Seeley John V, Micyus Nicole J, Bandurski Steven V, Seeley Stacy K, McCurry James D
Department of Chemistry, Oakland University, Rochester, Michigan 48309, USA.
Anal Chem. 2007 Mar 1;79(5):1840-7. doi: 10.1021/ac061881g. Epub 2007 Jan 24.
A microfluidic Deans switch was used as a comprehensive two-dimensional gas chromatography (GCxGC) modulator. The simplicity and wide temperature range of the Deans switch make it a promising alternative to existing modulation techniques. However, the Deans switch is a low duty cycle modulator; that is, it samples only a small portion of the primary column effluent. Like all low duty cycle modulators, the Deans switch produces inconsistent transfer of components from the primary to the secondary column if the primary peaks are undersampled. Theoretical simulations and experimental studies show that the relative standard deviation (RSD) of the fraction of material transferred from the primary column to the secondary column is less than 1% if the modulation ratio is greater than 2.5. But the RSDs increase rapidly as the modulation ratio is decreased below 2.5. Deans switch GCxGC was validated by analyzing the aromatic content of gasoline. A fast analysis (<10 min) produced narrow primary peaks and a modulation ratio of 1.7. The quantitative results were in good agreement with results obtained with differential flow modulation GCxGC and GC/MS, but the RSDs of single-component levels were approximately three times greater. The Deans switch modulator was also used for a slower gasoline analysis (33 min run time) that produced modulation ratios near 5. In this case, the quantitative results and RSDs were in excellent agreement with the differential flow GCxGC and GC/MS results. These studies demonstrate that a Deans switch can be an effective modulator provided that modulation ratios greater than approximately 2.5 are employed.
一种微流控迪恩斯切换器被用作全二维气相色谱（GCxGC）调制器。迪恩斯切换器的简单性和宽温度范围使其成为现有调制技术的一个有前景的替代方案。然而，迪恩斯切换器是一种低占空比调制器；也就是说，它仅对主柱流出物的一小部分进行采样。与所有低占空比调制器一样，如果主峰采样不足，迪恩斯切换器会导致组分从主柱到副柱的转移不一致。理论模拟和实验研究表明，如果调制比大于2.5，从主柱转移到副柱的物质分数的相对标准偏差（RSD）小于1%。但当调制比降至2.5以下时，RSD会迅速增加。通过分析汽油中的芳烃含量对迪恩斯切换GCxGC进行了验证。快速分析（<10分钟）产生了窄的主峰，调制比为1.7。定量结果与差分流调制GCxGC和GC/MS获得的结果吻合良好，但单组分水平的RSD大约大三倍。迪恩斯切换调制器还用于较慢的汽油分析（运行时间33分钟），其调制比接近5。在这种情况下，定量结果和RSD与差分流GCxGC和GC/MS结果非常吻合。这些研究表明，只要采用大于约2.5的调制比，迪恩斯切换器可以是一种有效的调制器。
