An environmentally friendly approach for the characterization of construction materials: determination of trace, minor, and major elements by slurry sampling high-resolution continuum source graphite furnace atomic absorption spectrometry.

A slurry sampling method was developed for the fast determination of Pb, Ni, Fe, and Mn in construction materials by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GFAAS). For sample introduction into the GF, stable slurries were prepared by sonicating 10 mg of ground solid sample in 10.0 mL of 1% (v/v) Triton X-100 and 1% (v/v) HNO3 solution for 1.0 min. The determination of the four elements was carried out in three measurement runs, with Ni and Fe being determined simultaneously. The HR-CS GFAAS measurements were performed using analytical lines with adequate sensitivity, considering the content of each element in the material: Pb at 283.306 nm (42%), Mn at 403.080 nm (6.7%), Ni at 232.003 nm (100%) and Fe at 232.036 nm (1.4%). The pyrolysis and atomization temperatures and the use of chemical modifiers were optimized using both aqueous standards and slurry samples. At optimal conditions, samples with concentrations of Pb from 1.5 to 80 µg g-1, Ni from 4.0 to 75 µg g-1, Mn from 2.0 to 600 µg g-1, and Fe from 0.15 to 60 mg g-1 could be determined using a unique sample suspension. To assess the validity of the method, a fly ash certified reference material (CRM) was analysed using the slurry sampling HR-CS GFAAS method; this CRM and the construction material samples were also analysed by HR-CS GFAAS after the digestion of the samples. The obtained results using both methods were statistically comparable (Student's paired t-test for two independent methods at a 95% confidence level) demonstrating the suitability of the proposed method.

Methylisothiazolinone response on disposable electrochemical platforms modified with carbon, nickel or gold-based nanomaterials.

Screen-printed carbon electrodes (SPCE) were modified with nanocomposite membranes based on polystyrene sulfonate (PSS) or poly(diallyldimethylammonium) (PDDA) matrices and different nanomaterials. Carbon nano-powders (CnP), carbon nano-fibers (CnF) and multi-walled carbon nano-tubes (MWCNTs) were incorporated on PSS matrix. Nickel was incorporated by ion exchange in PSS-CnP composite membranes. Gold nanoparticles (AuNp) were photochemically and electrochemically synthesised and introduced into PDDA membranes. The electrochemical behaviour of methylisothiazolinone (MIT) using these modified electrodes was studied by cyclic voltammetry in 0.1 mol L-1 NaOH. No electrochemical response is obtained on PSS-nanocarbon transducers at the assayed conditions. The nickel-based transducers allow the MIT identification but not quantification. Using AuNp-based electrochemical transducers, it is observed that in presence of MIT, the electron transfer for AuNp reduction is inhibited, and an oxidation peak appears at + 0.45 V, indicating an interaction between MIT and AuNp on the electrode surface. These facts support the usefulness of the AuNp-based electrodes for the determination of MIT. The intensity of the anodic peak observed at + 0.45 V vs. Ag/AgCl was used as analytical signal for MIT determination. A linear relationship between anodic peak current and MIT concentration is observed in the range 8.7 to 36 mg L-1 using the transducer prepared by incorporating gold into the PDDA membrane by ion exchange and synthesising AuNp electrochemically. For this electrode, the limit of detection is 2.6 mg L-1 and the reproducibility, expressed as relative standard deviation (RSD), is lower than 7%. Graphical abstractSchematic representation of the preparation of gold nanoparticles (AuNp) and poly(diallyldimethylammonium) (PDDA)-based platforms and methylisothiazolinone (MIT) electrochemical response on these nanostructured platforms.

Flow and batch systems for copper(II) potentiometric sensing.

A new carbon paste electrode modified with tetramethyl thiuram disulfide is prepared to use as copper potentiometric sensor in batch and flow analysis. The influence of pH and carbon paste composition on the potentiometric response is studied. The principal parameters of the flow system are optimized and the detection limits and the selectivity coefficients of the potentiometric sensor are calculated for static and flow mode. In both cases, the sensor shows high selectivity to copper ions but in flow analysis this selectivity is higher. The obtained detection limits are 4.6 x 10(-8) M for batch measurements and 2.0 x 10(-7) M for on-line analysis. The potentiometric sensor is applied to copper(II) determination in real samples in static and flow measurements. In both analysis modes, successful results are obtained.

Potentiometric carbon paste sensors for lead(II) based on dithiodibenzoic and mercaptobenzoic acids.

Dithiodibenzoic (DTB) acid and mercaptobenzoic (MB) acid were studied to characterize their abilities as modifier agents for lead(II) sensors. For both sensors, the best results were obtained with modified carbon paste electrodes with 24.1% of ligand. The pH influence on the potentiometric response was studied. The selectivity coefficients for both modified electrodes were tabulated. A potentiometric sensor based on DTB acid exhibited a more sensitive and selective response to lead ions than an MB electrode. The limits of detection for the DTB and MB electrodes were very similar, 5.01 x 10(-8) M and 3.98 x 10(-8) M, respectively, for lead(II) activity. The DTB sensor was applied to lead(II) ion determination in real samples and as an indicator electrode in potentiometric titrations. Natural and commercial humic acids were titrated using the DTB electrode to estimate the stability constant between these organic compounds and the lead(II) ions with successful results.