Mass spectrometry (MS) and coupled gas chromatography-mass spectrometry (GC-MS) are globally recognized as the primary techniques for the analysis of gases or vapors due to their selectivity, sensitivity, accuracy, and reproducibility. When thermal stress is applied, vapors or gases are released as a result of the reactions and changes that occur. The analysis of these gases during the thermally induced reaction is scientifically referred to as evolved gas analysis (EGA), which is essential for confirming the occurrence of the induced reactions. Pyrolyzers, thermobalances, or simple heaters can increase the temperature of the analyzed samples according to a programmed and software-managed ramp, allowing for control over both the heating rate and isothermal stages. The atmosphere can also be varied to simulate pyrolysis or thermo-oxidative processes. This way, each induced reaction generates a unique evolved gas, which can be linked to a theoretically hypothesized mechanism. Mass spectrometry (MS) and coupled gas chromatography–mass spectrometry (GC-MS) are fundamental analytical methods used for on-line thermally induced evolved gas analysis (OLTI-EGA).

This study evaluates a miniaturized Near-infrared spectroscopy MicroNIR/Chemometrics platform as a rapid tool for monitoring chloroform, a representative disinfection by-product from the trihalomethanes class. Two MicroNIR devices were tested in three configurations: reflectance measurements in glass vials and transmittance measurements in static and flow modes. Experiments were conducted with spiked distilled water over the 1–200 µg/L range relevant to regulations. Principal Component Analysis provided clear separation between blanks and chloroform-containing samples in all configurations. Partial Least Squares Discriminant Analysis achieved 100% specificity and non-error rate, with a root mean square error in prediction (RMSEP) of approximately 0.06–0.08 for static and flow measurements and 0.09–0.10 for vial mode. In the 1–20 µg/L range, Partial Least Squares Regression demonstrated comparable performance for static and flow measurements (R² = 0.91; RMSEP = 2.3 µg/L), while flow provided the lowest estimated limits of detection and quantification (2.6 µg/L and 7.9 µg/L, respectively). In the 20–200 µg/L range, flow showed the highest quantitative performance. The results support the feasibility of MicroNIR/Chemometrics as a rapid screening tool for chloroform in water, complementary to reference methods. Future work will focus on improving inter-campaign transferability, extending the approach to all regulated trihalomethanes, and validating it in real matrices.