HPLC and NMR methods for the quantitation of the (R)‐enantiomer in (−)‐(S)‐timolol maleate drug raw materials

Abstract

HPLC and 'H-NMR methods for the quantitation of the (R)-enantiomer in (-)-(3-timolol maleate were developed and validated. The HPLC method requires a 25 cm x 4.6 mm 5 p, m Chiracel OD-H (cellulose tris-3,5-dimethylphenylcarbamate) column, a mobile phase of 0.2% (v/v) diethylamine and 4% (v/v) isopropanol in h e m e at a flow rate of 1 d m i n and UV detection at 297 nm. A system suitability test was devised to venfy the separation of the (R)-and (3-enantiomers of timolol from other drug-related impurities. The NMR method requires the use of a high-field NMR spectrometer (>360 MHz) and a chiral solvating agent, (-)-(R)-Z, 2,2-trifluoro-l-(9-anthrylethanol) (R-TFAE). The limits of quantitation were 0.05% and 0.2% ( d m ) for HPLC and NMR, respectively. The methods were applied to the determination of the (R)-enantiomer in eight lots of raw material. The results for the two methods were in very good agreement, with results ranging from 0.1 to 4.1% KEY WORDS: timolol maleate, quantitation of enantiomers by HPLC, quantitation of enantiomers by NMR, optical purity, chiral separation, cellulose tris-3,5-dimethylphenylarbamate (Chiracel OD-H), chiral solvating agents Tim0101 maleate, I, marketed as the (Sbenantiomer, is a p-adrenergic blocker used for the treatment of hypertension, angina pectoris, and glaucoma. Existing purity standards for timolol maleate include a USP' monograph specifying a limit of 0.4% ( d m ) on individd related compounds, as determined by TLC, and a requirement that the specific rotation be between -ll. 7" and -12.5", calculated on the dried basis, determined with a mercury source at 405 nm in a 50 mdml solution in 1.0 N hydrochloric acid at 25°C. These specifications for specific rotation are the same as those reported by Mazzo and Loper.2 Recent developments in chiral technology and the low absolute value for specific rotation make this drug a good candidate for the development of new methods for the determination of enantiomeric impurities in raw materials.There have been reports in the literature on the separation of timolol enantiomers by HPLC using p-~yclodextrin~ (without derivatization) and Pirkle-type' columns after derivatization with a-naphthyl isocyanate. The separations shown were for rac-timolol. These methods were not validated for the quantitation of low levels of the (R)-enantiomer in (-)-(S)-timolol maleate. The resolutions obtained were low (1.08 on the Pirkle-type column and 3.00 on the p-cyclodextrin column), the (R)-enantiomer eluted on the tail of the 6)-timolol peak on the p-cyclodextrin column, potentially making quantitation of low levels &cult and problems associated with A method for the HPLC separation of timolol enantiomers on a cellulose tris-3,5-dimethylphenylcarbamate chiral stationary phase (Daicel Chiracel OD) was published by AboulEnein and Islam6 in 1990. Although it had been optimized for the separation of the (R)-and (S)-enantiomers of rac-timolol (resolution = 4.00), no data were provided on the selectivity of this method in the presence of other...

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“…The mean percentage recoveries and standard deviations were shown in Table 4. 5. Application to Pharmaceutical Formulation: The suggested methods were valid and applicable for the analysis of Combigan ® eye drops with no interference from the additives or preservative.…”

“…Various methods have been reported for both drugs individually. TM can be determined by titrimetric official methods USP 1 and BP 3 , HPLC methods 4,5 , HPTLC method 6 , chemiluminescence methods 7,8 , voltammetric determination 9-11 . The reported methods for BT were HPLC [12][13][14][15] , HPTLC 16 , UV Spectrophotometric method for the estimation of BT 17,18 , capillary electrophoresis 19 , gas chromatography with mass detection 20 . Also simultaneous determinations of both drugs were reported by spectrophotometric determination 21,22 , TLC-densitometry 23 and simultaneous estimation of TM and BT in nanoparticles formulation by RP-HPLC 24 .…”

LC method for the simultaneous determination of R‐timolol and other closely related impurities in S‐timolol maleate: Optimization by use of an experimental design

“…Concerning the column temperature, values below 158C cannot be reached easily with common LC equipment during routine analysis. Above 408C, which is the maximum temperature for operating conditions indicated by the column manufacturer, no significant changes in the elution order and retention times of the peaks were noticed [12,14,25].…”

“…In that study, the effect of each component of the mobile phase as well as that of the column temperature on the enantiomeric LC separation were studied separately. Other techniques have been reported in the literature for testing the enantiomeric purity such as proton nuclear magnetic resonance [13,14], which requires expensive equipment, and polarimetry [14], which is not suitable for detecting low levels (0.1%) of R-timolol.…”

Chromatographic Behavior of Bornyl Acetate Diastereomers Under the Conditions of Reversed-Phase High-Performance Liquid Chromatography (Hplc)

“…The advantage of this method lies in the possibility of separation and identification of a broad range of substances, including high-molecular compounds and compounds, characterized by chemical and thermal instability. Furthermore, the use of HPLC allows to solve the problem of the joint determination of spatial isomers of various substances with the use of special chromatography columns [8][9][10][11].…”