Portable liquid chromatography for on‑site analysis

High performance liquid chromatography (HPLC) is a dominant laboratory-based analytical technique, but despite its dominant position within analytical laboratories, HPLC has not seen significant application to-date in many important field-based applications. For example, a portable and field-deployable liquid chromatographyultraviolet/ mass spectrometric system (LC-UV/MS) would be of considerable value to facilitate on-site analysis for the pharmaceutical manufacturing sector, areas of industrial process monitoring, threat analysis, and environmental monitoring. However, there are major challenges associated with development of fully functional and field-deployable portable LC-UV/MS systems, particularly for the pharmaceutical manufacturing sector and related on-site industrial applications. Therefore the main aims of this research have been to; (1) Develop and demonstrate the analytical performance of miniaturized UV absorbance detectors with suitability for application within portable capillary LC systems; (2) Undertake a configuration and compatibility investigation into the coupling of a portable briefcase-sized capillary LC-UV platform with new portable mass spectrometric (MS) detector for point-of-need LC-UV-MS analysis; (3) Integrate and demonstrate the performance of the portable LC with industry-standard auto-sampling devices for automated process analysis within pharmaceutical laboratories; and (4) Undertake an in-field demonstration of the coupled portable LC/MS system for environmental analysis. Light-emitting diodes (LEDs) are small in size, have low power consumption requirements, short warm-up times, and deliver long lifetimes. These make LEDs attractive light sources for the miniaturization of absorbance-based detectors. However, LEDs are quasi-monochromatic with narrow emission spectra. This significantly limits the potential of LEDs for applications that require multi-wavelength detection capability. A number of limitations and improvements in low-UV LED-based absorbance detectors were investigated within the first phase of this research. A new miniature deep multi- LED UV absorbance detector was developed using low-cost LEDs, which could be operated in both individual wavelength (240, 255, and 275 nm) and scanning (230 – 300 nm) detection modes. The detector was mostly composed of off-the-shelf components, such as the LEDs, a trifurcated fiber assembly (TFFA), a commercial capillary Z-type flow cell, and the detector photodiodes. The detector was subsequently incorporated within a portable ‘briefcase-sized’ capillary LC system. The detector was characterized in terms of performance and was further benchmarked against a commercial variable wavelength capillary LC detector (Dionex UltiMate 3000RS). The developed detector showed low levels of stray light (<0.4%), delivered an effective path length of up to 99.0% of the detection flow cell, gave a wide dynamic range (0.5 to 200 μg/mL for sulfamethazine, carbamazepine, and flavone), and exhibited low noise levels (at 300 μAU level). Further to the above, in the second phase of this research, the design and performance demonstration of a compact, modular and broadband (D\(_2\) lamp-based) UV-Vis absorbance detector was investigated, as an alternative to the LED-based detectors. The detector was composed of a miniature D\(_2\) light source, an end-capillary extended optical pathlength (10 mm) flow-cell, and a miniature spectrometer. The assembled detector showed low levels of stray light (