Laser ablation is a process of solid sample analysis when coupled to this instrument. There are two common vendors of laser systems: Cetac and New Wave (also known as Merchantech (earlier company name)) and countless home-made systems.
Lasers couple differently with different material, and so a standard reference material of similar property to the sample is required.
There are key requirements of the ICP-MSICP-QQQ.
You can perform remote triggering by using the APG remote port on the rear of this instrument connected to the 'trigger' of the laser.
If you are using laser ablation, select [LA] as the [Sample Introduction] in the [Settings] dialog box. The spray chamber cooling function is automatically set to OFF.
An external remote signal can be used to start acquisition. You can specify whether or not to use a remote signal in the [Remote Signal Setting] dialog box. You can display this by right-clicking the [Sample Introduction] illustration in the Dashboard Pane, and then selecting [Remote Signal Setting] from the context menu. It is convenient to perform a positioning, warming up, and pre-ablating with the laser.
Typically the monitored masses in laser are low through to high mass (43, 88, 137, 232, 238) as well as Thorium oxide ratio (248/232), and laser induced mass bias as measured by uranium to thorium ratio (232/238). In the NIST glasses U = Th concentration (approx). The lens tuning is very similar to the soft extraction mode.
For a 50 micron spot, at 10Hz firing rate, with an energy around > 1 mJ/pulse then NIST 612 will give >500,000 cps (most elements), for a ThO/Th ratio of <1% and a bias if Th:U of 1:1. Th:U will be affected by the gas flow through the cell AND the gas flow in the plasma, as are oxides. Typically ThO/Th ratio is set using the argon gas flow (carrier), and the Th:U bias is controlled using the helium. Correct helium flow is set when the dark condensation bands around the ablation site disappear (sometimes this is difficult to see), or when U=Th counts.
The torch position is very important. Small adjustments make large differences.
Instrument configuration:
P/A factor setting the P/A factor requires a raster scan of at least 3 minutes duration, with signal >56,000 count/0.1 sec in the tune window (0.1 second). Tune P/A factors for every element you plan to study.
Instrument mode is Time resolved analysis (TRA)
Typical integration times are 0.03 seconds per mass, depending upon whether feature analysis is required (drilling down with the laser), or raster signal is acquired (dragging the laser over the sample surface with a pre-defined map).
The quantification of sample by laser ablation is always corrected for drift, since there are two sources of drift: the laser and the ICP-MSICP-QQQ. Typically a major element is analysed accurately by another technique, then the ratio of all signals to the major element is calculated. The proportional signal is then referenced to a standard of known element concentration. The unknown signal then is compared to the major in the sample, and then multiplied by the response factor from the standard.
Acquisition of data is gas blank (laser off) followed by standard (s), then sample(s) then standard(s) then gas blank (laser off). You can collect up to ten samples without a standard, assuming drift is linear.
The data analysis part of the software uses an integrator for TRA data. The integration area (stop time and start time) should be constant for all acquisitions, since the signal is proportional to the duration of the collection. If integration windows are set correctly, then good proportional data can be acquired and reported accurately.
You can use "100% Normalization-Calibration" for laser ablation data analysis. Proceed as follows:
The [100% Normalization-Calibration Setup] dialog box is displayed.
In a time resolved analysis, data can be saved as a csv file by using time chart count value (CPS).