Abstract:
Interior paint is a pigmented and liquified product which is commonly used in most New Zealand households. The application of interior paint to an object provides certain effects such as protection of surface together with changes of color and texture of the object.
The two main classes of interior paints are water-based and oil-based paint, each of which have their respective recommended uses and which possess relative advantages or disadvantages. Generally, users select water-based or oil-based paint based on their appearance after application, durability, drying time, clean-up process and eco-friendliness. In terms of the eco-friendliness, many paints report their level of volatile organic compounds (VOCs).
This project focuses on the forensic value of the measurement of VOCs being emitted from paint. The persistence profile of VOCs could be used to aid in the determination of the application time of paint at a crime scene. This could be of value in cases such as a person of interest repainting certain surfaces to hide evidence such as bloodstains, or to cover over drug residues at a former clandestine laboratory. The analyses carried out in this paint study are a useful indicator to determine the type and the persistence profile of VOCs that are emitted into an indoor ambience.
The goal of this study was to develop a simple method to reproducibly determine the VOCs that are emitted from a selected range of interior paints and compare the persistence profile across different brands over a 72 h time period, using equipment that might be available in a standard forensic analytical laboratory. Five New Zealand interior paint brands were selected, which were White Knight, Dulux, Resene, PPG Paints and British Paints. Three oil-based and three water-based wall paints were applied on multiple pine wood pieces, and an aging experiment was conducted to determine the persistence profile from these paints. After the application of interior paint onto the wood surface, VOCs that volatilized over selected short time intervals were sampled from the headspace above the paint using solid phase microextraction (SPME) coupled to gas chromatography-mass spectrometry (GC-MS). The retention times of the dominant VOCs being emitted were determined from the total ion chromatograms (TIC), with the identity of the compounds then being ascertained from
comparison of their mass spectra to the National Institute of Standards and Technology (NIST08) library and their order of elution. The selected compounds that are commonly found in paints are based on their classification: carbonyl, aromatic and aliphatic hydrocarbon. Extracted ion chromatograms (EIC) were used to determine the relative peak areas of the VOCs over time. One of the oil-based paints – “White Knight Strokes Gloss White” was used in an experiment to determine whether diurnal irradiation with sunlight affected the VOCs measured from the headspace above the paint. A batch of paint samples were placed such that they were exposed to sunlight while the second batch was aged in dark ambient. Only small differences were noted in the concentration of the VOCs selected in this project.
Throughout the study, the type of airborne VOCs, the changes of relative concentrations over time and the impact to VOCs from sunlight were evaluated. Potentially, the method and data conducted from this experiment can be utilized in future crime scenes to develop a model that can estimate the time since deposition (TSD) of a paint sample.