High temperature total consumption sample introduction system coupled to microwave plasma optical emission spectrometry (MIP-OES) for the analysis of aqueous samples

The high temperature torch integrated sample introduction system (hTISIS) is coupled to microwave plasma optical emission spectrometry (MIP-OES) for the first time. The goal of this work is to develop an accurate analysis of digested samples under continuous sample aspiration mode by coupling the hTISIS to a MIP-OES instrument. To achieve this, different operating conditions such as, nebulization flow rate, liquid flow rate and the spray chamber temperature were optimized in terms of sensitivity, limits of quantification (LOQs) and background equivalent concentration (BECs) for the determination of Ca, Cr, Cu Fe, K, Mg, Mn, Na, Pb and Zn, and these values were compared with those reported with a conventional sample introduction system. Under optimum conditions (0.8–1 L min−1, 100 μL min−1 and 400 ᵒC, respectively), the hTISIS improved MIP-OES analytical figures of merit and shortened 4-times wash out times with respect to a conventional cyclonic spray chamber, reporting an enhancement factor in the sensitivity among 2–47 times and LOQs from 0.9 to 360 μg kg−1. Once the best operating conditions were set, the magnitude of the interference caused by 15 different acid matrices (2, 5 and 10% w/w of HNO3, H2SO4, HCl and mixtures of HNO3 with H2SO4 and HNO3 with HCl) was significantly lower for the former device. Finally, 6 different digested oily samples (used cooking oil, animal fat, corn oil and the same samples after a filtration step) were analyzed by means of an external calibration approach based on the use of multielemental standards prepared in 3% (w/w) HCl solution. The obtained results were compared against those supplied by a conventional methodology employing an inductively coupled plasma optical emission spectrometry, ICP-OES, instrument. It was clearly concluded that the hTISIS coupled to MIP-OES afforded similar concentrations as compared to the conventional methodology

Speciation analysis by small-bore HPLC coupled to ICP-MS

Although high-performance liquid chromatography with inductively-coupled mass spectrometry (HPLC-ICP-MS) has established itself as the analytical technique of choice for elemental speciation analysis, there are remaining limitations, mainly concerning post-column dispersion effects and degradation of the ICP stability and ionization efficiency due to organic or saline mobile phases. The application of small-bore columns in conjunction with low dead-volume interfaces has proved very useful for overcoming these problems, since they can provide lower matrix load and reduced peak dispersion, along with minimization of sample size and solvent consumption, faster chromatographic separations, and better resolution and sensitivity. Since we expect more work to be reported in this area, we review recent research in the field of speciation analysis by small-bore HPLC-ICP-MS, with the emphasis on significant advances in methods and instrumentation, relevant applications and current limitations.Amanda Terol thanks the Fundación Ramón Areces for the postdoctoral grant (25th edition).This work was carried out in the frame of the Italian National Project PRIN-2010AXENJ8

Liquid-sample introduction in plasma spectrometry

Plasma-spectrometry techniques, namely inductively coupled plasma atomic emission spectrometry (ICP-AES) and plasma-based mass spectrometry (MS), are the most commonly used in analytical laboratories for elemental analysis in a wide variety of samples. In these techniques, the quality of the analysis strongly depends on appropriate selection of the sample-introduction system. For liquid samples, it basically comprises a nebulizer, which transforms the bulk solution into an aerosol, and a spray chamber, which modifies the characteristics of this aerosol and transports it to the plasma base through an injector tube. Sometimes, a desolvation system is incorporated to reduce the solvent load into the plasma. This article describes the different components of the sample-introduction system, emphasizing their main advantages and drawbacks. A review of the processes that affect the aerosol between generation and reaching the plasma is also included

Localized Quantitative Analysis of Polymeric Films through Laser Ablation–Inductively Coupled Plasma Mass Spectrometry

The present work shows, for the first time, the application of laser ablation connected to inductively coupled plasma mass spectrometry (LA-ICP-MS) to the localized quantitative analysis of inclusions in polymeric industrial films. The multielemental mapping capabilities of LA-ICP-MS has allowed to chemically examine unique defects appeared during the plastic processing. This analytical tool is perfectly suited to detect elements such as Al, Mg, Zr, Ti, Cr, P, Pb, Sb, Zn, and Si in those inclusions. A method for multielemental quantitative analysis of these defects has been developed in the present work. The profiling for more than 100 different defects in three samples has demonstrated that more than 50% of these inclusions contain aggregates of some of the aforementioned elements. Therefore, the distribution of elements used as additives or present in catalysts must be carefully controlled during the production of polymeric films in order to avoid degradation in their performance.Funding acquisition M.B. and J.L.T. Authors wish to thank to Total Research and Technology and to the Spanish Ministry of Science, Innovation and Universities for the financial support (project ref. PGC2018-100711-B-I100)

Application of Dispersive Liquid–Liquid Aerosol Phase Extraction to the Analysis of Total and Individual Phenolic Compounds in Fried Extra Virgin Olive Oils

Seventeen extra virgin olive oil samples from Valencian Community (Spain) were submitted to a domestic-frying process (180 °C) during different degradation times (5, 10, 30, 60, 120 min). A dispersive liquid–liquid aerosol phase extraction by using a methanol/water (50:50) extracting solution was used to isolate the polyphenol fraction. Total phenolic content (TPC) was determined, whereas the determination of seven individual target polyphenolic compounds (hydroxytyrosol, tyrosol, oleuropein, vanillic acid, p-coumaric acid, ferulic acid, and vanillin) was carried out by using ultrahigh-performance liquid chromatography coupled to a tandem mass spectrometer. Statistically significant differences in the TPC values were found for Blanqueta and Manzanilla samples from different harvesting years. The domestic-frying process impacted the TPC and the individual phenolic compounds content. Thermal treatment for 2 h gave rise to a 94% decrease in the TPC. A first-order kinetic model was suitable to accurately describe the degradation of the individual phenolic compounds.The authors wish to thank the Spanish Ministry of Science, Innovation, and Universities for the financial support (project ref. PID2021-127566NB-I00)

Quantitative elemental analysis of polymers through laser ablation – inductively coupled plasma by using a dried droplet calibration approach, DDCA

The so-called Dried Droplet Calibration Approach (DDCA) was applied for the first time to the determination of elemental concentration in polyethylene and polypropylene samples by means of inductively coupled plasma optical emission spectrometry (ICP-OES) and mass spectrometry (ICP-MS). Based on this novel calibration strategy, small volumes (c.a., 1 μL) of a series of multielemental aqueous standard solutions were deposited on the sample solid surface. Afterwards, the droplets were dried and a significant fraction of the remaining solid residues (i.e., 80% of their surface area) was ablated. The integrated signals were plotted against the mass of added analyte ablated per laser shot. The analyte concentration in the sample was obtained by extrapolation of the obtained calibration lines. A study demonstrating the existence of matrix effects was carried out, and it was noticed that carbon was not an appropriate internal standard because it did not compensate for changes in the absolute amount of ablated material as a function of the sample matrix. In contrast, elements such as Sc and Y mitigated this effect. External calibration using a polymeric support also proved to be inefficient from the point of view of accuracy. In contrast, the DDCA presented as an outstanding feature the compensation for matrix effects, because with this method both the sample and added standard were simultaneously ablated, and the generated aerosols reached the plasma together. The accuracy of the DDCA was demonstrated by means of the analysis of three polymer certified reference materials. It was verified that, in general terms, there were not significant differences between the elemental certified concentrations and those obtained by applying the DDCA. Furthermore, three polyethylene and three polypropylene samples were analyzed following both the DDCA and a reference method based on acid digestion and further ICP analysis. Both methodologies provided similar results for Al, Ti, Si, Cr, Ca, Zn and Mg. For elements either potentially volatile or present at low concentrations such as As, Hg and Ti in some polymers, there were significant discrepancies between certified and measured values

Analysis of bioethanol samples through Inductively Coupled Plasma Mass Spectrometry with a total sample consumption system

Bioethanol real samples have been directly analyzed through ICP-MS by means of the so called High Temperature Torch Integrated Sample Introduction System (hTISIS). Because bioethanol samples may contain water, experiments have been carried out in order to determine the effect of ethanol concentration on the ICP-MS response. The ethanol content studied went from 0 to 50%, because higher alcohol concentrations led to carbon deposits on the ICP-MS interface. The spectrometer default spray chamber (double pass) equipped with a glass concentric pneumatic micronebulizer has been taken as the reference system. Two flow regimes have been evaluated: continuous sample aspiration at 25 μL min− 1 and 5 μL air-segmented sample injection. hTISIS temperature has been shown to be critical, in fact ICP-MS sensitivity increased with this variable up to 100–200 °C depending on the solution tested. Higher chamber temperatures led to either a drop in signal or a plateau. Compared with the reference system, the hTISIS improved the sensitivities by a factor included within the 4 to 8 range while average detection limits were 6 times lower for the latter device. Regarding the influence of the ethanol concentration on sensitivity, it has been observed that an increase in the temperature was not enough to eliminate the interferences. It was also necessary to modify the torch position with respect to the ICP-MS interface to overcome them. This fact was likely due to the different extent of ion plasma radial diffusion encountered as a function of the matrix when working at high chamber temperatures. When the torch was moved 1 mm plasma down axis, ethanolic and aqueous solutions provided statistically equal sensitivities. A preconcentration procedure has been applied in order to validate the methodology. It has been found that, under optimum conditions from the point of view of matrix effects, recoveries for spiked samples were close to 100%. Furthermore, analytical concentrations for real samples following the preconcentration method and the direct determination were not significantly different. The quantification method was finally based on external calibration with standards containing 50% (v/v) ethanol content.C. Sánchez would like to thank the Ministry of Education, Culture and Sports, Spain for the grant FPU 13/01438

Profiling of Organic Compounds in Bioethanol Samples of Different Nature and the Related Fractions

Forty-one bioethanol real samples and related fractions, together with a biobutanol sample, have been analyzed with gas chromatography coupled to either mass spectrometry (GC–MS) or flame ionization detection (GC–FID). Bioethanol with different water contents, samples originated from several sources of biomass, first- as well as second-generation specimens, distillation fractions, samples stocked in containers made of four different materials, and, finally, a biobutanol sample have been analyzed. The number of the compounds found through GC–MS has been 130, including alcohols, aldehydes, ketones, esters, ethers, nitrogen compounds, organic acids, furane derivates as well as other species (e.g., limonene). Afterward, a quantitative determination of major components of bioethanol has been carried out. The achieved results have revealed that, besides ethanol and, in some cases, water, species such as acetaldehyde, methanol, and higher alcohols, as well as 1,1-diethoxyethane, may be present at concentrations above 500 mg L–1. While the source of bioethanol (nature of the raw material, ethanol generation, or water content) has a direct impact on its volatile organic compound (VOC) profile, the material of the container where the biofuel has been stored does not play a significant role. Finally, the results have demonstrated that, for a given production process, different distillation fractions contain unequal VOC profiles.Authors are grateful to the Spanish Ministry of Science, Innovation and Universities for the financial support (Project Ref. PGC2018-100711-B-I00). C.S. thanks to the Ministry of Education, Spain for the contract FPU 13/01438

Determination of fat-soluble vitamins in vegetable oils through microwave-assisted high-performance liquid chromatography

In this manuscript, a study of the effect of microwave radiation on the high-performance liquid chromatography separation of tocopherols and vitamin K1 was conducted. The novelty of the application was the use of a relatively low polarity mobile phase in which the dielectric heating effect was minimized to evaluate the nonthermal effect of the microwave radiation over the separation process. Results obtained show that microwave-assisted high-performance liquid chromatography had a shorter analysis time from 31.5 to 13.3 min when the lowest microwave power was used. Moreover, narrower peaks were obtained; hence the separation was more efficient maintaining or even increasing the resolution between the peaks. This result confirms that the increase in mobile phase temperature is not the only variable for improving the separation process but also other nonthermal processes must intervene. Fluorescence detection demonstrated better signal-to-noise compared to photodiode arrayed detection mainly due to the independent effect of microwave pulses on the baseline noise, but photodiode array detection was finally chosen as it allowed a simultaneous detection of nonfluorescent compounds. Finally, a determination of the content of the vitamin E homologs was carried out in different vegetable oils. Results were coherent with those found in the literature

Determination of trace elements in undiluted wine samples using an automatized total sample consumption system coupled to ICP-MS

A novel method for the elemental analysis of undiluted wine samples was optimized and validated. The method was based on the use of a high-temperature torch integrated sample introduction system (hTISIS) coupled to inductively coupled plasma mass spectrometry (ICP-MS). The operating conditions (hTISIS temperature and liquid flow rate) were optimized in terms of sensitivity and matrix effects. Low liquid flow rates allowed to continuously introduce organic samples into the plasma source with minimum soot as well as salty deposits formation at the ICP-MS interface and/or plasma thermal degradation. A double pass Scott-type spray chamber thermostated at 2ºC was taken as the reference sample introduction system. The results indicated that the hTISIS operated at 125ºC and 30 µL min-1 as liquid flow rate improved the sensitivity and mitigated the extent of matrix effects compared to the conventional system. Once the optimum conditions were selected, the method was validated and applied to the determination of sixteen trace elements (Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Mo, Cd, Nd, Sm, Gd, Tb and Pb) in ten real wine samples. The sample was merely aspirated to the nebulizer with no additional preparation. For the sake of comparison, the samples were microwave digested and analyzed using a conventional setup. Method detection limits achieved by the hTISIS were from 2 to 40 times lower than those found using the standard procedure and ranged from 0.002 to 6 µg kg-1. Furthermore, the accuracy of the quantification using the hTISIS was not significantly different as compared to that afforded by the conventional procedure and substantially improved in comparison with the direct analysis of wine using a Scott spray chamber. Sample throughput was close to 10 h-1 that was in clear contrast with 2 h-1, estimated when the digestion method was used. Finally, the suitability of the developed method for the routine analysis of wine samples was demonstrated by performing a 20-hours long analysis sequence. Good signal stability and accurate results were obtained for ten representative Italian and Spanish wines