Wang Shau-Chun, Lin Chiao-Juan, Chiang Shu-Min, Yu Sung-Nien
Department of Chemistry and Biochemistry, National Chung Cheng University, 168 University Road, Min-Hsiung, Chia-Yi 621, Taiwan.
Anal Chem. 2008 Mar 15;80(6):2097-104. doi: 10.1021/ac702222m. Epub 2008 Feb 16.
This paper reports a simple chemometric technique to alter the noise spectrum of a liquid chromatography-mass spectrometry (LC-MS) chromatogram between two consecutive second-derivative filter procedures to improve the peak signal-to-noise (S/N) ratio enhancement. This technique is to multiply one second-derivative filtered LC-MS chromatogram with another artificial chromatogram added with thermal noises prior to the other second-derivative filter. Because the second-derivative filter cannot eliminate frequency components within its own filter bandwidth, more efficient peak S/N ratio improvement cannot be accomplished using consecutive second-derivative filter procedures to process LC-MS chromatograms. In contrast, when the second-derivative filtered LC-MS chromatogram is conditioned with the multiplication alteration prior to the other second-derivative filter, much better ratio improvement is achieved. The noise frequency spectrum of the second-derivative filtered chromatogram, which originally contains frequency components within the filter bandwidth, is altered to span a broader range with multiplication operation. When the frequency range of this modified noise spectrum shifts toward the other regimes, the other second-derivative filter, working as a band-pass filter, is able to provide better filtering efficiency to obtain higher peak S/N ratios. Real LC-MS chromatograms, of which 5-fold peak S/N ratio improvement achieved with two consecutive second-derivative filters remains the same S/N ratio improvement using a one-step second-derivative filter, are improved to accomplish much better ratio enhancement, approximately 25-fold or higher when the noise frequency spectrum is modified between two matched filters. The linear standard curve using the filtered LC-MS signals is validated. The filtered LC-MS signals are also more reproducible. The more accurate determinations of very low-concentration samples (S/N ratio about 5-7) are obtained via standard addition procedures using the filtered signals rather than the determinations using the original signals.
本文报道了一种简单的化学计量技术，通过在两个连续的二阶导数滤波过程之间改变液相色谱 - 质谱（LC - MS）色谱图的噪声谱，以提高峰信噪比（S/N）。该技术是在进行另一次二阶导数滤波之前，将一个经过二阶导数滤波的LC - MS色谱图与另一个添加了热噪声的人工色谱图相乘。由于二阶导数滤波器无法消除其自身滤波器带宽内的频率成分，因此使用连续的二阶导数滤波程序处理LC - MS色谱图无法实现更有效的峰信噪比提高。相比之下，当在进行另一次二阶导数滤波之前，对经过二阶导数滤波的LC - MS色谱图进行乘法变换处理时，能实现更好的信噪比提高。经过二阶导数滤波的色谱图的噪声频谱，原本包含滤波器带宽内的频率成分，通过乘法运算可将其改变为覆盖更宽的范围。当这种修改后的噪声频谱的频率范围向其他区域移动时，作为带通滤波器的另一次二阶导数滤波器能够提供更好的滤波效率，以获得更高的峰信噪比。对于实际的LC - MS色谱图，使用两个连续的二阶导数滤波器实现的5倍峰信噪比提高，与使用一步二阶导数滤波器时的信噪比提高相同，而当在两个匹配的滤波器之间修改噪声频谱时，可将其提高到约25倍或更高，从而实现更好的信噪比增强。使用滤波后的LC - MS信号的线性标准曲线得到了验证。滤波后的LC - MS信号也更具重现性。通过使用滤波后的信号而非原始信号的标准加入法，可以更准确地测定极低浓度的样品（信噪比约为5 - 7）。
