This work explores the use of partial least squares (PLS) multivariate calibration to address the issues encountered in multianalyte differential pulse anodic stripping voltammetry (DPASV), particularly those arising from competition among metals for active sites on the working electrode and from the formation of intermetallic compounds. A simple and cost-effective method has been developed for the simultaneous determination of Pb(II), As(III), Cu(II), and Hg(II) ions in aqueous matrices by combining DPASV measurements using a commercial low-temperature gold screen-printed electrode (SPAuE) with a PLS-2 calibration model. The latter employs a central composite design (CCD) together with a new 4D-rotation strategy to ensure homogeneous distribution of concentrations for all four analytes. The methodology exhibits good analytical performance, with linear ranges up to 69 mu g/L, R2 values above 0.99, and repeatability and reproducibility below 8.9% and 11.9%, respectively. Additionally, it significantly improves accuracy compared to univariate calibration, achieving recoveries between 88.8% and 121.7%.

An efficient, fast, and sensitive method for the determination of estrone (E1), 17 beta-estradiol (E2), estriol (E3), ethinylestradiol (EE2), and beta-estradiol-17-acetate (E2Ac) in pharmaceutical formulations and spiked human urine was developed and validated using an unmodified commercial screen-printed carbon electrode. The utilization of linear sweep and square wave voltammetry was compared, and experimental conditions were optimized. In a 6.0 mmol L-1 phosphoric acid solution, the current intensity of the oxidation of the aromatic alcohol was used as the analytical response. The peak potential of each estrogen oxidation signal was found between 0.62 and 0.67 V. The detection limits were found to be for E1, E2, E2Ac, EE2, and E3 were 43, 25, 32, 42, and 44 nmol L-1 using linear sweep voltammetry and 20, 21, 37, 53, and 39 nmol L-1 using square wave voltammetry, respectively. The method was successfully applied to the determination of estrogens in a commercial and spiked drug tablets and spiked human male urine samples. The findings from this study establish a strong basis for the future application of the method in conjunction with high-performance liquid chromatography for the determination of estrogens in samples characterized by complex matrices.

A novel electrochemical sensor for Se(IV) determination is proposed using a glassy carbon electrode (GC) modified with electrochemically reduced graphene oxide (rGO) and electrochemically generated gold nano-particles (AuNPs). The GC/rGO/AuNPs electrode was characterized by cyclic voltammetry (CV) and scanning electron microscopy (SEM). The results showed a homogeneous distribution of gold nanoparticles with sizes ranging from 32.48 to 73.49 nm. Chemical and electrochemical parameters were optimized as follows: accumulation potential (Eacc) of-0.80 V (vs Ag/AgCl), accumulation time (tacc) of 120 s, frequency of 15 Hz, and 15 reduction cycles for rGO deposition. Using square wave anodic stripping voltammetry (SWASV), a limit of detection (LOD) of 0.63 mu g l-1 and a limit of quantification (LOQ) of 2.11 mu g l-1 were obtained. The method showed good reproducibility, repeatability, and accuracy. Finally, the proposed method was successfully applied to legume (Phaseolus vulgaris and Lens culinaris) and water samples, with results statistically comparable to electrothermal atomic absorption (ET-AAS).

We report an electroanalytical methodology for determining As(III) in natural waters using adsorptive stripping voltammetry with a Screen-printed carbon nanotube electrode modified with Alginate (ALG) from brown algae (CNTALG-SPE). The optimal conditions chosen in the electrode preparation were: CALG: 2.5 mg mL-1; CHNO3 0.01 mol L- 1; Eacc:-0.70 V and tacc: 900 s. Subsequently, the modified electrode (CNTALG-SPE) was used in the As(III) determination without accumulation step. The peak current was proportional to the As(III) concentration up to 25.0 mu g L- 1 (R = 0.992), with a 3a detection limit (DL) of 2.8 mu g L- 1. Finally, the method was validated using laboratory drinking water spiked with As(III) and was applied to the determination of As(III) in water samples from the Loa River (North of Chile) which contained As(III) and As(V). The results of the proposed method were compared with those obtained by adsorptive stripping voltammetry with HMDE and by Inductively Coupled Plasma Mass Spectrometry (ICP- MS. Astotal) techniques.

Wild edible mushrooms are a popular food considering their nutritional value. However, some mushroom species can harm human health by accumulating some elements excessively. To evaluate the pollution level of toxic elements in wild edible and non-edible mushrooms from two private natural areas in the Altos de Cantillana mountain range in Central Chile (Altos de Cantillana Natural Reserve and Cerro Poqui Nature Sanctuary) present in them were quantified. All mushrooms contained Pb, Zn, Fe, Cu, and Ni. Mushrooms obtained in Los Altos de Cantillana have higher amounts of metals. In mushrooms of the type Bovista brunnea (sample 27) there are maximum amounts of Pb (566.8 mu g/g), Zn (1152.3 mu g/g), and Cu (568.6 mu g/g) while those of the type Lycoperdon sp. (sample 14) have maximum amounts of Fe (17806.9 mu g/g) and Ni (27.6 mu g/g). On the other hand, only the species Stereum hirsutum (samples 1 and 4) has very low amounts of As (3.9 mu g/g and 6.5 mu g/g) and only this one and Phaeoclavulina flaccida contain low amounts of Cd (0.02 mu g/g and 0.04 mu g/g). On the other hand, Sb and Au were not found in any sample; all values were < LOQ (Limit of quantification). Although intraspecies differences were observed, not all were significant. It is important to highlight the analysis of wild mushroom species that people can consume, such as the genus Cyttaria, which should be evaluated for trace element content.

This work presents an adsorptive stripping voltammetric method for the speciation of antimony based on the formation of their complexes with Pyrogallol red (PGR). Both Sb(III) and Sb(V) form complexes with PGR, however Sb(III) forms complex rapidly whereas Sb(V) forms complex very slowly. After the SbV-PGR complex is formed, on the surface of the mercury electrode is reduced to SbIII-PGR. Then the electrochemical signal is the reduction of SbIII-PGR complex to Sb(0). The variation of peak current with pH, accumulation time (tacc), accumulation potential (Eacc), and PGR concentration (CPGR) were optimized. The best experimental conditions for Sb(III) were pH: 2.2 (0.1 mol L- 1, Phosphate buffer, PB), CPGR: 3.0 mu mol L- 1, and Eacc: -0.10 V obtaining a detection limit (DL) of 1.1 mu g L- 1 (tacc: 35 s). When measured at 2 h, the signal of the SbIII-PGR complex is almost the same and now it is possible to appreciate the increase in the signal due to presence of SbV-PGR complex, previously reduced to SbIII-PGR in the Hg electrode. This allows us to determine the total concentration of antimony. The developed method was validated by the determination of Sb(III) in spiked drinking water from the laboratory and spiked synthetic seawater with relative errors of less than 5.0 %. The method was successfully applied to the determination of Sb(III) and Sbtotal in an Industrial waste liquid sample comparing the results of Sbtotal by ICP-OES technique (RE: 0.6 %).

An edible Mushroom-Nafion modified glassy carbon electrode (M2N5-GCE) was prepared using a homogeneous mixture varying the concentrations of these, in addition to the origin of the mushroom (Shiitake, Lentinula edodes, M-1 and Abrantes, Agariscus bisporus, M-2) and applied to the As(III) determination by anodic stripping voltammetry. After choosing the optimal conditions in the preparation of the electrode, the second stage was to study the effects of various parameters such as supporting electrolyte, pH, accumulation potential, and time (E-acc, t(acc)). The optimum experimental conditions chosen were Britton Robinson buffer 0.01 mol L-1 pH:4.6; E-acc: -1.0 and t(acc): 60 s obtaining a signal of oxidation of As(0) to As(III) about 0.08 V. Peak current was proportional to arsenic concentration over the 19.6-117.6 mu g L-1 range, with a 3 sigma detection limit of 13.4 mu g L-1. The method was validated using As(III) spiked tap water from the laboratory with satisfactory results (RE:3.0 %). Finally, the method was applied to the determination of As(III) in water samples from the Loa River (Northern Chile) in the presence of As(V) in a concentration >20 times higher (RE: 2.3 %).

This work presents a fast and sensitive method, with an ex-situ bismuth film screen-printed carbon electrode (ex-situ Bi-SPCE), for the determination of Cr(VI) through adsorptive stripping voltammetry (AdSV) using Pyrogallol Red (PGR) as complexing agent. The method is based on the oxidation of PGR by Cr(VI) and posterior complexation with Cr(III). To obtain a sensitive and selective method, the effects of various parameters such as pH, ligand concentration of PGR (CPGR), accumulation potential, and accumulation time (Eacc, tacc) were optimized. The optimal conditions using Bi-SPCE prepared ex-situ were pH 4.5 (0.01 mol L-1 acetic acid/acetate buffer), CPGR: 2.6 mu mol L-1, Eacc: -0.70 V and tacc: 60 s. Peak current is proportional to Cr(VI) concentration over the range 0.23-12.0 mu g L-1, with a 3 sigma detection limit of 0.97 mu g L-1. The method was validated by determining Cr(VI) in tap water spiked with Cr(VI) and Cr(III). image

Four methods for the determination of As(III) in urine were developed, validated and applied to real samples using modified screen printed electrodes: Graphene and gold nanoparticles (GH-SPCE; AuNPs-SPCE); and gold modified Boron Doped Diamond (BDDE) and Edge Plane Pyrolytic Graphite (PGE). To obtain sensitive and selective methods, the effects of various parameters such as pH, accumulation potential, and time (Eacc, tacc) were optimized in the presence and absence of urine. The determination of As, in all four cases, was performed by ASV and the following LDs were obtained: 0.28 (GH-SPCE); 42.0 (AuNPs-SPCE / urine) µg/L. Whereas with BDDE and PGE LDs were 2.3 and 13.2 µg/L. Methodologies with GH-SPCE and AuNPs-SPCE/urine electrodes were applied to determine As(III) and As(T) in human urine samples from workers at the arsenic abatement plant. While BDDE and PGE were used to determine the concentration of As(III) in doped urine and water samples, because its reproducibility was low.

For the determination of progesterone (P4) electroanalytical studies were performed using mercury electrode (HMDE) and screen-printed boron-doped diamond electrode (BDD-SPE). The effects of pH, supporting electrolyte, accumulation potential and time (E-acc, t(acc)) were studied in both systems. The optimum conditions were: i) HMDE: pH 7,0; -0,1 V and t(acc): 40 s, ii) BDD-SPE: 0,5 mol L-1 H2S ; E-acc: 0,0 V and t(acc): 120 s. Under these conditions, the detection limit was 3.1 mu g L-1 for HMDE and 45.6 mu g L-1 for BDD-SPE. Both methods were validated and applied in the P4 determination on pharmaceutical formulations and milk samples.

Electrochemical oxidation of Paracetamol (PAR), Acetylsalicylic acid (ASA) and Caffeine (CAF) was investigated employing square wave stripping voltammetry (SWSV) using screen-printed carbon electrodes (SPCE). Determinations were performed in 0.1 mol L-1 BR buffer (pH 2.0) without accumulation step. SWV were obtained by scanning the potential from 0.00 to 1.40 V employing a scan increment of 4 mV, pulse amplitude 25 mV and frequency of 25 Hz. PAR, ASA and CAF presents oxidation signals at 0.45, 1.03 and 1.32 V. The detection limits were 1.2, 1.7 and 1.7 mg L-1, respectively. The method was applied in the PAR-ASA-CAF determination on pharmaceutical formulations.

A glassy carbon electrode (GCE) modified with electrochemically reduced graphene oxide (ErGO) and gold nanorods (AuNRs) (GCE/ErGO/AuNRs) was prepared for determining As(III) in bivalve mollusks samples (Mytilus chilensis). The modified electrode was characterized by cyclic voltammetry, scanning electron microscopy (SEM), and atomic force microscopy (AFM). Chemical and electrochemical parameters were optimized, observing that the presence of AuNRs provides selectivity, while the incorporation of ErGO improves the sensitivity of the modified electrode for the detection of As(III). Using square wave anodic stripping voltammetry (SWASV), a linear range of 2.0–60.0 µg L−1 with a detection limit (LOD) of 0.21 µg L−1 was obtained. The validation was made using water and mussel tissue-certified reference materials (TMDA-64.2 and ERM®-CE278k, respectively), showing good accuracy and reproducibility. The methodology allowed the determination of As(III) in real samples of marine resources, with excellent results (RSD < 2

A sensitive voltammetric method is reported for the simultaneous determination of Pb2+ and Cd2+ using a nafion-guanine-coated mercury film glassy carbon electrode. This modified electrode exhibited well-developed signals for the reduction of the adsorbed complexes Pb-Guanine and Cd-Guanine, at -0.59 and -0.76 V respectively. The effects of parameters such as pH, accumulation potential and time (E-acc, t(acc)) were optimized. These studies were done using metallic ions on their own and also mixed together. The best pH for the individual analysis of Pb2+ or Cd2+ were 2.2 and 6.1 respectively, whereas a pH of 5.0 (acetate buffer 0.01 mol L-1) was chosen for simultaneous determination. Under the optimized conditions (pH = 5.0; t(acc) = 60 s; E-acc = -1.0 V) reduction signal was found to be proportional to the concentration of Pb2+ and Cd2+ over the 6.6-35.0 mu g L-1 range, with 36 detection limits (DL) of 2.2 and 4.6 mu g L-1. However, for lower concentrations, a time of 120 s was applied, yielding a linear range from 0.5 to 12.0 mu g L-1 with DLs of 0.26 and 0.25 mu g L-1 for Pb2+ and Cd2+, respectively. If the guanine (G) is in the solution, the signals are much lower than in the modified electrode. The method was validated by determining Pb2+ and Cd2+ in certified reference material (GBW08607) and synthetic sea water (ASTM D665), spiked with 22 metal ions, with satisfactory results. Subsequently, the method was applied in bottled mineral waters and sea water samples without previous treatment.

A simple and fast amperometric sensor for As(III) determination has been developed using alginic acid (AA) and nPEDOT on gold nanoparticle–modified screen–printed carbon electrodes (AuNP–SPCE). To obtain a selective method for As(III) determination, the effects of various parameters, such as pH, supporting electrolyte, AA and nPEDOT concentration (CAA, CnPEDOT), and applied potential (Eapp), were studied. The optimal experimental conditions were chosen to be as follows: phosphoric acid pH 3.0 (0.05 mol L); CAA: 0.50 μg L −1 and CnPEDOT 50% w/v (Eapp: -0.30V). The peak current was proportional to the As concentration between 5.0 and 25.0 μg L (R=0.9903), with a detection limit (DL, 3) of 2.7 μg L and a sensitivity of 0.0481 mA/μg L. Four different modified electrodes were used in this study: AuNPs-SPCE, AA/AuNPs-SPCE, nPEDOT/AuNPs-SPCE and AA/nPEDOT/AuNPs-SPCE. It was found that in the presence of AA and nPEDOT, the current of the arsenic signal was higher than that obtained using each of the compounds individually. AA allowed the adsorption of the arsenic on the electrode obtaining good sensitivity and nPEDOT, an excellent conductor, improved the electronic transfer in the electroanalytical system. The advantages of this new procedure are fast complexation kinetics, high specificity, simplicity and speed. Finally, the best electrode (AA/nPEDOT/AuNPs-SPCE) was applied to the determination of total arsenic in a water sample from the Loa River (North zone) and two samples from the Central zone (Santiago and Fifth region) with satisfactory results. Values obtained were compared with an ICP-MS method. To determine Astotal, As(V) was reduced in the presence of thiosulfate in an acidic medium.

A simple and fast anodic voltammetric method was employed to determine traces of As(III) in urine samples using commercial screen-printed graphene electrodes without subsequent modification. To obtain a sensitive and selective method for As(III) determination, the effects of various parameters such as pH, supporting electrolyte concentration, accumulation potential (E-acc), accumulation time (t(acc)), and potential scan conditions were studied. The optimum experimental conditions were chosen to be as follows: pH of 2.8 (0.01 mol L-1 phosphate buffer), scan increment of 4 mV, pulse width of 80 ms, pulse period of 0.5 s, and pulse amplitude of 200 mV. Differential pulse voltammograms were obtained by scanning from -0.80 V to 0.80 V without applying an accumulation step. Under these conditions, one peak was observed at 0.27 V due to As-0 oxidation. After optimizing the experimental conditions, the anodic peak current for As was found to be linearly related to its concentration up to ca. 5.0 mu g L-1, with detection and quantitation limits (DLs, QLs) of 0.28 mu g L-1 and 0.92 mu g L-1, respectively. The developed method was validated by the determination of As(III) in spiked tap water from our laboratory, which showed an As(III) concentration of 50.64 +/- 0.10 mu g L-1 (spiked with 50.0 mu g L-1); two urine samples (where As was not detected) spiked with As(III) 0.73 mu g L-1 and 0.91 mu g L-1 (in the cell) showed an As(III) concentration of 0.70 mu g L-1 and 0.91 mu g L-1, respectively. The method was successfully applied to the determination of As-total in 16 urine samples obtained from workers occupationally exposed to inorganic arsenic compounds without previous treatment. The results obtained for As-total were compared with measurements made by an external analytical laboratory, which used HG-AAS. To determine As-total, As(V) was reduced in the presence of thiosulfate in an acid medium. The electrode showed good stability and repeatability.

Using the differential pulse anodic stripping voltammetry technique and an in-situ bismuth film deposited on a glassy carbon electrode, a simple and sensitive method for rapid Pb(II) and Cd(II) quantification was developed. The effect of the presence of Alizarin Red S (ARS) was studied, and an increase in the sensitivity of the method was obtained. The developed method was compared to another reported method that uses a 0.1 mol L-1 acetate buffer medium (pH 4.5). The optimal experimental conditions are listed as follows: [CH3COOH]: 30.0 mmol L-1; [Bi(III)]: 0.75 mg L-1; [ARS]: 40.0 mu mol L-1; [Fe(CN)64-]: 50.0 mu mol L-1; Edep: -1.40 V; tdep: 60 s. Under these conditions, the detection limits were 0.16 and 0.09 mu g L-1 and the linearity was maintained at values as great as 30.0 and 15.0 mu g L-1 for Pb(II) and Cd(II), respectively. The effect of 35 foreign ions as possible interferents was studied. The method was validated using two certified reference materials (TMDW and TMDA-61.3) with satisfactory results. Finally, the method was applied for the analysis of four natural water samples.

The determination of Sb(III) on an ex-situ bismuth screen-printed carbon electrode (ex-situ BiSPCE) by means of adsorptive stripping voltammetry (AdSV) using quercetin-5′-sulfonic acid as chelating agent was optimized. The effect of different experimental parameters such pH, ligand concentration (CQSA), accumulation potential (Eacc) and accumulation time (tacc) were studied to obtain a wide linear range, the highest sensitivity and the lowest detection limit. Ex-situ BiSPCE was analytically compared with a sputtered bismuth screen-printed electrode (BispSPE) under optimal conditions. The obtained analytical parameters suggest that ex-situ BiSPCE behaves much better than BispSPE and the first was selected for this study. Optimal parameters were pH=4.6; CQSA=10.0 to 20.0×10−6 mol L−1; Eacc=−0.5 V and tacc=60 s. Peak area is proportional to Sb(III) concentration up to 100.0 μg L−1 (tacc 60 s) and 45.0 μg L−1 (tacc 120 s) range, with detection limits of 1.2 μg L−1 (tacc 60 s) and 0.8 μg L−1 (tacc 120 s). The relative standard deviation for a Sb(III) solution (20.0 μg L−1) was 3.9% for ten successive assays. Thus, the effect of various interfering metal ions was studied and the methodology was validated using a spiked groundwater reference material with very satisfactory results.

A electrochemical biosensor for As(III) determination has been developed by immobilization of the Alcaligenis faecalis bacteria on gold nanoparticle-modified screen-printed carbon electrode (AuNPs-SPCE). The detection of As(III) is due to the catalytic activity of arsenite oxidase enzyme which oxidizes As(III) to As(V) producing an analytical signal. To enhance the performance of the biosensor, was optimized the amount of bacteria, amount of glutaraldehyde and incubation time applied in the preparation of the electrode, in addition to the effect of pH and applied potential. The analytical application was carried out applying 300 mV (pH = 7) obtaining a LOD of 6.61 mu mol L-1 (R = 0.9975) and 700 mV (pH = 12) obtaining a LOD of 1.84 mu mol L-1 (R = 0.9983). AF/AuNPs-SPCE was applied to the determination of total arsenic in Loa river water samples after reduction, with satisfactory results.

An efficient, fast and sensitive method for the determination of 17 beta-estradiol, (E2) and 17 alpha-ethinylestradiol (EE2) in pharmaceutical formulations and in urine was developed and validated using a hanging mercury drop electrode (HMDE), screen printed carbon electrodes (SPCE), and screen printed carbon nanotube electrodes (SPCNTE). Both analyzes are adsorbed on the working electrodes. To obtain sensitive and selective methods, the effects of various parameters such as pH, adsorption potential, and time (E-ads, t(ads)) were optimized. The optimum experimental conditions chosen for the two analyzes were pH: 10.0; E-ads: - 0.60 and t(ads): 30 s, when HMDE was used. Under these conditions, one reduction signal was found at -1.31 V for E2 and two reduction signals at - 0.23 V and -1.20 V for EE2. The detection limits (DLs) were found to be 0.3 mu g L-1 for E2, 14.8 mu g L-1 for EE2 at - 0.23 V, and 9.7 mu g L-1 for EE2 at -1.20 V. On the other hand, in screen printed electrodes E2 and EE2 present oxidation of the phenolic hydroxyl groups at 0.30, 0.31, 0.32, and 0.33 V (pH:10) with DLs of 242, 277; 182, and 191 mu g L-1 for SPCE and SPCNTE, respectively. The method was successfully applied to the determination of these analyzes in Primaquin (R) (E2), Gynera (R) (EE2), spiked urine (with EE2), and urine samples of women who used Tinelle (R) (EE2) as contraceptive drug.