3,4-Diaminobenzophenone as an Effective Reactive MALDI Matrix for Simple and Sensitive Detection of α-Ketoacid Compounds

Determination of α-ketoacids is very important for disease diagnosis as well as for quality control of food and pharmaceuticals. In order to determine α-ketoacids by a simple, rapid, and simultaneous method in complex samples, a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) method has been reported herein through the development of an efficient reactive matrix. In this method, a MALDI matrix, 3,4-diaminobenzophenone (DABP), is first used to generate imidazole derivatives through its rapid reaction with α-ketoacids, which enables simple, rapid, sensitive, and selective detection of α-ketoacids by MALDI-TOF MS. The ionization efficiency of α-ketoacids is significantly improved by the use of DABP as the reactive matrix, as compared with the common alkaline matrices, such as 1,5-diaminonaphthalene and 9-aminoacridine. After optimization, the proposed method shows a lower limit of detection (0.8 μM for α-ketoglutaric acid; 0.45 μM for pyruvic acid), good linearity (R2 > 0.999), high accuracy (95.1–102.9%), and acceptable reproducibility (RSD: 0.8–4.9%). Owing to the above advantages, this method can be successfully used for the determination of α-ketoacids in real samples, including α-KG-supplemented capsules, onions, and beer, thereby demonstrating its potential for routine determination of α-ketoacids in complex samples.