## 2 Results and Discussion
### Validation of SPMESH-DART-MS/MS against HS-SPME-GC-MS  
For validation, post-veraison Cabernet Sauvignon and Merlot grapes were collected from multiple commercial vineyard sites in California (\(n\) = 302 samples). IBMP was quantified by SPMESH-DART-HRMS/MS using the newly optimized protocol, and by the gold standard HS-SPME-GC-MS methodology. Using, SPMESH-DART-HRMS/MS, concentrations of IBMP ranged from undetectable (<0.71 ng/kg) to 17 ng/kg, with a mean value of 3.9 \(\pm\) 0.4. This range is representative of values reported elsewhere for these cultivars (8-15 ng/L) [10]. The newly optimized SPMESH-DART-HRMS/MS method was well correlated with SPME-GC-MS (R\({}^{2}\) = 0.84, \(p\) < 0.05) with a slope of near unity at 1.1 (Figure 4). The root mean squared error between the two methods was 1.28 ng/kg.  
Performance of the SPMESH-DART-HRMS/MS method against HS-SPME-GCMS was further assessed by Bland-Altman analysis, in which the difference between analytical methods for each sample is plotted as a function of sample concentration (Figure 5) [25; 26]. Separate calculations were performed for concentrations above and below 5 ng/kg because there was a noticeably higher variance at concentrations above this value. For concentrations below 5 ng/kg, the 95% confidence limit was \(\pm\)2.6 ng/kg, with negligible bias from the origin (0.7 ng/kg). For concentrations in the range of 5-17 ng/kg, the 95% confidence limit was \(\pm\)5.5 ng/kg, again with a negligible bias (1.7 ng/kg). Concentrations of IBMP in red wines are typically about 67% of their concentrations in fruit, and the sensory threshold of IBMP in red wines has been reported to be 15 ng/L (~15 ng/kg) [6; 27]. Thus, the new SPMESH-DART-HRMS/MS method should be a reliable alternative to HS-SPME-GCMS for identifying fruit likely to have suprathreshold concentrations of IBMP.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Bee-DiGregorio, 2020 [13]** & **Current Work** & **Current Work** & **Current Work** \\ \hline \hline \multicolumn{5}{c}{**SPMESH-SVP-DART-HRMS/MS**} & **HS-SPME-GCMS** & **SPMESH-SVP-DART-HRMS/MS** & **SPMESH-JumpShot** \\ \multicolumn{5}{c}{**HPMS/MS**} \\ \hline
**Calibration Range** & 6.25–400 ng/L & 3.4–540 ng/kg & 0.5–100 ng/kg & 1.5–40 ng/kg \\ \hline
**R\({}^{2}\)** & 0.99 & 0.99 & 0.97 \\
**LOD** & 4 ng/L (3.6 ng/kg)\({}^{\text{a}}\) & 1.2 ng/kg & \textless{}0.5 ng/kg & 1.5 ng/kg \\ \hline
**LOQ** & 12 ng/L (10.9 ng/kg) \({}^{\text{a}}\) & 4 ng/kg & 1.5 ng/kg & 5 ng/kg \\ \hline
**Recovery (@ s ng/kg)** & n.d. & 93\% & 110\% & n.d. \\
**Average \% RSD** & 32\% & 6\% & 5\% & 5\% \\
**Throughput (total)** & & & & \\
**MS analysis time for** & 17 min & 17.3 h & 17 min & 8.5 min\({}^{\text{b}}\) \\
**24 samples)** & & & & \\ \hline \hline \end{tabular}  
* Assuming density of grape homogenate to be 1.1 g/mL. \({}^{\text{b}}\) Throughput achievable by programming X-Y positioning stage to rapidly scan (10 mm/s) through inter-well regions of SPMESH sheet which lack extracted volatiles. Otherwise, if constant 0.5 mm/s scan rate is used for all regions, throughput is 17 min for 24 samples. n.d. = not determined  
\end{table}
Table 1: Figures of merit for SPMESH-DART-MS/MS of IBMP in grape homogenate.  
Figure 4: Correlation between IBMP measured by SPMESH-DART-Orbitrap MS/MS and HS-SPME-GC-MS. Undetectable values were set to the square root of the LOD (SPME-GC-MS = 1.2 ng/kg, SPMESH-DART-MS = 0.71 ng/kg).  
Figure 5: Bland–Altman agreement analysis for native IBMP measured in Merlot and Cabernet Sauvignon grapes harvested at commercial maturity in 2021 (\(n\) = 302). Bias (dotted lines) and upper/lower limits of agreement (solid lines) are shown represent average concentrations above and below 5 ng/kg. Samples for which IBMP was undetectable by one or both methods are shown as hollow triangles, and samples for which IBMP was detectable using both methods are shown as closed circles.