Letter: α,ω,N,N-Dimethylaminoalkylamines as possible derivatization agents for the analysis of small carbonyl compounds by low energy mass spectrometry

Reaction with α,ω-N,N-dimethylaminoalkylamines (2-dimethylaminoethylamine, 3- dimethylaminopropylamine, 4-dimethylaminobutylamine) to form Schiff bases followed by quaternization of the N,N-dimethylamino group by alkyl (deuteroalkyl) halides to generate fixed-charge fragments is suggested for the characterization of carbonyl compounds by matrix-assisted laser desorption ionization (MALDI) mass spectrometry. As model objects, some aliphatic aldehydes and alicyclic and steroid ketones were involved in the modification. Using gas chromatography mass spectrometry, the first modification stage proved to be quantitative. Not only the MALDI conditions but also the nanostructurized target provided spectra that revealed peaks for the cationic parts of derivatives. It was shown that the use of deuterated alkyl halides allows one to prepare deuterium-labeled standards for possible quantitative analysis.

Characterization of low-molecular weight iodine-terminated polyethylenes by gas chromatography/mass spectrometry and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry with the use of derivatization

Gas chromatography/mass spectrometry (GC/MS) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry, in conjunction with various derivatization approaches, have been applied to structure determination of individual oligomers and molecular-mass distributions (MMD) in low-molecular mass polyethylene having an iodine terminus. Direct GC/MS analysis has shown that the samples under investigation composed of polyethyelene-iodides (major components) and n-alkanes. Exchange reaction with methanol in the presence of NaOH gave rise to methoxy-derivatives and n-alkenes. Electron ionization mass spectra have shown that the former contained terminal methoxy groups indicating the terminal position of the iodine atom in the initial oligomers. MMD parameters have been determined with the aid of MALDI mass spectrometry followed by preliminary derivatization-formation of covalently bonded charge through the reaction of iodides with triphenylphosphine, trialkylamines, pyridine or quinoline. The mass spectra revealed well-resolved peaks for cationic parts of derivatized oligomers allowing the determination of MMD. The latter values have been compared with those calculated from GC/MS data.

Matrix effect in matrix-assisted laser desorption/ionization mass spectra of derivatized oligomeric polyols

RATIONALE

Herein we describe a strong matrix effect observed in the matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectra of silylated glycerol alkoxylates and manifested in the loss of the silyl groups in the presence of carboxyl-containing matrices.

METHODS

Commercially available glycerol alkoxylates containing three end OH groups as well as three matrices - 2,5-dihydroxybenzoic acid (DHB), 3-indoleacrylic acid (IAA) and 1,8,9-anthracenetriol (dithranol) - were chosen for the investigation. N,O-Bis(trimethylsilyl)trifluoroacetamide containing 1% trimethylchlorosilane, acetic anhydride and a formylation mixture (formic acid/acetyl chloride) were used for derivatization. Initial oligomers and derivatized products were analyzed by MALDI-ToF-mass spectrometry (MS) on an Autoflex II instrument, equipped with a nitrogen laser (λ 337 nm), in positive ion reflectron mode.

RESULTS

Only [M + Na](+) ions were observed for underivatized polymers and for completely derivatized polymers in the presence of DHB and dithranol, respectively. In the case of IAA the mass spectra revealed sets of peaks for underivatized, and for partially and completely derivatized oligomers. No similar 'matrix effect' was observed in the case of acylated glycerol alkoxylates (acyl = formyl, acetyl): only peaks for completely derivatized oligomers were obtained in all matrices: DHB, IAA and dithranol. Using 1,9-nonandiol, we showed that the 'matrix effect' was due to trans-silylation of carboxyl-containing matrices (DHB and IAA) during co-crystallization of silylated oligomers and matrices.

CONCLUSIONS

The obtained results show that matrix molecules can participate as reactive species in MALDI-ToF-MS experiments. The matrix should be carefully chosen when a derivatization approach is applied because the analysis of spectra of the completely derivatized products is particularly desirable in the quantitative determination of functional end-groups.

New suitable deprotonating matrices for the analysis of carboxylic acids and some acidic compounds by matrix-assisted laser desorption/ionization mass spectrometry in negative ion mode

RATIONALE

Direct non-derivatization analysis of organic acids and acidic compounds by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) in positive ion mode is not always possible due to the low ionization efficiency of analytes. Some new efficient deprotonating matrices were suggested that allowed the production of negative ions from acidic compounds during MALDI-MS experiments.

METHODS

Various tested carboxyl-containing compounds as well as compounds with acidic properties were mixed with the suggested deprotonating matrices [4-dimethylaminobenzaldehyde (DMABA), N,N-dimethylamino-p-phenylenediamine or 3-aminoquinoline] and applied on a standard MALDI target followed by recording MALDI mass spectra in negative ion mode.

RESULTS

All the tested acidic compounds mixed with the suggested deprotonating matrices produced abundant [M - H]^- ions under MALDI conditions. DMABA produced the strongest signals reflecting greater sensitivity of analysis.

CONCLUSIONS

The suggested deprotonating matrices are commercially available compounds and are good alternatives to well-known matrices of this kind and, in particular, the often used 9-aminoacridine. DMABA is the best of the tested potential matrices and is suitable for the detection of low molecular weight carboxyl-containing compounds, substituted phenols, and mixtures of naphthenic acids by (-)MALDI-MS.

Synthesis and photophysical properties of novel oxadiazole substituted BODIPY fluorophores

Using 3-phenyl-5-(5-phenyl-1H-pyrrol-3-yl)-1,2,4-oxadiazole, BODIPYs with the oxadiazole groups at the 1,7-positions were prepared and their photophysical properties were characterized.

Synthesis and photophysical properties of 1,7-aroyl BODIPYs: an experimental and theoretical study

The introduction of electron donating groups or electron withdrawing groups into the phenyl ring at the meso position of 1,7-aroyl BODIPY significantly influences the fluorescence quantum yield.

Electron ionization mass spectra of alkylated sulfabenzamides

Mono-, di- and trialkyl derivatives of 'sulfabenzamide' (N-4-aminophenylsulfonylbenzamide) have been prepared and their electron ionization (EI) mass spectra examined. It is found that the fragmentation of N-alkylsulfabenzamides (alkyl = CH(3) to n-C(5)H(11)) proceeds via a very specific rearrangement process. The proposed mechanism involves an intermediate formation of distonic molecular ions, and the driving force for this process is the formation of stable N-alkylphenylcyanide cations [R-N(+)≡CC(6)H(5)]. The findings are confirmed by exact mass measurements, tandem mass spectrometry (MS/MS) experiments and deuterium labeling.