A green, simple, quick and economical method is implemented for the first time for the simultaneous estimation of cetirizine (CTZ) and azelastine (AZE) as co-administered eye drops. The method relies on synchronous spectrofluorimetry with ∆λ = 60 nm. Cetirizine can be estimated at 231 nm and AZE can be measured at 294 nm, each at the other’s zero crossing point. All factors affecting the method were studied and properly optimized. Good correlation was obtained in the range of 0.1–2 µg mL−1 for both drugs. The limits of detection were 0.014 and 0.010 µg mL−1 and limits of quantitation were 0.043 and 0.029 µg mL−1 for CTZ and AZE, respectively. Moreover, ICH guidelines were carried out to validate the adopted method. The method was suitable for the analysis of CTZ and AZE in synthetic mixtures, eye drops and aqueous humor. The mean percentage of recoveries of CTZ and AZE in spiked aqueous humor were 99.83 and 99.37, respectively. Furthermore, Green Analytical Procedure Index (GAPI) and analytical Eco-scale approaches were used to evaluate the greenness of the suggested method.

A new analytical quality by design-assisted HPLC–UV approach is presented, for the first time, for the concurrent determination of cetirizine (CTZ) and azelastine (AZE) in raw materials, commercial eye drops and aqueous humor. The two drugs are co-administered as eye drops in severe ocular allergies. A 23 full factorial design was adopted for the chromatographic optimization to ensure the best analytical performance and reliability, as well as to save time, effort and solvent consumption. The parameters, including pH, acetonitrile ratio, and flow rate, were selected as independent factors. The responses analyzed were resolution and tailing of peaks. The separation was achieved through isocratic elution on C8 column with mobile phase made up of acetonitrile: 0.3% triethylamine of pH 5 (60:40 v/v) at a flow rate of 1.2 mL min−1 and detection at 216 nm. The elution time was less than 6 min. The approach was fully validated in accordance with International Council for Harmonization (ICH) guidelines. Good linearity was achieved over the concentration ranges of 1.0–30 and 0.5–10 µg mL−1 with limits of detection of 0.310 and 0.158 µg mL−1 and limits of quantification of 0.940 and 0.479 µg mL−1 for CTZ and AZE, respectively, with correlation coefficients of 0.9998. The intra- and inter-day precisions were lower than 2%. The good sensitivity of the approach permits the analysis of CTZ and AZE in spiked aqueous humor with mean percentage recoveries of 100.93 ± 1.42 and 100.11 ± 1.55, respectively. The statistical comparison between results of the developed method and the comparison method revealed no differences, indicating the accuracy of the method.

A new, simple and selective HPLC method was implemented for the simultaneous estimation of tafluprost (TFL) and timolol (TIM) in their new anti-glaucoma combination in the challengeable ratio of 3 and 1000 for TFL and TIM, respectively. Separation was achieved using a BDS Hypersil phenyl column and a mobile phase made up of acetonitrile: 0.015 M phosphate buffer (50:50 v/v, pH 3.5) delivered at 1 mL min−1 and the separation was completed in less than 6 min. UV detection was time programmed at 220 nm for the first 4.5 min and later at 254 nm. Mebeverine (MEB) was used as an internal standard (I.S.). The linearity was observed in the ranges of 0.6–45 and 50–2000 µg mL−1 with limits of detection (LOD) of 0.18, 16.48 µg mL−1 and limits of quantification (LOQ) of 0.55, 49.94 µg mL−1 for TFL and TIM, respectively. The method satisfied International Council for Harmonization (ICH) validation guidelines. The study was extended to the estimation of the studied drugs in their co-formulated eye drops as well as in their single dosage forms with acceptable percentage recoveries. Moreover, Green Analytical Procedure Index (GAPI) and analytical Eco-scale were investigated to confirm the greenness of the proposed HPLC method.

A green, simple and easy spectrofluorimetric method was studied for rapid estimation of tafluprost (TFL). The native fluorescence of TFL was measured at 292 nm after excitation at 220 nm. The results were linear in water over the concentration range 50–600 ng ml−1 with a correlation coefficient r = 0.9999 and intercept 1.1555. The limit of detection and limit of quantification were found to be 7.87 and 23.86 ng ml−1, respectively. Neither different pH nor surfactants enhanced the fluorescence intensity. The high sensitivity of this spectrofluorimetric method makes it suitable for analysis of low concentrations of tafluprost in commercially available ophthalmic formulations. This procedure was validated according to International Council for Harmonisation Guidelines.

A green, simple and sensitive HPLC method coupled with fluorescence detection was implemented for the quantitative determination of the anti-glaucoma drug tafluprost (TFL). Liquid chromatography was performed on HyperClone™ ODS (C18) column of dimensions; 150 × 4.6 mm i.d. and 5 μm particle size using a green eluent; ethanol:0.01 M phosphate buffer (60:40 v/v, pH 4.5) delivered at 1 mL min−1. Fluorescence detection was accomplished at 220 nm (excitation) and 292 nm (emission). Bimatoprost (BIM) was used as an internal standard (I.S.). In this method, TFL was eluted after 6.70 minutes. The method satisfied International Council for Harmonization (ICH) validation guidelines, as proved by good linearity (r = 0.9999, over the range 0.05–2 μg mL−1), accuracy (recovery average 100.13 ± 1.27%), precision, robustness and specificity. The limit of detection and limit of quantification were found to be 0.016 and 0.048 μg mL−1, respectively. The proposed method has been successfully applied for the estimation of TFL in eye drops and aqueous humor. For the first time, the approach was applied with acceptable results for the evaluation of the uniformity of TFL eye drops content. Furthermore, Green Analytical Procedure Index (GAPI) and analytical Eco-scale were used to prove that the proposed HPLC method is environmentally friendly.