M. Kuzmanović

Emission Spectrometric Analysis of Fresh Waters with U-Shaped D.C. Arc with Aerosol Supply

Abstract The application of a U-shaped d.c. arc with aerosol supply for analysis of fresh waters has been described. Limits of detection obtained with d.c. plasma compare well with those reported for ICP. A number of spectral lines and molecular bands were examined and the most suitable are selected to ensure the best limits of detection or wide dynamic ranges. Limits of detection in ng ml−1, given in the parenthesis, following the element symbol, are: Al(0.9), B(0.6), Ba(0.2), Be(0.15), Ca(0.05), Cd(3.5), Co(1.1), Cr(0.2), Fe(2.4), Ga(0.5), Hg(9.0), K(0.3), Li(0.008), Mg(0.4), Mn(0.3), Mo(0.7), Na(0.04), Ni(2.0), P(45), Pb(12), Si(9.0), Sr(0.04), Zn(1.3).

The role of demixing effect in analyte emission enhancement by easily ionized elements in d.c. plasma

Abstract The effect of easily ionized elements (EIE) in d.c. plasma (DCP) has been modeled and experimentally investigated. The introduction of the EIEs in the U-shaped DCP decreases a ‘potential barrier’ due to an internal radial electric field, which allows the partially ionized analyte better entry into the hot plasma zone and produces enhancement of the analyte spectral emission. Compared to the equilibrium concentration, the increased electron concentration in the fringe region due to large radial gradients is accounted for in the model. By comparing model predictions to experimental data, the validity of the model is tested. The main features of the effect, the large enhancement at small addition of EIE and almost equal enhancement of ion and atom line intensities, are fairly well described by the model. The results are believed to be applicable to the inverted Y-shaped DCP. The effect in the inductively coupled plasma (ICP) has been briefly discussed from the point of view of the proposed model.

The effect of potassium addition on plasma parameters in argon dc plasma arc

The effect of potassium addition on the radial distribution of temperature and electron number density in a U-shaped direct current (dc) argon plasma operating at different arc currents has been studied by optical emission spectroscopic techniques and the power interruption method. Spatially resolved electron number densities (ne) have been determined from measured radial profiles of Balmer-Hβ spectral line. The obtained electron number densities have been used for thermodynamic temperature (TLTE) evaluation with the assumption that the arc plasma is in a state of local thermodynamic equilibrium. The excitation temperatures (Texc) have been determined from the absolute integral emissivity of the argon line at 430.01 nm. For heavy particle temperature (Th) evaluations we have used a power interruption method. The obtained results have shown that an addition of KCl decreases both electron number density and temperature of the arc column. The magnitude of such an influence on plasma parameters increases with an increase in the KCl concentration and decreases with an increase in the arc current.

Optical Emission Studies of Copper Plasma Induced Using Infrared Transversely Excited Atmospheric (IR TEA) Carbon Dioxide Laser Pulses

Spatially resolved, time-integrated optical emission spectroscopy was applied for investigation of copper plasma produced by a nanosecond infrared (IR) transversely excited atmospheric (TEA) CO2 laser, operating at 10.6 μm. The effect of surrounding air pressure, in the pressure range 0.1 to 1013 mbar, on plasma formation and its characteristics was investigated. A linear dependence of intensity threshold for plasma formation on logarithm of air pressure was found. Lowering of the air pressure reduces the extent of gas breakdown, enabling better laser-target coupling and thus increases ablation. Optimum air pressure for target plasma formation was 0.1 mbar. Under that pressure, the induced plasma consisted of two clearly distinguished and spatially separated regions. The maximum intensity of emission, with sharp and well-resolved spectral lines and negligibly low background emission, was obtained from a plasma zone 8 mm from the target surface. The estimated excitation temperature in this zone was around 7000 K. The favorable signal to background ratio obtained in this plasma region indicates possible analytical application of TEA CO2 laser produced copper plasma. Detection limits of trace elements present in the Cu sample were on the order of 10 ppm (parts per million). Time-resolved measurements of spatially selected plasma zones were used to find a correlation between the observed spatial position and time delay. Index Headings: Laser induced Cu-plasma emission; Shock wave plasma; Copper target; Transversely excited atmospheric CO2 laser; TEA CO2 laser.

Quantitative analysis of the Raman spectra of mixtures of weakly interacting components by factor analysis methods

A system of 17 overlapped Raman spectra in the 250–350 cm–1 spectral region of the weakly interacting component mixture of 1,2-dichloroethane, dichloromethane and carbon tetrachloride has been subjected to the statistical methods of target factor analysis (TFA) and evolving factor analysis (EFA). The results have demonstrated that concentrations of substances with intense bands are successfully determined; however, there are difficulties in analyzing weak bands of one of the components, especially when applying a TFA technique. The results of such an analysis can be improved by minimal changes in one of the coordinates of a rotation vector. Comparison of these results with a synthetic spectral model suggests that problems with analysis of weak bands are caused by the presence of a strong band that greatly overlaps the weak one.

Vibrational Analysis of the β System of 10B18O

Ten bands of the β system (B2Σ+ − X2Σ+) of the 10B18O molecule have been observed for the first time. The spectrum was obtained by emission spectroscopy from a low‐pressure arc, at medium dispersion, and vibrationally analyzed using isotope shift measurements. Vibrational analysis gave the constants ωe and ωexe for both electronic states involved in the transitions.

Franck-Condon factors and r-centroids for the E 1Πu-X 1Σ g + system of Ag2

An array of Franck-Condon factors and r-centroids is reported for the bands of the E1Πu-X1Σg+ system of the Ag2 molecule. Both parameters were calculated using the Morse and Rydberg-Klein-Rees potentials. The results showed a reasonable agreement between the two sets of data for transitions, including lower vibrational levels (v ≤ 6). Differences appear with increasing v, but two sets of calculated Franck-Condon factors follow the same pattern. The predicted intensity distribution was compared with the estimated band intensity in the experimental spectrum.

A Power Interruption Technique for Determining the Difference Between Electron and Gas Temperatures in the Argon d.c. Arc Supplied with Aqueous Aerosol

The difference between electron and gas temperatures in a low current U‐shaped d.c. arc with aqueous aerosol supply was studied using a power interruption technique. Monitoring of the temporal evolution of recombination continuum after power switch‐off revealed that it was necessary to do a correction of the measured values due to a change in electron concentration. It was shown that the plasma studied was a two temperature type and that the temperature difference ranges from 1850 K to 600 K for arc currents from 3 to 10.5 A, respectively. A comparison with literature results for pure argon arc plasma shows that aerosol introduction reduces the temperature difference.

High-Resolution Spectra of the 10B18O and 11B18O: Rotational Analysis of the B–X Bands

Emission spectra of 10B18O and 11B18O isotopomers in the 230–330 nm region have been investigated by means of conventional high-resolution spectroscopy. The molecules were produced in a low-pressure arc by discharging 8 Torr of mixture containing argon and oxygen 18 in the ratio of 4:1 and the spectra have been recorded using Ebert-type spectrograph. The boron needed to produce BO has been present in the system as amorphous powder with natural abundance of 10B and 11B. Rotational analysis of the 0, 0 and 0, 1 bands has been performed and spectroscopic constants have been extracted. The results have allowed first determination of the equilibrium rotational constants Be and De for both isotope species 10B18O and 11B18O in their lower electronic state. Assuming a linear dependence of Be on (ν+1/2), the value of equilibrium distance re in the lower state has been derived.

Laser-Induced Breakdown Spectroscopy (LIBS): specific applications

A short overview of Laser Induced Breakdown Spectroscopy (LIBS) with emphasis on the new trends is presented. Nowadays, due to unique features of this technique, LIBS has found applications in a great variety of fields. Achievements in the application of LIBS in nuclear area, for hazardous materials detection and in geology were considered. Also, some results recently obtained at VINCA Institute, with LIBS system based on transversely excited atmospheric (TEA) CO2 laser, are presented. Future investigations of LIBS will be oriented toward further improvement of the analytical performance of this technique, as well as on finding new application fields.