Guilherme Luiz Scheffler

Review of the applications of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to the analysis of biological samples

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has received significant attention over the last 10 years and has been widely used for the analysis of biological samples. The technique allows the determination of elements and isotopes in biological tissues and related materials with a spatial resolution typically ranging from 10 to 100 μm. When compared to other techniques usually employed to obtain bioimages, the greater advantage of LA-ICP-MS is its higher sensitivity. The literature survey over the last 10 years concerning the use of LA-ICP-MS for biological tissue analysis is reviewed in this article. Instrumentation, strategies of calibration for quantitative analysis, challenges and recent advances in this field are discussed. Applications of the isotope ratio (IR), including tracer experiments, and isotope dilution (ID), are reviewed for biological samples (briefly for proteins, in order to show the utility of LA-ICP-MS). Bioimaging methods, studies and applications for animal and plants tissues are emphasized, demonstrating the importance of bioimaging of metals and metalloids in biomedical research, bioaccumulation and bioavailability studies for ecological and toxicological risk assessment in humans, animals and plants. The usefulness of the IR associated with bioimaging for predicting geographical origin, habitat, movement of subjects, diet and lifestyle are also demonstrated.

Recent applications of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for biological sample analysis: a follow-up review

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a feasible technique to obtain either quantitative elemental data or spatially resolved imaging/mapping of elements in biological tissues. Its popularity is due to the great detection capability of the setup, which has found central applicability in metallomics, nanoparticles uptake, labeling and tagging strategies in biological systems, elemental mapping of tissues and quantitative data for biomedical studies, besides utilization in a complementary manner with molecular mass spectrometry techniques. This article provides an update of recent progress and applications of LA-ICP-MS in the biological field, covering the time frame of the last three years. Key topics dealing with fast wash-out laser ablation cell developments, novel calibration strategies such as ink printing and dried-droplets, applications and mapping of elemental distribution in biological samples (animal, human and plant tissues), nanoparticle uptake, protein and single cell analysis are surveyed and critically discussed.

Advantages, drawbacks and applications of mixed Ar–N2 sources in inductively coupled plasma-based techniques: an overview

This review deals with mixed gas Ar–N2 plasmas, highlighting advantages, limitations and applications of them in inductively coupled plasma optical emission spectrometry (ICP OES), inductively coupled plasma mass spectrometry (ICP-MS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) techniques, covering publications in the last three decades. Fundamental plasma parameters (such as electron number density, excitation or ionization temperatures, oxides and spatial profiles of ion distribution), performance of the mixed gas Ar–N2 plasmas, and figures of merit are presented and discussed in order to demonstrate the effects of adding N2 to the Ar-ICP.

Effect of N2 on the emission profile and excitation temperature in axially viewed plasma-ICP OES

Fundamental studies were conducted in order to gain useful insights about energy transfer that takes place when a low flow (20 mL min−1) of N2 is introduced into the central channel of the Ar-ICP in inductively coupled plasma optical emission spectrometry (ICP OES). Axial and radial emission profiles of Mg(I), Mg(II) and Ar(I) were collected along and across the central channels of both Ar-ICP and Ar–N2-ICP. Axial profiles indicated a more energetic plasma close and above the load coil when N2 was added. On the other hand, radial profiles suggested a wider and more uniform central channel with the N2 flow addition. By computing the plasma robustness (Mg(II)/Mg(I) ratio) across the central ICP channel, a low (and uniform) energy coupling was found between the bulk plasma and the central channel of the Ar-ICP, which was significantly improved by adding N2. The results obtained also suggested that N2 plays an important role locally, but does not in the outer regions of the ICP, which in turn denoted an unlikely N2 diffusion. The better excitation conditions caused by N2 were confirmed by measuring the excitation temperature in the central channel of the ICP, using a set of Fe ionic lines, where the excitation temperature increased from 7480 K to 7910 K. The effectiveness of the improved plasma robustness was evaluated for diluted seawater and the results demonstrated that the analyte signal suppression induced by the concomitants was reduced. Accuracy was accessed by analyzing certified reference samples (water and sediment), whereas good agreement among the concentrations found and those certified were observed. These results indicated the absence of spectral interferences caused by N2. The estimated detection limits for both Ar-ICP and Ar–N2-ICP were fairly comparable, revealing that the mixed-gas plasma is a robust source for trace elements determination using axially viewed-ICP OES. It was concluded that addition of a low flow of N2 is a simple way to increase plasma robustness without sacrificing analyte sensitivity.

Advantages and effects of nitrogen doping into the central channel of plasma in axially viewed-inductively coupled plasma optical emission spectrometry.

The effects and benefits of N2 addition to the central channel of the ICP through the nebulizer gas used in ICP OES with axial view configuration were investigated in the present study. The N2 flow rate, nebulizer gas flow rate, RF power and sample uptake rate were evaluated and compared for two sample introduction systems (pneumatic nebulization/aerosol desolvation and conventional pneumatic nebulization). It was observed that N2 did not affect solution nebulization and aerosol transport but affects the ICP characteristics. The higher thermal conductivity of N2 (in comparison with Ar) changes energy distribution in the ICP, observed by monitoring the signals of Ar emission lines and sodium emission. The ratio Mg(II)-280.270 nm/Mg(I)-285.213 nm was utilized as a diagnostic tool for plasma robustness. The addition of N2 (20 mL min(-1)) increased plasma robustness significantly and mitigated effects caused by Na, K and Ca. For 40 spectral lines evaluated, it was observed that the emission signals of ionic spectral lines were in general more affected by N2 than those of atomic spectral lines. Detection limits, precision, sensitivity and linearity of calibration curves obtained using N2-Ar-ICP were almost similar to those obtained using Ar-ICP. The analysis of 5 different reference materials revealed that accuracy was not degraded by adding N2 to the Ar-ICP.

Elemental hair analysis: A review of procedures and applications

Although exogenous contamination and unreliable reference values have limited the utility of scalp hair as a biomarker of chemical elements exposure, its use in toxicological, clinical, environmental and forensic investigations is growing and becoming more extensive. Therefore, hair elemental analysis is reviewed in the current manuscript which spans articles published in the last 10 years. It starts with a general discussion of history, morphology and possible techniques for elemental analysis, where inductively coupled plasma-mass spectrometry (ICP-MS) is clearly highlighted since this technique is leading quantitative ultra-trace elemental analysis. Emphasis over sampling, quality assurance, washing procedures and sample decomposition is given with detailed protocols compiled in tables as well as the utility of hair to identify human gender, age, diseases, healthy conditions, nutrition status and contamination sites. Isotope ratio information, chemical speciation analysis and analyte preconcentration are also considered for hair. Finally, the potential of laser ablation ICP-MS (LA-ICP-MS) to provide spatial resolution and time-track the monitoring of elements in hair strands instead of conventional bulk analysis is spotlighted as a real future trend in the field.

Trace element determination in leather samples using on-line internal standardization, ultrasonic nebulization and axial view-ICP OES

A method has been developed to determine 15 elements in leather samples by ultrasonic nebulization axial view inductively coupled plasma optical emission spectrometry (USN-ICP OES) after calibration by on-line internal standardization (IS). Samples were ground in a lab blender and decomposed following a simple digestion protocol with nitric acid and hydrogen peroxide under microwave heating. Owing to the high chromium content in samples, judicious selection of analytical wavelengths was necessary, as well as the use of internal standardization on-line to compensate for matrix effects caused by sample loading on the nebulizer system and the ICP-source. Low-biased results were obtained by simple external calibration with aqueous standards. Unpredictable plasma-related matrix effects caused signal suppression that cannot be corrected by acid matrix-matched reinforcing of the major role of IS. Even though no reference material for leather samples is commercially available, two certified biological samples were used to estimate the accuracy (dogfish liver and bovine liver) of the proposed procedure. The experimental values achieved showed good agreement with the certified values only if IS was employed throughout. Spike and recovery experiments confirmed that the results of the proposed method were accurate. Fifteen elements were quantified in different leather samples, and indicated the presence of toxic elements, which were mainly Pb, Cd, Zn, V, Ni and Cr.

Internal standardization in axially viewed inductively coupled plasma optical emission spectrometry (ICP OES) combined with pneumatic nebulization and aerosol desolvation

Internal standardization using axially viewed inductively coupled plasma optical emission spectrometry (ICP OES) combined with pneumatic nebulization/aerosol desolvation was evaluated in the present study. The sample and internal standard (IS) solutions were mixed on-line. Spectral lines of In, Y, Ga and Ar were evaluated for internal standardization under robust plasma conditions to overcome matrix effects on Ba, Cd, Co, Cr, Zn, Pb, Sr, Mn, Cu, Ni and V quantification in digests of plant materials. In(II)230.606 nm was only effective for Cd and Pb whereas Y(II)371.029 nm or Ga(I)417.206 nm or Ga(I)294.364 nm were effective for the other investigated elements. Argon was not effective, suggesting that matrix effects were related to aerosol generation and its transport to the ICP. By using internal standardization accurate results were obtained for certified reference samples of plant materials and the relative standard deviation (RSD) was lower than 1% even for solutions with high acid concentration. The limits of quantification (LOQ) of Cr(I)357.869, Cr(II)267.716, Cu(I)327.393, Cu(II)224.700, Cd(I)228.802, Cd(II)214.440, Pb(I)217.000, Pb(II)220.353, Zn(I)213.857, Zn(II)206.200, Sr(II)407.771, Ba(II)233.527, V(II)292.464, Mn(II)257.610, Ni(II)232.003 and Co(II)228.616 nm were 0.070, 0.041, 0.065, 0.094, 0.033, 0.056, 1.33, 0.45, 0.065, 0.10, 0.005, 0.20, 0.12, 0.015, 0.10 and 0.047 μg g−1, respectively. It was concluded that the method is feasible for routine applications.

Direct determination of trace elements in austenitic stainless steel samples by ETV-ICPOES

Electrothermal vaporization (ETV) coupled to inductively coupled plasma optical emission spectrometry (ICPOES) was applied to the direct analysis of austenitic stainless steel powders using external calibration with increasing amounts of urban particulate matter (NIST 1648a) certified reference material. The method was first validated through the analysis of a reference material of free cutting steel, BCS 152/3, which was also analysed, following digestion in aqua regia, by ICPOES with external calibration using matrix-matched standard solutions. A four-step heating program, where the 30 s vaporization step was not ramped and followed a cooling step after pyrolysis, was used along with hemi-spherical graphite boats and trifluoromethane (CHF3, freon R-23) reaction gas, which resulted in sharp analyte signal peaks. Internal standardization with an argon emission line (415.859 nm) was applied throughout to compensate for sample loading effects on the plasma, improve the signal-to-background ratio and extend the linear dynamic range. Quantification limits ranged from 0.02 (Cd) to 200 (Si) μg g−1 in the solid using 5 mg aliquots, and are one or two orders of magnitude lower than those obtained by ICPOES with nebulization for several elements. The proposed method allowed determination of Al, Cd, Ce, Co, Cu, Mn, Pb, S, Si, Ti, V and Zn at levels in the 10 μg g−1 to 0.4% (m m−1) range, in agreement with results obtained by ICPOES following digestion. The method is suitable for alloy quality control, as it drastically reduces analysis time and cost by eliminating the acid digestion step altogether, which is quite attractive for industrial applications.

Experimental evidence of enhanced water dissociation and spatially dependent charge-transfer reactions in mix-gas inductively coupled plasma optical emission spectrometry

Water dissociation and spatial dependence of charge-transfer reactions among nitrogen species (N+/N2+) and argon levels in inductively coupled plasma are experimentally demonstrated in the present study. The emission of species with energy near 5 eV (close to that of OH and H–OH), the ratio ion/atom or ion/ion along the ICP axis, and signals of argon spectral lines covering a broad energy range were evaluated. A microporous membrane fitted to a pneumatic nebulizer/desolvation system (PN/DES-MD) was employed for introducing the sample solution into the ICP, reducing the water loading and magnifying the effect of N2 in the drier ICP. It was deduced that the addition of N2 promotes the dissociation of OH or H–OH especially at low distances from the load coil. The ICP robustness was deteriorated due to water removal through the membrane, but the effect was compensated by adding a low flow of N2 into the central channel of the ICP. Matrix effects were mitigated when the desolvation membrane was used in parallel with the addition of N2. Emission intensity of argon spectral lines revealed that charge-transfer reactions among N+ and medium-energy argon levels are probably not spatially dependent along the ICP axis while those involving N2+ and high-energy argon levels probably are. The charge transfer reaction among N2+ and Ar requires a longer time of interaction, suggesting that it may occur in a two step process. The precision was better when membrane desolvation was used, but the sensitivity was worse, keeping the instrumental limit of detection at the same level as that obtained without using the membrane. The accuracy was not degraded by using the PN/DES-MD as the sample introduction system and adding a low flow of N2 to the nebulizer gas.