COLNAGO, L. A.

GONZÁLEZ PÉREZ, M.

KNICKER, H.

MARTIN NETO, L.

NUNO, C. S.

TORRADO, P. V.

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Evaluation of magnetic field effect on quantification of aromatic components of humic acids by 13C CPMAS NMR.

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NUCLEAR MAGNETIC RESONANCEBEJOlR/~ USERS MEETI NG'::r:~j.' ~~!t,\lIUREMN,~ Workshop:~'I!/JIl"m NMR in South AmericarJ1!N1 {jfil c 'lJ 'lJffilv ~~@@~o~~~[lli)D~Extended Abstracts Book, ,'h Nuclear Magnetic Resonance Users Meeting / Workshop: NMR in South America May. 7-". Rio de Janeiro. BrazilEVALUATION OF MAGNETIC FIELD EFFECT ON QUANTIFICATION OF AROMATICCOMPONENTS OF HUMIC ACIDS BV 13CCPMAS NMRMartha González Pérez1•2('), Cristina Santín Nuno ', Luiz Alberto Colnaqo", Heike Knicker",Pablo Vidal Torrado'. Ladislau Martin Neto27. Escola Superior de Agricultura "Luiz de Oueiroz" (EsALQ-USP).Departamento de Solos e Nutrição de Plantas. C.P. 09. CEP 73478-900. Plrecicebe-Sp. Brazil.2. Embrapa tnstrumemeçéo Aqropecuerie. c.e. 741. CEP: 13560-970. São Certos, sr. Brazil.3. INDUROT, Universidad de Oviedo. Campus de Mieres, 33600 Mieres. Asturias. Spein.4. Technische Universitet München, Oepertment of Soit Science. 85350. Freising-Weihenstephan. Germany.(') e-mail: marta@cnpdia.embrapa.brKeywords: soil humic acids; NMR; VACP/MASHigh resolution 13C NMR spectroscopy. acquired with the CPMAS technique. nas been a powerful toei toanalyze chemical composition of soil organic mater (SOM), since 19801. The principal application of theCPMAS technique has been the quantification of the structural components of humic substances such as theamount of aromatic, aliphatic, carbonyl and carboxyl groups. As in ali NMR áreas. the use of high magneticfield spectrometers to SOM analysis has beco me popular. However, the uses of high magnetic fieldspectrometers (HMF) have introduced some undesirable effects. One of these effects, caused by MAS, hasbeen the cross-polarization profile breakage down. As the speed of MAS increase with the magnetic field, theoscillatory behavior of conventional CP became worse and consequently the quantification of the NMRsignals. For this reason it is not possible to compare the SOM group quantification obtained by CPMAS indifferent magnetic field spectrometers. To minimize this problem, Peerson introduced in 19932 the variableamplitude cross polarization (VACP) procedure that reduces oscillatory behavior of CP. This technique hasbeen used in most SOM NMR analysis up to 9.4 T, but as we are showing in this paper it is not enough tosolve the problem in higher field such as 17.6T (750 MHZ for 1H). The aim of the present work is to show thepoor efficiency of VACP pulse sequence in high magnetic field.The soil samples were collected from a reclaimed estuary in Asturias. Sp"ill. 11W;IS ~cl()ctc<l :1 pl()lil(~ IIIHIIlIpasture. The samples were collected at 0-20 cm depth (Pa). 40-GO em r1(~plll (I '11) ;l11C1110101111111()(l 1:111depth (Pc). Humic acids were extracted using the IHSS rnethod (cxtracuou with () 1 11101I I NI1(JlI 1111<1precipitatian with 6 moi L-1HCI).13C VACP/MAS NMR spectra were acquired with a Bruker DSX 2()() "IWCIIC1l1l11111l11111" "{' "''lOI1l111CPfrequency of 50.32 MHz. The samples were confined in a zirconium oxit k: lol()1 11111VIII1111, 11nlllJllllllcln c111',.polarizatian magic angle spinning technique was applied with <1 contact urru: 01 I 111'"1\ ",,1111111111" 1(1(1111IkHz and a pulse delay af 1 s. The spectra were subdivided imo clillerunt c:IIC!IIIICII ',Ilill lI!qu 111',Illk yl I. (O ~ripprn), N-alkyllmethaxyl C (45-60 pprn). O-alkyl C (60-110 ppm). aromatic-t : (110- lfiO j)1UIi). 11111loxyl t: (11111185 ppm) and carbonyl-C (185-245 ppm). The relative nC intensity distribuuon w"" c\(;jC:11I111i(:cI I 'y IIIII!( 1111111111the signal intensity in different chemical shift regions with an inteqration rouunc SlIpplic!cI wlIII 111(:111',1111 1li 1111software. The same technique and parameters were used on a Varian Unity 750 spcctronu-u» ;11Ilu~ I 'I:resonance frequency of 188.55 MHz.The figure 1andfigure 2 shaw the spectra measured on a 5 and 17.6 T spectrometers, respectively. I noshape and the intensity of resanance lines from aliphatic region from O to 110 ppm are similar in bathspectrometers. However, resonance lines from aromatic region from 110 to 165 ppm is are very weak 011spectra measured at 17.6 T. Most of the signals in this region is associated to the side band of the carboxylsignals at 183 ppm.The real aromatic region signal obtained at 17.6 T is shown in figure 3, after subtracting the side bands. Thisresult indicates the difficulties involved in the quantification of aromatic groups at HMF and cansequently thecamparison with published results.101Associaçào de Usuários de Ressonáncia Magnética Nuclear AUREMNPRADOlOO 250 200 150 \00 50ppm-so .100·Figure 1. 13CNMR VACP MAS spectra measured on a Bruker200 MHz spectrameter.Figure 2. 13CNMR VACP MAS spectra measured an a Varian750 MHz spectrometer.\ I =::SUlt IIh\~\ .,300 250 200 150 100 50 o ·50 ·100ppmFigure 3. 13C NMR VACP MAS spocrra 1I11~;I~un~don aVarian 750 MHz spectrameter after ~lILJII;\C1il\g tI\C! suonqside bands.Our results show the poor efficiency of VACP pulse SCQII(!I1CC111Iliqll magnetic field demonstrated by thedramatic suppression of aromatic signals from humic élr.ills .. IIIIIS. '!lw recommendation for SOM NMRresearchers is to be careful with the utilization 01 !-IMI 1)(!CiIlI',I' I/lI' VI\CP tcchnique has not been efficientenough to minimize the oscillatory behavior of convcntional CI' !1I1c1('1111:1111:0.lhe quality of spectra.REFERENCES1. Wilson. MA. 1987. NMR Techniques and Applicrniou- 1II (~lIllt'll!11111'-.1IY 1111t1';lIlIl:llI~lnistry. Pergamon Press. Oxford.2. Peersen. O.B.; Xiaaling. W.; Kustanavich. 1.; Smuh. c, I1 I Ilf,Ju (,', r-, 'I 11111:\IIH. U~.r I\prsp. EMBRAPA and CNPq/PACDT102

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Evaluation of magnetic field effect on quantification of aromatic components of humic acids by 13C CPMAS NMR.

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