# Quantitative Analysis of Caffe in Roasted Coffee: A Comparison of Brewing Methods
## 3 Results and Discussion
### Caffee Determination Methods
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Reference** & **R\({}^{2}\)** & **LOQ** & **LOD** & **RSD (\%)** & **Other Parameters/Information** \\ \hline
[29] & n.d. & n.d. & n.d. & n.d. & 5-point calibration curve (calibration range: 20-100 ppm) \\
[30] & 0.9994 & n.d. & n.d. & n.d. & 6-point calibration curve (calibration range: 0-0.632 ug) \\
[31] & 0.999 & n.d. & n.d. & n.d. & 6-point calibration curve \\
[32] & 0.9993 & n.d. & n.d. & n.d. & 6-point calibration curve (calibration range: 0-0.757 ug) \\
[33] & n.d. & n.d. & n.d. & 6-point calibration curve (calibration range: 0-0.757 ug) \\
[34] & -0.9985 & 0.1-0.2 mg/L & 0.03-0.06 mg/L & 0.74-4.44\% & 5-point calibration curve (calibration range 10, 20, 50, 100, 250 mg/L) \\
[36] & -0.994 & n.d. & n.d. & n.d. & external caffeine standard \\
[37] & n.d. & n.d. & n.d. & 4-valent caffeine standard \\
[38] & n.d. & n.d. & n.d. & external caffeine standard \\
[39] & n.d. & n.d. & n.d. & external caffeine standard \\
[40] & n.d. & n.d. & n.d. & external caffeine standard \\
[41] & 0.9963 & 0.3 mg/L & 0.10 mg/L & 1.54-2.4\% & 5-point calibration curve (calibration range: 5, 10, 25, 50, 100 mg/L) \\
[42] & n.d. & n.d. & n.d. & n.d. & n.d. \\
[44] & 0.9994 & 0.8134 ug/mL & 0.2684 ug/mL & calibration range: 0.225-1.125 mg/mL; \(j=12172\)\(\lambda=2.5241\) \\
[45] & 0.9999 & n.d. & n.d. & n.d. & calibration range: 20-1000 ng \\
[46] & 0.9881 & 2 ug/mL & 0.5 mg/mL & n.d. & calibration range: 0.0625-1 mg y = 18,940\(\lambda\) + 944.19 \\
[47] & 0.999 & n.d. & n.d. & n.d. & 3-70.6\% \(\lambda\) + 32.205 \\
[48] & n.d. & n.d. & n.d. & 4-valent caffeine standard \\
[49] & \(\geq\)0.999 & n.d. & n.d. & n.d. & 5-point calibration curve (calibration range: 10-35 ug/mL) \\
[50] & n.d. & n.d. & n.d. & external caffeine standard \\
[51] & n.d. & n.d. & n.d. & n.d. \\
[52] & 1.000 & 0.004 ug/mL & 0.001 ug/mL & intraday 0.40\% & calibration range: 0.005-5 ug/mL; y = 135,892\(\lambda\) + 1311.1 \\
[53] & 0.9992 & 1.75 mg/L & 0.52 mg/L & intraday 1.46\% & calibration range: 50-1000 mg/L; y = 150\% \(-\) 6.93 \\
[54] & n.d. & n.d. & n.d. & n.d. & 5-point calibration curve \\
[56] & n.d. & n.d. & n.d. & 4-valent caffeine standard \\
[57] & \(>\)0.99 & 151.0 mg/100 g & 45.0 mg/100 g & n.d. & 5/8-point calibration curve (calibration range: 23-117 mg/100 g;y = 1.6474\(\lambda\) \(-\) 1.2918 \\
[58] & 0.9978 & 0.35 ug/mL & 0.10 ug/mL & intraday 0.39\% & linear range: 0.0195-10 ug/mL; y = 10,373 x + 985.93 \\
[59] & n.d. & n.d. & n.d. & 5-point calibration curve \\
[60] & n.d. & n.d. & n.d. & external caffeine standard \\ \hline \end{tabular} Abbreviations: LOD\(-\)limit of detection; LOQ\(-\)limit of quantification; n.d. \(-\)do date; R\({}^{2}-\)comfficient of determination; RSD\(-\)relative standard deviations.  
\end{table} 
Table 3: Validation parameters for the high-performance liquid chromatography method. Researchers obtained a high R\({}^{2}\), exceeding 0.99, indicating the high precision and reliability of the measurement methods. However, there is limited information regarding other parameters--limit of detection, limit of quantification, and relative standard deviations. Only 27.6% of studies included these values [34; 41; 44; 46; 52; 57; 58]. Other studies used different methods for the determination of caffeine--spectrophotometry [43; 46; 54] and nuclear magnetic resonance (NMR) [35]. In the study by [PERSON] et al. [54], coffee samples were diluted in pure water and then extracted three times with a chloroform solution. The organic phases were evaporated, and the remaining extract was dissolved in chloroform. Caffeine content was measured at 270 nm. In the study by [PERSON] et al. [46], the prepared coffee samples were filtered and then alkalinized with sodium hydroxide solution to pH 12.5-12.7. Then, caffeine extraction was carried out in two portions of chloroform, and the organic layer was collected and diluted with chloroform. Caffeine absorbance was measured at 276 nm. In the study by [PERSON] et al. [43], caffeine content was at 274 nm.