Department of Chemistry and Biochemistry, Florida State University, 95 Chieftain Way, Tallahassee, FL 32306, USA.
Analyst. 2012 Feb 21;137(4):840-6. doi: 10.1039/c2an15911b. Epub 2011 Dec 14.
Free fatty acid (FFA) compositions are examined in feedstock for biodiesel production, as source-specific markers in soil, and because of their role in cellular signaling. However, sample preparation of FFAs for gas chromatography-mass spectrometry (GC-MS) analysis can be time and labor intensive. Therefore, to increase sample preparation throughput, a glass microfluidic device was developed to automate derivatization of FFAs to fatty acid methyl esters (FAMEs). FFAs were delivered to one input of the device and methanolic-HCl was delivered to a second input. FAME products were produced as the reagents traversed a 29 μL reaction channel held at 55 °C. A Design of Experiment protocol was used to determine the combination of derivatization time (T(der)) and ratio of methanolic-HCl:FFA (R(der)) that maximized the derivatization efficiencies of tridecanoic acid and stearic acid to their methyl ester forms. The combination of T(der) = 0.8 min and R(der) = 4.9 that produced optimal derivatization conditions for both FFAs within a 5 min total sample preparation time was determined. This combination of T(der) and R(der) was used to derivatize 12 FFAs with a range of derivatization efficiencies from 18% to 93% with efficiencies of 61% for tridecanoic acid and 84% for stearic acid. As compared to a conventional macroscale derivatization of FFA to FAME, the microfluidic device decreased the volume of methanolic-HCl and FFA by 20- and 1300-fold, respectively. The developed microfluidic device can be used for automated preparation of FAMEs to analyze the FFA compositions of volume-limited samples.
游离脂肪酸（FFA）的组成在生物柴油生产的原料中进行了检查，因为它们是土壤中特定来源的标志物，并且在细胞信号转导中起作用。然而，游离脂肪酸的气相色谱-质谱（GC-MS）分析的样品制备可能既耗时又费力。因此，为了提高样品制备的通量，开发了一种玻璃微流控装置，以自动将游离脂肪酸衍生化为脂肪酸甲酯（FAME）。FFA 被输送到装置的一个输入口，而甲醇-HCl 被输送到另一个输入口。当试剂流经保持在 55°C 的 29 μL 反应通道时，会生成 FAME 产物。通过实验设计方案确定了衍生化时间（T(der)）和甲醇-HCl:FFA（R(der)）的组合，该组合使十三烷酸和硬脂酸最大程度地转化为其甲酯形式的衍生化效率最大化。确定了在 5 分钟的总样品制备时间内，T(der) = 0.8 分钟和 R(der) = 4.9 的组合是两种 FFA 的最佳衍生化条件。在衍生化效率从 18%到 93%的范围内，用此 T(der)和 R(der)组合衍生了 12 种 FFA，十三烷酸和硬脂酸的效率分别为 61%和 84%。与游离脂肪酸到脂肪酸甲酯的常规宏观衍生化相比，微流控装置使甲醇-HCl 和 FFA 的体积分别减少了 20 倍和 1300 倍。开发的微流控装置可用于自动制备 FAME 以分析体积有限的样品中的 FFA 组成。
