Autenticity control, provenance testing and fraud detection using mass spectrometry

Transcription

1 Autenticity control, provenance testing and fraud detection using mass spectrometry Abdal-Azim Al-Terkawi Ersan Özelci Melissa-Jane Monks Narendra Lagumaddepalli Venkatareddy Seyed Mohsen Jebreiil Khadem, Surahit Chewle Tessema Fenta Mekonnen

2 Introduction Concept of Isotopes, Isotopic Ratio and Fractionation

3 Definition Isotopes Atoms of the same element (i.e., same number of protons and electrons) but different numbers of neutrons. Symbol: Z A X 3

4 Isotopes 4

5 Isotopes (example carbon) 13 C 12 C Average Atomic Mass: m (X)= m 1 % +m 2 % 100 m (C) = ( ) (0.9890) + ( ) (0.0110) = amu mass number exact weight [amu] abundance [%] Isotopic Ratio: R(X) = abundance of heavy isotope (X) abundance of light isotope (X) R(x)= =

6 Isotopes same number and distribution of electrons same chemical (and physical) reactions Differences in mass partitioning of isotopes differentially among phases Different rate or extent of chemical or physical reactions 6

7 Isotope Variations Isotopic variations in natural abundance of stable isotopes arising as a result of chemical or physical process. Occurs during: isotopic exchange reactions unidirectional or incomplete reactions physical processes : evaporation/condensation, melting/crystallization, adsorption/desorption, diffusion Radioactive decay 7

8 measurands fractionation factor : α A B = R A R B Where R A, R B are the isotope ratios in two phases (ex. carbonate and water, or water vapor and water, etc) measurement reporting convention: δ 18 O = 18 O 16 O 18 O 16 O sample standard 18 O 16 O standard Note that deltas are named after the heavy isotope So each isotopic measurement is reported relative to a standard 8

9 Fractionation mechanisms Equilibrium Isotope Fractionation A quantum-mechanical phenomenon, driven mainly by differences in the vibrational energies of molecules and crystals containing atoms of differing masses. Kinetic Isotope Fractionation Occur in unidirectional, incomplete, or branching reactions due to differences in reaction rate of molecules or atoms containing different masses. 9

10 Equilibrium Isotope Fractionation E = (n+½)hν ν = (½π) (k/μ) µ = (m1m2 )/(m1+m2) E is lower when a heavier isotope is substituted for a lighter one Example: a C-O bond where we substitute 18 O for 16 O. m 1 =12, m 2 = 16 or 18, 18 ν / 16 ν = ( 16 μ / 18 μ) = So, 18 E < 16 E 10

11 Kinetic Isotope Fractionation unidirectional reaction: The energy required to surmount this barrier: E a, lower zero point energy reactant molecule with a heavier isotope Transition state Reactants higher E a than the lighter isotope Energy Reactants E a Slower reaction Products heavy isotope depletion in the product. 11

12 Kinetic fractionation Kinetic energy of molecules of gas : Ek = 1 2 mv Consider two molecules of CO 2 : 12 C 16 O 2 (mass = 44) and 13 C 16 O 2 (mass = 45) 2 if their energies are the same, then: 1 1 mv = mv A A B B assuming ideal gas and the ratio of their velocities is: v v A B 1/2 1/2 m B 45 = = = ma 44 SO 12 C 16 O 2 can diffuse 1.1% further than 13 C 16 O 2 in a given amount of time This can be observed as gas moves through a fine capillary tube ( 12 C 16 O 2 arrives firs). 12

13 Instrumentation IR-MS MC-MS MC-ICP-MS

14 Stable Isotope Ratio Mass Spectrometer (IR-MS) Multi Collector Thermal Ionization Mass Spectrometer (MC-TIMS) 14

15 Multiple Collector Inductively Coupled Plasma Mass Spectrometer Mass Spectrometer Typical Repetition Precision [%] MC ICP - MS MC TIMS IR - MS

16 Elements determined by ICP-MS and approximate detection capability 16

17 Components of an ICP-MS System 17

18 Laser Ablation ICP-MS (LA-ICP-MS) Pulsed laser is used to ablate solid samples into the plasma Useful for solids No dissolution process required Useful for bulk analysis and feature analysis Oxide levels are much lower Interferences less of a problem Expensive! 18

19 Data analysis and quantification

20 Data analysis and Calibrations Semi-quantitative analysis --Concentration of each element Quantitative analysis --Comparison with known sample Isotopic ratio analysis --Specific isotopes of an element Isotopic dilution analysis --Spiked with enriched isotope 20

21 Detection of counterfeit tablets of an antiviral drug using δ 34 S measurements by MC-ICP-MS and confirmation by LA-MC-ICP-MS and HPLC-MC-ICP-MS Rebeca Santamaria-Fernandez et al. J. Anal. At. Spectrom., 2008, 23,

22 Detection of Counterfeit tablets 10 % of global market (2010) High cost for pharmaceutical industry Harmful consequences for consumer Anti-counterfeiting analytical methods needed 24

23 Stable isotopic fingerprints Stable isotopic fingerprints Sulfur isotope ratio ( 34 S/ 32 S) Standartization Vienna-Cañon Diablo Troilite scale (V-CDT) δ 34 S V-CDT Sample ( ) = δ 34 S V-CDT ( )= ( 34 S: 32 S) δ 34 S ssssssssssss ( 34 S: 32 S) VV CCCCCC 11 ( 34 S: 32 S) ssssssssssss δ 34 S V CDT WWWWWWWW ( 34 S: S) WWWWWWWW standards: Main working standard NIST RM8553 δ 34 S = 16±0,3 Evaluation of instrumental performance NIST 8556 δ 34 S = 17,44±0,3 NIST RM8554 δ 34 S = -0,3±0,3 25

24 Measuring technique: Multicollector ICP-MS Approaches for sample introduction I. direct liquid introduction MC-ICP-MS II. III. solid laser ablation LA-MC-ICP-MS HPLC separation HPLC- MC-ICP-MS 26

25 Results: direct liquid introduction MC-ICP-MS genuine tablets counterfeit counterfeit 27

26 Results: approaches in comparison counterfeit genuine tablets Overlapping authenticity any approach suitable counterfeit product identification 28

27 Summary on Reliability and Accuracy

28 IR-MS:- for light elements (H, C, N, O, S) TI-MS:- for heavier elements / difficulties for light elements TI-MS:- precise and accurate (RSD 0.05%) Extensive sample preparation Low IE for elements of IE>7.5 ev Time consuming measurement ICP-MS High IE efficiency Less preparation Easy to operate Poor precision ( % RSD) due to low instrumental mass discrimination and analyte spectral overlap with interferences L. Balcaen et al. Spectrochimica Acta Part B 65 (2010)

29 To avoid poor precisions of ICP-MS: SI-ICP-MS enables to RSD 0.05%, Q-based, double focusing and TOF measurements MC-ICP-MS several ion beams simultaneously (saving time) with RSD 0.002% Interferences spectral interferences and mass discrimination effect from Isobaric spectral overlap eg. 40 Ar + to 40 K + & 40 Ca + L. Balcaen et al. Spectrochimica Acta Part B 65 (2010) Polyatomic molecules:- from sample matrix, plasma gas and/or molecular oxides. eg. 40 Ar 35 Cl + at m/z 75, Ar 2 +, ArO + or ArOH+ Doubly charged ions (decrease intensity and overlap other isotopes) Backgrounds :-from stray light inside MS & electronic noise from detector R. Thomas, 2008, 2nd Ed. P CRC press. 31

30 Non-spectrometric effect Matrix effects (suppression of analyte signals) Physical effects (eg. buildup of salts at interface of sampler cone) Ways to compensate interferences High resolution and quadruple MS: MC-ICP-HRMS or MC-ICP-TripQ-MS Separate the analyte of interest (LC or GC-MC-ICP-MS) Internal standards for matrix interferences Cool/cold plasma technologies for lower IE elements reduced polyatoms from plasma source Collision/reaction cells before entering to MS, avoid polyatomic & molecular Mathematical corrections eg. 114 Cd + is interfere by 114 Sn +, 114 Cd + = total count at Sn +, R. Thomas, 2008, 2nd Ed. P CRC press. 32

31 measure interference free 118 Sn + and ratio of 114 Sn + / 118 Sn + taken as correction which is constant and known natural abundance, 114 Cd + = mass [(0.65%/24.23%)x( 118 Sn + )] Two main limitations of Isotopic ratio analysis Cost of the analysis:- requires standards and certified reference materials like NIST isotopic standards, usually very expensive Limited to elements having more than 1 stable isotopes. 33

32 Measurement of longitudinal sulfur isotopic variations by laser ablation MC-ICP-MS in single human hair strands Rebeca Santamaria-Fernandez et al. Anal. Bioanal. Chem. 2009, 394,

33 Sample preparation : Acid digestion in Microwave Longitudinal Laser ablation Atoms, Ions, Molecules, Clusters, Particles Pulsed Laser Beam Laser Ablation 35

34 Optimization 32 S & 34 S Measurements In house references of horse hair External references (NIST) Mass bias Bracketing 36

35 measurements: Variation of isotopic ratio UK citizen < 1.2 Traveler > 5 37

36 Thank you for your attention! 38