Previous to 1990, Inductively Coupled Plasma Spectroscopy (ICP), photomultiplier tubes (PMTs) were used as the detector. PMTs were very sensitive, durable, and widely used. The disadvantages of PMTs as detectors were mainly their size and that they measured one wavelength of information. Also, most simultaneous systems at that time employed PMTs in a Roland Circle design where multiple PMTs were positioned on the focal plane of the grating. Because of size constraints, only about 35 PMTs could be used, one for each wavelength. Also, the background information contained single points that were acquired separately.
In the early 1990s, the first solid state detection system was employed in a commercially available ICP system and was of the photo diode type. Shortly thereafter, solid state detection systems began to replace the PMT systems. The most popular of these were charge coupled devices (CCD), charge injection devices (CID) and segmented charged coupled devices (SCD). These detectors could be designed with thousand of active areas (pixels) that could acquire large amounts of analytical and background information simultaneously. However, most of this information was not used on a routine basis, therefore not utilizing the huge store of analytical information.
By optimizing signal processing as well as increasing the processing speed of a SCD, this detector is now able to acquire and store thousands of usable ICP emission lines as well as the corresponding background signal with a minimal amount of storage space required. File sizes are such that using the Universal Data Acquisition (UDA) mode can be run for all analyses, all of the time. This has resulted in four main advantages to the ICP user: Easy data validation, access to all wavelength information, automated detection limit calculations for all wavelengths and optimal inter-element correction (IEC) capabilities. All of these will be presented in detail in the following presentation.
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