Chemometric approach for the discrimination of petroleum based accelerants from fire debris

Petroleum-based accelerants are commonly associated with arson-related fire. In most arson cases, accelerants such gasoline, kerosene and diesel used to increase the rate and intensity of fire. However, other petroleum based accelerants such as turpentine and thinner cannot be ignored because of their easy availability. These accelerants composed of hundreds of compounds that can make identification of fire debris very difficult. Furthermore, the complex nature of petroleum based accelerants pose a problem for the arson investigator to determine the origin of the fire and the cause of the fire. Therefore, correct identification of accelerants is crucial to arson investigation. The application of gas chromatography/mass spectrometry (GC/MS) and chemometric techniques for petroleum-based accelerant identification is presented in this study. Extraction of accelerant was done by using dynamic adsorption-elution headspace technique and analyzed using GC-FID and GC-MS. The petroleum based accelerants used in this study were gasoline, diesel, kerosene, turpentine and thinner. Chemometric approaches were employed to simplify data obtained by allowing them for more accurate classification to their respective groups. Principal component analysis (PCA), cluster analysis and soft independent modeling class analog analysis (SIMCA) were explored for their effectiveness in establishing accelerant groupings. This was done on normalized data of total ion chromatogram and peak areas which were obtained from GC-MS. The extraction of fire debris using the dynamic adsorption/elution technique was successful in isolating the accelerants compounds from the samples. Beside that, PCA and cluster analysis were successfully classify the accelerants according to their respective groups compared to SIMCA analysis

Electromembrane extraction and electrochemical measurement system for heavy metal ions detection in aquatic environmental samples

Water contamination is a worldwide problem which deserves attention due to its negative impact on ecosystem, human health as well as economic growth. Heavy metals are a group of the pollutants that have received particular attention due to their high toxicity even at concentration as low as parts per billion (ppb). Technology advancement in the field of separation and detection of heavy metals has introduced sensitive and selective analytical instruments for real aquatic environmental samples. However, real sample matrices can reduce the quality of results. In modern analytical chemistry, there is a high demand for accurate quantification of trace and ultra-trace of heavy metals from real aqueous samples. In the present study, electromembrane extraction (EME) and electrochemical techniques were combined to develop effective electrodes which can separate, pre-concentrate and determine heavy metals such as Pb(II), Cr(VI) and Cd(II) in real aqueous samples. Electrochemically reduced graphene oxide-graphite reinforced carbon (ErGO-GRC) was utilised in conjunction with square wave anodic stripping voltammetry (SWASV) for the determination of Pb(II). Meanwhile, selective and sensitive determinations of Cr(VI) was carried out using ex-situ prepared nafion-coated antimony film on graphite reinforced carbon (NSbFE-GRC) by square wave adsorptive stripping voltammetry (SWAdSV) in the presence of diethyltriamine pentacetic acid (DTPA). Ex-situ prepared NSbFE-GRC was also used for simultaneous determination of Pb(II) and Cd(II) by SWASV. Simple polyvinylidene fluoride (PVDF) flat sheet membranes were synthesised and characterised in order to combine these developed electrochemical techniques with EME. Heavy metals were extracted from an aqueous sample solution into an acidic acceptor phase in the lumen of a PVDF membrane bag by the application of voltage across the supported liquid membrane (SLM), consisting of organic solvent and complexing carriers. Parameters affecting the EME were optimised for heavy metals. The PVDF–ErGO–GRC electrode system attained enrichment factors of 40 times and 80% extraction with relative standard deviation (n = 5) of 8.3% for Pb(II). Good linearity in the range of 0.25-2 nM was obtained with correlation coefficient of 0.999. The Pb(II) ions detection limit of PVDF–ErGO–GRC electrode was 0.09 nM. Meanwhile, the PVDF–NSbFE–GRC system attained enrichment factors of 86.6 times, 95.6% extraction, and good linearity in the range of 10-60 pM with correlation coefficient of 0.9933. Furthermore, the limit of Cr(VI) detection was found to be around 0.83 pM for the developed PVDF–NSbFE–GRC electrode. On the other hand, the PVDF–NSbFE–GRC was able to attain enrichment factors of 49.3 and 68.4 times, 82.6% and 114.0% extractions, and good linearity ranging from 2 to 10 pM with correlation coefficients of 0.9953 and 0.9883 for Pb(II) and Cd(II), respectively. Furthermore, the limits of detection for Pb(II) and Cd(II) were found to be around 0.65 pM and 0.60 pM, respectively. A chargeable battery operated portable EME system was developed for quantitative determination of heavy metals. The newly developed single setup electrochemical system was applied to the analysis of real aqueous samples such as tap water, industrial waste water, river water and sea water, and it was able to extract with percentage of extraction in the range of 78.7 -103.0% compared to commercially available direct current power supply

PVDF-ErGO-GRC electrode: a single setup electrochemical system for separation, pre-concentration and detection of lead ions in complex aqueous samples

An effective electrode was developed based on electromembrane extraction (EME) and square wave voltammetry (SWV) for simultaneous separation, pre-concentration and determination of lead (II) (Pb(II)) ions in complex aqueous samples. Electrochemically reduced graphene oxide-graphite reinforced carbon (ErGO-GRC) was utilized in conjunction with the SWV. Pb(II) ions were extracted from an aqueous sample solution into an acidic acceptor phase (1 M HCl) in the lumen of the polyvinylidene fluoride (PVDF) membrane bag by the application of voltage of maximum 6 V across the supported liquid membrane (SLM), consisting of organic solvent and di-(2-ethylhexyl)phosphoric acid (D2EHPA). The parameters affecting the EME were optimized for Pb(II) ions. The optimum EME conditions were found to be 20% D2EHPA in 1-octanol impregnated in the wall of PVDF membrane (PVDF17) as the SLM, extraction time of 20 min, pH of sample solution of 8 and a voltage of 5 V. The PVDF-ErGO-GRC electrode system attained enrichment factors of 40 times and 80% of extraction with relative standard deviations (n=5) of 8.3%. Good linearity ranging from 0.25 to 2 nM with coefficients correlation of 0.999 was obtained. The Pb(II) ions detection limit of PVDF-ErGO-GRC electrode was found to be 0.09 nM. The newly developed single setup electrochemical system was applied to complex aqueous samples such as tap, river and sea water to evaluate the feasibility of the method for applications

A sensitive, selective and rapid determination of lead(II) ions in real-life samples using an electrochemically reduced graphene oxide-graphite reinforced carbon electrode

In this study, a sensitive and cost-effective electrochemically reduced graphene oxide (ErGO) on graphite reinforced carbon (GRC) was developed for the detection of lead (Pb(II)) ions present in the real-life samples. A film of graphene oxide (GO) was drop-casted on GRC and their electrochemical properties were investigated using cyclic voltammetry (CV), amperometry and square wave voltammetry (SWV). Factors influencing the detection of Pb(II) ions, such as grades of CRC, constant applied cathodic potential (CACP), concentration of hydrochloric acid and drop-casting drying time were optimised. GO is irreversibly reduced in the range of -0.7 V to -1.6 V vs Ag/AgCl (3 M) in acidic condition. The results showed that the reduction behaviour of CO contributed to the high sensitivity of Pb(II) ions detection even at nanomolar level. The ErGO-CRC showed the detection limit of 0.5 nM and linear range of 315 nM in HCl (1 M). The developed electrode has potential to be a good candidate for the determination of Pb(II) ions in different aqueous system. The proposed method gives a good recovery rate of Pb(II) ions in real-life water samples such as tap water and river water