Vacuum-assisted headspace single-drop microextraction: Eliminating interfacial gas-phase limitations
Vacuum-assisted headspace single-drop microextraction: Eliminating interfacial gas-phase limitations
复制标题
真空辅助顶空单滴微萃取：消除界面气相限制
DOI：
10.1016/j.aca.2019.09.056
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发表时间：
2019
影响因子：
6.2
通讯作者：
Colussi, Agustín J.
中科院分区：
文献类型：
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作者：
Psillakis, Elefteria;Koutela, Niki;Colussi, Agustín J.
顶空单滴微萃取(HS-SDME)忽略了气相的限制，并假定速率控制主要存在于液态水和/或有机相中，而不是在顶空中。在这里，我们证明了界面气体约束的存在，并建议使用降低的顶空压力来消除它们。为了描述HS-SDME的压力依赖性，系统被分解为两个界面步骤：(I)用双膜理论建立的蒸发步骤(水-顶空界面)和(Ii)用阻力模型建立的微滴(顶空-微滴界面)对分析物的吸收。以正辛醇中较大的亨利定律溶解常数(HOA>； 103M atm−1)和以水为溶剂的低至中等亨利定律挥发常数(KH)为模型分析物。我们发现，在远低于标准HS-SDME程序中使用的1 大气压下采样，所有分析物的提取时间都显著缩短。萘萃取的加速，强调了通过界面气体层的传质对有机溶剂滴的作用，因为它很容易蒸发到顶空。当降低采样压力时，观察到较大的增长速度，表明气体侧的限制在蒸发和吸收步骤中都是重要的。结合顶空-微滴界面传质的模型计算证实，当采样压力从1 atm降低到0.04atm时，气相阻力大大消除(>；96%)，这一影响几乎与分析物分子质量无关。讨论了这两个界面步骤的相对重要性及其气液两相的局限性，并用KHandHAa预测了真空对HS-SDME的正效应。
Gas-phase limitations have been neglected in headspace single-drop microextraction (HS-SDME) and rate control has been assumed to primarily reside in the liquid water and/or organic phases, but not in the headspace. Herein we demonstrate the presence of interfacial gas constraints and propose using reduced headspace pressures to remove them. To describe the pressure dependence of HS-SDME, the system was decoupled into two interfacial steps: (i) the evaporation step (water-headspace interface) formulated using the two-film theory and (ii) the analyte uptake by the microdrop (headspace-microdrop interface) formulated using the resistance model. Naphthalene, acenaphthene, and pyrene were chosen as model analytes for their large Henry’s law solubility constants in n-octanol (HOA> 103M atm−1), and their low to moderate Henry’s law volatility constants in water as a solvent (KH). We have found that extraction times were significantly shortened for all analytes by sampling at pressures well below the 1 atm used in the standard HS-SDME procedure. The acceleration of naphthalene extraction, whose facile evaporation into the headspace had been assumed to be practically pressure independent, highlighted the role of mass transfer through the interfacial gas layer on the organic solvent drop. The larger accelerations observed for acenaphthene and (especially) pyrene upon reducing the sampling pressure, suggested that gas-sided constraints were important during both the evaporation and uptake steps. Model calculations incorporating mass transfers at the headspace-microdrop interface confirmed that gas-phase resistance is largely eliminated (>96%) when reducing the sampling pressure from 1 to 0.04 atm, an effect that is nearly independent of analyte molecular mass. The relative importance of the two interfacial steps and their gas- and liquid-phase limitations are discussed, next to the use ofKHandHOAto predict the positive effect of vacuum on HS-SDME.