Gas chromatography/mass spectrometry (GC MS) Interpretation of EI spectra

Transcription

1 Gas chromatography/mass spectrometry (GC MS) Interpretation of EI spectra Arpad Somogyi CCIC MSP MSP Summer Workshop July 13, 2016 Important goals in chromatography Achieve the best separation Little band broadening narrow chromatogram peaks efficient column Dynamic range Separate and detect the small in the close vicinity of the big Reproducibility Stable peak positions, retention times Even with the best column diffusion always plays a role! Parameters to control diffusion Particle size (Column type) Flow rate 1

2 The Van Deemter Equation Original paper: Van Deemter JJ, Zuiderweg FJ and Klinkenberg A (1956). "Longitudinal diffusion and resistance to mass transfer as causes of non ideality in chromatography". Chem. Eng. Sc. 5: Youtube: HETP = height equivalent to a theoretical plate, a measure of the resolving power of the column [m] (Height = Length/number of plates=l/n) A = Eddy diffusion parameter, related to channeling through a non ideal packing [m] B = diffusion coefficient of the eluting particles in the longitudinal direction, resulting in dispersion [m 2 s 1 ] C = Resistance to mass transfer coefficient of the analyte between mobile [m] and stationary phase [s] u = Linear Velocity [m s 1 ] 2

3 Schematics and a picture of a GC MS instrument autosampler Quadrupole Ion trap Time of flight (TOF) Orbitrap GC column and oven GC controller Figure with chemical structures of GC columns and column selection: en_gc_csg.pdf 3

4 Applications: access/gc ms technique and its analytical applications in science and technology pdf Environmental monitoring Food, beverage, flavor, and fragrance analysis Forensic and criminal cases Biological and pesticides detection Fermentation control Security and chemical warfare agent detection Astro chemistry and Geo chemical research Medicine and Pharmaceutical Applications Petrochemical and hydrocarbon analysis Clinical toxicology Energy and fuel applications Industrial use Academics Slides with your specific projects Fatty acid analysis Spider hormones Caffeine in urine Sugar alcohols 4

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6 The Nitrogen Rule Compounds* that contain even number of N atoms have even number of nominal molecular weight Compounds* that contain odd number of N atoms have odd number of nominal molecular weight But what about singly protonated molecules and accurate molecular weights?? * Common organic compounds Ion Stabilities Even electron ions are more stable than odd electron (radical) ions How about protonated molecules: even electron or not? And how about ions formed by electron impact (EI) ionization? 6

7 Selected Isotope Ratios and 13C Contributions Accurate elemental masses: C: H: O: N: Cl: Br: S: Use of Isotope Ratios to Distinguish Structures 7

8 Increasing 13C contribution in polyalanines R e la tiv e In te n s ity R e la tiv e In te n s ity (exact mass) (average mass) m / z (Ala) 5 C 15 H 29 O 6 N m (exact mass) (average mass) / z (Ala) 25 C 90 H 129 O 26 N 25 (Ala) 25 C 90 H 129 O 26 N (nominal mass) R e la tiv e In te n s ity (exact mass) (average mass) (Ala) 50 C 150 H 252 O 51 N (nominal mass) m / z 8

9 R e la tiv e In te n s ity a (average mass) [Ala 5 +H] (exact mass) D eviance from nom inal m ass (dalton) c average mass exact mass m /z m /z 100 b (average mass) R e la tiv e In te n s ity [Ala 50 +H] (exact mass) m /z [Ala 120 +H] + 9

10 Characteristic Isotope Distribution of Selected Transition Metal Elements 10

11 Origin of m/z 190? Metal element? 11

12 Transition Metal? Isotope Ratios to Identify Chemical Compositions No Accurate Mass! 12

13 Isotope Ratios to Identify Chemical Compositions No Accurate Mass! What Happened? 10 B: 25% 11 B: 100% 13

14 Renormalized Isotope Distribution in the M +. Region Identify Compounds

15 Identify Compounds Halogen? Identify Compound Use Isotope Distribution in the M +. Region 15

16 Identify Compounds 16