2.3 Modulated differential scanning calorimeter (MDSC)
The MDSCTM uses both the linear heating rate as well
as a modulated (sinusoidal) heating rate to determine the total heat
flow rate, see Eq. 1. The linear heating rate provides information on
the total heat rate while the sinusoidal heating rate provides the heat
capacity information from a fraction of the heat flow
[27].
\begin{equation}
\frac{\text{dQ}}{\text{dt}}=C_{P}\beta+f\left(T,\ t\right)\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (1)\nonumber \\
\end{equation}Where \(\frac{(dQ}{dt)}\) is the total heat flow due to the linear
heating rate (equivalent of standard DSC), \(C_{P}\) is the heat
capacity component calculated from the heat flow due to the sinusoidal
heating rate, \(\beta\) is the linear heating rate of the sample,\(C_{P}\beta\) is the reversing heat flow while \(f(T,\ t)\) is the
kinetic component of total heat flow known as the non-reversing heat
flow which can be calculated from the difference between the reversing
heat flow and total heat signal component.
In this study, a Discovery DSC® (TA Instruments, Inc.
New Castle, DE, USA) equipped with a modulated Differential Scanning
Calorimeter (MDSCTM) software using a Liquid Nitrogen
Cooling Accessory (LNCA) at atmospheric pressure was used for all
measurements. Helium gas at a flow rate of 50 mL/min was purged through
the MDSCTM. The MDSCTM equilibrated
at a temperature of -150 ˚C and measurements were performed at an
underlying heating rate of 3 K/min up to a temperature of 100 ˚C;
amplitude of modulation 1 K and period of 60 s for the sample mass of 2
mg – dry biomass weight. Temperature and heat capacity calibrations
were performed with a MDSCTM certified Indium
reference material (Part No. 915061.901) and a sapphire for the specific
heat capacity determinations (Part No. 9703790.901), respectively at
similar operating conditions as used for the samples. The data were
analysed using a TRIOS software v4.1.1.33073 (TA Instruments Inc. USA).
All procedures were done in triplicate. All dataset are openly available
in [28].