Mass spectrometry. Talián Csaba Gábor PTE Institute of Biophysics

Transcription

1 Mass spectrometry Talián Csaba Gábor PTE Institute of Biophysics

2 The 0 th law of mass spectrometry It is not mass spectroscopy! Or is it still that? Mass spectroscopy: separation of particles with different mass and charge Mass spectrography: visualising the picture of the separated particles simultaneously on a photographic plate Mass spectrometry (MS): electronic detection of particles separated in space (and time), in a successive way

3 Principles Formation of ions from any appropriate matter Separation of ions based on m/z Detection of ions qualitatively and quantitatively according to the m/z abundance function mass spectrum

4 Why is MS good? High sensitivity range of qualitatíve detection limit: g range of quantitatíve detection limit: g Broad dynamic range of mass amu (atomic mass unit, Da) Specificity and reproducibility of the results Low amount of sample needed µg pg

5 Historical overview I. 1886, Goldstein discovery of gas phase ions (anode rays) 1897, Thomson discovery of e -, defining its m/z (Nobel prize 1906) 1912, Thomson first mass spectrometer (parabola spectrograph) 1918, Dempster electron-impact ionisation 1942 first commercial device 1948, Cameron, time-of-flight (TOF) analyser Eggers

6 Historical overview II. 1953, Paul, Steinwedel quadrupole and ion trap analyser (Nobel prize, 1992) 1966, Munson, Field chemical ionisation 1973, McLafferty coupling HPLC and MS 1978, Yost, Enke triple quadrupole (QqQ) analyser 1984, Fenn electrospray (Nobel prize, 2002) 1987, Karas et al. MALDI (matrix assisted laser desoption ionisation)

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8 General set-up Data processing, control Sample introduction Ion source Analyser Detector Vacuum system

9 Vacuum system mbar Diffusion oil pump és turbomolecular pump Increase of ionisation efficiency, sensitivity and resolution Prevention of particle collisions Modify trajectory or kinetic energy of the ion Quench the ion charge Fragment the ions different masses

10 Sample introduction directly gases, volatile compounds Spray HPLC, GC Heat accompanying the ionisation process Strong electric field

11 Ionisation Heat (+ exchange of charge in electrolit) Electric field Foton Impact from electrons Collision of atoms, ions Main determinants: properties of the sample matter, stability, solvent Influences the sensitivity, structural information available

12 electron-impact ionisation (EI) Collision with an electron-beam emitted from a heated cathode (Re, W, 70eV) Matters to be easily evaporated, up to Da, high temperature Intensive, stable, well reproducible Appropriate for a limited range of matters, high fragmentation rate (in source decay, ISD)

13 N Filament Extraction lenses Sample Inlet Collector Source magnets S

14 Soft ionisation methods Chemical ionisation, CI Fast atom/ion bombardment, FAB/FIB Plasma desorption, PD Field desorption, FD strong electric field

15 Chemical ionisation Ion-molecule reactions (methan): CH 4 + e - CH e - CH 4 + CH 4 + CH 3 + CH 5 + CH 3+ + CH 4 C 2 H 5+ + H 2 CH 5+ + M CH 4 + [M+H] + [M+1] + C 2 H 5+ + M [M+C 2 H 5 ] + [M+29] +

16 Elektrospray/ionspray ionisation (ESI, ISI) Spray-forming method Metal capillary, 2-5 kv, facing a strong reverse charge Spraying gas through outer concentric tube (N 2 ) Heated N 2 counter-current solvent evaporation Non-volatile, polar organic compounds

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18 Matrix assisted laser desorption ionisation (MALDI) Organic matrix (mustard acid, α-cyano-4-oh-cinnamic acid, 2,5-dihydroxi-benzoic acid) sample dissolved in matrix and dried onto metal plate Laser impulses Matrix absorbes energy, ionises and desorbes sample particles fast, mild, sensitive, good for blend samples as well examination of macromolecules

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20 Separation of ions Static magnetic field Dynamic magnetic field Static electric field Dynamic electric field Kinetic energy and time of flight Storage time

21 Sector analysers Magnetic field strength by trajectory Electric field strength by kinetic energy High resolution, high sensitivity, broad mass range Expensive, slow, bulky, great requirements for technical assistance

22 r=mv 2 /zee r=mv/zb =(m/z)(v/b)

23 Quadrupole analyser

24 TOF (time of flight) analyser Time of arrival in the detector depends on the mass and charge (acceleration voltage) Need for long collision- and field-free route Corrections (ion mirror reflectron) Cheaper, high resolution, broad mass range MALDI + TOF protein analytics

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26 Ion trap

27 Advantages of the ion trap analyse over conventional linear quadrupols: ~ times greater sensitivity larger scan speed wider range of mass to study better mass resolution simple set-up, lower costs Disadvantage: worse quantitative measurements

28 Detectors Registration of A ion current Characteristics of the detector: sensitivity speed of following changes in ion current enhancement factor electric noise level (dark current) stability (lifetime) Point detectors (sequential detection of ions) chaneltron Array detectors (simultaneous detection of ions) application: magnet analyser

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30 Nitrogen rule: if the molecule ion contains an odd number of N atoms, its mass number is always, if it does not contain any N atom or their number is pair, then the molar peak is always at a pair m/z number A - element monoisotopic e.g. 19 F, 31 P, 127 I, H A + 1 element A + 2 element one isotop with a mass number 1 amu bigger, then the most frequent isotop e.g. 12 C 13 C, 14 N 15 N one isotop with a mass number 2 amu bigger, then the most frequent isotop e.g. 35 Cl 37 Cl, 79 Br 81 Br

31 Resolution R= m/ m 10 % rule: valley between two peaks of similar intensity must not be more than 10% of the peak height Example 1. separation of simply charged m/z 1000 and 1001 ions needs R=1000 resolution Example 2. CO M=27, nominal mass: 28, m = 0, N 2 M=28, R = 2500 resolution needed

32 Tandem mass spectrometry I. MS/MS, MS 2

33 Tandem mass spectrometry II. Triple quadrupol instrument: Possible ways to select ions Parent/precursor ion scan Daughter/product ion scan Constant neutral loss scan Selected ion / multiple reaction monitoring (SIM, MRM)

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35 Medical applications of mass spectrometry I. Sample introduction: fluidic biological samples, appropriately prepared serum, blood, urine, liquor, solid tissue extracts etc. 1 examination may yield rapid diagnostic opinion for about 30 metabolic diseases Diagnostics at protein (enzyme) level Identification of sequence differences Identification of posttranslational modifications Study of conformational changes Quantitative examination of protein expression profiles

36 Medical applications of mass spectrometry II. Diagnostics at metabolite level: inherited metabolic diseases carnitine ester profile determination: primary/secondary carnitine deficiency, fatty acid oxidation disorders, organic acidurias amino acid profile determination: aminoacidopathies guanidine-compounds: disorders of creatine synthesis disorders of bile acid synthesis homocystein: hiperhomocysteinaemias purines, pirimidines galaktosaemia disorders of steroid synthesis, cholesterol synthesis disorders of hormon synthesis (triiodo-thyronine, catecholamines) disorders of carbohydrate metabolism

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40 Medical applications of mass spectrometry III. Newborn screening Generally examination on a whole/ healthy population, recognition of sick persons Setting up normal range; it can be highly variable for different metabolites Setting up cut-off values Aim: demonstration of vast differences not biological variability, no need for very precise measurements

41 Early diagnosisi can preceed the development of symptoms, a well timed therapy may alleviate or prevent the later complications Selective screening = diagnostics: Examination of samples from patients displaying symptoms Aim: demonstration of smaller metabolic aberration Requires accurate, sensitive measurements, min. 2x, preferably fasting and after meal samples

42 WHO criteria for populationwide screening programmes The disease screened represents a great problem for healthcare Acceptable and efficient therapy exists for the patients identified Appropriate institutions for diagnostics and cure are available There is recognisable early or latency period There is suitable examination method or test The population can accept these methods or tests The etiology of the disease and its transition from early to developped state is thoroughly clarified There is regulated agreement upon who is to be regarded a patient Expenses of the screening and therapy do not substantially exceed the expenses due to late diagnosis The screening is a recurrent or continuous programme

43 Applications in proteomics Determination of molar mass Sequencing Examining the position of disulphide bridges Conformation studies Active centre / binding site determination Research on protein-ligand interactions

44 Other applications Pharmaceutical research: pollution profile Forensics: e.g. drug-screening, dopping, poisons Agriculture: e.g. active components of wine (resveratrole) Environment (dioxines), food-industry Nucleic acid sequencing Etc.

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