## 2 Results and Discussion
### Real Samples Analysis  
All the nut-based beverages used in this study were obtained from the local market in Thessaloniki, Greece. Different varieties of nut-based beverages (almond drink, chocolate almond drink, peanut drink, walnut drink) were analyzed as well as samples from different companies derived from almond. All samples were stored in the refrigerator (+4 \({}^{\circ}\)C). Results are illustrated in Table 3. Identification of analytes was performed with (National Institute of Standards and Technology=Environmental Protection Agency=National Institutes of Health) NIST=EPA=NIH Mass spectral library NIST 05. Similarity indices were >95% for the analytes in Table 3. As it can be observed, there are significant differences in the volatile profile of drinks derived by different nuts (i.e., almond, peanut, walnut) as well as of almond drinks from different producers. \begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Analyte** & **Linear Range (ng g\({}^{-1}\))** & **Regression Equation** & **R\({}^{2}\)** & **LOQs (ng g\({}^{-1}\))** & **LODs (ng g\({}^{-1}\))** \\ \hline heptane & 10–5000 & y = (0.0311 \(\pm\) 0.0017)x + (0.0055 \(\pm\) 0.0047) & 0.9942 & 1.00 & 0.33 \\ a-pinene & 500–10000 & y = (0.2883 \(\pm\) 0.0102)x + 0.507 \(\pm\) 0.0240 & 0.995 & 5.00 & 1.67 \\ toluene & 10–10000 & y = (0.7959x \(\pm\) 0.0616) + (0.1382 \(\pm\) 0.0141) & 0.9983 & 1.00 & 0.33 \\
2-methylpyrazine & 10–10000 & y = (0.3866x \(\pm\) 0.0360) + (0.0757 \(\pm\) 0.0068) & 0.9963 & 1.00 & 0.33 \\
3-heptanone & 10–10000 & y = (0.3523x \(\pm\) 0.0152) + (0.0859 \(\pm\) 0.0761) & 0.9944 & 1.00 & 0.33 \\ heptanal & 100–25000 & y = (0.0571x \(\pm\) 0.0006) + (0.0024 \(\pm\) 0.0032) & 0.9996 & 1.00 & 0.33 \\
2-octanone & 10–2500 & y = (0.10157x \(\pm\) 0.0508) + (0.0697 \(\pm\) 0.0623) & 0.9925 & 1.00 & 0.33 \\
1-heptanol & 10–25000 & y = (0.8018 \(\pm\) 0.0104) + (0.0084 \(\pm\) 0.0003) & 0.992 & 1.00 & 0.33 \\ benzaldehyde & 10–25000 & y = (1.644x \(\pm\) 0.0245) + (0.0551 \(\pm\) 0.0301) & 0.992 & 1.00 & 0.33 \\
1-octanol & 10–25000 & y = (1.979x \(\pm\) 0.0256) + (0.2554 \(\pm\) 0.0244) & 0.999 & 1.00 & 0.33 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Regression equations, linear range, Limits of Detection (LOD) and Limits of Quantification (LOQ) values for the target analytes. \begin{table}
\begin{tabular}{l l l l l l l} \hline \hline \multirow{2}{*}{**Analyte**} & \multicolumn{2}{c}{**Within Day (n = 5)**} & \multicolumn{4}{c}{**Between Days (3 \(\times\) 4 days)**} \\ \cline{2-7}  & **Found \(\pm\) SD (ug g\({}^{-1}\))** & **RSD (\%)** & **Recovery (\%)** & **Found \(\pm\) SD (ug g\({}^{-1}\))** & **RSD (\%)** & **Recovery (\%)** \\ \hline heptane & 966 \(\pm\) 55 & 57 & 96.6 & 984 \(\pm\) 11 & 11.0 & 98.5 \\ a-pinene & 1013 \(\pm\) 108 & 10.7 & 101.3 & 979 \(\pm\) 12 & 12.1 & 99.8 \\ Toluene & 1016 \(\pm\) 80 & 7.9 & 101.6 & 979 \(\pm\) 78 & 8.0 & 97.9 \\
2-methylpyrazine & 1157 \(\pm\) 17 & 1.4 & 1157 & 1023 \(\pm\) 18 & 1.8 & 102.3 \\
3-heptanone & 1123 \(\pm\) 19 & 1.7 & 112.3 & 1026 \(\pm\) 34 & 3.4 & 102.6 \\ Heptanal & 813 \(\pm\) 24 & 2.9 & 81.3 & 856 \(\pm\) 33 & 3.9 & 85.7 \\
2-octanone & 991 \(\pm\) 12 & 1.2 & 99.1 & 943 \(\pm\) 12 & 1.3 & 94.4 \\
1-heptanol & 1182 \(\pm\) 46 & 3.9 & 118.2 & 1094 \(\pm\) 81 & 7.4 & 109.4 \\ benzaldehyde & 1157 \(\pm\) 52 & 4.6 & 115.7 & 1067 \(\pm\) 131 & 12.3 & 106.7 \\
1-octanol & 889 \(\pm\) 112 & 1.3 & 88.9 & 921 \(\pm\) 45 & 4.9 & 92.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Accuracy and precision results of method validation for the determination of volatile compounds in nut-based milk alternative drinks.