Highly sensitive determination of total free amino acids by carbon optical emission spectrometry coupled with headspace injection

Amino acids are widely involved in the processes of biosynthesis and physiological activities, as important basic substances for synthesis and metabolism in living organisms. The content of free amino acids in food, environment and clinical medicine fields, is of great significance for nutritional evaluation and health monitoring. Herein, a new method was proposed for rapid and sensitive determination of total free amino acids (TFAA), through detecting the carbon optical emission spectrometry (OES) of CO 2 , which was converted from the amino acids reacted with ninhydrin. All the free amino acids were converted into CO 2 without any pre-separation steps. To improve the sensitivity and convenience, headspace injection was utilized to pre-concentrate the generated CO 2 , and subsequently directly transported to a miniature microplasma excitation source for detecting the characteristic emission line of carbon at 193.04 nm. Under the optimal experimental conditions, the achieved limit of detection (LOD) was 0.17 μM, and the relative standard deviation (RSD) was 4.9% (65 μM, n = 7). It has been successfully applied to the determination of TFAA in a variety of certified reference materials (CRMs) and real samples to prove its accuracy and reliability. Moreover, owing to the small size, low power and reduced time consumption of the proposed method and instrument, it is promising for rapid screening and on-site analysis in various fields.