Mass spectrometry aldehydes

Mass Spectrometry Aldehydes and ketones typically give a prominent molecular ion peak m their mass spectra Aldehydes also exhibit an M— 1 peak A major fragmentation pathway for both aldehydes and ketones leads to formation of acyl cations (acylium ions) by cleavage of an alkyl group from the carbonyl The most intense peak m the mass spectrum of diethyl ketone for example is m z 57 corresponding to loss of ethyl radi cal from the molecular ion... 

An example of how information from fragmentation patterns can be used to solve structural problems is given in Worked Example 12.1. This example is a simple one, but the principles used are broadly applicable for organic structure determination by mass spectrometry. We ll see in the next section and in later chapters that specific functional groups, such as alcohols, ketones, aldehydes, and amines, show specific kinds of mass spectral fragmentations that can be interpreted to provide structural information. 

To identify the specific aldehyde that is actually involved in the light-emitting reaction of living luminous bacteria, Shimomura et al. (1974a) extracted and purified the aldehyde from 40 g each of the bacterial cells of P. phosphoreum, Achromobacter (Vibrio or Photobacterium) fischeri, and an aldehydeless mutant of A. fischeri. The aldehyde fractions were purified, and then oxidized with Tollens reagent (silver oxide dissolved in ammonia) to convert the CHO group into the COOH group. Then the acids obtained were analyzed by mass spectrometry. The results indicated that P. phosphoreum had contained a mixture of aldehydes dodecanal (5%), tetradecanal (63%) and hexadecanal (30%), as shown in Table 2.2. Thus, tetradecanal was clearly predominant in... 

Properties of panal (Nakamura etal., 1988a). Purified panal is a colorless, amorphous solid, soluble in alcohols, water, ethyl acetate, and chloroform. The absorption spectrum (Fig. 9.3) shows a single peak (A.max 217nm, e 15,300). Optical rotation [a]D —17° (c 0.9, methanol). Mass spectrometry and NMR analysis showed that panal is a sesquiterpene aldehyde, C15H18O5 (Mr 278.30), with the structure shown below. 

For those aldehydes and ketones which are volatile enough, gas chromatography of the headspace gases can be used, and this has been used to measure acetone, butyraldehyde, and 2-butanone in oceanic waters. In a gas chromatography-mass spectrometry analysis of a single sample of volatile materials concentrated from inshore waters onto Tenax GC, MacKinnon [ 139] reported tentative identification of methyl isopropyl ketone, bromoform, 4-methyl-2-pentanone, 2-hexanone, and 2-hexanal. 

For more volatile compounds in soils, such as aromatic hydrocarbons, alcohols, aldehydes, ketones, chloroaliphatic hydrocarbons, haloaromatic hydrocarbons, acetonitrile, acrylonitrile and mixtures of organic compounds a combination of gas chromatography with purge and trap analysis is extremely useful. Pyrolysis gas chromatography has also found several applications, heteroaromatic hydrocarbons, polyaromatic hydrocarbons, polymers and haloaromatic compounds and this technique has been coupled with mass spectrometry, (aliphatic and aromatic hydrocarbons and mixtures of organic compounds). 

Preparation of 4-12-cvclohexenvloxv )-stvrene. A stirred mixture of 34.36g (0.096 mole) methyltriphenylphosphonium bromide and 10.75g (0.096 mole) potassium t-butoxide in 200ml dry THF is treated drop-wise with a solution of 16.16g (0.080 mole) of 4-(2-cyclohexenyl)-benzaldehyde in 30ml THF under inert atmosphere. Once the addition of aldehyde was completed, the mixture was stirred at room temperature for another 2 hours. Ether and water were then added to the reaction mixture until clearly separated phases were obtained with no solid residue. The organic layer was separated and washed three times with water, dried over magnesium sulfate and evaporated. The resulting semi-solid was triturated in 10% ethyl acetate-hexane mixture to remove most of the triphenylphosphine and the evaporated extract was purified by preparative HPLC using hexane as eluent. This afforded 9.35g (58%) of the pure monomer, which was fully characterized by H and C-NMR as well as mass spectrometry. 

Liedtke, R.J. Djerassi, C. Mass Spectrometry in Structural and Stereochemical Problems. CLXXXIII. A Study of the Electron Impact Induced Fragmentation of Aliphatic Aldehydes. J. Am. Chem. Soc. 1969,97,6814-6821. 

Nagy K, PoUreisz F, Takats Z, Veky K. 2004. Atmospheric pressure chemical ionization mass spectrometry of aldehydes in biological matrices. Rapid Commun Mass Spectrom 18 2473. 

Peters R, Hellenbrand J, Mengerink Y, Wal Van der S. 2004. On-line determination of carboxylic acids, aldehydes and ketones by high-performance liquid chromatography-diode array detection-atmospheric pressure chemical ionization mass spectrometry after derivatization with 2-nitrophenylhydrazine. J Chromatogr A 1031 35. 

Identification. Identification of the carbonyl PFBOA derivatives was performed by mass spectrometry using electron impact ionization running in the scan mode. It was confirmed that fragment m/z 181 was the main fragment of all analyzed aldehydes (6). Figure 1 shows as an example the mass spectrum of the PFBOA derivative of methi-onal. To increase the selectivity of the method, all aldehyde analyses were run in the... 

Analysis of Aldehydes in Beer Using Solid-Phase Microextraction with On-Fiber Derivatization and Gas Chromatography/Mass Spectrometry. 

A new, fast, sensitive, and solventless extraction technique was developed in order to analyze beer carbonyl compounds. The method was based on solid-phase microextraction with on-fiber derivatization. A derivatization agent, 0-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBOA), was absorbed onto a divinyl benzene/poly(dimethylsiloxane) 65- xm fiber and exposed to the headspace of a vial with a beer sample. Carbonyl compounds selectively reacted with PFBOA, and the oximes formed were desorbed into a gas chromatograph injection port and quantified by mass spectrometry. This method provided very high reproducibility and linearity When it was used for the analysis of aged beers, nine aldehydes were detected 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, pentanal, hexanal, furfural, methional, phenylacetaldehyde, and (E)-2-nonenal. (107 words)... 

Vesely, R Lusk, L. Basarova, G. Seabrooks,J. Ryder, D. Analysis of Aldehydes in Beer using Solid-Phase Microextraction with On-Fiber Derivatization and Gas Chromatography/ Mass Spectrometry. J. Agric. Food Chem. 2003, 51, 6941-6944. 

The second example was the pyruvate decarboxylase catalyzed formation of (ll )-l-hydroxy-l-phenyl-2-propanone (PAC) with benzaldehyde as substrate (Fig. 5 a) [64]. This second reaction shows one potential limitation of this method. Some compounds are too volatile for direct measurement by MALDl mass spectrometry or they do not ionize directly due to their nonpolar character. In this case, these compounds have to be derivatized prior to their measurement in order to reduce their volatihty and to introduce ionizable functions. This is, however, often very easy using well estabhshed quantitative reactions, e.g., formation of oximes from aldehydes and sugars (Fig. 5b). 

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