Atmospheric pressure chemical ionization carotenoid analysis

Atmospheric Pressure Chemical Ionization (APCI)/MS APCI/MS is used to analyze compounds of intermediate molecular weight (100-1,500 da) and intermediate polarity and is particularly useful for the analysis of biochemicals such as triacylglycerides, carotenoids, and lipids (Byrdwell, 2001). For volatile, nonpolar compounds of low molecular weight, GC/MS is preferred to APCl/MS whereas APl-electrospray/ MS provides better results for larger, more polar materials. The selection of APCl/MS over GC/MS or APl-electrospray/MS depends on the compounds to be analyzed. Many LC/MS instruments can be easily switched between APCl/MS and APl-electrospray/MS so that it can be rapidly determined which ionization process is more suitable to a given chemical. Additional manipulations such as pre and postcolumn derivatization reactions (Nagy et al., 2004 Peters et al., 2004) or coulometric oxidation (Diehl et al., 2001) can make the chemicals of interest more amenable to detection by APCI. 

Pajkovic, N. van Breemen, R. 2005. Analysis of carotenoids using atmospheric pressure chemical ionization mass spectrometry. In Modem Methods for Lipid Analysis by Liquid Chromatography (Byrdwell, C., Ed.). AOCS Publishing, Champaign, IL, pp. 413 30. 

The first online coupling of TLC and MS for the analysis of carotenoids was applied for detection of neoxanthin, violaxanthin, lutein, and P-carotene in spinach extract. Separation on Cjg RP HPTLC plate was followed by extraction of the carotenoids by means of CAMAG TLC-MS interface. After the elution of compounds from the sorbent with methanol, 1% acetic acid was added to the effluent to augment the ionization in the atmospheric pressure chemical ionization (APCI) source, which operated in positive mode [25]. 

Lately, LC—MS analysis of carotenoids and retinoids has been reported for food matrices such as fish eggs [104] and infant formula [105,106]. Atmospheric pressure chemical ionization (APCI) is the method of choice for their detection in the positive ion mode Retinol gives an intense dehydrated pseudomolecular ion, [MH—H20], at zzz/z 269 retinyl esters are fragmented in the ion source producing [MH—fatty acid—H20] ions (i.e., retinol dehydrated at zzz/z 269) carotenoids generate several ions such as [M + H]" ", [M]" ", and [M—H]" ". The ESI interface is better for the ionization of xanthophylls when semiaqueous mobile phases are used for their separation. 

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