Abstract
ABSTRACT
Rationale
According to the mass spectrometry (MS) design principles, the ions generated in an atmospheric pressure ion source must pass through a narrow‐bore capillary in order to maintain the needed system vacuum pressure. The ion transmission efficiency through the inlet capillary is one of the key factors directly influencing the analytical performance of MS. Its design and operating parameters, including inner diameter, length, temperature, and those related to the ion source operation, can alter ion diffusion losses, gas flow dynamics, and space‐charge effects both around and inside the inlet capillary, thereby influencing ion sampling efficiency and transmission efficiency to the mass analyzer.
Methods
A comprehensive simulation of ion transmission efficiency through an MS inlet capillary has been performed in this study by adjusting the important design and operating parameters.
Results
The simulation results show that the ion transmission efficiency through the inlet capillary is positively correlated with the inner diameter of the capillary and negatively correlated with the length of the capillary. Specifically, under the conditions of a capillary diameter of 0.8 mm and a temperature of 573.15 K, the ion transmission efficiency through a 10‐cm‐long capillary can reach 90%. The efficiency decreases with a reduction in the inner diameter or an increase in the length. When the temperature exceeds 573.15 K, the flow field inside the capillary transits from laminar to turbulent flow, leading to a sharp decline in ion transmission efficiency. For every 100‐K increase in temperature beyond this point, the ion transmission efficiency decreases by 10%–20%.
Conclusions
The main results from this study have provided crucial design guidelines, emphasizing the use of larger diameters, moderate lengths, and strict temperature control below the turbulent transition threshold to maximize ion transmission and overall instrument sensitivity for MS instruments.