Chemical fingerprinting:A new technology for characterizing complex substances

Introduction

Complex substances refer to materials composed of multiple components, such as biological tissues, food, pharmaceuticals, petroleum, etc. The characterization of complex substances involves analyzing and identifying their composition, structure, properties, and functions, which is crucial for scientific research and industrial applications. However, due to the diverse composition, intricate structures, and variable properties of complex substances, traditional characterization methods often struggle to obtain comprehensive, accurate, and reliable information.

Principles of Chemical Fingerprinting Technology

Chemical fingerprinting is a liquid-based characterization technology that utilizes the interactions between a liquid and complex substances to generate characteristic spectral signals, reflecting the chemical features of the complex substances. The liquid can be water, organic solvents, or mixed solvents, each with different properties such as polarity, solubility, and reactivity. When the liquid comes into contact with the complex substance, processes like adsorption, dissolution, diffusion, exchange, and reaction occur, leading to the formation of various species such as molecules or ions in the liquid. These species interact with light through absorption, scattering, or emission, creating characteristic spectral signals. By measuring and analyzing these spectral signals, the chemical information of the complex substance, such as composition, structure, phase state, and function, can be obtained.

Chemical fingerprinting technology can utilize different light sources and detectors to achieve spectral measurements across various wavelength ranges and resolutions. Common light sources include visible light, ultraviolet light, infrared light, and Raman lasers, while common detectors include absorption spectrometers, fluorescence spectrometers, Raman spectrometers, and Fourier transform infrared spectrometers. Based on the combination of different light sources and detectors, chemical fingerprinting technology can be categorized into absorption chemical fingerprinting (ACF), fluorescence chemical fingerprinting (FCF), Raman chemical fingerprinting (RCF), and Fourier transform infrared chemical fingerprinting (FTIR-CF).

Figure 1: Component Fingerprint Analysis Experiment Case

Methods of Chemical Fingerprinting Technology

The methods of chemical fingerprinting technology primarily include four steps: sample preparation, liquid selection, spectral measurement, and data analysis.

1.Sample Preparation

Sample preparation is one of the most crucial and challenging steps in chemical fingerprinting technology, directly affecting the effectiveness and results of subsequent steps. Sample preparation involves three main stages: sample selection, sample processing, and sample loading.

Sample Selection: This involves choosing the appropriate complex substance as the analysis object based on the research purpose and requirements. Factors such as the source, type, quantity, quality, and representativeness of the sample should be considered to ensure the reliability and comparability of the samples.

Sample Processing: This involves necessary pretreatment of the selected complex substance to facilitate subsequent liquid contact and spectral measurement. Sample processing mainly includes operations such as cleaning, drying, crushing, sieving, mixing, and homogenizing the samples to remove impurities, adjust moisture content, alter morphology, and increase uniformity.

Sample Loading: This involves placing the processed complex substance on a suitable carrier for spectral measurement to achieve effective contact with the liquid. Sample loading mainly involves determining parameters such as sample weight, sample thickness, sample shape, and carrier material to ensure the stability and reproducibility of the spectral signals.

2.Liquid selection

Liquid selection involves choosing an appropriate liquid as the characterization medium based on the properties of the complex substance and the requirements of spectral measurement. Factors to consider include the liquid's polarity, solubility, reactivity, stability, and transparency, to ensure effective interaction with the complex substance and clear spectral signals.

Liquids can be single or mixed, and different proportions or sequences of liquids can be used to increase the amount of information and differentiation. Liquid selection can also be optimized according to different light sources and detectors to enhance the intensity and resolution of the spectral signals.

3.Spectral Measurement

Spectral measurement involves using various light sources and detectors to measure and record the spectral signals generated after the liquid interacts with the complex substance. Factors to consider include the wavelength range, power, and stability of the light source; the sensitivity, resolution, and noise of the detector; and the experimental conditions such as temperature, humidity, and time, to ensure the accuracy and consistency of the spectral signals.

Spectral measurement can be performed in different modes, such as static mode, dynamic mode, scanning mode, and mapping mode, to suit different sample characteristics and experimental goals. Various techniques such as single-point, multi-point, imaging, and holographic techniques can be employed to enhance the spatial distribution information of the spectral signals.

4.Data Analysis

Data analysis involves using mathematical statistics and machine learning methods to process and interpret the obtained spectral data, extracting the chemical information of the complex substance. Factors to consider include the quality, quantity, and dimensionality of the data to ensure its validity and reliability.

Different methods such as baseline correction, peak fitting, normalization, dimensionality reduction, clustering, classification, and regression can be used for data preprocessing, feature extraction, pattern recognition, and quantitative analysis. Various algorithms, including principal component analysis (PCA), partial least squares (PLS), support vector machines (SVM), artificial neural networks (ANN), and deep learning (DL), can be employed to improve the interpretability and predictability of the data.

Application Fields

1.Food

Food is a complex substance composed of various ingredients, with diverse forms and properties. Characterizing food is a significant aspect of food science and engineering, as it reflects the quality, safety, and nutrition of food, as well as its interactions with factors such as processing, storage, and consumption.

Chemical fingerprinting technology can provide rapid, comprehensive, and quantitative characterization of food, reflecting its chemical composition, structural features, and functional properties. For example, absorption chemical fingerprinting technology can be used for the variety identification and quality evaluation of tea leaves; fluorescence chemical fingerprinting technology can be utilized for the authentication and geographical origin tracing of honey; Raman chemical fingerprinting technology can be employed for the component analysis and adulteration detection of milk powder.

2.Pharmaceuticals

Pharmaceuticals are complex substances composed of various ingredients, with diverse forms and effects. Characterizing pharmaceuticals is a crucial aspect of pharmaceutical science and engineering, as it reflects the composition, structure, properties, and efficacy of drugs, as well as their interactions with factors such as preparation, storage, and use.

Chemical fingerprinting technology can provide simple, sensitive, and accurate characterization of pharmaceuticals, reflecting their chemical composition, structural differences, and functional states. For example, absorption chemical fingerprinting technology can be used for quality control and active ingredient determination of traditional Chinese medicine; fluorescence chemical fingerprinting technology can be utilized for the content determination and degradation monitoring of antibiotics; Raman chemical fingerprinting technology can be employed for crystal form identification and homogeneity evaluation of solid preparations.

3.Petroleum

Petroleum is a complex substance composed of various components, with diverse forms and properties. Characterizing petroleum is a significant aspect of petroleum science and engineering, as it reflects the source, composition, properties, and value of petroleum, as well as its interactions with factors such as exploration, extraction, processing, and utilization.

Chemical fingerprinting technology can provide efficient, comprehensive, and quantitative characterization of petroleum, reflecting its chemical composition, structural features, and functional properties. For example, absorption chemical fingerprinting technology can be used for geochemical analysis and geographical source discrimination of crude oil; fluorescence chemical fingerprinting technology can be utilized for quality evaluation and additive detection of diesel; Raman chemical fingerprinting technology can be employed for composition analysis and aging monitoring of asphalt.

Prospects of Chemical Fingerprinting Technology

Chemical fingerprinting technology is a new method for characterizing complex substances. It has the advantages of being simple, fast, sensitive, non-destructive, and reproducible, enabling efficient, comprehensive, and quantitative characterization of complex substances. This technology has broad applications in fields such as biological tissues, food, pharmaceuticals, and petroleum, providing new methods and tools for scientific research and industrial applications.

Chemical fingerprinting technology also has enormous development potential and can be improved and innovated in the following aspects:

Sample Preparation: Developing simpler, more efficient, and more intelligent sample preparation methods to reduce human interference and errors, thereby increasing the reliability and comparability of samples.

Liquid Selection: Utilizing a wider variety of higher-performance, lower-cost liquids as characterization media to increase information content and differentiation, enhancing the intensity and resolution of spectral signals.

Spectral Measurement: Developing more advanced, more sensitive, and more stable light sources and detectors to expand wavelength range and resolution, improving the accuracy and consistency of spectral signals.

Data Analysis: Adopting more powerful, more intelligent, and more automated data analysis methods to handle big data and high-dimensional data, extracting valid information, and achieving pattern recognition and quantitative analysis.

Chemical fingerprinting technology, with its broad application prospects and development space, is a promising new method for characterizing complex substances. As scientific and technological advancements continue and demand grows, chemical fingerprinting technology will continue to improve and innovate, offering more possibilities for the characterization of complex substances.