Cadmium (Cd) and lead (Pb) concentrations and their relationship to the cocoa content of chocolates commercialized in Brazil were evaluated by graphite furnace atomic absorption spectrometry (GF AAS) after microwave-assisted acid digestion. Several chemical modifiers were tested during method development, and analytical parameters, including the limits of detection and quantification as well as the accuracy and precision of the overall procedure, were assessed. The study examined 30 chocolate samples, and the concentrations of Cd and Pb were in the range of <1.7-107.6 and <21-138.4 ng/g, respectively. The results indicated that dark chocolates have higher concentrations of Cd and Pb than milk and white chocolates. Furthermore, samples with five different cocoa contents (ranging from 34 to 85%) from the same brand were analyzed, and linear correlations between the cocoa content and the concentrations of Cd (R(2) = 0.907) and Pb (R(2) = 0.955) were observed. The results showed that chocolate might be a significant source of Cd and Pb ingestion, particularly for children.

This paper presents a portable quantitative method for the on-site determination of uric acid in urine using surface-enhanced Raman spectroscopy (SERS) and gold nanoparticle-coated paper as a substrate. A procedure was developed for the rapid preparation of cost-effective SERS substrates that enabled the adequate control of a homogeneous active area and the use of small quantities of gold nanoparticles per substrate. The standard addition method and multivariate curve resolution-alternating least squares (MCR-ALS) were applied to compensate for the matrix effect and to address overlapping bands between uric acid and interference SERS spectra. The proposed methodology demonstrated better performance than conventional univariate methods (in terms of linearity, accuracy and precision), a wide linear range (0-3.5 mmol L(-1)) and an adequate limit of detection (0.11 mmol L(-1)). For the first time, a portable SERS method coupled with chemometrics was developed for the routine analysis of uric acid at clinically relevant concentrations with minimal sample preparation and easy extension for the on-site determination of other biomarkers in complex sample matrices.

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Plasmonic nanoparticle aggregates are one of the most widely employed nanostructures as colloidal surface enhanced Raman spectroscopy (SERS) substrates mainly due to their ability to generate huge near-field enhancements. However, the available definitions to determine the enhancement factor, a key parameter to quantitatively describe the quality of SERS substrates, exhibit important limitations to adequately describe the performance of colloidal plasmonic nanoparticle aggregates as SERS platforms. Herein, we introduce a new figure of merit named active concentration enhancement factor (ACEF) to assess the SERS enhancement factor of colloidal gold nanoparticle aggregates, which shows significant improvements to characterize the SERS performance with respect to formerly reported parameters. The determination of the analyte active concentration, that is, the concentration of analyte molecules that effectively contributes to the SERS signal, was achieved according to a strategy that involves a rigorous modeling of the extinction spectra of the colloidal gold nanoparticle aggregates. Furthermore, the experimentally obtained ACEF values can be directly compared with theoretically calculated electromagnetic field enhancement factors. We believe that the figure of merit introduced might help to strengthen the development and design of SERS substrates.

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