Potential of far-ultraviolet absorption spectroscopy as a highly sensitive analysis method for aqueous solutions. Part II: monitoring the quality of semiconductor wafer cleaning solutions using attenuated total reflection

Far-ultraviolet (FUV) spectroscopy combined with attenuated total reflection (ATR) is employed for direct measurement of the concentrations of semiconductor wafer cleaning fluids such as SC-1 (aqueous solution of NH(3) and H(2)O(2)) and SC-2 (aqueous solution of HCl and H(2)O(2)). FUV spectra of these aqueous solutions in the 170-200 nm region are highly sensitive to changes in both hydrogen bonding and hydration. Although ATR measurement results in lower absorptivity compared to transmittance measurement, it is possible to increase absorption with greater evanescent wave penetration depth using a low refractive index internal reflection element (IRE). We adopt quartz as an IRE material. Since the refractive index of quartz becomes lower than that of water in the low energy side of an intense absorption band due to the n --> sigma* transition of water, the quartz IRE yields non-total reflection wavelength regions. However, near 175 nm the effective absorptivity of the tail of water's absorption band can be successfully enlarged, making the FUV-ATR technique suitable for measuring the concentrations of the components in the semiconductor wafer cleaning fluids. In the present study we prepared the same cleaning fluids as those used in actual semiconductor fabrication and measured their FUV-ATR spectra in the 150-300 nm wavelength range. It was found that even with the quartz IRE one can measure FUV-ATR spectra under total reflection conditions at 175 nm or above. We created calibration models for predicting both NH(3) and H(2)O(2) in the concentration ranges of 0-10% in SC-1 using multiple linear regression (MLR). The standard deviations of the models were 0.033% and 0.265% for NH(3) and H(2)O(2), respectively. The same procedure was repeated under the same conditions for HCl and H(2)O(2) in SC-2, yielding corresponding values of 0.018% for HCl and 0.178% for H(2)O(2).     

Temperature measurements of turbid aqueous solutions using near-infrared spectroscopy

We report a method that uses near-infrared spectroscopy and multivariate analysis to measure the temperature of turbid aqueous solutions. The measurement principle is based on the fact that the peak wavelength of the water absorption band, with its center near 1440 nm, shifts with changes in temperature. This principle was used to measure the temperatures of 1 mm thick samples of aqueous solutions containing Intralipid (2%), which are often used as optical phantoms for biological tissues due to similar scattering characteristics. Temperatures of pure water and aqueous solutions containing glucose (100 mg/ml and 200 mg/ml) were also measured for comparison. For the turbid Intralipid solutions, the absorbance spectrum varied irregularly with time due to the change in scattering characteristics. However, by making use of the difference between the absorbance at 1412 nm and the temperature-independent absorbance at 1440 nm, we obtained SEPs (standard error of prediction) of 0.3 degrees C and 0.2 degrees C by univariate linear regression and partial least squares regression, respectively. These accuracies were almost the same as those for the transparent samples (pure water and glucose solution).     

Direct determination of peracetic acid, hydrogen peroxide, and acetic acid in disinfectant solutions by far-ultraviolet absorption spectroscopy

In this paper we propose a rapid and highly selective far-ultraviolet (FUV) spectroscopic method for the simultaneous determination of peracetic acid (PAA), hydrogen peroxide, and acetic acid (AA). For this purpose we developed a novel FUV spectrometer that enables us to measure the spectra down to 180 nm. Direct determination of PAA, H(2)O(2), and AA, the three main species in disinfectant solutions, was carried out by using their absorption bands in the 180-220-nm region. The proposed method does not require any reagents or catalysts, a calibration standard, and a complicated procedure for the analysis. The only preparation procedure requested is a dilution of H(2)O(2) with pure water to a concentration range lower than 0.2 wt % in the sample solutions. Usually, the required concentration range can be obtained by the 10 times volume dilution of the actual disinfectant solutions. As the measured sample does not leave any impurity for the disinfection, it can be reused completely by using a circulation system. The detection limit for PAA of the new FUV spectrometer was evaluated to be 0.002 wt %, and the dynamic ranges of the measured concentrations were from 0 to 0.05 wt %, from 0 to 0.2 wt %, and from 0 to 0.2 wt % for PAA, H(2)O(2), and AA, respectively. The response time for the simultaneous determination of the three species is 30 s, and the analysis is applicable even to the flowing samples. This method may become a novel approach for the continuous monitoring of PAA in disinfectant solutions on the process of sterilization.     

Water evaporation analysis of L-phenylalanine from initial aqueous solutions to powder state by vibrational spectroscopy

The water evaporation from L-phenylalanine (L-phe) aqueous solutions at different initial pH (0-13) was studied by vibrational spectroscopy. Next, the attenuated total reflection-Fourier transform infrared (ATR-FT-IR) spectra of aqueous solutions were compared to those recorded after drying for 72 h at 21 degrees C at appropriate initial pH values. Micro-Raman results collected after the water evaporation process are also presented and interpreted. Between pH = 2.5 and 8.76 a white non-transparent gel was observed, possibly due to the presence of the NaCl salt. The significant differences of the band intensities of L-phe functional groups noticed at pH near pK(a) values indicate the structural changes of L-phe molecules due to dimer formation (hydrogen bonds between the -COOH and -CO(2)(-) groups, and the -NH(3)(+) and -NH(2) groups). The presence of the hydrophobic interactions leads to the aggregation of L-phe molecules, most probably via phe-phe stacking as well as complexes of phe with Na(+) ions, HCl, or H(2)O molecules.     

Highly selective colorimetric detection of hydrochloric acid using unlabeled gold nanoparticles and an oxidizing agent

We report a colorimetric system for the detection of HCl in aqueous environments using unlabeled gold nanoparticle (AuNP) probes. This nonaggregation-based detection system relies on the ability of chloro species to cause rapid leaching of AuNPs in an aqueous dispersion containing a strong oxidizing agent, such as HNO(3) or H(2)O(2). The leaching process leads to remarkable damping of the surface plasmon resonance peak of the AuNP dispersion. This method works only with AuNPs of a particular size (～30 nm diameter). It is highly selective for HCl over several common mineral acids, salts, and anions. This simple and cost-effective sensing system provides rapid and simple detection of HCl at concentrations as low as 500 ppm (far below the hazard limit) in natural water systems.     

Monitoring the temperature of dilute aqueous solutions using near-infrared water absorption

An alternative spectroscopic approach for monitoring the temperature of aqueous solutions is presented. The method is based upon the temperature-induced spectral changes undergone by the second overtone (around 960 nm) of the near-infrared (NIR) water absorption band. Single and multilinear regression analysis are tested in order to evaluate the predictive ability of temperature. A linear dependence is found when measurements are performed at a single wavelength, but a lower prediction error is obtained when multilinear models are applied. No matrix effects produced by moderately concentrated common dissolved ions are found in a broad range of pH. A signal-to-noise ratio allows a precision of 0.5 degrees C for temperature monitoring. A prediction error of 0.77 degrees C (single linear regression) and 0.25 degrees C (multilinear approach) are achieved in a range from 15 to 90 degrees C. Advantages in terms of instrumentation and data analysis required are discussed.     

UV-light induced photodegradation of 17alpha-ethynylestradiol in aqueous solutions

The photodegradation of 17alpha-ethynylestradiol (EE2) in aqueous solutions induced by UV-light was preliminarily studied in this paper by means of fluorescence, UV and infrared spectra. The result suggested that EE2 in aqueous solutions underwent photodegradation under irradiation with UV disinfection lamp (lambda = 254 nm, 30 W), but the photodegradation was not observed under high pressure mercury lamp (lambda > or = 365 nm, 250 W). The photodegradation of 1.6-20.0 mg/l EE2 in aqueous solutions at a given initial pH value of 6.8 was pseudo-first order reaction. Increasing the initial concentration of EE2 lowered the photodegradation rate. The photodegradation rate of EE2 reached the lowest value at pH about 5.0, higher pH values of 6.0-8.0 benefited the photodegradation. Ferric ions can promote the photodegradation of EE2 in aqueous solutions at pH value of 2.0-5.0.     

Spectroscopic features of laser-induced breakdown in water and aqueous solutions in ultrasonic field

It is established that the action of ultrasound leads to both sharp enhancement of the acoustic emission and increase in the intensity of spectral lines of laser-excited elements dissolved in aqueous salt solutions (NaCl, NaHCO₃, CaCl₂), which provides a new method of combined laser–ultrasonic spark spectroscopy. The task of synchronization of the acoustic and optical emission has been solved, which reveals dependence of the intensity of spectral lines on the phase of ultrasonic wave action.     

Solubility of chlorine in aqueous hydrochloric acid solutions

The solubility of chlorine in aqueous hydrochloric acid solutions was studied. The effects of HCl concentration and temperature on the solubility were evaluated, and the thermodynamic parameters of the dissolution were calculated. It was found that the solubility isotherms had a minimum at about 0.5M HCl concentration at all the temperatures studied and that solubility decreased with the increase of temperature at all the HCl concentration range investigated.     

Preparation of diamond-like carbon films by cathodic micro-arc discharge in aqueous solutions

Diamond-like carbon films (DLC) and silicon doped diamond-like carbon films were deposited on Ni substrate by cathodic micro-arc discharge at room temperature in aqueous solutions. The deposit potential was 130 V. The structure of the films was characterized by a scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Raman spectra and XPS analysis demonstrated that the films were diamond-like carbon clearly. SEM observation showed that the DLC films were uniform and the thickness was about 200 nm. Potentiodynamic polarization curve indicated the corrosion resistance of the Ni substrate was markedly improved by DLC films.     

Molar absorptivities of glucose and other biological molecules in aqueous solutions over the first overtone and combination regions of the near-infrared spectrum

Molar absorptivities are measured for water, glucose, alanine, ascorbate, lactate, triacetin, and urea in the near-infrared spectral region at 37 degrees C. Values are based on the Beer-Lambert law and cover the first overtone (1550-1850 nm; 6450-5400 cm(-1)) and combination (2000-2500 nm; 4000-5000 cm(-1)) spectral windows through aqueous media. Accurate calculations demand accounting for the impact of water displacement upon dissolution of solute. In this regard, water displacement coefficients are measured and reported for each solute. First overtone absorptivities range from 2 to 7 x 10(-5) mM(-1)mm(-1) for all solutes except urea, for which absorptivity values are below 0.5 x 10(-5) mM(-1) mm(-1) across this spectral range. Molar absorptivities over the combination spectral region range from 0.8 to 3.2 x 10(-4) mM(-1) mm(-1), which is a factor of four to five greater than the first overtone absorptivities. Accuracy of the measured values is assessed by comparing calculated or modeled spectra with spectra measured from standard solutions. This comparison reveals accurately modeled spectra in terms of magnitude and position of solute absorption bands. Both actual and modeled spectra from glucose solutions reveal positive and negative absorbance values depending on the measurement wavelength. It is shown that the net absorbance of light is controlled by the magnitude of the absorptivity of glucose compared to the product of the absorptivity of water and the water displacement coefficient for glucose.     

Separation of aniline from aqueous solutions using emulsion liquid membranes

An emulsion liquid membrane process is developed to separate aniline from dilute aqueous solution. Aniline (amino-benzene) is a carcinogenic chemical common in industry and industrial wastewater. Due to aniline's high boiling point (183°C) and low concentration in wastewater, more traditional methods of separation such as distillation are very energy intensive. This emulsion process is offered as a low energy alternative. All separations occur in a Rushton stirred tank. The membrane phase consists of kerosene and the surfactant sorbitan monooleate (span 80). Hydrogen chloride solution is the internal phase. This study also examines the effects of HCl concentration, aniline concentration, and the amount of emulsion on separation. Up to 99.5% of the aniline is removed from solutions containing 5000 ppm in as little as 4 min depending on process conditions. Leakage is minimal and swelling is only about 3% after 5 min of processing. Approximately 98% of the membrane phase (both kerosene and span 80) is successfully recovered and recycled by using heat and/or adding 2-propanol for demulsification.     

Detection of chromium in wastewater from refuse incineration power plant near Poyang Lake by laser induced breakdown spectroscopy

A laser induced breakdown spectroscopy (LIBS) system was developed for determination of toxic metals Cr in wastewater collected from a refuse incineration power plant near Poyang Lake. The plasma was generated by focusing a pulsed Nd:YAG laser at 1064 nm on the surface of liquid. Experimental conditions were optimized for improving the sensitivity and repeatability of the LIBS system through a parametric dependence study in potassium bichromate (K(2)Cr(2)O(7)) aqueous solutions. Calibration curves for Cr I 425.43 and 357.87 nm lines are compared and the limit of detection is found to be 39 and 86 ppm, respectively. This calibration curve of Cr I 425.43 nm has been used for quantification of Cr in wastewater collected from a refuse incineration power plant near Poyang Lake where the concentration of Cr is found to be 97 ppm. The results between LIBS and standard analytical technique such as atomic absorption spectroscopy were compared, and the relative standard deviation was 8.5%.     

Some properties of aqueous titanium isopropoxide-hydrogenperoxide solutions and their decomposition to produce titanium dioxide

The preparation of aqueous titanium isopropoxide-hydrogen peroxide solutions, their light absorption spectra, optical density changes based on the transformation to colloids, thermal analysis of the dry colloids to titanium dioxide and the spontaneous explosions of the residues produced after vacuum evaporation of the solutions transforming titanium dioxide powders, were studied. The solutions were prepared by dissolving titanium tetra isopropoxide in an aqueous hydrogen peroxide solution. Component isopropanol was expelled from the mixture by vacuum evaporation. The presence of various H₂O₂/Ti ratios of residues produced by the evaporation, and the variation of absorption spectra with the concentration of hydrogen-peroxide suggested that the hydrogenperoxide content in the solute species was determined by the concentration of hydrogen peroxide in them. The thermal analysis of the dry colloids revealed that they suddenly decompose exothermally and consist of titanium, water and hydrogenperoxide. X-ray powder diffraction revealed that the dry colloid was amorphous and the heated product of the colloid at 440°C was in the anatase form and also that the explosion products were the same. SEM revealed that the fine dry colloid deformed above 609°C.     

Modification of water,aqueous solutions,and dielectric films in diffuse discharge formed by fast electron preionization at the short front of a voltage pulse

Formation of a diffuse discharge at a short front of voltage pulse (less than 1 ns), as well as when placing water, water solutions, and dielectric film inside the discharge, is studied. A volumetric discharge was observed in water on the anode when placing dielectric film (polyethylene, vinyl chloride-methyl methacrylate (VCMMA), etc.), water, or aqueous solutions of 3% hydrogen dioxide or 18% KMgO₄ inside the discharge. The change in the absorption spectrum of substance was found after multiple discharge switching on. Fourier analysis of the infrared absorption spectra showed the difference between the spectra of exposed and unexposed polyethylene film. The changes in the absorption spectra of water, 3% hydrogen dioxide and 18% KMgO₄ aqueous solutions are related with expansion of the band of valence oscillations of OH-groups without clearly expressed maxima (for the studied liquids). Therefore, volumetric diffuse discharge in molecular and atomic gases can be used in modifying dielectrics, water and aqueous solutions.     

Selective removal of cesium ions from aqueous solutions using different inorganic metal hexacyanoferrate-prepared sorbents

Mg-Fe–hexacyanoferrate (MgFeCF) and Ni-Fe–hexacyanoferrate (NiFeCF) were prepared and characterized using X-ray diffraction, Fourier-transform infrared spectroscopy spectra, and thermal analysis. The isotherm study showed that the sorption data fit with the Langmuir and Freundlich isotherms at 25?±?1°C. The sorption capacities of the prepared sorbents for MgFeCF and NiFeCF were found to be 154.32 and 180.83?mg?g^?1, respectively. The adsorption of cesium by MgFeCF and NiFeCF is exothermic and spontaneous processes. Kinetic study indicated that the adsorption of cesium on MgFeCF and NiFeCF fits with the pseudo-second-order kinetic model. Desorption tests indicated that the sorption process is relatively stable. The new sorbents are promising efficient materials for cesium removal from aqueous solutions and sea water. The possibility of reusing the sorbents after stripping the metal ions was studied using 0.5?M HCl, and its efficiency for cesium removal was found to be 98% after five runs.     

Adsorption of ammonium dinitramide (ADN) from aqueous solutions. 1. Adsorption on powdered activated charcoal

Investigations on the adsorption of ammonium dinitramide (NH(4)N(NO(2))(2)) (ADN) from aqueous solutions on powdered activated charcoal (PAC) were carried out in order to find out an effective and easier method of separating ADN from aqueous solutions. The effectiveness of PAC in the selective adsorption of ADN from aqueous solutions of ADN (ADN-F) and ADN in presence of sulfate (SO(4)(2-)) and nitrate (NO(3)(-)) ions (ADN-PS) was examined and compared using batch and column methods. The adsorption process follows both Langmuir and Freundlich adsorption isotherms and the isotherm parameters for the models were determined. The observed data favor the formation of monolayer adsorption. The adsorption capacities were found to be 63.3, 119, 105.3 and 82 mg of ADN per g of PAC for ADN-F (batch), ADN-PS (batch), ADN-F (column) and ADN-PS (column), respectively. Break-through curves for ADN-F and ADN-PS were obtained for the optimization of separation of ADN from aqueous solutions. Elution curves were generated for the desorption of ADN from PAC using hot water as eluent.     

Nature of hydrogen bonding of water molecules in aqueous solutions of glycerol by attenuated total reflection (ATR) infrared spectroscopy

Attenuated total reflection infrared (ATR-IR) spectroscopy was performed on glycerol/water solutions in order to gain a better understanding of the strong hydrogen bonding of glycerol as a humectant. The OH stretching band after eliminating the contribution of glycerol OH in the glycerol/water solutions was decomposed using three Gaussian components. With increasing glycerol concentrations up to 50 volume %, the decrease of the 3428 cm(-1) component (middle H-bond component) and the increase of the 3562 cm(-1) component (longer H-bond component) suggested the breaking of H bonds among water molecules. On the other hand, the 3242 cm(-1) component (shorter H-bond component) remained unchanged. It was expected that water molecules surrounding glycerol molecules are retained by strong H bonding between H atoms of water and O atoms in C-O of glycerol when aqueous solutions containing glycerol are introduced in human skin.     

Highly sensitive analysis of boron and lithium in aqueous solution using dual-pulse laser-induced breakdown spectroscopy

We have applied a dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) to sensitively detect concentrations of boron and lithium in aqueous solution. Sequential laser pulses from two separate Q-switched Nd:YAG lasers at 532 nm wavelength have been employed to generate laser-induced plasma on a water jet. For achieving sensitive elemental detection, the optimal timing between two laser pulses was investigated. The optimum time delay between two laser pulses for the B atomic emission lines was found to be less than 3 μs and approximately 10 μs for the Li atomic emission line. Under these optimized conditions, the detection limit was attained in the range of 0.8 ppm for boron and 0.8 ppb for lithium. In particular, the sensitivity for detecting boron by excitation of laminar liquid jet was found to be excellent by nearly 2 orders of magnitude compared with 80 ppm reported in the literature. These sensitivities of laser-induced breakdown spectroscopy are very practical for the online elemental analysis of boric acid and lithium hydroxide serving as neutron absorber and pH controller in the primary coolant water of pressurized water reactors, respectively.     

Two-dimensional infrared spectroscopy and principal component analysis studies on a new azobenzene derivative supramolecular system based on hydrogen bonds

Infrared (IR) spectra of a supramolecular assembly with an azobenzene derivative and intermolecular hydrogen bonds have been measured in the temperature range from 30 to 200 degrees C to investigate heat-induced structural changes and thermal stability. Principal component analysis (PCA) and two kinds of two-dimensional (2D) correlation spectroscopy, variable-variable (VV) 2D and sample-sample (SS) 2D spectroscopy, have been employed to analyze the observed temperature-dependent spectral variations. The PCA and SS 2D correlation analyses have demonstrated that the complete decoupling of hydrogen bonds in the supramolecular assembly occurs between 110 and 115 degrees C, which is in good agreement with the results of a differential scanning calorimetry (DSC) study for the heating process. The PCA of the IR spectra in the region of 3600-3100 cm(-1) has illustrated that there are at least four principal components for the different NH2 and CONH species in the present supramolecular system. The VV 2D correlation spectroscopy study has provided information about the structure and strength of hydrogen bonds of NH2 and CONH groups and their temperature-dependent variations. The different species of hydrogen-bonded NH2 and CONH groups in the supramolecular system can be clarified by the VV 2D correlation analysis. The VV 2D correlation analysis has also revealed the specific order of the temperature-induced changes in the hydrogen bonds of NH2 and CONH groups.