Modulation ratio in comprehensive two-dimensional gas chromatography
Modulation ratio in comprehensive two-dimensional gas chromatography
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DOI：
10.1021/ac052270b
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发表时间：
2006-07-01
影响因子：
7.4
通讯作者：
Marriott, Philip J.
中科院分区：
文献类型：
--
作者：
Khummueng, Weeraya;Harynuk, James;Marriott, Philip J.
综合二维色谱法采用串联耦合的两柱布置，其中来自第一柱的流出物被收集或采样，然后根据所选择的调制周期被引入到第二柱。这通过在柱结处或附近使用调制器来实现。应用该技术的考虑因素之一是调制器的周期，其决定了第一柱流出物的采样持续时间。在这里，我们建议，采样率可以最有效地描述了一个新的术语，称为调制比（M-R）。这被定义为第一列峰标准偏差（4 sigma）的4倍除以调制周期（P-M）或峰的半高宽度（w（h））的1.6985倍的比率：M-R = 4 sigma/ P-M = w（B）/P-M =（w（h）x 1.6985）/P-M。4 σ值通常被认为是峰底宽度（w（B））。优选使用4 σ作为分子而不是简单地使用σ，因为当用于实验的PM值等于σ时，则MR值被计算为4，这意味着主峰将被调制类似于通常推荐用于综合多维分离的4倍。调制数（N-M）这一定义不太明确的术语之前已被使用并被提议为每个峰的调制数，因此，其旨在表达对主色谱柱峰进行采样的方式;这是一个主观且未得到充分表征的值。当报告实验条件时，M-R的使用应该为用户提供有意义的和严格定义的值。M-R的效用通过高斯峰和拖尾峰的调制过程的数学模型证明，由调制比的实验研究支持。结果表明，对于痕量化合物的分析，精确的定量测量正在进行，实验应进行与M-R至少为3。相反，对于半定量方法或主要组分的分析，M-R接近1.5就足够了。
Comprehensive two-dimensional chromatography employs a serially coupled two-column arrangement where effluent from the first column is collected or sampled and then introduced to the second column according to a chosen modulation period. This is effected by use of a modulator at or near the column junction. One of the considerations in applying the technique is the period of the modulator, which determines the sampling duration of the first column effluent. Here, we propose that the sampling rate can be most effectively described by a new term, called the modulation ratio (M-R). This is defined as the ratio of 4 times the first column peak standard deviation (4 sigma) divided by the modulation period (P-M) or 1.6985 times the half-height width of the peak (w(h)): M-R = 4 sigma/ P-M = w(b)/P-M = (w(h) x 1.6985)/P-M. The 4 sigma value is more commonly recognized as the peak base width (w(b)). The use of 4 sigma as the numerator is preferred to simply sigma because when the PM value used for an experiment is equal to sigma, then the MR value is calculated to be 4, implying that the primary peak will be modulated similar to 4 times as is normally recommended for a comprehensive multidimensional separation. The less well-defined term of modulation number (N-M) has been previously used and proposed as the number of modulations per peak and, therefore, is intended to convey the manner in which the primary column peak is sampled; this is a subjective and not well-characterized value. The use of M-R should provide users with a meaningful and strictly defined value when reporting experimental conditions. The utility of M-R is demonstrated through a mathematical model of the modulation process for both Gaussian and tailing peaks, supported by an experimental study of the modulation ratio. It is shown that for the analysis of trace compounds where precise quantitative measurements are being made, the experiment should be conducted with an M-R of at least 3. Conversely, for semiquantitative methods or the analysis of major components, an M-R of similar to 1.5 should suffice.