You have to trace the TG/DTG curve in nitrogen at a certain heating rate. by the analysis of DTG curve, the temperature range between onset and finish of the first process with mass loss is represented by the decomposition temperature. Please also take into accound that in inert atmosphere, it also exist the posibility of sublimation/evaporation, since quinoline is liquid which boils around 235 C.

Sir, I already carried TGA of our sample in presence of N2. However, I want some reference that I can add to my future publication.

Please attach the TA curve.  I only found this in ISIWEB:

Thermal decomposition of quinoline and isoquinoline. The role of 1-indene imine radical

By:Laskin, A (Laskin, A); Lifschitz, A (Lifschitz, A)

JOURNAL OF PHYSICAL CHEMISTRY A

Volume: 102

Issue: 6

Pages: 928-946

DOI: 10.1021/jp9729831

Published: FEB 5 1998

View Journal Information

Abstract

The thermal reactions of quinoline and isoquinoline were studied behind reflected shock waves in a pressurized driver single pulse shock tube over the temperature range 1275-1700 K and densities of similar to 3 x 10(-5) mol/cm(3). The decomposition products found in the postshock mixtures of quinoline and isoquinoline and their production rates were identical for both isomers. They were C2H2, C6H5CN, HC=CCN, C6H6, HCN, C6H5-C=CH, and C4H2. Trace quantities of C6H4, C5H5N and C5H4N-C=CH were also found, The total disappearance rates of quinoline and isoquinoline are the same, and in terms of a first-order fate constant they are given by k(total) = 10(13.0) exp(-75.5 x 10(3)/RT) s(-1) where R is expressed in units of cal/(K mol), The same product distribution in the two isomers can be accounted for if the production of I-indene imine radical as an intermediate is assumed. A kinetic scheme containing the reactions of both quinoline and isoquinoline with 72 species and 148 elementary reactions accounts for the observed product distribution, The reaction scheme is given, and the results of computer simulation and sensitivity analysis are shown.

I think that you should take into account the boiling without decomposiion, since the quinoline has an aromatic structure which is generally highly-stable. also, be aware of the fact thar quinoline is hydroscopyc

Thank you very much sir. I will try to analyse suitability of JPC paper suggested by you.