Soares Samara, Rocha Fábio R P
Center for Nuclear Energy in Agriculture, University of São Paulo, Av. Centenário, 303, 13416-000 Piracicaba, SP, Brazil.
Center for Nuclear Energy in Agriculture, University of São Paulo, Av. Centenário, 303, 13416-000 Piracicaba, SP, Brazil.
Talanta. 2019 Jul 1;199:285-289. doi: 10.1016/j.talanta.2019.02.064. Epub 2019 Feb 18.
Although usual in analytical chemistry, separations of volatile analytes by distillation are time-consuming, whereas gas diffusion through membranes is characterized by low efficiency. These limitations directly hinder sample throughput and sensitivity. In this work, a simple and inexpensive approach is proposed for separation of volatile analytes by microdistillation. It consists of an eppendorf type tube containing the acceptor solution suspended inside a 50 mL Falcon capped tube containing the sample. The bottom of the sample tube is submitted to controlled heating in a water bath to promote analyte volatilization to the headspace, thus favoring its collection into the acceptor solution. The efficiency of the approach was evaluated by determination of methanol in biodiesel, whose threshold limit is 0.2% (m/m) according the current legislation. Measurements were based on discoloration of an acidic potassium permanganate solution (750 μL), caused by oxidation of methanol with consequent reduction to Mn(II). The analytical measurements were based on intensity of the reflected radiation acquired as digital images by the camera of a smartphone under controlled lighting. Values of the G channel were used as analytical parameter because of the complementarity with the color of the potassium permanganate solution. Under heating at 70 °C for 40 min, the transference of methanol to the acceptor solution was estimated at (98 ± 3)%. A linear response was achieved within 0.025% and 0.200% (m/m) methanol, with coefficient of variation (n = 10) and limit of detection (99.7% confidence level) estimated at 3.7% and 0.009% (m/m) respectively. The procedure requires only 100 μg of potassium permanganate and 200 μL of sample and generates as low as 950 μL of residue per determination. Because of the selectivity provided by microdistillation, the results obtained by the proposed approach agreed with the reference procedure at the 95% confidence level. The proposed approach is a simple, efficient, and cost-effective alternative for separation and determination of volatile species.
尽管蒸馏分离挥发性分析物在分析化学中很常见，但耗时较长，而通过膜的气体扩散效率又很低。这些局限性直接阻碍了样品通量和灵敏度。在这项工作中，提出了一种用于通过微蒸馏分离挥发性分析物的简单且低成本的方法。它由一个装有接受溶液的艾本德型管组成，该管悬浮在一个装有样品的50 mL带盖离心管内。样品管底部在水浴中进行受控加热，以促进分析物挥发到顶空，从而有利于其收集到接受溶液中。通过测定生物柴油中的甲醇来评估该方法的效率，根据现行法规，甲醇的阈值限制为0.2%（m/m）。测量基于酸性高锰酸钾溶液（750 μL）的褪色，这是由于甲醇被氧化并随后还原为Mn(II)所致。分析测量基于在受控光照下由智能手机摄像头获取的作为数字图像的反射辐射强度。由于与高锰酸钾溶液颜色的互补性，使用G通道的值作为分析参数。在70°C加热40分钟的情况下，甲醇向接受溶液的转移率估计为(98±3)%。在甲醇含量为0.025%至0.200%（m/m）范围内实现了线性响应，变异系数（n = 10）和检测限（99.7%置信水平）分别估计为3.7%和0.009%（m/m）。该方法仅需要100 μg高锰酸钾和200 μL样品，每次测定产生的残渣低至950 μL。由于微蒸馏提供的选择性，所提出的方法获得的结果在95%置信水平下与参考方法一致。所提出的方法是一种用于分离和测定挥发性物质的简单、高效且经济有效的替代方法。
