Nuclear Magnetic Resonance (NMR) spectroscopy for the study of organic compounds and functional groups

Transcription

1 Nuclear Magnetic Resonance (NMR) spectroscopy for the study of organic compounds and functional groups S. Decesari, M. Paglione, N. Zanca, E. Finessi, F. Moretti (Institute of Atmospheric Sciences and Climate, National Research Council of Italy)

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3 ES&T 2001

4 NMR AND ATMOSPHERIC AEROSOL Major defects inherent to NMR spectroscopy: Poor sensitivity, Very poor sensitivity of the advanced, most informative techniques ( 13 C, 15 N, 2D), Implementations for OA on-line measurements unsuitable, Automaticity in analysis not always suitable, Requires adequate access to NMR facilities (depending on applications).

5 13 C NMR spectra of water-soluble organic aerosol samples (from 8 x 24 h HiVol samples!) Sannigrahi et al., ES&T 2006

6 How NMR spectra of atmospheric aerosol look like: Importance of the magnetic field NIST1648 standard of urban aerosol (Saint Louis) 800 MHz 500 MHz Experiments performed at the EMSL PNNL, Richland, WA

7 The proton chemical shift (DMSO-d 6 ) 1,3,5-TMB SOA (D 2 O) HO HO O O O HOOC COOH

8 Effect of multiplicity 3O L L 3O 3O 5O 5O 5O 5O 5O 5O Suzuki et al., ES&T 2001

9 Effect of multiplicity

10 Effect of multiplicity X NH 2 + DEA + Facchini et al., ES&T 2008

11 A classical use of NMR: studying reaction products and kinetics in organic and aqueous solutions Hu et al., Thermodynamics and kinetics of the hydrolysis of atmospherically relevant organonitrates and organosulfates, Atmos. Chem. Phys., 11, , 2011

12 A classical use of NMR: studying reaction products and kinetics in organic and aqueous solutions Zhao et al., Formation of aqueous-phase -hydroxyhydroperoxides ( -HHP): potential atmospheric impacts, Atmos. Chem. Phys., 13, , 2013

13 NMR for molecular identification in SOA samples -pinene ozonolysis (PSI chamber) x x x x Pinonic acid

14 NMR for molecular identification in SOA samples Methyl-tetrols x Isoprene SOA from low-nox photooxidation experiments

15 Finessi et al. (Anal. Chem. 2014) LC-NMR

16 Availability of 1 H-NMR chemical shift data for SOA tracers pinonaldehyde, pinonic acid, pinic acid, norpinonic acid, norpinic acid Schrader et al., J. Chrom., 2005, Chacon-Madrid et al. ACP 2013 methyl-tetrols and other tetrols Eddingsaas et al., JPC methylglyceric acid and esters Birdsall et al. ACP 2013 glycolic acid sulfate, lactic acid sulfate glyoxal (monomer, oligomers, imidazoles) Olson et al., EST 2010 Yu et al., EST 2011 methyl-glyoxal mono- and di-hydrate Donarski et al., Anal. Methods, methyl-1,2,3-butanetricarboxylic acid measured by Magda Claeys on synthetized standards

17 NMR for elucidating reaction mechanisms during SOA experiments (DMSO-d 6 ) 1,3,5-TMB SOA (D 2 O) HO HO O O O HOOC COOH

18 NMR for elucidating reaction mechanisms during SOA experiments Maksymiuk et al., Phys. Chem. Chem. Phys., 2009, 11,

19 NMR for elucidating reaction mechanisms during SOA experiments Renard et al., Radical mechanisms of methyl vinyl ketone oligomerization through aqueous phase OH-oxidation: on the paradoxical role of dissolved molecular oxygen, Atmos. Chem. Phys. Discuss., 13, , 2013

20 SOA systems studied by NMR spectroscopy H (1D) (in preparation) H (1D) Cavalli et al., ACP 2006, (in preparation) H (1D), COSY, HSQC Maksymiuk et al. PCCP 2009, Bones et al. JGR 2010 H (1D) Cavalli et al., ACP 2006 H (1D) (in preparation) H (1D) Angove et al., Atmos. Environ H (1D) (in preparation)

21 Aqueous SOA systems studied by NMR spectroscopy H (1D) Yu et al., ES&T 2011 H (1D) Chang and Thompson, Atmos. Environ H (1D), HSQC, HMBC Renard et al., ACPD 2013

22 NMR for molecular identification in ambient WSOA Levoglucosan (DL ~ 1 ng/m 3 )

23 Intercomparison of analytical techniques for anhydrosugars analysis concentration (µg punch -1 ) total mea n total RSD% EC- PAD1 EC- PAD2 EC- PAD3 EC- PAD4 EC- PAD5 EC- MS GC- MS1 GC- MS2 LC- MS NMR Levoglucosan lab mean lab I.C Pietrogrande et al., submitted

24 Alkyl-amines in Mace Head MACE HEAD (polluted easterly air masses) MACE HEAD (clean weasterly air masses) MSA DMA + MMA + MSA DMA + DEA + DEA + DEA + DEA chemical shift (ppm) chemical shift (ppm) Amines / WSOC = 6% (0.2 13%) MSA / WSOC = 1% (0 3%) Amines / WSOC = 12% (2 27%) MSA / WSOC = 8% (1 14%) Suzuki et al Facchini et al., ES&T 2008

25 Alkyl-amines Mace Head, Ireland DEA + DEA + DMA chemical shift (ppm) S. Pietro Capofiume, Po Valley, Italy TEA + TEA + DMA chemical shift (ppm)

26 Melpitz K-Puzsta Monte Cimone

27 100% OC GC/MS Not extracted or not eluted UCM Resolved not dentified Identified species 100% OC 1 H-NMR spectroscopy Not extracted UCM: unresolved complex mixture UCM UCM Resolved not dentified Identified species chemical shift (ppm)

28 NMR for chemical structure elucidation of ambient WSOA H-C-O H-C-C= H-C Ar-H Functional group budget can be used to constrain the choice of surrogates for WSOC in microphysical models (Fuzzi et al., GRL 2001; Decesari et al., ACP 2006)

29 NMR for chemical structure elucidation of ambient WSOA Acyls H 2 C H 2 C C=O C=O R OH 0.60 Aromatic/ aliphatic HC-C=O / sum aliphatics Marine OA SOA BB Hyyttiala clean Brazil BB UK SU rural Mace Head HC-O / sum aliphatics C H 2 C H 2 C H NH SO H H C C OH OR Alcoxyls

30 Derivatization 1 H-NMR Carboxylic acids to methyl-esters: (Tagliavini et al., ACP 2006) R 1 COOH + CH 2 N 2 CH 2 Cl 2 R 1 COOCH 3 Ketons to methylhydroxyl-imines: O R 1 + H 3 C O NH 2 R 2 (b.p C) CHCl 3 R 1 N O CH 3 R 2 (Moretti et al., ES&T 2008)

31 Carboxylic group distributions in fractions of WSOC µgc m HDO HDO HDO Ion-exchange chromatography NC (Neutral compounds) # * NC DEAE column a H-Ar MDA (Mono-/di-acids) HC-O HC-C= H-C µgc m MDA PA (Polyacids) H-Ar HC-O HC-C= H-C PA H-Ar HC-O HC-C= H-C µgc m (Tagliavini et al., ACP 2006) C-H =C-CH HC-O vinilyc aromatic COOH undefined

32 2D NMR spectroscopy HSQC COSY Duarte et al., EST 2008

33 more samples: the EUCAARI project ( )

34 EUCAARI May 2008 intensive observation period HULIS in Cabauw, K-Puztsa, Melpitz, Mace Head (all IOPs during May 2008) CBW_F2 - MPZ_F2 - KP O=C-(CH 2 ) n=1-3 -C=O HC-C=O 0.03 HC (with no aliphatic chains) aromatics HC-O CBW_F2 MPZ_F2 F4 Suwannee River fulvic acid

35 Factor analysis on collections of H-NMR spectra of WSOC samples MSA EPA-PMF 3.0v N-NMF_ Projected Gradient Positive Matrix Factorization of US Environmental Protection Agency (EPA) software 3.0v with Multilinear Engine (ME) algorithm Non-negative Matrix Factorization with Projected gradient bound-constrained optimization N-NMF_ Multiplicative MCR-ALS MCR-WALS Non-negative Matrix Factorization with multiplicative update approach Multivariate Curve Resolution-Alternating Least Squares Multivariate Curve Resolution-Weighted Alternating Least Squares

36 recovery (% OC) 100% 80% 60% 40% 20% 0% EGA extraction recovery FTIR NMR (FGs) IC AMS (FGs) 2D NMR (FGs) (n.i.) AMS (identified m/z) GC GC x GC x GC GC (n.i.) (n.i.) (n.i.) HR-MS techniques (identified m/z) NMR (molecular speciation) # resolved components (n.i.)

37 summary of advantages and shortcomings of NMR for atmospheric aerosol analysis 1. 1 H-NMR spectroscopy is a potential useful (underexploited) analytical tool for molecular identification in SOA and ambient OOA samples allowing quantification of polar molecules (polyols, amines) at ng/m 3 levels without derivatization. 2. In principle, 1 H-NMR analysis is a quasi-universal detection method for organic compounds, but practically the analysis is selective for compounds with simple J couplings between atoms. 3. The unresolved complex mixture (UCM) is even more prominent in 1 H-NMR analysis than in GC/MS but the intervals of chemical shift at which the UCM bands are found retain chemical information which can be used for functional group analysis. 4. Spectral analysis can be supported by factor analysis techniques for spectral deconvolution. 5. Fine structural analysis of both individual compounds and UCM functionalities can be achieved using a combination of 2D techniques, but with a much greater degree of sophistication with respect to 1 H-NMR methods and depending on the availability of large ( 1 mgc) samples. 6. Overall, NMR spectroscopy is a flexible analytical tool providing applications stretching from the pure functional group analysis to classical molecular speciation (with all intermediate steps ).

38 Conclusions 1. NMR analysis for atmospheric aerosol analysis is still in its infancy with only a moderate increase in use in the very recent years. The scarse availability of spectral libraries of atmospheric importance limits further developments. 2. With respect to chromatographic techniques, the selectivity of NMR spectroscopy is less influenced by the experimental conditions making this technique very useful for explorative analyses. 3. With respect to MS analysis, NMR spectroscopy is certainly less influenced by inorganic matrice effects. 4. The use of simple 1 H-NMR techniques provides simultaneous molecular speciation and functional group analysis with adequate sensitivity ( 100 µgc) for analytical purposes. 5. Extending the analysis from selected ( golden ) samples to series of samples provides opportunity to apply chemometric techniques for spectral deconvolution (hence increasing resolution). 6. A more detailed chemical characterization can be achieved employing poorly sensitive 2D ( 1 H- 1 H, or 1 H- 13 C) techniques but this approach, suitable only for golden samples, can pay back in providing info otherwise difficult to obtain. There is the problem of the long sampling times which increase the risk of artificacts and modifications.