Akbar Montaser

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.

Ultratrace and Isotope Analysis of Long-Lived Radionuclides by Inductively Coupled Plasma Quadrupole Mass Spectrometry Using a Direct Injection High Efficiency Nebulizer

The direct injection high efficiency nebulizer (DIHEN) was explored for the ultrasensitive determination of long-lived radionuclides ((226)Ra, (230)Th, (237)Np, (238)U, (239)Pu, and (241)Am) and for precise isotope analysis by inductively coupled plasma mass spectrometry (ICPMS). The DIHEN was used at low solution uptake rates (1-100 μL/min) without a spray chamber. Optimal sensitivity (e.g., (238)U, 230 MHz/ppm; (230)Th, 190 MHz/ppm; and (239)Pu, 184 MHz/ppm) was achieved at low nebulizer gas flow rates (0.16 L/min), high rf power (1450 W), and low solution uptake rates (100 μL/min). The optimum parameters varied slightly for the two DIHENs tested. The detection limits of long-lived radionuclides in aqueous solutions varied from 0.012 to 0.11 ng/L. The sensitivity of the DIHEN was improved by a factor of 3 to 5 compared with that of a microconcentric nebulizer (MicroMist used with a minicyclonic spray chamber at a solution uptake rate of 85 μL/min) and a factor of 1.5 to 4 compared with that of a conventional nebulizer (cross-flow used with a Scott type spray chamber at a solution uptake rate of 1 mL/min). The precision of the DIHEN ranged from 0.5 to 1.7% RSD (N = 3) for all measurements at the 10 ng/L concentration level (∼3 pg sample size). The sensitivity decreased to 10 MHz/ppm at a solution uptake rate of 1 μL/min. The precision was about 5% RSD at a sample size of 30 fg for each long-lived radionuclide by the DIHEN-ICPMS method. The oxide to atom ratios were less than 0.05 (except ThO(+)/Th(+) ) and decreased under the optimum conditions in the following sequence: ThO(+)/Th(+) > UO(+)/U(+) > NpO(+)/Np(+) > PuO(+)/Pu(+) > AmO(+)/Am(+) > RaO(+)/Ra(+). Atomic and oxide ions were used as analyte ions for ultratrace and isotope analyses of long-lived radionuclides in environmental and radioactive waste samples. The analytical methods developed were applied to the determination of long-lived radionuclides and isotope ratio measurements in different radioactive waste and environmental samples using the DIHEN in combination with quadrupole ICPMS. For instance, the (240)Pu/(239)Pu isotope ratio was measured in a radioactive waste sample at a plutonium concentration of 12 ng/L. This demonstrates a main advantage of DIHEN-ICPMS compared with α-spectrometry, which cannot be used to selectively determine (239)Pu and (240)Pu because of similar α energies (5.244 and 5.255 MeV, respectively).

Nebulizer diagnostics: fundamental parameters, challenges, and techniques on the horizon

Nebulizer diagnostic techniques provide fundamental information for the quantitative assessment and prediction of the quality of the aerosol used for plasma spectrometry. Recent advances in aerosol diagnostic techniques are reported, with an emphasis on micronebulizers used in inductively coupled plasma spectrometry. The qualities of an ideal nebulizer in generating an analytically ideal aerosol for plasma spectrometries are described. Optical imaging and non-imaging methods used to obtain droplet size and velocity, number density, volume flux and span information are examined. In addition to established techniques, the capabilities of two novel aerosol diagnostic instruments, the optical patternator and rainbow refractometer, are presented. The optical patternator allows for the rapid elucidation of two-dimensional spray structure, planar mass distribution and spatial droplet size distributions. Rainbow refractometry/thermometry permits the determination of droplet temperature, droplet temperature–size correlations, and droplet temperature–velocity correlations. The capabilities and limitations of each technique are summarized. Prospects for future aerosol diagnostic techniques are discussed.

Determination of 236U/238U isotope ratio in contaminated environmental samples using different ICP-MS instruments

This paper considers use of the 236U isotope to monitor the spent uranium from nuclear fallout using inductively coupled plasma mass spectrometry (ICP-MS) in soil samples collected in the vicinity of the Chernobyl Nuclear Power Plant (NPP). Sector field ICP-MS (ICP-SFMS) and quadrupole based ICP-MS without and with hexapole collision cell (ICP-CC-MS) were used for uranium isotope analysis. In addition, a multiple ion collector ICP-MS (MC-ICP-MS) was used for high-precision isotope ratio measurements. A 238U+ ion sensitivity of 18 GHz ppm−1, 12.4 GHz ppm−1 and 16 GHz ppm−1, respectively, was observed in ICP-SFMS, ICP-CC-MS and MC-ICP-MS with ultrasonic nebulizer. An absolute sensitivity of 3600 counts fg−1 was achieved for uranium by using a direct injection high efficiency nebulizer for solution introduction in ICP-SFMS. The detection limit for 236U was in the fg g−1 range and abundance ratio sensitivity for 236U/238U was 5 × 10−6, 3 × 10−7, 6 × 10−7, and less than 3 × 10−7 in ICP-SFMS, MC-ICP-MS, quadrupole ICP-MS and ICP-CC-MS at mass resolution m/Δm = 300, respectively. Interlaboratory comparison yielded a good accuracy (0.4–1.6%) of 236U/238U isotope ratios ranging from 1.5 × 10−3 to 3.2 × 10−4 measured in samples containing 100 ng of uranium. The 236U/238U isotope ratios and spent uranium fraction were determined in Chernobyl soil samples using single ion detector ICP-MS and multiple ion collector ICP-MS (MC-ICP-MS). In comparison to 235U/238U isotope ratio, the 236U/238U isotope ratio provided more sensitive and accurate determination of the portion of spent uranium from Chernobyl NPP in spent/natural uranium mixture in soil samples down to 0.1%. The concentration of Chernobyl spent uranium in upper 0–10 cm soil layers in investigated areas in the vicinity of Chernobyl NPP amounts to 2.4 × 10−9 g g−1 to 8.1 × 10−7 g g−1 depending mainly on the distance to the Chernobyl reactor.

The Development of a Spectral Data Base for the Identification of Fibers by Infrared Microscopy

A detailed study of the application of infrared (IR) microscopy for single fiber analysis has been initiated. Spectra of single synthetic fibers were obtained rapidly and reproducibly with minimal sample preparation. Minor spectral variations, caused by deformation of the fibers during sample preparation, were observed between samples. These spectral variations were never sufficient to prevent the identification of the polymeric materials. An IR spectral library of 43 polymer fibers, which were distinguishable by their IR spectra, was constructed. The chemical subclass of unknown fibers, with the exception of acetates and nylons, could be accurately identified by a computer search using an absolute derivative difference searching algorithm.

A helium inductively coupled plasma for atomic emission spectrometry

Abstract An annular helium inductively coupled plasma (He ICP) was generated at atmospheric pressure. No external cooling was used to stabilize the plasma. Aqueous solution was injected into the plasma without any difficulty. Preliminary results revealed that the annular He ICP was capable of exciting elements such as Cl and Br which possess high excitation energies. Atomic emission detection limits for Cl and Br were improved by factors of 63 and 34, respectively, as compared to the results obtained from the argon inductively coupled plasma. The excitation temperature of the annular He ICP (4180 K) was less than that of an Ar ICP (5570 K).

Ultratrace and isotopic analysis of long-lived radionuclides by double-focusing sector field inductively coupled plasma mass spectrometry using direct liquid sample introduction

Abstract This report is concerned with the investigation of double-focusing sector field inductively coupled plasma mass spectrometry (DF-ICPMS) for ultratrace and isotopic ratio analysis of long-lived radionuclides (226Ra, 230Th, 232Th, 233U, 237Np, 238U, and 241Am) using the direct injection high efficiency nebulizer (DIHEN). A new shielded torch arrangement, known as the guard electrode, improves relative sensitivity by a factor of six when the DIHEN is used. Absolute sensitivity with the DIHEN is on the order of 1300 (226Ra) to 1700 (238U) counts/fg at a solution consumption rate of 5 μL/min. This is a factor of from three to 20 better than the results obtained by a conventional nebulizer-spray chamber arrangement (e.g., ultrasonic and pneumatic nebulizers). The DIHEN-DF-ICPMS is successfully tested for isotope ratio measurements of 235U/238U standards and environmental radioactive waste solutions.

Inter-laboratory note. Evaluation of a low sample consumption, high-efficiency nebulizer for elemental analysis of biological samples using inductively coupled plasma mass spectrometry

The applications of a pneumatically driven high-efficiency nebulizer (HEN), operated at a solution uptake rate of 85 µl min–1, are reported for the analysis of digested biological standard reference materials using argon ICP-MS. Laser Fraunhofer diffraction also is used to acquire droplet-size distributions for the tertiary aerosol from the HEN. Three Standard Reference Materials (SRM 1566 Oyster Tissue, 1577a Bovine Liver and 1571 Orchard Leaves, National Institute of Standards and Technology) are microwave/nitric acid digested and analysed by external calibration with four internal standards. Results for the measurement of 10 elements in the SRMs are presented. In general, good agreement is obtained between the measured and certified values. The droplet-size distributions of the tertiary aerosol of biological materials tested are nearly identical to that of the digestion blank solution consisting of 10% HNO3.

Computer simulation of argon-nitrogen and argon-oxygen inductively coupled plasmas

Abstract The properties of mixed-gas Ar-N2 and Ar-O2 inductively coupled plasmas (ICPs) are obtained by computer simulation. The results from the simulations are compared with existing experimental data. The reasons for the deviations are discussed, and inferences are drawn to connect the simulated results to recommendations for practical analytical measurements using ICP atomic emission and ICP mass spectrometries. The effect of the concentration of N2 and O2 in the outer gas flow (0%–100%) and injector gas flow (0%–20%) and the influence of the active power (800–1500 W) on the distribution of the plasma temperatures, electric and magnetic fields and tangential velocity are investigated. In general, mixed-gas plasmas move closer to the state of local thermodynamic equilibrium (LTE) as the concentrations of the molecular gases (N2 and O2) in the outer gas flow are increased. In contrast with the experimental results, the LTE model predicts that mixed-gas plasmas have maximum temperatures (9900–10100 K) comparable with Ar ICPs (10 600 K). The predicted temperature of the mixed-gas plasma is reduced as the concentration of the molecular gas is increased. The temperatures of Ar-O2 ICPs are estimated to be higher than those of Ar-N2 plasmas, except when the outer gas flow contains 100% N2 or O2.

A tutorial discussion on measurements of rotational temperature in inductively coupled plasmas

Abstract The intensities in the rotational fine structure of electronic bands such as B2Σ+u → X2Σ+g of N+2, A2Σ+ → X2Πi, of OH and B3Σu− → X3Σ−g of O2 are often used for measurements of rotational temperature prevailing in plasma sources such as the inductively coupled plasmas (ICP) and microwave induced plasmas (MIP). Certain misconceptions (such as the incorrect use of Hunds rule, the use of transition probability in conjuction with the equation for line strength, and the incorrect assignment of rotational lines) in the calculations of rotational temperatures have led to erroneous results. The main point of this paper is to emphasize that the interpretation of the rotational intensity distribution depends on both the angular momentum coupling and on the resolution of the instrument used. In this report, the introductory theory of rotational temperature measurement is reviewed and examples of correct and incorrect calculations are cited for ICP and MIP discharges sustained in argon, helium, argon-nitrogen, argon-oxygen and argon-air.