Thin thickness gilding determined by x-rays ratios from EDXRF-spectra

A by-product of energy-dispersive X-ray fluorescence (EDXRF)-analysis consists of using the ratios of selected X-ray peaks to determine the thickness of multilayered objects. Three different methods were developed in the past, all because the two main K or L X-lines from an EDXRF spectrum emitted by a chemical element have a distinct energy and are differently attenuated by an overlying layer. This specific subject has many papers dedicated, but only a few considerations were devoted to the limits of these methods, that is, the range, for example, of gold thickness that can be usefully determined by each method. This paper defines these limits in the specific case of thin gilding (with d < 1 μm). Three typical situations were considered, and the following artefacts were studied: two artefacts on gilded lead, where the gold leaf is superimposed to a white lead pigment, both in the painting “La Fornarina” of Raphael, dated 1520 AD, and in the imperial carriage of Dom Pedro II emperor of Brazil. In this last case, the white lead pigment was painted over the wood structure of the carriage; four artefacts on gilded copper, three crowns and a pendant, from the tomb of the Lady of Cao, from the Moche civilization of the North of Peru, dated around 350 AD; finally, an artefact on gilded silver, a vase from the Chavín civilization of the North of Peru, dated around 1000-200 BC.     

Palynological origin, phenolic content, and antioxidant properties of honeybee-collected pollen from Bahia, Brazil

The aim of this study was to determine the palynological origin, phenolic and flavonoid content, and antioxidant properties of twenty-five samples of bee pollen harvested during a nine-month period (February-November) from the Canavieiras municipality (northeastern Brazil). Of the 25 samples analyzed, only two (February 01 and 02) were heterofloral. The predominant pollens in the samples analyzed during that month were: Cecropia, Eucalyptus, Elaeis, Mimosa pudica, Eupatorium, and Scoparia. Ethyl acetate fractions were analyzed by HPLC-DAD. The flavonoids isoquercetin, myricetin, tricetin, quercetin, luteolin, selagin, kaempferol, and isorhamnetin were detected. The flavonoid present in all 22 samples was isolated and identified as isorhamnetin 3-O-b-neohesperidoside. The total phenolic contents determined using the Folin-Ciocalteu reagent ranged from 41.5 to 213.2 mg GAE/g. Antioxidant activities based on the 1,1-diphenyl-2-picryl hydrazyl (DPPH), 2,2-azinobis 3-ethylbenzothiozoline-6-sulfonic acid (ABTS), and Fe2+ ion chelating activity assays were observed for all extracts, and correlated with the total phenolic content.     

Software-switching between direct absorption and wavelength modulation spectroscopy for the investigation of ADC resolution requirements

We present a tunable diode laser spectrometer that can be software-switched between a wavelength modulation spectroscopy (WMS) operation mode and the direct absorption spectroscopy (DAS) technique on a per-scan basis. The new setup allows a direct comparison between the two techniques under equal hardware and system environment conditions. In this work, we compare the impact of analog-to-digital converter resolution for operation in WMS and DAS mode. Example concentration evaluations show that in the DAS approach, relative absorptions smaller than the least significant bit can be measured with scan averaging and FIR-filtering applied. With full resolution, both techniques show similar performance in our setup, with a slight advantage for the WMS implementation.