## 4 Discussion  
The objective of this work was to investigate if the commonly used analytical techniques of FTIR, SPME-GCMS, and \({}^{1}\)H qNMR can be used to identify the source distillery of a baijiu sample for authentication purposes using an appropriate statistical treatment. The results suggest that FTIR is not an effective method to determine the origin of the baijiu samples using Principal Component Analysis (PCA). However, it does have some ability  
Figure 10: PLS correlation plot showing the prediction of ethanol content (%ABV) by FTIR-ATR spectroscopy correlated to the \({}^{1}\)H qNMR calculation of the ethanol content of 27 authenticated baijiu samples. Figure 9: FTIR-ATR spectra obtained on 27 authenticated baijiu samples. Expansion insert shows the C-O stretch absorbances that are highly correlated to ethanol content showing the variance in these absorbances in the observed 38–66 %ABV range of the samples analyzed. to discern the approximate %ABV of a sample when observed directly and can be used definitively for this purpose if chemometric models are developed utilizing Partial Least-Squares regression. Excellent correlation can be observed to a standard error of prediction of 0.75 %ABV. Given the common use of FTIR and the fast, simple analysis, it could be attractive as a first screening method for a suspect sample. Further analysis of the data from 1H NMR will be applied to the exploration of using FTIR to predict the concentrations of methanol, acetic acid, and ethyl esters via PLS chemometric approaches. Once these chemometric approaches are developed, they can be used to screen for outlier samples where the FTIR prediction is very different from the reported ethanol content on the label. For example, three of the baijiu samples in this study appear to be mislabeled in terms of %ABV based on FTIR, PLS modeling outliers, and qNMR calculation. These incorrect label values may point to baijiu products that have been counterfeited or adulterated. SPME-GCMS does appear to be able to identify sample origin in some cases. Unfortunately, multiple samples were only available for three distilleries; however, significant differences in volatile components were detected. The instrument used has the added advantages of being full portability, therefore removing the need for a physical laboratory. The analysis is fast and simple, and the identification of chemicals is also possible. For example, in this study, samples from distillery 1 clearly contained more ethyl esters, which would impart a fruitier aroma. \({}^{1}\)H NMR shows great promise to develop a rapid check of baijiu authenticity based on congener distribution. Many studies and review articles exist demonstrating the correlation between major ethyl ester and acid components with baijiu flavor and the fermentation and ageing processes applied [30; 32; 33; 34]. The current NMR study demonstrates that the major esters are readily quantified, which would allow for the development of a correlation between either baijiu style, or even the production distillery and the particular ester distributions. Acid components are also observed, as their presence is necessary to form the various esters. It should be noted that the esters formed between acid components and the various fused alcohols (1-propanol, isopentanol, isobutanol) are not observed by \({}^{1}\)H NMR, as the low concentration of these fused alcohols leads to the concentration of these minor, but sensorially important, esters to be below the limit-of-detection of the \({}^{1}\)H NMR experiments performed on our instrument under the experimental conditions we can provide. Modern digital spectrometers operating at higher magnetic fields, utilizing advanced multi-peak suppression techniques performed on state-of-the-art cryogenically-cooled probes, may have an opportunity to observe these lower concentration congeners.