Fundamental studies about non-spectral interferences in high-power microwave induced plasma optical emission spectrometry (MIP-OES) are very limited so far. The goal of this work is to investigate non-spectral interferences originating from calcium (0.5% w w⁻¹ calcium nitrate), carbon (5.0% w w⁻¹ glycerol) and sulfur (5.0% w w⁻¹ sulfuric acid) matrices in commercial high-power MIP-OES based on a Hammer cavity. To this end, the influence of the nebulizer gas flow rate on the signal of several atomic and ionic lines of a total of 10 elements (As, Co, Cu, Mg, Mn, Mo, Sc, Se, Sr and Zn) has been studied for each matrix. Compared to the 1.0% w w⁻¹ nitric acid reference solution, the emission signal for atomic lines with E_sum values lower than 3.26 eV was enhanced in the presence of calcium but it was suppressed for the remaining atomic and ionic lines tested. Calcium matrix effects originate from changes in both plasma excitation conditions and ion–atom equilibrium. With regard to the 5.0% w w⁻¹ glycerol and 5.0% w w⁻¹ sulfuric acid solutions, no signal changes were noticed for the 1.0% w w⁻¹ nitric acid solution since no significant differences were observed either in the aerosol size and transport or in the plasma excitation conditions. A comparison of matrix effects in MIP-OES with those obtained in inductively coupled plasma optical emission spectrometry (ICP-OES) under similar experimental conditions reveals that the former source is more sensitive to the presence of the calcium matrix. In contrast, MIP-OES is a more robust technique for elemental analysis when operating with 5.0% w w⁻¹ glycerol and 5.0% w w⁻¹ sulfuric acid solutions. In fact, matrix-based signal enhancements observed in ICP-OES for As and Se are eliminated when operating in MIP-OES.

Microwave induced plasma optical emission spectrometry (MIP-OES) has gained widespread attention in the last few years for trace elemental analysis. Among the new generation of MIPs it is worth to mention the microwave-sustained inductively coupled atmospheric-pressure plasma (MICAP) for which previous works have shown similar detection capabilities to those afforded by ICP-OES. Nevertheless, this instrument has not been applied yet to complex matrix sample analysis. Therefore, the goal of this work is to evaluate MICAP-OES performance (e.g., analytical figures of merit, matrix effects, etc.) for elemental analysis of samples of different nature (e.g., environmental, food and polymers). To this end, both spectral and non-spectral interferences were investigated for 19 elements (Ag, Al, As, B, Ca, Cd, Co, Cr, Cu, Fe, Ga, In, Mg, Mn, Ni, Pb, Sr, Tl, Zn) in the presence of inorganic acid, organic and saline solutions and compared to a 5 % w w^-1 HNO₃ solution. Unlike previous MIPs, experimental data showed that the optimum nebulizer gas flow rate for a given emission wavelength was mostly independent of matrix characteristics. Regarding matrix effects, this device was highly robust operating both inorganic acid and organic matrices. Interestingly, when operating saline matrices, changes on emission signal by easily ionizable elements were less significant than those early reported by alternative MIP cavities. Moreover, due to MICAP spectrometer design employed allows real-time simultaneous analysis, Rh, Pd, Sc and Y were suitable internal standards to minimize non-spectral interferences. Finally, MICAP-OES can be successfully applied to the elemental analysis of different complex matrix samples (i.e., CRM-DW1 Drinking water; BCR-146 Sewage sludge industrial; BCR-185 Bovine liver; BCR-278R Mussel tissue; NIST-1549 Non-fat milk powder; ERM-EC681k Polyethylene (high level) and BCR-483 Sewage sludge amended soil).

The overall objective of this work is the evaluation of different competitive aptamer assays based on inductively coupled plasma mass spectrometry (ICP-MS) detection for the determination of β-conglutin (food protein allergen from lupin) in flour samples. To this end, two competitive aptamer assay schemes were developed using either thiolated aptamers chemisorbed onto gold nanoparticles (AuNPs) or biotinylated aptamers linked to streptavidin-AuNPs. The influence of ICP-MS detection mode (i.e., conventional vs single particle) on assay performance was explored. In the case of the thiolated aptamer, the limit of detection (LoD) obtained using the single particle mode was improved 2-fold as compared to the LoD provided by the conventional mode. With regards to the biotinylated aptamer, the use of the conventional mode provided a 5-fold improvement of LoD as compared to that obtained for the single particle one. Using the optimized conditions, the best LoD of 2 pM was obtained with the biotinylated aptamer operating with conventional ICP-MS detection. When compared to previous reports using the same aptamer in a competitive assay, the developed method significantly improved the LoD by at least an order of magnitude. Different flour samples containing lupin were successfully analyzed according to European Conformity guidelines for the analysis of food contaminants.

High-power microwave induced plasma optical emission spectrometry (MIP-OES) constitutes a serious alternative to inductively coupled plasma optical emission spectrometry (ICP-OES) for elemental analysis. To improve the analytical capabilities of MIP-OES, dispersive liquid–liquid microextraction (DLLME) procedures seems to be, a priori, a very promising choice for trace and ultra-trace analysis in complex matrices. Nevertheless, to date, DLLME has never been coupled to MIP-OES. The goal of the present work is to investigate the capability of MIP-OES as a detector in DLLME procedures. To this end, spectral and non-spectral interferences caused by the presence of common DLLME extractants (i.e., chloroform and supramolecular solvent based on 1-decanol and THF) in MIP-OES have been evaluated. Results reveal the occurrence of both spectral and non-spectral interferences due to carbon-based molecular bands emission in MIP-OES. Carbon-based molecular emission (i.e. C₂ and CH) significantly affects analyte wavelengths above 328 nm. By the appropriate selection of experimental conditions (i.e. analyte wavelength and nebulizer gas flow rate), both spectral and non-spectral interferences could be mitigated allowing elemental analysis by means of DLLME-MIP-OES. Different DLLME methodologies have been developed for Cd determination in water samples (i.e., tap, sparkling and synthetic seawater) by MIP-OES. These methodologies afford an enrichment factor of 46 and 42 for chloroform and supramolecular-based solvent DLLME procedures, respectively, and a limit of detection (LoD) of 1 μg L⁻¹. This LoD is 100-fold lower than that obtained by conventional MIP-OES (i.e. no DLLME) due to both analyte preconcentration and the beneficial effect of organics on aerosol generation and transport. These analytical figures of merit are equivalent to those previously reported for DLLME-ICP-OES and allows Cd determination in water samples according to current international policies.