Highly sensitive determination of methionine by solvent-based de-emulsification dispersive liquid-liquid microextraction using bio-stabilized silver nanoparticles

In this study, a solvent-based de-emulsification dispersive liquid-liquid microextraction method coupled with surface plasmon resonance of silver nanoparticles was developed for determination of trace levels of methionine. The stable and dispersed silver nanoparticles were synthesized by applying ascorbic acid as reducer and Stenotrophomonas sp. bacterial suspension as bio-stabilizer and then preconcentrated in organic phase according to a facile dispersive liquid-liquid microextraction procedure based on 1-octanol as extraction solvent, methyltrioctylammonium chloride (aliquat 336) as disperser and acetone as de-emulsifier. The presence of methionine influenced the intensity of plasmon resonance absorbance of silver nanoparticles, which was employed as a colorimetric probe for the determination of this amino acid. Under the optimal conditions, the linear analytical range of 5.6 to 234.5 nmol/L and a detection limit of 3.4 nmol/L were achieved for methionine. The relative standard deviation for seven replicate measurements of 33.5 and 107.2 nmol/L of methionine was 4.3 and 2.1%, respectively. The suggested method was successfully applied for the determination of methionine in biological samples.