Developing a GCxGC technique can be daunting at first glance. There are two ovens, two columns, and a modulator all with variables that can affect method performance. Luckily, a few tried and true tips are available to help take the guesswork out of GCxGC method development. To start with, the first dimension separation should be maximized, then the first and second column dimensions should be matched, and finally, the modulation time should be kept short. GCxGC performance can be considerably optimized by following these three simple tips.
Maximize Resolution in the FIRST Dimension
When starting aGCxGC analysis，必须始终牢记第一个维度。必须选择适当的固定相和列尺寸，以优化第一个维度分离的效率（即分辨率）。30 m x 0.25 mm ID列是一个不错的起点，但对于非常棘手的分离，或者如果您需要超级电荷分离，则可以选择60 m。选择良好的第一维分隔后，用户可以从主要列中选择一个不同的（即正交）的第二维列相位，该列将利用紧密洗脱（或凝聚）第一维峰的差异（图1和2）。
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Figure 1.Resolution in first dimension is maximized using an efficient PAH-specific column.
匹配第一列和第二列尺寸
如果第一维列为0.25 mm ID×0.25 µm，则最好是第二维柱也为0.25 mm×0.25 µm（图2）。这将提供最佳的样品加载能力，并减少超载第二维列的机会。此外，这是在整个分析过程中保持一致流量的最简单方法。该规则的例外是大气压力探测器（例如FID和ECD）。在这种情况下，线性速度可以通过降低第二维列的内径来通过列并进入检测器。
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Figure 2.After the first dimension is optimized, the second dimension is used to exploit differences in closely eluting 1D peaks. The second dimension column id and film thickness match the first dimension column.
保持第二维间隔时间短
The second dimension separation time is generally known as the “modulation time”. It is the period during which the first dimension column effluent is sampled in the second dimension. In practice, Michelle Misselwitz, an experienced analytical chemist, and others wanted to sample the first dimension effluent more rapidly than the first dimension peak width (this is known as “slicing”). They wanted to do this quickly so that they can maintain the first dimension column separation. Ideally, Misselwitz and others wanted to slice first dimension peak 3 to 5 times. So, if the first dimension peak width is 6 seconds, the second dimension separation time (i.e. modulation time) should not exceed 2 seconds (Figure 3). If the modulation time is 10 seconds, then the first dimension peak width should be at least 30 seconds wide (Misselwitz hopes one doesn’t have this wide of a peak)!
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Figure 3.The first dimension peak width is 9 seconds. Therefore, we want a maximum of a 3 second 2D separation time. This will give 3 slices across each peak and preserve the first dimension resolution.
Want to Learn More about the Benefits of GCxGC?
许多人可能听说过GCXGC，但没有人完全理解它如何改变实验室。有些人避免使用GCXGC，因为其技术方面的方面高度高；其他人则认为它的能力被过度宣传到它不再在常规实验室中占有一席之地。但是，GCXGC是用于广泛应用的强大工具，并且具有提高生产率，节省时间并提高分析物识别的信心的几个优势。
This information has been sourced, reviewed and adapted from materials provided by LECO Corporation.
For more information on this source, please visitLECO Corporation.