Identification of compound classes in soil and peat fulvic acids as observed by electrospray ionization tandem mass spectrometry

Soil and peat fulvic acids obtained from the International Humic Substances Society were fractionated by their solubility in methanol and analyzed by electrospray ionization tandem mass spectrometry. Precursor and product ion experiments produced mass spectra that indicated the presence of benzene, phenol, dihydroxy benzene, furan and thiophene carboxylic acids. Standards were used to substantiate the fragmentation patterns observed in the product ion spectra of the fulvic acid samples. This study makes significant progress into the direct identification of individual compounds in humic substances using a non-degradation technique.     

The proton magnetic resonance spectra of some disubstituted acetophenones

An accurate measurement of the chemical shifts and the coupling constants of some disubstituted acetophenones has been made. The acetophenones studied contained nitro, bromo or amino groups substituted in either the 3,4 or 2,5 positions. For compounds with no substituent adjacent to the acetyl group, the chemical shifts and the coupling constants estimated by the simple additivity of the substituent increments were found to be in reasonable agreement with the experimental values. The two nitro, bromo derivatives substituted in positions 2 and 5 probably prefer the conformer in which the proton H-6 is adjacent to the acetyl methyl group whilst the 3,4-disubstituted bromo, nitro and bromo, amino derivatives prefer the conformer in which the H-6 proton is adjacent to the carbonyl group.     

Substituent effects on meta-proton chemical shifts in substituted benzenes

The chemical shifts at infinite dilution and coupling constants of some meta-substituted nitrobenzenes (C₆H₄NO₂X) were determined in CDCI₃ solutions (X = CHO, OCH₃, CI, Br, NH₂, NO₂) and in CCI₄ solutions (X = OCH₃, CI, Br). Substituent effects on the chemical shift of the meta-hydrogen are analysed in terms of existing theories.     

Self-esterification of fulvic acid model compounds in methanolic solvents as observed by electrospray ionization mass spectrometry

The self-esterification of two fulvic acid model compounds in methanolic solvents was studied by electrospray ionization mass spectrometry (ESI-MS). The strongly acidic tetrahydrofurantetracarboxylic acid rapidly self-esterified to form mono- and dimethyl esters when stored in methanol, even at reduced temperatures. The weakly acidic analogue, cyclopentanetetracarboxylic acid, reacted minimally under the same conditions. The use of 50:50 methanol/water as a solvent reduced self-esterification of the strong acid. However, the presence of water promoted the formation of multiply charged ions in the ESI mass spectra. The use of water and 50:50 acetonitrile/water as solvents eliminated self-esterification but the mass spectra still contained multiply charged ions. This study implies that the use of methanolic solvents with humic substances may compromise analytical data through the formation of methyl esters.