Quantitative extraction of chromium VI and III from tanned leather: a comparative study of pretreatment methods

In this study, seven pretreatment methods for chromium speciation in tanned leather were evaluated: acidic mineralization, ethylenediaminetetraacetic acid (EDTA) extraction, diethylenetriaminepentaacetic acid (DTPA) extraction, alkaline extraction (NH4OH), ammonium nitrate extraction (NH4NO3), water extraction, and phosphate buffer extraction. Acidic mineralization permitted the decomposition of the organic matter and ensured the complete digestion of leathers, giving access to the total content of chromium in each sample using inductively coupled plasma-atomic emission spectrometry (ICP-AES). From all the extractant media tested, EDTA proved to be the most efficient, allowing the extraction of Cr(VI) and Cr(III) as a Cr(III)-EDTA complex, quantitatively. Method validation is presented for EDTA extraction and direct mineralization. For the EDTA extraction, method detection limit (MDL) and method quantification limit (MQL) for total Cr in leather were 3.4 ppb and 11.2 ppb (µg of total Cr per L of extraction solution), respectively. Due to the lack of leather certified reference materials (CRMs) for Cr(VI), accuracy was evaluated by spiking leather samples with a Cr(VI) solution. The spike recovery of EDTA microwave assisted extraction ranged from 91.0 to 108.6%. Interday precision was also evaluated and all variation coefficients were below 5%, for both mineralization and EDTA extraction. This article provides an efficient procedure to extract quantitatively chromium from leather, while maintaining the speciation, which can be further followed by ion chromatography-inductively coupled plasma-mass spectrometry (IC-ICP-MS).

Modifications in the methods to extract pectin from cv. “Pedro Sato” guavas during ripening

Guava is a highly perishable fruit due to its intense metabolism during ripening, with a shelf life of up to five days at room temperature. The loss of firmness during ripening is caused by the activity of hydrolytic enzymes that promote dissolution of the pectin constituents of the cell wall. Although guava is considered to be rich in pectin, the amounts reported in the literature do not exceed 2.4%, a content indicating it is not responsible for the firmness of guava. The aim of this study was to extract pectin from the guava pulp during 7 days of ripening by two methods (ethanol and EDTA extraction) and suggest modifications in the methods by adding to the extraction residue, cellulase and pectinase to degrade the cell wall structure of the fruit and obtain larger amounts of pectin, which would imply the participation of pectin in the maintenance of fruit firmness. It was possible to infer there were no differences in the pectin levels extracted by the two methods, due to sugar contamination. As from the new stage in the execution by the two methods, the extraction was more efficient: 9.10% of pectin with EDTA and 7.63% with ethanol. The pectin contents found were higher than those mentioned in the literature, better explaining their responsibility in fruit firmness.

Influence of selected heavy metals (As, Cd, Cr, Cu) on nematode communities in experimental soil microcosm

Summary In this study, the effects of arsenic, cadmium, copper and chromium treatments were examined on a nematode community structure and proportion of functional groups in the microcosm for 30 days. The toxic effects on the nematode community did not correspond with metals mobility (EDTA extraction) in soil as it was expected. The most toxic element with a significant degradation of community structure was chromium (low mobile), which negatively affected almost all observed ecological parameters (abundance, diversity and ecological indices). On the other hand, cadmium and arsenic influence was negligible even in the plots treated with the highest concentrations and the communities resembled to the control samples. Copper showed a stimulative effect on the community under low concentration (40 mg.kg-1), while under higher concentrations the stimulation was replaced by stress responses. The widely used ecological indices, such as the Maturity Index 2-5, Structure Index, and Shannon-Weaver Index and c-p groups showed the best bioindication potential among nematode parameters.