Tapered RF Ion Guide for Ion Collection and Beam Convergence
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Solution Overview
Problem
Conventional multi-pole RF ion guides face limitations in collecting and converging ions efficiently due to increased ion spread when the diameter of the hole in the atmospheric-pressure partition wall is enlarged, leading to reduced ion transport efficiency and potential electrode interference.
Innovation Solution
A mass spectrometer with an ion transport optical system featuring N rod electrodes arranged in an N-pole configuration at the ion-entrance and a quadrupole configuration at the ion-exit, with specific voltage applications to efficiently collect and converge ions, minimizing electrode interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the diameter of the hole in the atmospheric-pressure partition wall is increased to introduce a larger amount of ions into the intermediate vacuum chamber, then the ion transport amount is improved, but the spread of the ultrasonic gas stream increases causing ions to disperse more widely
Solution Approach 1:
The patent changes the geometric parameters of the rod electrodes, specifically making the inscribed circle diameter at the ion-exit end smaller than at the ion-entrance end. This parameter change allows the ion guide to handle increased ion flow while maintaining convergence capability. The gradual reduction in inscribed circle diameter along the ion transport direction enables the system to accept larger ion bundles from enlarged holes while still converging them effectively at the exit.
2Area of stationary object
If the inscribed circle of the rod electrodes on the ion-entrance side is increased to collect dispersed ions, then the ion-collecting area is improved, but the strength of the multi-pole RF electric field decreases reducing ion-collecting capability
Solution Approach 1:
The patent applies local quality by having different inscribed circle diameters at different locations along the ion guide. The ion-entrance end has a larger inscribed circle to collect dispersed ions, while the ion-exit end has a smaller inscribed circle to maintain strong RF electric field strength for effective ion convergence. This spatial variation in geometric quality allows each section to optimize for its specific function: collection at the entrance and convergence at the exit.
3Productivity
If the interval of rod electrodes at the ion-exit end is decreased to enhance ion convergence, then the ion-converging effect is improved, but electrode interference and electric discharge may occur
Solution Approach 1:
The patent carefully optimizes the interval parameter between rod electrodes at the ion-exit end. The inscribed circle diameter is reduced to enhance convergence, but the reduction is controlled to maintain sufficient spacing that prevents electrode interference and electric discharge. This parameter optimization balances convergence efficiency with electrode reliability, achieving high ion transport efficiency without compromising system stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves higher ion transport efficiency and sensitivity by effectively collecting and shaping ions into a thin beam, reducing spatial spread and enhancing analysis sensitivity compared to conventional designs.
Implementation Method 1
an RF (radio frequency) ion guide which utilizes a cooling effect through the collision of ions with a residual gas
Implementation Method 2
The RF ion guide transports ions while confining them to a predetermined space by means of a pseudopotential mainly generated by an RF electric field
Implementation Method 3
the ions and other neutral particles supplied through a small hole (or capillary) in the atmospheric-pressure partition wall are introduced into the intermediate vacuum chamber by being carried by an ultrasonic gas stream formed on the exit side of that hole
Data Source
AI summary
An ion transport optical system includes N rod electrodes forming an N-pole arrangement externally tangent to a circle of diameter A1 at an ion-entrance end, where N is an even number not smaller than six. Four electrodes form a quadrupole arrangement externally tangent to a circle of diameter A2 at an ion-exit end, where A2<A1. At least two of them are arranged obliquely to the central axis of the N-pole or quadrupole arrangement. At least four of the N electrodes are shaped such that the cross-sectional radius of their arc-shaped portion facing the central axis at the ion-exit end is smaller than that at the ion-entrance end. A voltage generator applies a DC voltage to the four electrodes and another DC voltage, which differs from the first one, to the N−4 remaining electrodes, in addition to RF voltages of opposite phases alternately applied to the N electrodes.