José Chirinos

Direct injection high efficiency nebulizer-inductively coupled plasma mass spectrometry for analysis of petroleum samples

Abstract Direct injection high efficiency nebulizer (DIHEN)-inductively coupled plasma mass spectrometry (ICPMS) is investigated for analysis of petroleum samples dissolved in volatile organic solvents. To minimize solvent loading, the solution uptake rate is reduced to 10 μl/min, far less than the level (85 μl/min) commonly used for aqueous sample introduction with the DIHEN, and oxygen is added to the nebulizer gas flow and outer flow of the ICP. Factorial design is applied to investigate the effect of nebulizer tip position within the torch and the nebulizer and intermediate gas flow rates on the precision and the net signal intensity of the elements tested for multielemental analysis. Cluster analysis and principal component analysis are performed to distinguish the behavior of different isotopes, oxide species and doubly charged ions. The best operating conditions at a solution uptake rate of 10 μl/min are: RF power=1500 W, nebulizer gas flow rate=0.10–0.12 l/min, intermediate gas flow rate=1.5 l/min and DIHEN tip position=3–4 mm below the top of the torch intermediate tube. Acceptable recoveries (100±10%) and good precision (less than 3% relative standard deviation) are obtained for trace elemental analysis in organic matrices (a certified gas oil sample and a custom-made certified reference material) using flow injection analysis. Because of high blank levels, detection limits are 1–3 orders of magnitude higher for organic sample introduction than those acquired for aqueous solutions.

Use of emulsion systems for the determination of sulfur, nickel and vanadium in heavy crude oil samples by inductively coupled plasma atomic emission spectrometry

A useful and rapid procedure is described for the determination of sulfur, nickel and vanadium in crude oil by inductively coupled plasma atomic emission spectrometry. Samples were prepared by emulsifying crude oil in water. Aqueous inorganic solutions with the same amount of emulsifier and solvent were used as calibration standards. Heavy crude oils were analysed and the results were compared with those obtained by digestion methods. To evaluate the accuracy of the method, National Institute of Standards and Technology Standard Reference Materials, 1622c Sulfur in Residual Fuel Oil and 1634a Trace Elements in Fuel Oil, were analysed. No statistically significant differences were observed between the results obtained by this method and the certified values. The precision of the method was in the range from 1 to 3% relative standard deviation.

Analytical evaluation of a dual micronebulizer sample introduction system for inductively coupled plasma spectrometry

The analytical performance of a dual nebulization system is evaluated for sample nebulization at lower solution uptake rates in inductively coupled plasma optical emission spectrometry (ICP-OES). The system is essentially a modified cyclonic spray chamber that allows the simultaneous operation of two micronebulizers. This work is focused on the optimization and evaluation of the main analytical figures of merit of this sample introduction system. The usefulness of this dual micro-nebulizer in practical ICP-OES studies is demonstrated by using a tandem calibration technique and by operating this system for hydride generation studies. Results showed that this system presents similar figures of merit to a conventional spray chamber but that the non-spectroscopic interferences, usually present at lower solution uptakes rates, can be compensated for by using the tandem calibration technique with this system. Additionally, the two micronebulizers coupled to the modified cyclonic spray chamber can be used for efficient volatile hydride generation from sub-mL amounts of samples. Interference effects by transition metals have been shown to be corrected by the addition of thiourea. The analytical applicability of the dual system was checked by analyzing two standard reference materials: NIST 1577b, Bovine Liver and NIST 1566a Oyster Tissue. The accuracy achieved when using different calibration techniques and hydride generation are within the certified values when applying the significance t-test at the 95% confidence level.

Application of TLC and LA ICP SF MS for speciation of S, Ni and V in petroleum samples

A coupling of thin layer chromatography with laser ablation ICP SF MS was developed for the fractionation of Ni, V, Fe and S in crude oil and its fractions (saturate, aromatic, resin and asphaltene). The detection limits were 18 ng g(-1) and 23 ng g(-1) for nickel and vanadium, respectively, and a sample could be characterized in terms of the metal distribution as a function of species polarity within 10 min. The method was used to characterize the metal distribution in crude oils of different origins and their different fractions.

Multi-element optimization of the operating parameters for inductively coupled plasma atomic emission spectrometry with a charge injection device detector for the analysis of samples dissolved in organic solvents

A multi-element optimization of the operating parameters for simultaneous ICP-AES with a CID detector for the analysis of samples dissolved in organic solvents was carried out. Some statistical experimental designs were used to evaluate the influence of the operating parameters on the effect of volatile organic solvents and to obtain the best plasma conditions for multi-element analysis. The lower limit of detection was used as the optimization criteria. A factorial study showed that nebulizer pressure is the factor that strongly affects the signal-to-root background ratio of the elements under study. The best operating conditions of the plasma for simultaneous determination were obtained using some objective functions reported in the literature. A multi-element analysis of NIST SRM 1085 a Wear Metals in Oil was accomplished using the plasma operating conditions established by the simultaneous optimization. No statistically significant differences were observed between the measurements made and the certified values. The precision of the method was in the range 1–3% expressed as RSD percentage.

Investigation of the direct injection high efficiency nebulizer for axially and radially viewed inductively coupled plasma atomic emission spectrometry

A direct injection high efficiency nebulizer (DIHEN) is explored for introduction of the sample aerosol into the central channel of the axially and radially viewed inductively coupled plasma (ICP) of a commercial ICP atomic emission spectrometer (ICPAES). The DIHEN is a micro-nebulizer that requires very low solution uptake rates (1–100 µL min−1) and nebulizer gas flow rates (<0.2 L min−1) compared to conventional nebulizer-spray chamber arrangements (∼1.0 mL min−1 and ∼1.0 L min−1, respectively). Signal-to-background ratios (SBRs), detection limits, and precision of the DIHEN are comparable or superior to those of the conventional sample introduction system, but the Mg II 280.270/Mg I 285.213 nm ratios are lower with the DIHEN, indicating that the DIHEN is more susceptible to matrix effects than the conventional nebulization system, for both the axial and radial ICPAES systems. Matrix effects are further investigated by comparing intensity ratios with and without 0.1% and 0.5% Na for several spectral lines having energy sum ranging from 7.93 to 14.79 eV. Replacement of Ar with Ar–O2 and Ar–N2 mixtures in the outer gas flow of the plasma improves SBRs and Mg II 280.270/Mg I 285.213 nm ratios of the DIHEN, and reduces matrix effects. By reducing solution uptake rate from 60 to 30 µL min−1, matrix effect is also reduced. Operation of the radial instrument at 1700 W reduces matrix effect compared to the effect noted for the axial instrument at 1500 W. Finally, the utility of the technique in practical ICPAES studies is demonstrated using a custom made organo-metallic standard for As, Hg, and Pb in xylene.

Performance of a Dual Sample Introduction System with Conventional Concentric Nebulizers for Simultaneous Determination of Hydride and Non-Hydride Forming Elements by ICP-OES

Abstract A dual sample introduction system that combines the benefits of nebulization and vapour generation in a single device is described. It consists of two commercial conventional concentric nebulizers coupled to a modified cyclonic chamber. The effect(s) of the solvent load produced by the amount of liquid carried for the system by the two nebulizer assemblies is investigated. Better sensitivities, similar precision and DLs (with the exception of hydride forming elements) were obtained compared with those obtained with the system working in single mode. Long term stability was less than 7% with the dual mode, being 2% and 6% for the non-hydride and hydride forming elements, respectively, in the single mode operation. DLs obtained are of the same order of magnitude as those reported by several authors, with the exception of Se whose conditions were in compromise with the optimal reached for the rest of the elements. Accuracy of the dual system was proved by analyzing NIST 1648, urban particulate matter, with satisfactory results.

Determination of sulfur in crude oils and related materials with a Parr bomb digestion method and inductively coupled plasma atomic emission spectrometry

A useful and rapid procedure is described for the determination of sulfur in crude oil and related materials by inductively coupled plasma atomic emission spectrometry. The sample is digested by a Parr oxygen combustion bomb method and the sulfur content can be determined easily using simple aqueous solutions as calibration standards. The sample preparation only takes 20 min approximately. Some Venezuelan crude oils and similar materials were analysed and the results are compared with those obtained by X-ray fluorescence. To evaluate the accuracy of the method, a National Institute of Standards and Technology Standard Reference Material 1622 c Sulfur in Residual Fuel Oil was analysed. No statistically significant differences were observed between the results obtained and the certified value. The precision of the method is in the range from 1 to 3% expressed as relative standard deviation.

Optimization of experimental parameters for the determination of mercury by MIP/AES

A system using a microwave induced plasma, as an emission source was optimized for total mercury determinations. The system contains a flow injection section in which mercury is reduced and deposited on a gold/platinum collector, and carried to the emission source. The microwave was generated in a Surfatron cavity. An experimental design was applied to optimize parameters concerning plasma conditions, amalgamation, desorption and mercury vapor generation. The limit of detection of the method was 14 pg ml(-1) of mercury, using peak area mode while LDs was 1.3 pg ml(-1) using peak height mode, with a 2% RSD and a linear dynamic range of almost three orders of magnitude. The accuracy was assessed using a certified reference material of atmospheric particulate National Institute of Standards and Technology (NIST) 2704. No significant difference at 95% confidence level was observed between the certified value and our result.

Determination of normal human intrathyroidal iodine in Caracas population.

This study focuses on the determination of iodine content in healthy thyroid samples on male population from Caracas, Venezuela. Contribution to establish a baseline of iodine content in thyroid glands and hence to compare the iodine thyroid concentration of the Venezuelan population with other countries is also our objective. Male post-mortem individual samples were analyzed using a spectrophotometric flow injection method, based on the Sandell-Kolthoff reaction. The median intrathyroidal iodine concentration was 1443+/-677 microg/g (wet weight), ranging from 419 to 3430 microg/g, which corresponds to a median of total iodine content of 15+/-8 mg (ranging from 4 to 37). These results were higher than those values reported in the literature. No correlation of iodine content with age or weight of the healthy gland was found.