TRENDS AND FUTURE PROSPECTS - Total-Reflection X-Ray Fluorescence Analysis and Related Methods - page 445

apriori . However, none of these detectors is ideally suited for energy-
dispersive detection of X-rays in common laboratories to date.
An X-ray color camera may also be regarded as a new type of X-ray
detector. It was developed as a new product of the Institute for Scientific
Instruments in Berlin and PNSensor in Munich, Germany. The SL-cam  is a
compact instrument for X-ray mapping and was already mentioned in Sec-
tion 4.1.3.3. It is based on a polycapillary lens combined with an energy-
dispersive array detector or CCD and visualizes the elemental composition of a
sample in real time. An area of 12 × 12 mm 2 is depicted with 264 × 264 pixels;
the spatial resolution is 8 μ m at best. Because all spectra of the individual pixels
are taken simultaneously, the elemental distribution of a sample can be
displayed online representing individual elements by different colors. Images
at a 1 : 1 ratio are produced with a parallel polycapillary lens; magnifications are
possible with a conical lens and both can easily be exchanged. Real-time
observations enable or simplify insitu investigations by X-ray analyses as
mentioned in Section 7.2.5.
7.2METHODICALDEVELOPMENTS
Some special subjects of methodical development belong to continuous and
recent trends. The detection of light elements is a problem of X-ray fluores-
cence analysis in general but a challenge for TXRF in particular. Further
developments are related to ablation and deposition techniques. They aim at
thin-layer analysis while a destruction of the samples is accepted as is also the
case for several methods of thin-layer analysis. A continuing trend of investi-
gations is tied up with the variant of grazing exit X-ray fluorescence (GE-XRF)
because of particular strong points.
Reliable quantification is a continuing trend that aims at avoiding matrix
effects or taking them into account. A recently revived trend is a reference-free
quantification only based on physical models and parameters. For most methods
of spectrochemical analyses, such an aim is considered to be unattainable
because of extremely complex chemical processes. For TXRF and related
methods, however, this aim is within reach. Another difficult task for TXRF
is a time-resolved insitu analysis, but efforts have been made in this direction.
7.2.1DetectionofLightElements
Several obstacles hamper the detection of light elements especially. The eight
elements C, N, O, F, Ne, Na, Mg, and Al have their K α peaks in the low-energy
region between 0.25 and 1.5 keV. They can be overlapped with, and therefore
interfered by, 16 L α and 16 L β peaks of medium- Z elements [55]. A spectral
resolution of 100 eV of the detector is not sufficient to resolve all these peaks
(see Figure 4.12). Further problems are related to fluorescence excitation,
energy-dispersive detection, and quantitative evaluation.