Knowledge Bank

Mass spectrometry relies heavily on the initial ionization step, influencing metabolic coverage and detection limits in complex mixtures. Existing ionization methods struggle with samples of diverse physiochemical properties (polar/non-polar and high/low molecular weight) using a single source. To overcome this, we present a novel ionization source capable of sequential ionization across a wide range without requiring sample preparation or chromatography. This ionization mandates constant voltage changes as various analytes require different voltages for ionization. Herein, we have developed a simple, robust, and highly sensitive dynamic spray source with voltage ramping capabilities, coupled with conductive glass emitters, enabling detection of molecules with varying physiochemical properties and biological samples from a single source with automatic voltage tuning capable of high throughput application. Our dynamic spray source features an electrodeless design with a single emitter made of disposable conductive borosilicate class capillaries, operating within a DC voltage of 0 to ±8 kV. The voltage waveform increases or decreases linearly over time, enabling conventional nanoelectrospray ionization (nESI) at initial voltages (1-2 kV) and transitioning to micodroplet/gas-phase ionization for atmospheric chemical ionization (APCI). This method works in both positive and negative-ion modes, allowing for the sequential detection of diverse analytes in complex mixtures and biofluids. At higher voltages (>4 kV), corona discharge is initiated at the pointed tips of the borosilicate glass capillaries, generating nonthermal plasma. Initially, commercially available conductively plated PicoTips were used, but their high cost and limited size options led to the development of in-house conductive emitters. Three methods—silver ink coating, chemical silver plating, and gold-palladium sputter coating—were explored to create affordable, stable capillaries capable of plasma generation. Sputter coating proved most effective, improving ionization efficiency by automatically optimizing voltage conditions for sensitive nonpolar analytes while maintaining emitter stability for extended analysis of small volumes The dynamic spray source operates under ambient conditions, enabling high-throughput analysis of an equimolar mixture of 20 biomolecules, including dietary supplements, fatty acids, drugs, sugars, and amino acids. This approach streamlines metabolite profiling, reduces resource demands, and expands applications for portable mass spectrometry. Overall, dynamic spray ionization provides robust biomolecule detection from complex mixtures using a single conductive glass emitter, offering a powerful platform for high-throughput biomedical research.