Application of Chemometric Analysis to Complexity in Isothermal Calorimetric Data

Abstract

The interpretation of complexity in isothermal calorimetric data is demanding. The observed power signal is a composite of the powers arising from each of the individual events occurring (which can involve physical, as well as chemical, change). The challenge, therefore, lies in deconvoluting the observed data into their component parts. Here, we discuss the potential use of chemometric analysis, because it offers the significant advantage of being model-free, using principal component analysis to deconvolute data. Using model data, we discovered that the software required a minimum trivariate data matrix to be constructed. Two variables, power and time, were available from the raw data. Selection of a third variable was more problematic, but it was found that by running multiple experiments the small variation in the number of moles of compound in each experiment was sufficient to allow a successful analysis. In general we noted that it required a minimum 2n + 2 repeat experiments to allow analysis (where n is the number of reaction processes). The data outputted from the chemometric software were of the form intensity (arbitrary units) versus time, reflecting the fact that the software was written for analysis of spectroscopic data. We provide a mathematical treatment of the data that allows recovery of both reaction enthalpy and rate constants. The study demonstrates that chemometric analysis is a promising approach for the interpretation of complex calorimetric data.

Thermal Analysis

“…O'Neill et al (17) explore the use of chemometric analysis for deconvoluting complex calorimetric signals into individual reaction processes. The analysis requires a minimum 2n + 2 repeat experiments to recover both reaction enthalpy and rate constants for n processes.…”

Combination of Silica Sol and Potassium Silicate via Isothermal Heat Conduction Microcalorimetry

“…However, the reaction orders changed too fast and too frequently (Figure 4, S1, and S2). Based on the understanding of data simulation, 29 the initial power-time curve can be divided into many points via OriginPro 7.5, for example, 17000 points for an initial power-time curve or in a time period chosen appropriately, more than 60 points in one minute which is equivalent to one point or several points per second. In the appropriate chosen section of the curve, calculations were made according to equation 2, and the data points (Φ, q) of the reaction orders (m＋n＝3.0) were found.…”

Calorimetric Determination of Rate Constants and Enthalpy Changes for Zero-Order Reactions

“…The inherent beauty of heat as an analytical marker for the process and progress of reactions is its ubiquity, meaning that kinetics of reaction in almost any sample are amenable to calorimetric investigation. Isothermal calorimetric data (i.e., power versus time) can have complex forms representing the sum of many simultaneous or consecutive processes, and a series of methodologies for quantitative analysis of the data, including first-, second-, and n th-order solution phase kinetics, consecutive kinetics, direct calculation, chemometric analysis, solid-state kinetics, and fitting to integrated rate laws, have been described in the literature. However, quantitative analysis of isothermal calorimetric data for zero-order reactions has not been previously discussed.…”