Proposition of a simple method for chromium (VI) determination in soils from remote places applying digital images: A case study from Brazilian Antarctic Station

Abstract

In this study, we proposed a straightforward approach that could be used for Cr redox speciation in soil samples from remote places. For this aim, soil samples under strong anthropogenic impact, from the vicinity of the Brazilian Antarctic Station were studied. Control samples with no direct impact, were also collected further (4 km) from the station. A preliminary laboratory evaluation for Cr (VI) presence was performed using X-ray absorption spectroscopy. The proposed method was based on a hot alkaline extraction to promote the quantitative extraction of Cr (VI) from soil samples. The colorimetric reagent 1,5-diphenylcarbazide (DPC) was added to the extracts to form a violet complex with Cr (VI). A simple and inexpensive commercial scanner was used to acquire the digital images of the formed complex. Partial Least Squares models were constructed with the following average color descriptors: red (R), green (G), blue (B), hue (H), saturation (S), value (V), relative color descriptors (r, g and b) and luminosity (L). The results obtained with this scanner approach were consistent with the official method that uses a spectrophotometer at 540 nm. Besides that, this is the first study that reports Cr redox speciation in soils from Antarctica, which is regarded as the less polluted place on the Earth.

Low-cost vacuum compatible liquid cell for hard X-ray absorption spectroscopy

“…The tetrahedral configuration is characterized by the highest bond strengths (lower Debye Waller factor) and the shortest metal-oxygen distances. These results are consistent with literature [23,30]. In order to demonstrate the compatibility of the cell with cryogenic applications, the same 200 mM solution of Na 2 SeO 4 (Se IV standard) was loaded into the cell, deep quenched at 77 K (by immersing the cell in liquid nitrogen) and fast cooled down to 77 K into the cryostat.…”

“…The 3 eV energy separation between the Cr III pre-edge features is in agreement with the 2-3 eV octahedral crystal field splitting between the t 2g and e g levels measured for several Cr III compounds in octahedral coordination [27]. The study of the intensities of the pre-peaks in Cr K edge has been proposed to quantify and distinguish between the Cr VI /total Cr content in Crcontaminated soil and water samples [23]. Se K edge XANES spectra are shown in panel b) of Figure 3.…”

Developing a population-state decision system for intelligently reprogramming extracellular electron transfer in Shewanella oneidensis

“…Samples were then taken at given time intervals. The Cr(VI) concentration of supernatants was determined using the 1,5-diphenylcarbazide (DPC) method (44). The colorimetric reagent DPC was added to form a violet complex with Cr(VI), which was then analyzed at 540 nm.…”

Chromium speciation in leather samples: an experiment using digital images, mobile phone and environmental concepts

“…A 50 µL aliquot of the supernatant solution was collected and diluted 200-fold. Later, 700 μL of 0.2% (w/v) DPC solution was added and, after this, the pH was adjusted to 1.0 with 5 mol L -1 H2SO4 solution until the solution changed to a pink color 12 . To verify the performance of the proposed method, addition and recovery experiments were employed.…”