Chemometrics in Analytical Spectroscopy provides students and practising analysts with a tutorial guide to the use and application of the more commonly encountered techniques used in processing and interpreting analytical spectroscopic data. In detail the book covers the basic elements of univariate and multivariate data analysis, the acquisition of digital data and signal enhancement by filtering and smoothing, feature selection and extraction, pattern recognition, exploratory data analysis by clustering, and common algorithms in use for multivariate calibration techniques. An appendix is included which serves as an introduction or refresher in matrix algebra. The extensive use of worked examples throughout gives Chemometrics in Analytical Spectroscopy special relevance in teaching and introducing chemometrics to undergraduates and post-graduates undertaking analytical science courses. It assumes only a very moderate level of mathematics, making the material far more accessible than other publications on chemometrics. The book is also ideal for analysts with little specialist background in statistics or mathematical methods, who wish to appreciate the wealth of material published in chemometrics.
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Many analytical methods typically used to examine these changes (e.g. thermal analysis [14] or amino acid analysis [12]) result in loss of the sample, even if this is a very small amount, which has obvious drawbacks when applied to heritage objects. Analytical techniques also often require specialist instrumentation (e.g. scanning electron microscopy [3] or pyrolysis gas chromatography [16]) or involve lengthy preparation (e.g. amino acid analysis [12]). Fourier Transform -Infrared spectroscopy (FTIR) can be used to detect alterations in protein composition and has been shown to reveal changes to the hierarchical structure of collagen. [17] When used with an attenuated total reflectance (ATR) attachment it is fast and requires little or no sample preparation [18]. Although FTIR-ATR can leave a small imprint on a malleable sample such as leather, the damage is minimal, and no sample is lost. These factors mean that multiple analyses can be carried out across an object, providing a better evaluation of the entire object on which to base conservation decisions and make it an ideal technique for the analysis of heritage objects. Advances in instrumentation, for example portable instruments or FTIR microscopes which do not require direct contact, increasingly provide the ability to analyse larger objects and remove risks of damage [19]. Despite this, whilst FTIR has been successfully applied to the analysis of many collagen-based materials including historic parchments [20] its application to leather is less well explored. This is largely because FTIR spectra obtained from leather is complicated by the presence of tanning agents, making it very difficult to accurately assign all peaks in the spectrum [21, 22]. However, peaks relating specifically to the collagen backbone (amide I, amide II and amide II) can be identified, and changes in these peaks have been shown to change when conformational changes within the collagen occur [21, 23]. The hydrolysis or oxidation breakdown pathways of leather will result in other changes to the functional groups present which will be represented by changes to the related peaks in the FTIR spectra, for example an increase in carboxylic acid and amine groups due to cleavage of the peptide chains (Fig. 1) [10].
Currently, portable Raman spectrometers, which can measure intact samples are more readily available than IR spectrometers with such a capability. Consequently, to date, progress towards the development of biospectroscopy-based bioanalytical approaches for the analysis of intact crops has been limited primarily to the use of Raman spectroscopy, although this technique has only been recently employed for whole sample analysis [25,26,27,28]. Several other techniques outside the MIR range such as near-IR (NIR), ultraviolet (UV) and Visible light, as well as hyperspectral analysis have been used to assess quality parameters in tomato [29,30,31]. However, few of these studies provide detailed biochemical insight into the changes occurring in vivo during development and ripening and have traditionally focused solely on classification performance or correlation between traditional quality parameters and spectral data [32]. Furthermore, the potentially small measurement area, as well as the higher energy of NIR, UV, visible, and Raman instruments, increases the light penetration depth into the sample over a very small area making it potentially difficult to obtain reliable biological information. MIR spectroscopy in contrast offers sampling modes with very well-defined measurement areas and light penetration depths [19], which permit biochemical investigations when combined with known chemical compositions of plant tissues under investigation [33,34,35,36,37]. Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy is one method with a very well-defined light penetration depth, where macro measurements over larger areas are possible [19]. In other fields, ATR-FTIR spectroscopy has proved exceptional at providing both biochemical insight into biological samples, as well as providing strong discriminating power in combination with classification models [20, 34]. This suggests a need to evaluate the use of Raman complementary methods such as reflectance spectroscopy including ATR-FTIR spectroscopy within crop science. In order to increase the capacity for spectroscopy-based methods to provide biochemical information as well as classification performance, it is imperative to assess complementary approaches aimed at developing multi-sensor platforms, which will be required for complex systems.
Biospectroscopy is a powerful analytical tool and potential sensor technology for linking fundamental plant biology and applied crop sciences as part of developing precision horticulture systems. The development of surface techniques including MIR spectroscopy that are applicable to both homogenous and for heterogeneous substances has opened the door for analysis of intact tissues and non-destructive measurements in vivo. However, to date the degree to which MIR spectroscopy has been used to study intact plants has been limited, as has the evaluation of portable equipment that may be readily retooled for use in horticultural applications [25]. The ATR-FTIR sampling mode, probes the main groups of biochemical compounds within tomato fruit epidermal surface layers, such as cutin, wax, and phenolic fractions of the cuticle, as well as cellulose, pectin, carbohydrates, and lignin-like compounds as primary cell wall constituents (Tables 1 and 2), and is thus ideal for the study of plant epidermis as it relates to horticultural parameters. Biospectroscopy based multi-compound analysis, within plant organs in vivo, offers an alternative methodology to conventional ways of studying cuticle and cell wall structure during development or in response to industrial processing [33, 36]. In this regard, MIR biospectroscopy will prove useful for deciphering the molecular details of changing epidermal structures during tomato fruit development and ripening. This is critical because the detailed mechanisms behind cuticle formation are debated, and little is known about the relationship between cuticle structure and postharvest characteristics in whole tomato fruit [10, 13].
Most elements needed to transition this approach from a lab-based analytical method to an applied sensor technology for routine monitoring are already available including portable spectrometers, fast data analysis tools, and the minimal to no sample preparation required for most crop plants making this a realistic possibility. To realise this potential, application of biospectroscopy to additional model plant systems is needed alongside the evaluation of new portable equipment, similar to that recently developed for Raman spectroscopy [25]. With these advances, rapid analysis with optical sensors such as MIR spectroscopy will further permit the automatic characterization of healthy fruit development, and enabling abnormalities related to damage or disease to be reliably identified. In addition, further development of biospectroscopy in the plant and crop sciences will contribute to a better biological and biochemical understanding of plant surface layers, and how these affect the traits of plant organs such as fruit; thereby, contributing to both molecular plant biology and industrial horticulture for better crop production.
This review represents many significant methods of chemometrics applied as data assessment methods originated by many hyphenated analytical techniques containing their application since its origin to today.
On the other hand, vibrational spectroscopic techniques like infrared and Raman have acquired special significance whereas they merge a variety of features (Doty et al. 2016; Mou et al. 2008). Recently, Fourier transform infrared (FTIR) spectroscopy is now being incorporated as a genuinely valuable GSR evaluation method with sufficient precision and flexibility for the detection of organic compounds in GSRs (Bueno et al. 2012; López-López et al. 2012). Raman spectroscopy is also being implemented as a viable approach for the study of gunfire traces, with an emphasis on segregation in the formation of sourcing ammunition and the caliber of ammunition (Latzel et al. 2012). It must explain the composition of a vast number of organic and inorganic components detected at the crime scene while also attempting to reconstruct its source, which must be non-destructive and very simple to utilise. In addition, the instrumental flexibility of handheld, durable, mapping and detecting methods allows for a range of valuable analytical choices (Sharma and Lahiri 2009; Zeichner 2003).
This review offers a valuable overview of present scientific studies which used vibrational spectroscopy techniques combined with chemometrics in forensic ballistics scenarios; in fact, an evaluation one of most major aspects of forensic evidence like explosive traces, body fluids, and gunshot residue (Fig. 1). 2ff7e9595c
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