Eric H. van Veen

On the accuracy of temperature measurements in turbulent jet diffusion flames by coherent anti-stokes-raman spectroscopy

Coherent anti-Stokes-Raman spectroscopy (CARS) has been applied to determine profiles of mean and standard deviation of temperature and of probability density functions for the Delft turbulent jet diffusion flames fed with Dutch natural gas. Several improvements to the CARS data reduction are introduced and special attention is paid to the effect of spatial averaging. It is shown that the error due to the limited resolution is at most 40 K for mean temperatures around 750 K. The CARS results are compared to the Raman-Rayleigh results obtained earlier for the same flames. Within experimental uncertainty, the results from the two independent nonintrusive laser diagnostic techniques are the same, except for the low central part of the flames. The difference can be a consequence of the occurrence of large methane concentrations and of the sensitive dependence on upstream boundary conditions.

Evaluation of a microwave desolvation system in inductively coupled plasma mass spectrometry with low acid concentration solutions

The behaviour of a desolvation system based on microwave heating (termed a microwave desolvation system, MWDS) with low acid concentration solutions was evaluated in inductively coupled plasma mass spectrometry. Studies included water, sulfuric acid, perchloric acid, nitric acid and hydrochloric acid. The best performance of the MWDS was obtained at low liquid uptake rate and low acid concentrations. The analytical behaviour of the MWDS depends on the nature and composition of the solution used. In comparison with water, acid solutions provide up to four times higher ion intensities for the elements tested. In comparison with nitric and hydrochloric acid, sulfuric and perchloric acid provide higher ion intensities but also higher CeO+/Ce+ ratios whereas Ba2+/Ba+ ratios are lower. The limits of detection (LODs) are of the same order of magnitude for all acid solutions used, unless the specific isotope/solvent combinations suffer from spectral interference. In comparison with the conventional sample introduction (CS) without desolvation system the MWDS provides between 2 and 14 times higher ion intensities for the isotopes tested. For nitric and hydrochloric acid solutions the MWDS gives rise to lower CeO+/Ce+ratios and higher Ba2+/Ba+ ratios. For sulfuric and perchloric acid these tendencies are the opposite. For the isotopes that are not subject to interference, the LODs obtained with the MWDS are up to a factor of 10 lower than those obtained with CS.

Thermometry for turbulent flames by coherent anti-Stokes Raman spectroscopy with simultaneous referencing to the modeless excitation profile

An optimal system for temperature measurements by coherent anti-Stokes Raman spectroscopy (CARS) in turbulent flames and flows is presented. In addition to a single-mode pump laser and a modeless dye laser, an echelle spectrometer with a cross disperser is used. This system permits simultaneous measurement of the N2 CARS spectrum and the broadband dye laser profile. A procedure is developed to use software to transform this profile into the excitation profile by which the spectrum is referenced. Simultaneous shot-to-shot referencing is compared to sequential averaged referencing for data obtained in flat flames and in room air. At flame temperatures, the resultant 1.5% imprecision is limited by flame fluctuations, indicating that the system may have a single-shot imprecision below 1%. At room temperature, the 3.8% single-shot imprecision is of the same order as the best values reported for dual-broadband pure-rotational CARS. Using the unique shot-to-shot excitation profiles, simultaneous referencing eliminates systematic errors. At 2000 and 300 K, the 95% confidence intervals are estimated to be +/- 20 and +/- 10 K, respectively.

Electrothermal vaporization of mineral acid solutions in inductively coupled plasma mass spectrometry: comparison with sample nebulization

Abstract The analytical behaviour of an electrothermal vaporization (ETV) device for the introduction of mineral acid solutions in inductively coupled plasma mass spectrometry (ICP-MS) was evaluated. Water, nitric acid, hydrochloric acid, perchloric acid and sulphuric acid in concentrations within the 0.05–1.0 mol l −1 range were studied. For all the acids tested, increasing the acid concentration increases the ion signal and deteriorates the precision. The magnitude of the signal enhancement depends on the analyte and on the acid considered. Acid solutions give rise to ion signals that are between 2 and 10 times higher than those with water. Among the acids tested, sulphuric acid provides the highest signals. The addition of palladium reduces matrix effects due to the acids and increases the signal in ETV ICP-MS. In comparison with conventional sample nebulization (CS), the ETV sample introduction system provides higher sensitivities (between 2 and 20 times higher) at the same acid concentration. The magnitude of this improvement is similar to that obtained with a microwave desolvation system (MWDS). The ETV sample introduction system gives rise to the lowest background signals from matrix-induced species. Due to this fact, the limits of detection (LODs) obtained for the isotopes affected by any interference are lower for ETV sample introduction than those obtained with the CS and the MWDS. For the isotopes that do not suffer from matrix-induced spectral interferences, the ETV gives rise to LODs higher than those obtained with the CS. For these isotopes the lowest LODs are obtained with MWDS.

Fourier Deconvolution of Overlapping Line Pairs in Inductively Coupled Plasma-Atomic Emission Spectrometry

A deconvolution procedure utilizing Fourier transformation has been developed to reduce line overlap in ICP-AES. Line broadening is caused by physical processes and by instrumental broadening. Convenient deconvolution, however, turns out to be restricted to broadening common to the emission lines in the spectral window, i.e., to instrumental broadening. Deconvolution for the “true” instrumental broadening function and for a Gaussian approximation to this function yields similar results, but the former allows for fast automated data processing with regard to any spectral region and sample composition. A straightforward procedure is reported for the determination of this function independent of wavelength. At the present noise level, a twofold reduction in linewidth can be achieved for emission lines having a small physical width in comparison to the instrumental width. With data acquired from both a high- and a medium-resolution monochromator, results from overlapping line pairs show linear analytical curves and improved detection limits. Due to the decrease in signal-to-noise ratio on deconvolution, the detection limits measured for isolated lines cannot be attained.