Scheme of the detection procedure of sarcosine in human urine: The sample was divided into two portions, one them was added with sarcosine, and after filtration, centrifugation, and acidification, was tested with Tiiii-Si•1 (upper scheme). The other portion, after filtration, centrifugation, and acidification, was tested (control sample) with Tiiii-Si•1 (lower scheme). The XPS Br 3D spectra of Tiiii-Si•1 slides dipped (A) in the sarcosine-added sample and (B) in the control sample are reported sideways.