Developing a versatile gradient elution LC/ELSD method for analyzing cellulose derivatives in pharmaceutical formulations

Liquid chromatography combined with evaporative light scattering detection is a powerful tool for analyzing polymeric excipients used in pharmaceutical formulations. A versatile, gradient elution liquid chromatographic method utilizing evaporative light scattering detection (ELSD) has been developed for analyzing several types of cellulose ether and ester derivatives in pharmaceutical formulations. This single method was proven to be capable of differentiating six types of cellulose ether and ester derivatives. The influence of ELSD instrument parameters on the detector response and sensitivity has been studied by a statistical design of experiments. It was found that lowering gas flow rate increased peak area response significantly. Increasing nebulizer temperature also increased peak area response. In contrast, evaporator temperature has very minor impact on peak area response, but had a significant impact on noise level. Thus, signal to noise ratio was significantly lower for low evaporator temperature setting. Despite the logarithmic relationship between peak area responses versus concentrations, sufficient selectivity, precision and accuracy were achieved. The method has been validated for assaying hypromellose acetate succinate (HPMCAS) polymer in a pharmaceutical formulation.     

Size exclusion chromatography with evaporative light scattering detection as a method for speciation analysis of polydimethylsiloxanes. I: Influence of selected factors on the signal intensity of the detector

Evaporative light scattering detector (ELSD) is widely recognized as a universal tool in chromatography. In this paper, the characteristics of the ELSD detector response and the influence of different factors on the signal intensity are described. Further, results are presented on the influence of some selected factors on the signal intensity and repeatability of results for linear structure polydimethylosiloxanes (PDMS), differing in molecular weight and viscosity. The following factors were studied: (i) the flow velocity of the nebulising gas, (ii) the temperature of the drift tube and the detection cell, and (iii) the flow velocity of the mobile phase, as they all constitute important parameters of the detector. Based on such studies, the optimal parameters of detector indications can be selected for a specific analysis. The results confirmed the possibility to select one set of values for those parameters that allow for analysis of linear PDMS molecules with viscosities ranging from 10 to 60,000 cSt. The following optimal and common parameter values were specified: temperature drift tube 50 °C, carrier gas pressure (for nebulisation) 140 kPa, and mobile phase flow rate 0.7 ml/min. A high repeatability of the results was demonstrated as the relative standard deviation was less than 2.5%. This type of tests for polydimethylosiloxanes has not been presented in any previous publication.     

Development and validation of a novel LC non-derivatization method for the determination of amikacin in pharmaceuticals based on evaporative light scattering detection

A novel method for the direct determination of the aminoglycoside antibiotic amikacin and its precursor component kanamycin was developed and validated, based on reversed phase LC with evaporative light scattering detector (ELSD). ELSD response to amikacin was found to be enhanced by: (a) use of ion-pairing acidic reagents of increased molecular mass, (b) increase of mobile phase volatility and (c) decrease of peak width and asymmetry (obtained by controlling the mobile phase acidity and/or ratio of organic solvent to water). Utilizing a Thermo Hypersil BetaBasic C₁₈ column, the selected optimized mobile phase was water–methanol (60:40, v/v), containing 3.0 ml l⁻¹ nonafluoropentanoic acid (18.2 mM) (isocratic elution with flow rate of 1.0 ml min⁻¹). ELSD experimental parameters were: nitrogen pressure 3.5 bar, evaporation temperature 50 °C, and gain 11. Amikacin was eluted at 8.6 min and kanamycin at 10.4 min with a resolution of 1.5. Logarithmic calibration curves were obtained from 7 to 77 μg ml⁻¹ (r > 0.9995) for amikacin and 8 to 105 μg ml⁻¹ (r > 0.998) for kanamycin, with a LOD equal to 2.2 and 2.5 μg ml⁻¹, respectively.

In amikacin sulfate pharmaceutical raw materials, the simultaneous determination of sulfate (t_R = 2.3 min, LOD = 1.8 μg ml⁻¹, range 5–40 μg ml⁻¹, %R.S.D. = 1.1, r > 0.9997), kanamycin and amikacin was feasible. No significant difference was found between the results of the developed LC–ELSD method and those of reference methods, while the mean recovery of kanamycin from spiked samples (0.5%, w/w) was 97.3% (%R.S.D. ≤ 2.0, n = 6). Further, the developed method was applied for the determination of amikacin in pharmaceutical formulations (injection solutions) without any interference from the matrix (recovery from spiked samples ranged from 95.6 to 103.8%).     

Development and validation of a reverse phase liquid chromatography method for the quantification of rasagiline mesylate in biodegradable PLGA microspheres

In the present study, a reverse phase high performance liquid chromatographic method was developed and validated for the determination of rasagiline mesylate in biodegradable microspheres. Chromatographic separation was carried out on a RP-18 column using a mobile phase consisting of acetonitrile:water (5:95, v/v) adjusted at pH 3.1. Flow rate was 1.0 ml min⁻¹ and UV detection at 290 nm. Acyclovir was used as the internal standard. The calibration curve was linear over the range 0.5–20.0 μg ml⁻¹. R.S.D. for precision was <1.8%. Accuracy ranged between 99.01% and 102.55% with a R.S.D. lower than 1.3%. LOD and LOQ were 0.07 μg ml⁻¹ and 0.23 μg ml⁻¹, respectively. The method was simple, rapid, and easy to apply, making it very suitable for routine analysis of rasagiline mesylate in biodegradable PLGA microspheres. It could be also used with reliability for the determination of the drug in other pharmaceutical dosage forms.     

Size exclusion chromatography with evaporative light scattering detection as a method for speciation analysis of polydimethylsiloxanes. II. Validation of the method for analysis of pharmaceutical formulations

The aim of this study was to demonstrate the usefulness of the size exclusion chromatography with evaporative light scattering detection (SEC-ELSD) method in the identification and quantitative analysis of polydimethylsiloxanes (PDMS). The process of validation for the method was conducted, and the values obtained were compared with the acceptance criteria. Particularly important was the conclusion that SEC-ELSD method showed a high specificity for PDMS. PDMS is an organosilicon polymer and for this reason, it does not exist as a concrete chemical species. Depending on the length of the chain, PDMS can be toxic for organism. So far, the SEC-ELSD method has not been applied for the control of pharmaceutical products containing such PDMS as dimeticone or simeticone. The safety of use and effectiveness of such pharmaceutical products relies on the control of their quality. Therefore, the analytical methods and procedures that meet acceptance criteria for qualitative and quantitative analysis of the PDMS should be used. In the case of the analysis of pharmaceutical products, the acceptance criteria are established and recommended by, for example, the Pharmacopoeias, the U.S. Food and Drug Administration (FDA), the International Conference on Harmonisation (ICH) and the World Health Organization (WHO). The progress of knowledge, however, requires the development of new analytical tools which are able to solve incoming problems. In the case of pharmaceutical formulations containing PDMS, which are used not only by adults but also by children, it is necessary to use analytical methods which are characterized by a high specificity.