The parameters (1) accucracy in elemental measurements, (2) accuracy in isotopic measurements, (3) detection sensitivity, (4) mass resolution and (5) mass calibration are the most importat parameters for spectroscopic instruments. In the following a short overview of these parameters of the LMS are given. Further information can be found in the publication section.
Measurements on elements using standard samples
The LMS instrument can be calibrated using measurements on standard reference materials/samples. With this procedure one gets for each element a so called releative sensitivity coefiicient (RSC) factor. Using these factors for each element an unknown sample can be measured straigh forward. The measurement accuracy is hereby in the low per cent level. Below, an overview of these RSC factors is shown using the standard reference materials 664 and 661 from NIST. The ns-laser system in the IR range was hereby used (see Tulej, 2011).
Measurements on isotopes
Depending on the abundance of the element in the sample measurements on elemental isotopes can be done in the sub per cent level. High resolution measurements (>600) is hereby the crucial key parameter. Further information can be found in the bachelor thesis written by Stefan Meyer in 2011 (see publication list).
With the Laser-ablation Time-of-Flight Mass Spectrometer designed in our group a detetion sensitivity in the low ppb range is possible. Below, a typical spectrum measured with the LMS instrument from NIST SRM (Standard Reference Material) 665 is shwon. Ti49 with ~300ppb is clear visible.
Mass resolution and performance optimiser
Using the deticated self-writtem computer-controlled performance optimiser based on a adaptive particel swarm algorithm a mass m/δm resolution exceeding 800 is possible! Below, the Fe54 peak from NIST SRM 664 before and after only one iteration of the optimser is shown. The mass resolution was increased by a factor of about 4.5 from m/δm of 122 to 743!
After the first optimiser iteration the laser fluence and the distance between sample and entrance plate can be shifted slightly to start the next optimiser iteration. Finally a mass resolution m/δm over 800 can be reached. Below, the optimised Fe54 peak of the NIST SRM 664 is shown. The mass resolution of the optimised peak is hereby ~885.
Mass calibration with an accuracy in the per mille and sub permille range is achievable. Bellow, the mass calibration and the resulting residuals of a NIST SRM (Standard Reference Material) 664 is shown. The residuals behave random around a relative error of 0, no systematic trend is visible.