Acetone as a greener alternative to acetonitrile in liquid chromatographic fingerprinting.

A considerable amount of chemical waste from liquid chromatography analysis is generated worldwide. Acetonitrile is the most employed solvent in liquid chromatography analyses since it exhibits favorable physicochemical properties for separation and detection, but it is an unwelcome solvent from an environmental point of view. Acetone might be a much greener alternative to replace acetonitrile in reversed-phase liquid chromatography, since both share similar physicochemical properties, but its applicability with ultraviolet absorbance-based detectors is limited. In this work, a reference method using acetonitrile and high-performance liquid chromatography coupled to an ultraviolet photodiode array detector coupled to a corona charged aerosol detector system was developed to fingerprint a complex sample. The possibility of effectively substituting acetonitrile with acetone was investigated. Design of experiments was adopted to maximize the number of peaks acquired in both fingerprint developments. The methods with acetonitrile or acetone were successfully optimized and proved to be statistically similar when only the number of peaks or peak capacity was taken into consideration. However, the superiority of the latter was evidenced when parameters of separation and those related to greenness were heuristically combined. A green, comprehensive, time- and resource-saving approach is presented here, which is generic and applicable to other complex matrices. Furthermore, it is in line with environmental legislation and analytical trends.

Assessment of the complementarity of temperature and flow-rate for response normalisation of aerosol-based detectors.

The solvent dependency of the detection response is a major limitation of corona-charged aerosol detection (C-CAD). The present study empirically investigates the utility of temperature and flow-rate gradients to overcome solvent gradient limitations of C-CAD. In preliminary flow-injection investigations, it is demonstrated that the response of C-CAD remains relatively unaltered with variations in flow-rate when used with water-rich eluents. Based on these findings two separation approaches were developed and their utility for C-CAD response normalisation was demonstrated using a mixture of eight analytes. In the first approach the use of a solvent gradient is replaced with a temperature gradient performed under isocratic mobile phase conditions. Detection response is further enhanced by mixing a secondary stream of pure acetonitrile with the column effluent, yielding a 3-fold increase in detection response. In the second approach, flow-rate programming is used to improve speed of isocratic-temperature gradient separation. The use of simultaneous variation in flow-rate and column temperature reduced the separation time by 30%, with relatively uniform analyte response. Lastly, an inverse-gradient solvent compensation approach was used to evaluate the response homogeneity and the applicability of the above approaches for quantitative analysis. Good peak area reproducibility (RSD%<15%) and linearity (R(2)>0.994, on a log-scale) over the sample mass range of 0.1-10 µg was achieved. The response deviation across the mixture of eight compounds at seven concentration levels was 6-13% compared to 21-39% when a conventional solvent gradient was applied and this response deviation was comparable to that obtained in the inverse gradient solvent compensation approach. Finally, applicability of these approaches for typical pharmaceutical impurity profiling was demonstrated at a concentration of 5 µg/mL (0.1% of the principal compound).

Effects of eluent temperature and elution bandwidth on detection response for aerosol-based detectors.

Aerosol detectors provide generally uniform response for most analytes, independent of their optical properties, and have the advantage of being compatible with elevated temperature mobile phases. Therefore, aerosol detectors present an attractive detection alternative for high temperature liquid chromatography (HTLC) separations. The present study has investigated the effects of HTLC conditions using aqueous mobile phases on the detection response of an evaporative light-scattering detector (ELSD) and a corona-charged aerosol detector (C-CAD). The response of the ELSD was increased up to 5-fold by increasing the separation temperature from 30°C to 180°C. The C-CAD showed much smaller increases in response under the same conditions. This increase in response was found not to result from the increased temperature for the mobile phase but rather from compression of the elution bandwidth at elevated temperature. The effect of bandwidth on detector response was confirmed using flow-injection studies in which the same amount of analyte was introduced into the detector at varying bandwidths. Furthermore, it is shown that a temperature gradient can be used to counteract the effects of varying bandwidths associated with isocratic-isothermal separations, with relatively constant bandwidth and detector response being observed with appropriate temperature gradients. This study demonstrates the necessity to consider the elution bandwidth in HTLC-aerosol detector analysis.