@article{Johnson2014,
	title = {Quantitative solid-state {13C} {NMR} with signal enhancement by multiple cross polarization},
	volume = {239},
	issn = {10907807},
	url = {http://www.sciencedirect.com/science/article/pii/S1090780713003005},
	doi = {10.1016/j.jmr.2013.11.009},
	abstract = {A simple new method is presented that yields quantitative solid-state magic-angle spinning (MAS) (13)C NMR spectra of organic materials with good signal-to-noise ratios. It achieves long ({\textgreater}10ms) cross polarization (CP) from (1)H without significant magnetization losses due to relaxation and with a moderate duty cycle of the radio-frequency irradiation, by multiple 1-ms CP periods alternating with (1)H spin-lattice relaxation periods that repolarize the protons. The new method incorporates previous techniques that yield less distorted CP/MAS spectra, such as a linear variation ("ramp") of the radio-frequency field strength, and it overcomes their main limitation, which is T1\$ρ\$ relaxation of the spin-locked (1)H magnetization. The ramp of the radio-frequency field strength and the asymptotic limit of cross polarization makes the spectral intensity quite insensitive to the exact field strengths used. The new multiCP pulse sequence is a "drop-in" replacement for previous CP methods and produces no additional data-processing burden. Compared to the only reliable quantitative (13)C NMR method for unlabeled solids previously available, namely direct-polarization NMR, the measuring time is reduced by more than a factor of 50, enabling higher-throughput quantitative NMR studies. The new multiCP technique is validated with 14-kHz MAS on amino-acid derivatives, plant matter, a highly aromatic humic acid, and carbon materials made by low-temperature pyrolysis.},
	journal = {Journal of Magnetic Resonance},
	author = {Johnson, Robert L and Schmidt-Rohr, Klaus},
	month = feb,
	year = {2014},
	pmid = {24374751},
	keywords = {Aromaticity, Complex organic matter, Cross polarization, MPCP, Quantitative CP, Ramp CP},
	pages = {44--49},
}

{"_id":"pKJ3wSr93nXqzZokA","bibbaseid":"johnson-schmidtrohr-quantitativesolidstate13cnmrwithsignalenhancementbymultiplecrosspolarization-2014","author_short":["Johnson, R. L","Schmidt-Rohr, K."],"bibdata":{"bibtype":"article","type":"article","title":"Quantitative solid-state 13C NMR with signal enhancement by multiple cross polarization","volume":"239","issn":"10907807","url":"http://www.sciencedirect.com/science/article/pii/S1090780713003005","doi":"10.1016/j.jmr.2013.11.009","abstract":"A simple new method is presented that yields quantitative solid-state magic-angle spinning (MAS) (13)C NMR spectra of organic materials with good signal-to-noise ratios. It achieves long (\\textgreater10ms) cross polarization (CP) from (1)H without significant magnetization losses due to relaxation and with a moderate duty cycle of the radio-frequency irradiation, by multiple 1-ms CP periods alternating with (1)H spin-lattice relaxation periods that repolarize the protons. The new method incorporates previous techniques that yield less distorted CP/MAS spectra, such as a linear variation (\"ramp\") of the radio-frequency field strength, and it overcomes their main limitation, which is T1$ρ$ relaxation of the spin-locked (1)H magnetization. The ramp of the radio-frequency field strength and the asymptotic limit of cross polarization makes the spectral intensity quite insensitive to the exact field strengths used. The new multiCP pulse sequence is a \"drop-in\" replacement for previous CP methods and produces no additional data-processing burden. Compared to the only reliable quantitative (13)C NMR method for unlabeled solids previously available, namely direct-polarization NMR, the measuring time is reduced by more than a factor of 50, enabling higher-throughput quantitative NMR studies. The new multiCP technique is validated with 14-kHz MAS on amino-acid derivatives, plant matter, a highly aromatic humic acid, and carbon materials made by low-temperature pyrolysis.","journal":"Journal of Magnetic Resonance","author":[{"propositions":[],"lastnames":["Johnson"],"firstnames":["Robert","L"],"suffixes":[]},{"propositions":[],"lastnames":["Schmidt-Rohr"],"firstnames":["Klaus"],"suffixes":[]}],"month":"February","year":"2014","pmid":"24374751","keywords":"Aromaticity, Complex organic matter, Cross polarization, MPCP, Quantitative CP, Ramp CP","pages":"44–49","bibtex":"@article{Johnson2014,\n\ttitle = {Quantitative solid-state {13C} {NMR} with signal enhancement by multiple cross polarization},\n\tvolume = {239},\n\tissn = {10907807},\n\turl = {http://www.sciencedirect.com/science/article/pii/S1090780713003005},\n\tdoi = {10.1016/j.jmr.2013.11.009},\n\tabstract = {A simple new method is presented that yields quantitative solid-state magic-angle spinning (MAS) (13)C NMR spectra of organic materials with good signal-to-noise ratios. It achieves long ({\\textgreater}10ms) cross polarization (CP) from (1)H without significant magnetization losses due to relaxation and with a moderate duty cycle of the radio-frequency irradiation, by multiple 1-ms CP periods alternating with (1)H spin-lattice relaxation periods that repolarize the protons. The new method incorporates previous techniques that yield less distorted CP/MAS spectra, such as a linear variation (\"ramp\") of the radio-frequency field strength, and it overcomes their main limitation, which is T1\\$ρ\\$ relaxation of the spin-locked (1)H magnetization. The ramp of the radio-frequency field strength and the asymptotic limit of cross polarization makes the spectral intensity quite insensitive to the exact field strengths used. The new multiCP pulse sequence is a \"drop-in\" replacement for previous CP methods and produces no additional data-processing burden. Compared to the only reliable quantitative (13)C NMR method for unlabeled solids previously available, namely direct-polarization NMR, the measuring time is reduced by more than a factor of 50, enabling higher-throughput quantitative NMR studies. The new multiCP technique is validated with 14-kHz MAS on amino-acid derivatives, plant matter, a highly aromatic humic acid, and carbon materials made by low-temperature pyrolysis.},\n\tjournal = {Journal of Magnetic Resonance},\n\tauthor = {Johnson, Robert L and Schmidt-Rohr, Klaus},\n\tmonth = feb,\n\tyear = {2014},\n\tpmid = {24374751},\n\tkeywords = {Aromaticity, Complex organic matter, Cross polarization, MPCP, Quantitative CP, Ramp CP},\n\tpages = {44--49},\n}\n\n\n\n\n\n\n\n\n\n\n\n","author_short":["Johnson, R. 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