Exposition

Monolithic quartz quadrupole

Exhibit no. 212

The quadrupole mass analyzer separates ions based on the stability of their trajectories in the oscillating electric fields. It consists of four parallel rods with a hyperbolic or circular cross-section. The opposing quadrupole rods are connected together electrically, and a radio frequency (RF) voltage and a DC voltage is applied between one pair of rods and the other. The quadrupole mass analyzer was developed in parallel with the quadrupole ion trap by the Nobel prize-winning mass spectrometry pioneer, Wolfgang Paul.

The exhibit is a monolithic fused-silica mass filter with a hyperbolic geometry from HP 5972 Series Mass Selective Detectors manufactured by Hewlett-Packard in 1993. The spectrometer served as a single quadrupole detector for GC.  The four hyperbolic segments were coated on the inside with a conductive material and the opposing segments were connected together. The quadrupole was housed in a square aluminum tube called the radiator, which heated the quadrupole to about 150 °C. High temperatures helped to keep the quadrupole clean. It operated at 1 MHz and transmitted ions between 1 and 700 Da. The monolithic quadrupole was introduced in 1988 (HP 5971 MSD).

The monolithic quadrupole substrate was fabricated using a molybdenum or tungsten mandrel at the elevated temperatures required to form quartzes. Once the quartz conformed to the mandrel, the piece was allowed to cool. Since the metal contracted more strongly than the substrate, the mandrel could easily be removed. In the next step, conductive strips and low-conductivity strips were applied to the interior surfaces. The conductive strips were deposited on the hyperbolic surfaces by means of a metallization tape and the assembly was fired at elevated temperature. The tape was also wrapped over the ends of the substrate to facilitate electrical connections. The low-conductive strips were formed from a zirconium oxide slurry containing a bonding agent. It was allowed to air dry and then fired until the strip was solidified and adhered to the substrate.

Wikipedia: Quadrupole mass analyzer
Wikipedia: Wolfgang Paul

 

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