## 2 Results and Discussion
### Figures of Merit  
In Table 3 we compare the LODS, linear range, accuracy, precision, recovery, sample volume and sample preparation time obtained by the proposed methodology and by other microextraction-based approaches. As it can be seen, the proposed work shows better sensitivity than most reported methodologies, even when using very sensitive instrumental systems such as GC-MS/MS [12]. The obtained LODs are only higher when compared to a methodology that uses larger amounts of sample volume [3]. The achieved accuracy, precision and recovery compares favorably with those depicted in Table 3, with the exception for a report using MEPS in combination with GC-MS/MS [12], although our proposed analytical approach uses much lower amounts of sample volume. Finally, as it can be seen, HT-BA\(\upmu\)E-\(\upmu\)LD/LVI-GC-MS(SIM), presents a much faster sample preparation time (0.45 min/sample) than the other microextraction-based methodologies using a high throughput configuration. Figure 2 exemplifies total ion chromatograms from assays performed on spiked and unspiked urine sample, obtained by HT-BA\(\upmu\)E-\(\upmu\)LD/LVI-GC-MS(SIM), under optimized experimental conditions, where good selectivity and sensitivity are noticed, showing no endogenous interfering peaks at the retention times of the target compounds, including the IS. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **KET** & **NKET** \\ \hline
**LOD (\(\mu\)g L\({}^{-1}\))** & 1.0 & \\ \hline
**LLOQ (\(\mu\)g L\({}^{-1}\))** & 5.0 & \\ \hline
**Linear range (\(\mu\)g L\({}^{-1}\))** & 5.0 to 1000.0 \\ \hline
**Calibration plot (\(n\) = 10)** & y = 0.0032x + 0.0066 & y = 0.0032x + 0.029 \\ \hline
**\(r^{2}\)** & 0.9990 & 0.9970 \\ \hline
**Intra-day assays (\(n\) = 6)** & \\  
*1000.0 \(\mu\)g L\({}^{-1}\)** & \(-2.5\pm 6.2\) & \(-9.1\pm 5.6\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Intraday (\(n\) = 6) and interday (\(n\) = 18) accuracy (%) and precision (\(\pm\) relative standard deviation (RSD), %), recovery yields (% \(\pm\) RSD, %) and matrix effects (% \(\pm\) RSD, %) using four spiking levels, as well as limits of detection (LODs), lower limits of quantification (LLOQs), linear ranges and \(r^{2}\), for KET and NKET in urine matrices, obtained by BA\(\mu\)E-\(\mu\)LD/LVI-GC-MS(SIM), under optimized experimental conditions. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Microextraction Technique** & **HF-LPME** & **MEPS** & **SBSE** & **SPME** & **HF-LPME** & **HT-BA\(\mu\)E** \\ \hline
**Instrumental system** & GC-MS & GC-MS/MS & HPLC-UV & GC-MS & GC-FID & LVI-GC-MS \\ \hline
**LODs(\(\mu\)g L\({}^{-1}\))** & 0.1–0.25 & 5 & 2.3-9.1 & 100 & 8 & 1.0 \\ \hline
**Linear range(\(\mu\)g L\({}^{-1}\))** & 0.5–50 & 10–250 & 30–3000 & 100–15000 & 3–350 & 5.0–1000.0 \\ \hline
**Accuracy (\%)** & 88.3–108 & 91.4–105.6 & n.a. & 105.9–113.6 & 75.2–119.3 & 85.5–112.1 \\ \hline
**Precision (\%)** & \(\leq\)10.1 & \(\leq\)9.2 & \(\leq\)8.9 & \(\leq\)14.8 & \(\leq\)8.9 & \(\leq\)12.6 \\ \hline
**Recovery (\%)** & 85.2–101 & 72.5–100.7 & 90.8 & n.a. & n.a. & 84.9–105.0 \\ \hline
**Sample volume (mL)** & 2 & 0.25 & 3 & 1 & 3 & 0.5 \\ \hline
**Sample preparation time** & & & & & & \\ **(min/sample)** & 60 a  & 7.42 b  & 40 c  & 21 d  & 20 c  & 45 \\ \hline
**Reference** & [3] & [12] & [9] & [16] & [10] & This work \\ \hline n.a. Information not available. a Multi-tube vortexer. Number of simultaneous microextractions not available. b  & This work \\ \hline n.a. Information not available. a Multi-tube vortexer. Number of simultaneous microextractions not available.[ENDFOOTNOTE] & 3  & This work \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of the proposed method with other previously reported microextraction approaches for the determination of KET and NKET in urine samples.