Analisi di Fluorescenza X a dispersione di energia

Analisi di Fluorescenza X a dispersione di energia Tradizionale ed in Riflessione Totale (EDXRF e TXRF)

The EM spectrum – X-Rays 400 ke. V 40 ke. V 1 ke. V 40 e. V

Interactions of X-Rays with matter Elastic (Rayleigh) Scattering X-ray Source Photoelectric absorption Sample Inelastic (Compton) Scattering

X-ray fluorescence Photoelectron Incident photon Fluorescence photon

Competition: Auger effect Photoelectron Incident photon Auger electron

Fluorescence yield

Transition probabilities Germanium

X-Ray line families - K Fe K Ag K

X-Ray line families - L Pb L

Typical energy dispersive set-up Pulse height discriminator ADC

TXRF and EDXRF geometries TXRF Conventional EDXRF Energy-dispersive detector X-ray tube Primary beam Sample Fluorescence radiation Totally reflected beam Sample on Optical flat Comparison shows a difference in the geometric grouping of excitation and detection units

The XRF quantification problem enhancement absorption

The XRF quantification problem Monochromatic

Thin layer approximation No dependence on other elements (matrix)

TXRF EDX detector Incident X -ray beam Reflected X-ray beam Reflector n (x-ray range ) = 1 - - i ~ 10 -6 ~ 10 -8 critical 2 critical (Si, 17. 5 ke. V) = 0. 1° = 1. 75 mrad • Thin sample layer deposited on a reflector • The total reflection effect makes the sample support “almost invisible”

TXRF basics Quartz reflector Mo K radiation reflectivity Incident beam transmittivity Reflected beam Refracted beam

TXRF basics Quartz reflector Mo K radiation Line intensity IL ( 1 + R ) Background IB ( 1 - R ) sin

Detection limits

Easy quantification - Taking ratios

Internal standard – relative sensitivities Compare with theory CALIBRATE QUANTIFY UNKNOWNS

Mo Ka - calibration curve

Principle of TXRF EDX detector ADVANTAGES • Background reduction • Double excitation of sample by both the primary and reflected beam • Small distance sample-detector (~1 mm) large solid angle Incident X -ray beam Reflected X-ray beam Reflector • Small sample volumes required • Detection limits in the pg range with X-ray tube excitation DISAVANTAGES • Collimated beam required • Sample preparation necessary for non liquid samples

Comparison between TXRF and EDXRF spectrum

Main Advantages of TXRF • No matrix effects • A single internal standard greatly simplifies quantitative analyses • Calibration and quantification independent from any sample matrix • Simultaneous multi-element ultra-trace analysis • Several different sample types and applications • Minimal quantity of sample required for the measurement (5 µl) • Unique micro analytical applications for liquid and solid samples • Excellent detection limits (ppt or pg) for all elements from sodium to plutonium • Excellent dynamic range from ppt to percent • Possibility to analyse the sample directly without chemical pre-treatment • No memory effects • Non destructive analysis • Low running cost

The TXRF equipment Main components: • Double anode Mo/W X-ray tube • Multilayer monochromator Mo. K , WL / , Bremsstr. • TXRF and EDXRF chambers • High resolution Si(Li) detector

Front view

Back view Minimum angular step • monochromator 0. 0074° • tube shield 0. 0016°

Alignment window Control • multilayer • tube shield Visualise • X-ray line counts • Total counts

The main features of the TX 2000 Spectrometer • TXRF and EDXRF (traditional 45° geometry) spectroscopy in the same equipment • Automatic switching of primary beam (Mo. K W/L and Bremsstrahlung 33 ke. V) using double anode Mo/W X-ray tube, based on innovative software. We select the energy required using a high reflectivity 80% (WL /L /Mo. K ) multilayer. We can choose also other X-ray tubes and monochromatise the energy that you need • 3. 8 liters UHV (Si(Li) 20 mm 2 detector area) high resolution detector <137 e. V (K Mn radiation at 5. 89 ke. V), with an ultra-thin and highly corrosion resistant window (8 mm Dura-Beryllium) • Minimal distance between the sample and the detector (mounted to the axis normal plane of the sample). In this position the detector is also completely out of the primary beam, as the angle between the incident and the reflected beams is so large • Instrumental detection limits for more than 50 elements below 10 pg • Helium device to improve the detection limits for the light elements • The spectrometer is fully automated and you can control different total reflection conditions for different energies from the PC, using stepping-motors moving monochromator and tube shield and MS Windows software.

Multielement standard - WL K Zn K L L M Cu Ni Co W L scatter Fe Mn Tl, Pb, Bi Sr Al Si Cd Ag Cr KCa Ba Ba Ni Cu

Multielement standard - Mo. K Sr K K L L L Ga M Zn Cu Ni Tl, Pb, Bi Si Sr Al K Co Fe Mn Cr Ca Ba Ba Tl Pb Bi Tl Mo scatter Pb Bi Sr Zn Pb Bi

Multielement standard – 33 ke. V

Elemental sensitivity periodic table Excitation radiation W-L Line W-white Line Mo-K Line Detection Limits < 5 pg 5 -10 pg 10 -30 pg 30 -100 pg >100 pg

Sample holder A droplet of 10 µL is pipetted on a carrier with a diameter of 3 cm The droplet leaves a dry residue after evaporation. www. italstructures. com isinfo@italstructures. com

Sample preparation scheme

Preparation of a TXRF measuring sample Aliquotation of some m. L Pipetting on clean carrier Addition of some µL internal standard Drying by evaporation Homogenization by shaking Taking off some µL Si(Li)-Detector Measurement

Applications • Environmental Analysis: water, dust, sediment, aerosol • Oils and greases: crude oil, essential oil, fuel oil • Medicine: toxic elements in biological fluids and tissue samples • Pigments: ink, oil pants, powder • Forensic Science: analysis of extremely small sample quantities • Pure chemicals: acids, bases, salts, solvents, water, ultra pure reagents • Semiconductor Industry (direct or after VPD-VPT) • Nuclear Industry: measurements of radioactive elements

Spectrum of detection limits Chromium in distilled water

Example of detection limits Chromium in distilled water Concentration (ppb) Volume µl (5 x N) Live Time (seconds) Detection Limit (ppt) Detection Limit (pg) = ppt x µl/1000 24. 5 10 (5 x 2) 500 370 3. 70 24. 5 50 (5 x 10) 500 120 6. 00 24. 5 50 (5 x 10) 300 170 8. 50 24. 5* (spectr. ) 100 (5 x 20) 500 70 7. 00 24. 5 100 (5 x 20) 1000 55 5. 50 24. 5 100 (5 x 20) 5000 35 3. 50 1. 97 10 (5 x 2) 500 4. 00 1. 97 10 (5 x 2) 300 440 4. 40 1. 97 50 (5 x 10) 500 80 4. 00 1. 97 50 (5 x 10) 300 125 6. 25

Choice of the anode

counts / channel Forensic: gunshot powder

Forensic: fiber analysis

Food industry: wine K K Mo K 40 k. V 30 m. A 500 s Ca L L Ca S Cu Fe Ga Rb Mo scatter Cl Si Zn P Cr K Al Mn Sr Pb Pb Zn Rb Ga int standard

Industrial application case study: Petrochemical transformation Process assistance and quality control Monitor corrosion phenomena and possibly give indications on the origin (Fe, Ni, Cr, Mn) Individuate transport processes of elements deriving for catalyst (Co, Ni, Pt, Rh, Cr, Cu, …) Logistics • Search the probable causes of deterioration (contamination) of the products during Transport and Stocking – Reflects on product price and on logistic costs (e. g. ship stop)

Applications ü ü Raw materials for intermediate products Intermediate compounds for the synthesis of final products destined to high consumption markets Cosmetics Detergents Lubrication Paper Industry Plastics Food industry Leather industry The limits for the metals content are regulated by different norms, mostly dictated by Acceptance Specifications of the client.

Olefin C 10 -13 70 ppb 17 ppb Ctz. : Pt, Ni

Linear paraffin C 10 -13 50 ppb 8 ppb

Detection limits: ICP-OES vs. TXRF ICP-OES (ASTM: D 5708 -B) Campione : 10 g @ 25 ml

Correlation ICP-OES vs. TXRF Ø Paired t-test : results do not differ significantly Ø Linearly correlated

Conclusions

Environmental: soil Microwave mineralisation in 10 ml HNO 3. Final volume 50 ml K K Fe K Si S L Fe Ca Ga Rb Mn Sr Rb Fe escape Ca Al Mo scatter L As Ga Pb Ni Zn Cu Pb

Environmental: gasoline Internal standard Counts Standard Petrol ICP Pb 0. 324 g/l Mo X-ray tube 35 k. V, 30 m. A Sample: 10 µL Live time: 200 s Scattered radiation

Environmental: compost microwave TXRF no treatment ARPAVRING_3 -02: esercizio di interconfronto

Particulate matter monitoring Multi-stage Cascade impactors can be used in order to collect the particulate matter onto standard quartz carriers that can be analysed directly with the TXRF without any sample preparation.

Comparison of Important Analytical Features of the Three Competitive Methods Analytical Features ICP-MS TXRF INAA Samples Volume or mass 2 -5 m. L 5 -50 µL 10 -200 mg Preparation of solid Digestion or suspension None Dissolvation portion < 0. 4% < 1% Any Diluition of acids 1: 100 None Consumption Yes No No Detection limits Excellent Very good Element limitations H, C, N, O, F, P, S Z < 13 Z < 9; Tl, Pb, Bi Spectral interferences Several Few Isotope detection Yes No No Calibration Several external and internal standards One internal standard Some pure element foils Matrix effects Severe None Memory effects Yes No No Time consumption < 3 min < 20 min – 30 days Equipment Ar-plasma + quadrupole MS Special EDS Nuclear reactor + spectrometer Capital costs Medium Very high Running costs High Low High Maintenance Frequently Seldom Detection Quantification Expenditure

Benefits and Drawbacks of TXRF Applied to Element Analyses Benefits: Drawbacks or limitations: • Unique micro analytical capability • Impossibility of totally nondestructive analysis • Great variety of samples and applications • Limitation for non-volatile liquids • Simultaneous multielement determination • Exception of low-Z elements • Low detection limits • Restriction to flat or polished samples • Simple quantification by internal standardization • No matrix or memory effects • Wide dynamic range • Non-destructive surface and thinlayer analysis • Simple automated operations • Low running costs and maintenance • Limitation by high matrix contents

References R. Klockenkämper, Total-Reflection X-Ray Fluorescence Analysis, John Wiley and Sons Inc. , New York, 1997, ISBN 0 -471 -30524 -3 Spectrochimica Acta Part B: Atomic Spectroscopy TXRF Special Issues – TXRF conference proceedings Vol. 44, 46, 48, 52, 54, 56, 58, Issue Issue 5 10 2 7 10 11 12 (1989) (1991) (1993) (1997) (1999) (2001) (2003)

References Handbook of X-Ray Spectrometry Rene E. Van Grieken Andrzej A. Markowicz ISBN: 0824706005 Publisher: Marcel Dekker Total Reflection XRF (TXRF), P. Kregsamer, C. Streli, P. Wobrauschek, Book chapter "Handbook of X-ray Spectrometry", Ed: R. Van Grieken, A. Markowicz, Marcel Dekker, 2002 Total Reflection X-ray Fluorescence Analysis, P. Wobrauschek, C. Streli, Chapter in : Encyclopedia of Analytical Chemistry, Ed. : R. A. Meyers, Wiley & Sons, 2000, 13384 -13414