Admittance Relaxation Time Distribution (aRTD) for Quantification of Protein Concentration

The admittance relaxation time distribution (aRTD) has been proposed for the quantification of protein (albumin and ɣ-globulin) concentration $c$ . The aRTD extracts peaks of distribution function ɣ [S] at relaxation times $\tau $ [s] from measured admittance $Y$ [S]. In order to clarify the relationship between ɣ, $\tau $ , and $c$ , aRTD was performed on solutions and porcine subcutaneous adipose tissue (SAT) with an injected current frequency $f$ from 10 Hz to 1 MHz under the albumin concentration $^{\text {Alb}} {c}$ of 0.80–2.30 g/dL, the ɣ-globulin concentration $^{\text {Glo}} {c}~{R} ^{{2}}$ above 0.8, which is much larger than ${R} ^{{2}}$ between $c$ and P1 extracted by iRTD. The aRTD on SAT provides additional correlation through ɣP2 at $\tau _{\text {P2}}$ , which increases proportionally to $^{\text {Glo}} {c}$ and inversely proportional to $^{\text {Alb}} {c}$ and $^{\text {PM}} {c}$ . The average fitting error $\epsilon $ of aRTD is, moreover, smaller than $\epsilon $ of iRTD by 12%, which highlights aRTD accuracy in the fitting.