Integrated liquid chromatography-heated nebulizer microchip for mass spectrometry

Area of Science:

• Analytical Chemistry
• Microfluidics
• Mass Spectrometry

Background:

• Existing liquid chromatography-mass spectrometry (LC-MS) chips often rely on electrospray ionization, limiting the efficient ionization of nonpolar compounds.
• There is a need for integrated microfluidic devices capable of handling diverse analyte polarities for comprehensive analysis.

Purpose of the Study:

• To present a new integrated microchip for LC-MS that overcomes limitations of current technologies.
• To demonstrate the chip's capability for efficient ionization of both nonpolar and polar analytes using atmospheric pressure photoionization (APPI).

Main Methods:

• Fabrication of a silicon-glass microchip with integrated components: packed LC channel, frit, optical detection channel, and heated vaporizer.
• Utilizing atmospheric pressure photoionization (APPI) for gas-phase ionization of analytes.
• Evaluating quantitative performance including limit of detection, linearity, and repeatability for polycyclic aromatic hydrocarbons (PAHs).
• Demonstrating laser-induced fluorescence (LIF) detection for fluorescent compounds prior to vaporization.

Main Results:

• The integrated microchip successfully vaporizes LC eluent and facilitates efficient APPI of nonpolar (PAHs) and polar (SARMs) analytes.
• Preliminary quantitative analysis showed a limit of detection down to 5 ng mL(-1), excellent linearity (r>0.999), and good repeatability for signal response (RSD=2.6-4.0%) and retention time (RSD=0.3-0.5%).
• Successful determination of fluorescent compounds using LIF detection was achieved.

Conclusions:

• The developed integrated microchip represents a significant advancement in LC-MS technology, particularly for the analysis of nonpolar compounds.
• The chip's design and APPI capability offer a versatile platform for sensitive and quantitative analysis of a wide range of analytes.
• The integration of optical detection further enhances its applicability for specific compound classes.