Since 1989, wavelet transform (WT) has attracted much interest of chemists working on signal and image processing, and the WT-based techniques have been successfully applied to the chemical signal processing. This approach has been demonstrated as fast in computation with localization and having quick decay properties, in contrast to the popular methods existing, especially to the fast Fourier transform. More than 370 papers have been published up to the year 2002 which covered applications of WT in various fields of chemistry, including analytical chemistry, chemical physics, and quantum chemistry. In this paper, we report on applications of WT to data compression, data smoothing and denoising, baseline and background correction, resolution of multicomponent overlapping signals, regression and classification, and analytical images processing in analytical chemistry. Through this report we wish to induce greater interest of chemists in WT and to obtain greater benefits from using the WT-based techniques.

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Over recent decades sulfur fumigation has been becoming abused in processing some freshly harvested Chinese medicinal herbs, although it is questioned whether sulfur fumigation can result in changes in efficacy and safety of the herbs. One of the herbs commonly processed by sulfur fumigation is Codonopsis Radix (Dangshen). A report showed that lobetyolin content in sulfur-fumigated Dangshen was lower than in air-dried Dangshen. Whereas there is no investigation designed to compare the chemical profiles of the sulfur-fumigated Dangshen and the air-dried Dangshen. In the present study, a rapid and versatile ultra-high-performance liquid chromatography coupled with ultra-high resolution quadrupole time-of-flight mass spectrometry (UHPLC UHD Q-TOF MS/MS) method was developed for comprehensive analysis of the chemical profiles of sulfur-fumigated and air-dried Dangshen samples. Principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA) demonstrated that there were significant chemical differences between sulfur-fumigated and air-dried Dangshen samples. Among the changed components, 57 compounds were identified, in which 15 sulfur-containing compounds were detected only in sulfur-fumigated samples. The established methods were successfully applied to discriminate sulfur-fumigated Dangshen among commercial samples. Whether the chemical changes caused by sulfur fumigation affect the clinical efficacy and safety of Dangshen needs to be further investigated.

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A novel method based on wavelet transform is proposed in this work for approximate derivative calculation. An approximate first derivative of an analytical signal can be expressed as the difference between the two scale coefficients C 1, which were generated from any two Daubechies wavelet functions. The optimal results for both synthetic and experimental data were obtained with the use of the Daubechies wavelet functions D 8 and D 18. Our work demonstrated that the new method can enhance the signal-to-noise ratio at higher order derivative calculation and retain all major properties of the conventional methods.

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