Improved sensitivity in mass spectrometric quantification of serum growth hormone (GH) by amphiphilic conjugation

Improved sensitivity in mass spectrometric quantification of serum growth hormone (GH) by amphiphilic conjugation

Cristian Arsene, Dirk Schulze and André Henrion

Physikalisch-Technische Bundesanstalt

38116 Braunschweig

Germany

Introduction

Enhancement of sensitivity was needed for a previously developed [1] mass spectrometric GH quantification method to be applicable with oral glucose suppression tests as used e.g. in diagnosis of acromegaly. Chemical modification of the substrate so as to reducing matrix suppression effects has been discussed several times [2] as a way to signal enhancement in electrospray-ionization mass spectrometry. Typically, the tags used are providing the molecule with additional charges and non polar regions in order to increase its chance to form cations in the electrospray.

Method

With the present study a new reagent, N-(3-Iodopropyl)-N,N,N-dimethyloctyl-ammonium iodide (IPDOA), has been used to obtain improved signals for the tryptic peptide aa42-64 (T6) chosen for quantification of GH. Modification by IPDOA was done after isolation of T6 (and labeled internal standard, T6*) from the serum digest by semipreparative 2D liquid chromatography (LC). Reversed phase LC/MS-MS was used for quantification of the peptide then.

Preliminary results

Method performance has been evaluated using GH-depleted serum spiked with recombinant hGH (22 kDa) at target concentrations 0.5, 1.0, 2.0, 4.0 and 8.0 µg/L. An improved LOQ (0.5 µg/L compared to previously 1.7 µg/L) and CV= 3.4% were found for the modified method.