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).
[67] Formate dehydrogenase
Publisher Summary This chapter discusses the determination of formate dehydrogenase. The assay depends on measurement of the rate of increase of optical density at 340 mμ consequent on the reduction of diphosphopyridine nucleotide (DPN) in the presence of formate. The complete reaction system in a 1.5 ml silica cell (1 cm light path) consists of 0.25 ml of phosphate buffer, 0.25 ml of sodium formate, 0.1 ml of DPN, enzyme extract, and water to a total volume of 1 ml. The blank cell lacks formate and DPN. The reaction is started by addition of enzyme to both cells, and the rate of increase of extinction at 340 mμ is measured. Enzyme may be placed initially in both test and blank cell and the reaction be started by adding formate to the test cell. One unit of enzyme is defined as the amount of enzyme that catalyzes the reduction of 1 micromole of DPN per minute under the conditions of assay. Specific activity is expressed as units of enzyme per milligram of protein. The purified enzyme is specific for formate: no activity has been detected with methanol, ethanol, formaldehyde, oxalate, acetate, pyruvate, or malate.
Mesozoic rifting and basin inversion along the northern African Tethyan margin: an overview
Abstract The northern African Tethyan margin registered three major rifting episodes from the latest Palaeozoic-earliest Mesozoic to the earliest Cenozoic. Break-up of Gondwana was initiated in the late Carboniferous. Along the northern African-Arabian plate margin rifting propagated westward from the northeastern Arabian margin to Morocco during the Permian and Triassic, and was accompanied by Mid-Late Triassic-earliest Liassic extensive alkaline flow basalts. Rifting continued during the Liassic, e.g. in the Moghrebian Atlas troughs. A second stage of rifting occurred in the Late Jurassic and continued into, or was rejuvenated during, the Early Cretaceous. Along the east Mediterranean margin, some large E-W trending rifts formed, often with associated volcanism, e.g. southern Sirt and Abu Gharadig. Most researchers believe the oceanization of the eastern Mediterranean basin occurred at this time. Flexural subsidence affected the Moghrebian Atlas, including the Riffian-Tellian domain, where a thick flysch series was deposited. Two short-lived, but widespread and tectonically important, compressional or wrench-dominated events occurred during the Santonian and the latest Maastrichtian. From Morocco to Oman, most sedimentary basins were folded and inverted at these times. The Santonian event resulted from onset of the collision between the African-Arabian and Eurasian plates. New stress-fields favoured NE-SW extension along the African plate margin, generating or rejuvenating some rifts, e.g. in the Euphrates trough and in the Libya-Tunisia region (northwestern Sirt, Pelagian Sea). Rifting and magmatism continued in these regions into the Paleocene. During the Mesozoic, therefore, the northern margin of the African-Arabian plate registered both rifting resulting in the oceanization of the Tethys and rifting resulting from the initiation of the closure of the Tethys. The intraplate domain exhibited echoes of the tectonic events affecting the margin.