Abstract
The use of corrosive substances for criminal intent has recently increased in many countries, with 619 violent assaults recorded from 2019 to 2020 only in the UK. Criminals often conceal corrosive solutions, such as common household cleaners, in inconspicuous plastic bottles and splashing the content in order to incapacitate a victim while committing a robbery or to cause physical harm. There is currently no method available to law enforcement for the safe identification of these corrosive substances without being exposed to them. In this work, the feasibility of a near infrared (NIR) handheld spectrometer for the screening of corrosive inorganic solutions through plastic bottles is investigated. First, a training set comprising samples of five different corrosives was used to build a spectral library for data analysis and chemometric model design. Four models were then tested on three hundred samples of corrosive substances, as well as harmless substances such as water and soft drinks, to evaluate their performance. The models designed identified the corrosive substances in scenarios of concentrated solutions, showcasing the potential capability of this technique for the pre-screening of corrosive substances.
Highlights
Recent reports in the UK have shown an increasing trend in the use of corrosive substances for different criminal activities
The present study focused on evaluating the applicability of portable near infrared (NIR), as an on-field test of corrosive substances
At the training stage, which entails both data collection and data analysis, each corrosive was prepared in aliquots of at least two different concentrations, each tested in three types of plastic containers
Summary
Recent reports in the UK have shown an increasing trend in the use of corrosive substances for different criminal activities. These pre-treatment methods are often combined with multivariate data analysis methods such as Partial Least Square Regression (PLSR) [16], Soft Independent Modelling of Class Analogies (SIMCA) [17] and Principal Component Analysis (PCA) [18] in order to identify the main sources of variability among the classes defined by the user and, in turn, assist in the clustering of new unknown samples These approaches have become a standard practice when using NIR for analytical purposes, in the design of supervised methods, in different scientific fields [8,9,12,19–22]. The methodology explored during this study was restricted exclusively to the tools available within the SCiOTM and its associated software to assess the potential implementation of such commercial instruments among the intended end users, e.g., police forces This is, to the best of the authors’ knowledge, the first study to assess the use of NIR, and portable NIR, for the qualitative analysis of corrosive substances in criminal investigations
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