Charged tag founded in N-(1-chloroalkyl)pyridinium quaternization for quantification of fatty aldehydes

• A new derivatization method named N-(1-chloroalkyl)pyridinium quaternization was developed to label fatty aldehydes.
• All the reagents are commercially available and could be removed by adding deionized water.
• Thirteen kinds of free fatty aldehydes (C6C18) were detected in human thyroid tissues.
• Concentrations of long chain nonvolatile fatty aldehydes (C10C18) in thyroid carcinoma tissues were higher than those in paired para-carcinoma tissues (p < 0.05).

N-(1-chloroalkyl)pyridinium quaternization was developed for the derivatization of fatty aldehydes. Differing from common pre-charged reagents, non-charged pyridine and thionyl chloride were designed to add permanently charged tag on aldehydes. Pyridine was far less competitive than charged derivatives in ionization. Thionyl chloride in excess was quenched by deionized water, converting into less residual sulfur dioxide bubbles. Thus solutions could be tested directly by mass spectrometry without further post-treatments. Pyridine-d5 labeled fatty aldehydes were prepared as internal standards. Mixed derivatives were then analyzed by high performance liquid chromatography coupled to positive electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS). Analytical parameters including reaction yield, stability, precision, linearity, and detection limits (LODs < 0.3 pg mL−1) were carefully validated. This method facilitated the analysis low content (ng mL−1) levels of free aliphatic aldehydes (C6C18) in human thyroid carcinoma and para-carcinoma tissue with a simple pretreatment procedure. Content of long chain nonvolatile aldehydes (C10C18) remarkably increased in thyroid carcinoma tissues (p < 0.05).

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