A gas-phase biosensor for environmental monitoring of formic acid: laboratory and field validation.
In order to encourage more exposure measurements to be performed, a formic acid gas-phase biosensor has been developed for this purpose. In the present paper, an enzyme based biosensor has been validated with respect to analyte selectivity and on-site use. To ensure that the sampler developed measures the compound of interest the biosensor was exposed to three near structural homologues to formic acid, i.e. acetic acid, methanol and formaldehyde. These vapours were generated with and without formic acid and the only compound that was found to have an effect on the performance of the biosensor, albeit a small one, was acetic acid. The field test was performed in a factory using formic acid-containing glue for glulam products. In parallel to the measurements with the biosensor a well defined reference method was used for sampling and analysing formic acid. It was found that the biosensor worked satisfactorily in this environment when used in a stationary position. It was also shown that the biosensor could determine formic acid vapour concentrations down to 0.03 mg m(-3).
A diffusion tube sampler for the determination of acetic acid and formic acid vapours in museum cabinets
A passive, diffusion-tube sampler has been developed for the quantification of acetic acid and formic acid vapours in ambient air. The sampling rates of the diffusion tube and the response times were calculated to be 0.88 ml min−1 and 3.8 min for acetic acid and 1.02 ml min−1 and 3.3 min for formic acid, respectively. The sampler has been deployed unobtrusively in museum environments to collect pollutants over a period of typically 1–2 weeks. Determination of the collected analytes was performed using ion chromatography. Under laboratory test conditions, the results of the sampler for replicate analyses were found to be repeatable and reproducible; typical RSD values were less than 5% for the collection of acetic and formic acid vapours from atmospheres of approximately 187 and 88 mg m−3, respectively. Detection limits of 44 and 13 μg m−3 were calculated for a two week sampling period for acetic acid and formic acid, respectively. The mass of acids collected by the passive sampler increased linearly with atmospheric acid concentrations up to approximately 386 mg m−3 acetic acid and 194 mg m−3 formic acid. In an atmosphere containing approximately 187 and 88 mg m−3 of acetic and formic acid vapours, respectively, the mass of acids collected by passive samplers increased linearly for exposure times between 2 and 75 h. The sampler has been used to investigate the concentration of acetic acid and formic acid vapours in museum cabinets where damage to artefacts by atmospheric pollution has been observed.
Interaction of Diclofop-Methyl and MCPA on Wild Oats (Avena fatua)
Diclofop-methyl {methyl 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoate} loses part of its activity on wild oats (Avena fatua L.) when it is applied in combination with ester or amine formulations of MCPA {[4-chloro-o-tolyl)oxy] acetic acid.} Uptake of diclofop-methyl is reduced in the presence of commercial formulations of MCPA, particularly amine formulations, which are only partly compatible with the diclofop-methyl formulation. With added MCPA, regardless of formulation, hydrolysis of diclofop-methyl to the acid diclofop is slowed down, both in intact wild oat plants and in a crude leaf extract. At the same time, conversion of any acid formed to inactive conjugates is accelerated in the presence of MCPA. It is concluded that the loss of activity of diclofop-methyl by MCPA can be accounted for by the effects of MCPA on uptake and metabolic conversion of diclofop-methyl.