An Overview of XRF Basics

3. Sample Preparation Techniques
for XRF Analysis

3.1 Introduction

X-ray fluorescence (XRF) analysis is a fast, non-destructive and environmentally friendly analysis method with very high accuracy and reproducibility. All elements of the periodic table from beryllium to californium can be measured qualitatively, semi-quantitatively and quantitatively in powders, solids and liquids. Concentrations of up to 100% are analyzed directly, without any dilution, with reproducibilities better than ±0.1%. Typical limits of detection are from 0.1 to 10 ppm. Most modern X-ray spectrometers with modular sample changers enable fast, flexible sample handling and adaptation to customer-specific automation processes.

XRF samples can be solids such as glass, ceramic, metal, rock, coal, or plastic. They can also be liquids, like petrol, oil, paint, solutions, blood or even wine. With an XRF spectrometer both very small concentrations of very few ppm and very high concentrations of up to 100% can be analyzed directly without any dilution process. Based on its simple and fast sample preparation requirements, XRF analysis is a universal analysis method, that has been widely accepted in the fields of research and industrial process control. XRF is particularly effective for complex environmental analysis and for production and quality control of intermediate and end products.

The quality of sample preparation for XRF analysis is at least as important as the quality of measurements.
An ideal sample is prepared so that it is:

representative of the material
homogeneous
thick enough to meet the requirements of an infinitely thick sample
without surface irregularities
composed of small enough particles for the wavelengths to be measured

With XRF it is not necessary to bring solid samples into solution and then dispose of solution residues, as is the case with all wet-chemical methods. The main prerequisite for exact and reproducible analysis is a plain, homogeneous and clean analysis surface. For analysis of very light elements, e.g. beryllium, boron and carbon, the fluorescence radiation to be analyzed originates from a layer whose thickness is only a few atom layers to a few tenths of micrometer and which strongly depends on the sample material (Table 6). Careful sample preparation is therefore extremely important for analysis of light elements.

Table 6: Layer thickness (h, in µm), from which 90%
of the fluorescence radiation originates
Sample matrix		Graphite	Glass	Iron	Lead
Line		h_(90%, µm)	h_(90%, µm)	h_(90%, µm)	h_(90%, µm)
U	Lα₁	28000	1735	154	22.4
Pb	Lβ₁	22200	1398	125	63.9
Hg	Lα₁	10750	709	65.6	34.9
W	Lα₁	6289	429	40.9	22.4
Ce	Lβ₁	1484	113	96.1	6.72
Ba	Lα₁	893	71.3	61.3	4.4
Sn	Lα₁	399	44.8	30.2	3.34
Cd	Kα₁	144600	8197	701	77.3
Mo	Kα₁	60580	3600	314	36.7
Zr	Kα₁	44130	2668	235	28.9
Sr	Kα₁	31620	1947	173	24.6
Br	Kα_1,2	18580	1183	106	55.1
As	Kβ₁	17773	1132	102	53
Zn	Kα_1,2	6861	466	44.1	24
Cu	Kα_1,2	5512	380	36.4	20
Ni	Kα_1,2	4394	307	29.8	16.6
Fe	Kα_1,2	2720	196	164	11.1
Mn	Kα_1,2	2110	155	131	9.01
Cr	Kα_1,2	1619	122	104	7.23
Ti	Kα_1,2	920	73.3	63	4.52
Ca	Kα_1,2	495	54.3	36.5	3.41
K	Kα_1,2	355	40.2	27.2	3.04
Cl	Kα_1,2	172	20.9	14.3	2.19
S	Kα_1,2	116	14.8	10.1	4.83
Si	Kα_1,2	48.9	16.1	4.69	2.47
Al	Kα_1,2	31.8	10.5	3.05	1.7
Mg	Kα_1,2	20	7.08	1.92	1.13
Na	Kα_1,2	12	5.56	1.15	0.728
F	Kα_1,2	3.7	1.71	0.356	0.262
O	Kα_1,2	1.85	2.50	0.178	0.143
N	Kα_1,2	0.831	1.11	0.08018	0.07133
C	Kα_1,2	13.6	0.424	0.03108	0.03124
B	Kα_1,2	4.19	0.134	0.01002	0.01166

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An Overview of XRF Basics

3. Sample Preparation Techniques for XRF Analysis

3.1 Introduction

3. Sample Preparation Techniques
for XRF Analysis