does UniQuant compare with other programs?
versus Fine-Step scanning
does UniQuant™ compare with Other Programs?
X-Ray Spectrometers are always supplied with what
we will call Spectrometer Software.
Examples are WinXRF of ARL and SuperQ of Philips AXR.
Briefly speaking, Spectrometer Software contains of 2 programs,
- The Control Software with which Analytical Programs
(AP’s) for Data Collection
are defined for controlling the spectrometer and sample
changer. The AP will control
the measurement of a sample with a specified set of instrumental
parameters like kV,
mA, collimators, analysing crystals, detectors and measuring
- The Evaluation Program (EP) which is for conversion
of the measured intensities to
elemental concentrations and possibly mass/area of thin
UniQuant falls in this category.
There are various type of Evaluation Programs,
each one making use of its own typical
way of Data Collection:
- Mathematical Model (MM) program.
This is still the most widely used. The MM is an equation
that approximates the more
accurate ‘Full Physical Equation’. It comprises calibration
coefficients such as for
slope factor, background, line overlaps and interelement
The latter are predicted by theory (theoretical Alpha’s)
and/or found by calibration
(regression Alpha’s). The remaining coefficients must be
found by calibration using
Regression Analysis of several or many standards. Because
of the approximations made
by the MM, a calibration must be made for each ‘family’
of samples, like a family of beads
and a family of a particular type of alloy. Once all coefficients
have been established,
the MM is called the analytical equation. A set of simultaneous
analytical equations is
used to convert intensities from an unknown sample to concentrations.
Generally, each family of samples uses its own specific
Analytical Program (AP) for
Regression analysis was first used in XRF analysis in 1967
by the present author
when with Philips. In the same year, he developed the DJ
mathematical model and backed
it up with ‘theoretical Alpha’s’ and ‘regression Alpha’s’.
Publishing was postponed until 1973.
- UniQuant’s method requires just one Analytical Program
(AP), for which UniQuant exactly
prescribes the instrumental parameters.
The complete AP comprises 114 fixed spectral positions,
which are rather evenly
distributed over the entire XRF spectrum of interest. Each
such position is tuned to the
wavelength of a potentially present element. One may say
that UniQuant makes a smart
(coarse) step scan of the spectrum. On the other hand its
method of measuring is in principle
the same as with the conventional MM method, see above.
UniQuant converts intensities to concentrations by using
the ‘Full Physical Equations’
of which most input data are ‘Fundamental Parameters’. As
a consequence, calibrations are
feasible for an extremely wide range of concentrations.
UniQuant’s method has reduced the ‘calibration curve’ to
a simple horizontal line,
Kappa versus concentration, where Kappa is the instrumental
sensitivity for a given XRF line.
Kappa is independent of samples. The problem of some 1500
potential line overlaps is solved
in a unique, rigorous and elegant way by using line overlap
Kappa’s, which equally are
instrument sensitivities for interfering XRF lines.
UniQuant simultaneously solves concentrations and line overlap
corrections (in mass%)
- SQ programs (FSS+FP programs)
Most spectrometer manufacturers offer a program that use
intensity data as obtained
by Fine Step Scanning (FSS) of the spectrum. The
intensities are first converted to net XRF
intensities which in turn are converted to concentrations
by using Fundamental Parameters (FP).
Examples are SemIQ of PANalytical, QuantAS of Thermo and
SSQ of Siemens.
The names of these programs would suggest that results are
However, for certain types of samples, the results may be
accurate, thus quantitative,
provided that a ‘library of standards’ contains data of
a suitable standard.
Especially if high energy XRF lines are used, the library
standard must have about the
same mass, height and dilution as the unknown sample.
Example 1: An unknown bead requires a ‘library standard’
of a bead with the same dilution
and total mass as the unknown.
Example 2: an unknown oil sample requires a ‘library
standard’ of oil with the same
total mass (height) as the unknown.
Example 3: The analysis of a dust filter may be accurate
only if no high energy XRF lines
are used, else substantial errors would occur through ‘non-infinite’
thickness of the sample.
While scanning over XRF lines from trace elements, the effective
measuring time is very
short, for example less then one second. It is then difficult
to distinguish between
background and any fluorescent radiation. As a result, a
trace element is easily overlooked.
Inspired by UniQuant, some SQ programs have therefore been
modified so that certain
elements can be measured with fixed position and adequate
Even so, the burden now is on the analyst who is to specify
for which elements this new
feature is to apply. And, what to do when a sample is totally
(Regression and Alpha’s)
||Fixed spectral positions**
||Fixed spectral positions
||Fine step scan
||Yes, in library
|Regression analysis using standards is possible?
|Line overlap corrections
|Requires measurement of interfering line
|What if interfering line coincides?
|Solves problem of mixture Lanthanide’s?
|Catch (weights) dilution for beads?
|Weight of bead may vary widely?
||Not if higher energy XRF lines are used
||Not if higher energy XRF lines are used
|Catch volume for liquid samples?
|Lower Detection Limits (LLD)relative to Conventional
at same measuring time
|Mass may vary?
|Mass found also?
|Is each result reported with a confidence interval?Actually
a condition for being quantitative!
||High only for 'easy' samples
|| Features for SQ programs shown above are to the best
of my knowledge.
||spectral positions are rather evenly distributed over
entire XRF spectrum,
therefore, one may say that UniQuant makes use of a
smart coarse step scan
||It is common practice to speak
about Precision (reproducibility) and
Accuracy of an analysis. For programs that can work
with totally unknown samples,
I here add the characteristic of Reliability.
Its meaning is best explained by an example:
An SQ program reports 27 %Fe in a sample whilst UniQuant
reports 55 ppm Fe.
What happened? The sample contained much Pb of which
one XRF line interfered the
analyte FeKa line . The SQ program intelligently diverted
from FeKa to FeKb.
But the FeKb line gave the totally wrong result of 27%
Fe. Either the library standard
used was not an appropriate one or FeKb was itself not
free from spectral interference
(line overlap). Such problems can hardly occur with
UniQuant, which is reliable
(rugged) in this respect.
(SVS) versus Fine-Step (FS) scanning
In conventional quantitative
XRF analysis, intensities are measured at fixed spectral
Almost ten years ago, spectrometer manufacturers started
to make software for analysing
totally unknown samples for which no standards are available.
They have all chosen the
same method of intensity measurements, namely by Fine-Step
(FS) scanning of the X-Ray
spectrum. At the same time, Omega Data Systems started to
develop the UniQuant software
which is based on far better concepts. It was like choosing
the highest mountain to climb.
Others may reach the top of a mountain only to find out
that their mountain is much lower
than Mount UniQuant.
Like conventional methods, UniQuant is based on intensity
measurements at fixed
spectral positions. Although UniQuant was originally intended
for standardless analysis
of totally unknown samples, it has been so far developed
that with the use of standards
and regression analysis, it may give results that are as
precise and accurate as with
conventional XRF analysis.
The advocates of Fine-Step
In sales situations and at symposia, sometimes it is
emphasised that Fine-Step scanning
is far better than measuring at fixed positions, in particular
in view of trace analysis. If this
would be true, why then is conventional quantitative XRF
analysis based on fixed
spectral positions and not on Fine-Step scanning? The arguments
used are clearly in
defence against UniQuant. This leaflet reviews several of
the false arguments in favor
of Fine-Step scanning.
What is Smart-Variable-Step
In SemiQuantitative (SQ) programs, intensity
measurements are generally done by
Fine-Step (FS) scanning of the wavelength spectrum.
In contrast, the quantitative UniQuant™ (UQ)
program prescribes measurements to be made
at about 100 spectral positions. The goniometer scans the
entire spectrum in varying
steps from one position to the next, where each position
corresponds with an XRF
wavelength of one of 78 elements. We refer to this method
as Smart-Variable-Step (SVS)
scanning. The predicate 'Smart' is used here because for
a given total time per sample,
all potentially present elements are measured with highest
To appreciate the relative merits of both FS and SVS
scanning methods one should be aware
that the SQ programs and UniQuant differ fundamentally in
their concepts of finding net
peak intensities, which are the gross peaks corrected for
background continuum and
spectrally interfering XRF lines.
SQ: The concept of SQ programs makes the use of FS scanning
mandatory. This is
because, for the purpose of line overlap corrections, very
many (over a thousand)
spectrally interfering lines must be measured in addition
to the about 100 analyte lines.
UQ: Due to its concept,
UniQuant can abstain from measuring any of the potentially
3000 interfering lines and devote all its time to the 100
SQ: When an interference is strong, an SQ program may
itself search an alternative free
analyte line. If things get difficult, the help of the analyst
is required and this is where the
use of spectrograms comes in.
UQ: In the results obtained
from each analyte line, UniQuant gives a full quantitative
account of corrections made for the various line overlaps.
Thus it tells exactly which
elements caused an interfering line and to what extent in
What is the magic here?
The answer is that UniQuant fully exploits the combination
of two favorable facts:
spectrometers can be programmed for spectral positions (wavelengths)
with avery high precision.
analyte XRF lines and interfering XRF lines are always at
their same spectral
position (apart from
chemical shift of soft XRF lines).
Thus, there is no need for scanning and/or searching.
SQ: With SQ programs, scanning speed must be relatively
fast in order to keep the total
measuring time within 15 minutes. This fast scanning leads
to relatively large counting
errors. To partially compensate for this, instrumental parameters
are chosen for highest
possible intensity. However, this is at the expense of spectral
resolution making the line
overlap corrections even more difficult. The time of scanning
across XRF lines of trace
elements is so short that their intensity may not be distinguishable
from the stochastic
fluctuations of the background. On the other hand, the same
fluctuations are easily
mistaken as peaks from a trace elements. A partial solution
of this problem is possible
for samples of which it is known which trace elements can
be expected and which not.
The analyst may then enter certain directives to the program
for the scanning speed
to slow down where it may be useful or to skip specified
ranges of the spectrum
assuming that these do not contain lines from unexpected
It should be clear that such specific approach may not work
for less well known samples.
UQ: UniQuant measures
trace elements much the same way as in conventional analysis,
that is with fixed time, 10 seconds for example. This is
a factor 100 longer than with FS
scanning, where the dwelling time in the vicinity of the
peak is as low as 0.1 seconds.
As a consequence, with UniQuant, Detection Limits are better
by a factor 10 with respect
to SQ programs if the latter are not tailored to sample
What about background
The most simple case is that of an XRF peak without
any spectral interference in its vicinity.
The background under the peak can easily be calculated from
additional measurements at
both sides of the peak. Any program can do that. However,
the situation is far less simple
when a lot of interfering lines are cluttering in the vicinity
of the analyte line.
SQ: It may be impossible to find a spectral position
in the vicinity of the analyte line that is
suitable to measure a background intensity.
UQ: In such cases,
the background may be determined by considering a wide spectral
range, like one would do visually. This is exactly what
UniQuant does. Fine-step scanning
would not have an advantage. On the contrary, fine-step
scanning tempts to look at too
small spectral ranges with the danger of overestimating
What about confirmation by
other lines of the same element?
Suppose that Zr is analysed by its ZrLa line. If
this line gives a net intensity whilst Zr is
not expected to be present, one may suspect that the ZrLa
peak intensity is due to a
spectral interference by a line from another element or
by a spectral impurity of the
radiation that is incident to the sample. In order to verify
if indeed Zr is present, one
may check the intensities of other XRF lines of Zr, like
ZrKa and ZrLb.
SQ: If a fine-step scan was made across the entire
spectrum, data for ZrKa and ZrLb
are available. This is sometimes presented as an advantage
for FS scanning based
SQ programs. The truth is that such verification may be
very much needed by SQ programs.
UQ: By contrast, for
UniQuant such checks are not required. This is because,
of its results, UniQuant gives a
full account of which parts a peak intensity
composed of, namely:
continuum in equivalent mg/kg.
impurity in equivalent mg/kg.
line overlaps in equivalent mg/kg and from which elements.
error in equivalent mg/kg and this is possible for UniQuant
measures with fixed times
at the spectral positions of interest.
Any of the calibrated programs can in
principle be used for any sample.
The calibration constants differ only slightly. For totally
program uses 76+36
A single "all
metal monitors" program for drift corrections
supports all calibrated programs.
Each of the 9 monitor samples is a “100“ % element
for maximum stability,
easy cleaning and replacement.
UniQuant™5 unites in ONE WORLD:
XRF analysis using standards and standardless
XRF analysis, all quantitative
and reports in all cases:
an uncertainty interval for each calculated
concentration or sample mass (thickness),
a requirement for programs to be QUANTITATIVE.
UniQuant™ 1989...2021 is a trademark
of Thermo Fisher Scientific Inc.
Copyright © 2021 Thermo Fisher Scientific Inc. All rights reserved.