Chemometric study on the forensic discrimination of soil types using their infrared spectral characteristics

Soil has been utilized in criminal investigations for some time because of its prevalence and transferability. It is usually the physical characteristics that are studied, however the research carried out here aims to make use of the chemical profile of soil samples. The research we are presenting in this work used sieved (2mm) soil samples taken from the top soil layer (about 10cm) that were then analysed using mid infrared spectroscopy. The spectra obtained were pre-treated and then input into two chemometric classification tools: Nonlinear iterative partial least squares followed by linear discriminant analysis (NIPALS-LDA) and partial least squares discriminant analysis (PLS-DA). The models produced show that it is possible to discriminate between soil samples from different land use types and both approaches are comparable in performance. NIPALS-LDA performs much better than PLS-DA in classifying samples to locatio

Importance of biosensors

• The term biosensor appeared in the 1960s to define the use of bio electrodes involving enzyme electrodes that presented and bio catalytic activity. In 1962, Leyland C. Clark brought the very rudimentary model of biosensors forward with the early invention of an oxygen electrode in which the electrochemical detection of oxygen or hydrogen peroxide could be used for a broad choice of bio analytical purposes. Since then, biosensors have expanded giving rise to a vast frontier of interdisciplinary research that combines biology, analytical chemistry, physics and bio-electronics. From the first bulky biosensors built as academic curiosity, the field has shown a great deal of attractiveness thus becoming a research area that has successfully commercialized devices for multiple applications in a market that is worth many billion dollars. Different uses in medico-clinical, environmental, food-agricultural, security and forensic science, and other fields are making these devices increasingly popular. The question of defining what we can consider as a biosensor is difficult, but the most accepted concept nowadays is to be a device comprising of a biological recognition element attached or integrated into a transducer. • The research developed in this area is certainly increasing. A Scopus study in the publication period 1972-2014 using the word ‘biosensor’ revealed an exponential trend in the number of publications in this field (Figure 1). In the same temporal period the study revealed that the USA remains as the most important country in terms of research in biosensors, followed by China and Germany (Figure 2). However if this period is restricted to the last 5 years (2009-2014) the study reveals that China’s influence in this field is gaining momentum and countries like South Korea and India are increasingly researching in these areas with a higher number of publications being released in this field (Figure 3). • It is likely that the publication trend will continue and with biosensors becoming smaller through miniaturization and into the nanoscale range, the number of applications and research devoted to this field will only increase

Design of a virtual sensor data array for the analysis of RDX, HMX and DMNB using metal-doped screen printed electrodes and chemometric analysis

The detection of explosive substances is a subject of high importance in several areas including environmental health, de-mining efforts (land and sea) and security and defence against terrorist activity. The use of electrochemical methods for the detection of these substances has increased in recent years but still is quite restricted to the most common explosives. The electrochemical detection of explosive nitroamines and taggant substances in solution using a virtual sensor array of metal-doped screen printed electrodes and differential pulse voltammetry was achieved. The multiple sets of voltammetric data from the different electrodic systems using Differential Pulse Voltammetry (DPV) were integrated using multivariate analysis (PCA, NIPALS and LDA) and matched with known substances present in explosives. These combinations created a mathematical array which separated the explosives, even if the electrochemical information is buried or mixed with the background noise. Two explosive substances: octogen (HMX- 1,3,5-Trinitroperhydro-1,3,5-triazine) and cyclonite (RDX- Hexahydro-1,3,5-trinitro-1,3,5-triazine) and a taggant agent 2,3-dimethyl-2,3-dinitrobutane (DMNB) were subjected to electrochemical analysis using a solid carbon- based screen printed electrode modified with silver, gold and platinum in aqueous solutions. Keywords

Extraction of wood compounds by use of subcritical fluids

A study of the extraction of oak wood compounds with subcritical water-ethanol mixtures as extractant, with an ethanol content between 0-60%, is reported. Identification and characterisation of the extracted compounds have been made by spectrophotometry and gas chromatography with either flame ionisation or mass detectors. Extraction was performed statically manner by use of a single cycle or repeated cycles. All variables affecting the extraction process were studied and optimised. Extraction time and temperature are 60 min and 200ºC, respectively. Comparison of the extract thus obtained with commercial extracts showed the former to be rich in compounds characteristic of the commercial extracts. The method enables manipulation of the extract composition by changing the temperature and water/ethanol ratio used. It is faster than the traditional procedures for obtaining wood extracts

The forensic analysis of soil by FTIR with multivariate analysis

Over the past few years more and more studies have been carried out in an attempt to utilize chemical profiles of soil using a wide variety of analytical methods. The value of soil as evidence rests with its prevalence at crime scenes and its transferability between the scene and the criminal. This can be of value for comparison if the scene of crime is known, but could also be so in the identification of a scene. The main basis for the comparison of sites to determine provenance is that soils vary from one place to another. The aim of this work is to find simple methods to identify soil provenance based on FTIR and multivariate analysi

Sequential Spectrophotometric determination of methanol and iron in vinegar by a flow injection-pervaporation method

An easily automatable sequential flow-injection-pervaporation method is proposed for the photometric determination of methanol and iron in vinegar. The method is based on separation of the methanol from the sample matrix by pervaporation followed by its oxidation to formaldehyde with permanganate, decolouration of the latter with S2O5-2 and subsequent reaction of formaldehyde with p-rosaniline to yield a violet reaction product with maximum absorption at 567 nm. Iron is determined by an existing method based on reaction with thiocyanate in acidic medium and monitoring at 508 nm. After optimisation by either the univariate or multivariate approaches, as required, the linear range was established for methanol (4-1000 mg L-1) and iron (0.18-20 mg L-1); The proposed method was then compared with reference methods for methanol and iron in terms of repeatability (2.452 mg L-1 and 0.245 mg L-1, respectively), reproducibility (4.435 mg L-1 and 0.356 mg L-1, respectively), detection limit (LOD=82 and 0.234 mg L-1, respectively) and traceability. The throughput was nine samples per hour

Method for the simultaneous determination of total polyphenol and anthocyan indexes in red wines using a flow injection approach

A simultaneous and fast method for the determination of total polyphenol index (t.p.i.) and total anthocyan index (t.a.i.) has been developed by a flow injection approach and a diode array spectrophotometer for monitoring at 280 nm and 520 nm, respectively. Linear ranges were obtained from 20 to 70 index units and from 20 to 500 mg l-1 for t.p.i. and t.a.i., respectively. The results provided by the proposed method agree with those obtained using the polyphenol index at 280 nm and the Ribereau-Gayon method for the determination of total anthocyans. The sample throughput was 25-30 samples per hour. Analytical features such as repeatability, reproducibility and detection and quantification limits as well as the results of a robustness study based on the Steiner-Younden procedure are also given

Two-parameter determination in vinegar by a flow injection-pervaporation system

A flow-injection method (FI) for the sequential determination of ethanol and acetic acid in vinegar is reported. The determination of ethanol is based on the oxidation of the pervaporated ethanol by Cr2O7K2. The acetic acid is determined by an acid-base reaction with Thymol Blue as the indicator. Both reactions are monitored photometrically at 600 nm using a single detector. Optimisation studies and assessment of the sequential FI method are also reported. The linear determination range is between 0-12 % (v/v) for ethanol and 0-10 % (grams of acetic acid in 100 ml) for acetic acid. The sample throughput of the sequential manifold is 7 per hour. The new method has been applied to vinegar samples and the results obtained are in excellent agreement with those from the reference methods used in Spain

Semiautomatic flow-injection method for the determination of volatile acidity in wines

A flow-injection (FI) method based on analytical pervaporation was assessed for its routine use in the determination of volatile acidity in winery laboratories. The new method was compared with both the official method and the Mathieu method, which is most often used in Spanish wineries, by testing 30 different wines, including young and aged, and sweet and dry wines from Montilla-Moriles appellation d´origine. The robustness of the new method was established and then all three methods were studied in terms of range of linearity and regression of the calibration curve, repeatability, reproducibility, sensitivity, detection and quantification limits (LOD and LQ, respectively) and time of analysis. The FI method surpasses the Mathieu method in reproducibility and both the Mathieu and official methods in LOD and LQ and sensitivity; it also requires less personnel involvement and shorter analysis time. The statistical criteria established by the “Office International de la Vigne et du Vin” were applied to the data and the results obtained indicated that the differences between the analytical parameters of the 3 methods are not significant and can be applied indistinctly. The correlation of the methods was studied by taking them 2 by 2, and the corresponding equations, coefficients and deviations confirmed the statistical results. Thus, the new method can be used in winery laboratories with clear advantages over its 2 counterparts (the routine and official methods)

Determination of ethanol in beverages by flow injection, pervaporation and density measurements

A fast, clean and easy to automate flow injection-pervaporation method for the determination of ethanol in different beverages using density measurements is proposed. The method is based on separation of the ethanol from the sample using a pervaporation module, thus obtaining in the acceptor chamber of the pervaporator a water-alcohol mixture, the density of which is measured. After optimisation by either the univariate or multivariate approach as required, a linear range between 0-40% was established. Then, the assessment of the method versus a reference one was studied in terms of repeatability (0.12% v/v), reproducibility (0.32% v/v), detection limit (0.11% v/v) and traceability. The sample throughput was 15 samples h-1. The method was in agreement with the reference methods used in the European Union