a cost-effective analysis.
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Appendix A Supplementary data
Supplementary data to this article can be found online at