Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195, USA.
Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195, USA.
J Chromatogr A. 2020 Jun 7;1620:460982. doi: 10.1016/j.chroma.2020.460982. Epub 2020 Feb 18.
Dynamic pressure gradient modulation (DPGM) is investigated for comprehensive two-dimensional gas chromatography (GC × GC) with time-of-flight mass spectrometry (TOFMS) detection. With DPGM, a commercial pneumatic "pulse" valve is opened to introduce a suitably high auxiliary gas pressure at a T-junction connecting the first dimension (D) and second dimension (D) columns during the modulation period (P), temporarily stopping the D flow. The valve is then closed for the duration of a pulse width (p) to "re-inject" temporally focused D eluate onto the D column for separation. This flow modulation technique is observed to be compatible with TOFMS detection using a D flow rate of 4 ml/min for the separation of a 90-component test mixture. A 25 min separation window using a P = 1 s and p = 200 ms for full modulation (and 100% duty cycle) provided an average W = 4.5 s and W = 130 ms for a 2D peak capacity of n = 2700 (100 peaks per min). The detector response enhancement factor (DREF) serves as a metric for the enhanced sensitivity of the modulated relative to the unmodulated D peaks, with DREFs ranging between 10 and 20 and about a 5-fold improvement in signal-to-noise ratio (S/N). The bilinear "quality" of the GC × GC data is studied using the chemometric method parallel factor analysis (PARAFAC). Since PARAFAC requires sufficiently trilinear data, the reproducibility of the D peak shape for a given analyte is confirmed using lack-of-fit (LOF) and percent variation (R) metrics. The limit-of-detection (LOD) for the representative analyte hexadecane is determined using PARAFAC, providing an LOD of 0.7 ppb (±0.03 ppb) for three replicates. Seven heavily overlapped analytes are also fully resolved by PARAFAC down to the part-per-million (ppm) concentration level, producing reproducible spectra with a majority of spectral match values (MV) over 800 (RSD ≤ 7.1%). This study provides promising results for DPGM as a flow modulation technique compatible with GC × GC-TOFMS, providing high sensitivity data suitable for chemometric analysis.
动态压力梯度调制（DPGM）用于研究带有飞行时间质谱（TOFMS）检测的全面二维气相色谱（GC×GC）。在调制周期（P）期间，通过 DPGM，使用商业气动“脉冲”阀在连接一维（D）和二维（D）柱的 T 形接头上引入适当高的辅助气压，暂时停止 D 流。然后，在脉冲宽度（p）的持续时间内关闭阀门，以“重新注入”暂时聚焦的 D 洗脱液到 D 柱上进行分离。这种流量调制技术与使用 4ml/min 的 D 流速用于分离 90 组分测试混合物的 TOFMS 检测兼容。使用 P=1s 和 p=200ms 进行全调制（100%占空比），可提供 25min 的分离窗口，2D 峰容量为 n=2700（100 个峰/分钟），得到的平均 W=4.5s 和 W=130ms。检测器响应增强因子（DREF）是衡量调制相对于未调制 D 峰的灵敏度增强的指标，DREF 值在 10 到 20 之间，信号噪声比（S/N）提高约 5 倍。使用化学计量学方法平行因子分析（PARAFAC）研究 GC×GC 数据的双线性“质量”。由于 PARAFAC 需要足够的三线性数据，因此使用失拟（LOF）和百分比变化（R）指标确认给定分析物的 D 峰形状的可重复性。使用 PARAFAC 确定代表性分析物十六烷的检测限（LOD），为三个重复提供 0.7ppb（±0.03ppb）的 LOD。通过 PARAFAC 还完全解析了七个严重重叠的分析物，直到百万分之一（ppm）浓度水平，产生具有大多数光谱匹配值（MV）超过 800（RSD≤7.1%）的可重复光谱。这项研究为 DPGM 作为与 GC×GC-TOFMS 兼容的流量调制技术提供了有希望的结果，提供了适合化学计量分析的高灵敏度数据。
