Infrared band strengths and their temperature dependence of the hydrohalocarbons HFC-134a,HFC-152a,HCFC-22, HCFC-123 and HCFC-142b

The absolute strengths of the IR absorption bands of five halocarbons, proposed as substitutes of chlorofluorocarbons, have been measured at 293, 273 and 233 K in the wavelength region 600–1500 cm⁻¹. The band strengths were derived from measurements performed using an FT-IR spectrometer operating at 0.1 cm⁻¹ instrumental resolution. The values obtained are compared to those from previous studies. Only a slight temperature dependence was observed, indicating a small increase of the band strengths at decreasing temperatures.     

Line broadening mechanisms in the low pressure laser-induced plasma

The spectral profiles of Ca and Rb lines have been studied in a laser induced plasma as a function of pressure (1–10 torr) and delay time with respect to the plasma initiation (1–10 μs). Measurements were made in a plasma induced by the 1064-nm output of a Nd:YAG laser on a calcium carbonate matrix, doped with Rb. Spectral profiles were measured in absorption using a narrow-band cw Ti:Sapphire laser. It was shown that in the case of a trace element (Rb in a CaCO₃ matrix), the broadening mechanism was Doppler-dominant, whereas for a major matrix component (Ca), resonance broadening was the main contributor to the line shape. The plasma was shown to be non-equilibrium provided by the difference between the kinetic (3000 K) and the excitation (8000 K) temperatures. The electron number density at delay times of 5–10 μs and pressures of 1–10 torr was estimated not to exceed 10¹⁵ cm⁻³. The number densities of Ca atoms in the ground and the excited (23 652 cm⁻¹) states were evaluated by measuring line width and peak absorption at 732.6 nm. They were found to be in the range of (1.5–2.2)×10¹⁷ cm⁻³ for the ground state and (1.5–33)×10¹¹ cm⁻³ for the excited state.     

Microwave induced plasma atomic emission spectrometry: a suitable detection system for the determination of volatile halocarbons

Microwave induced plasma atomic emission spectrometry (MIP-AES), a highly sensitive detection system for organometal compounds, was coupled to an automated purge and trap gas chromatographic system for the determination of volatile halogenated hydrocarbons in environmental water samples. Optimisation of the parameters affecting the injection and detection system led to relative detection limits from 1 to 14 ng · L^–1 for chlorine- and bromine-compounds and from 10 to 75 ng · L^–1 for iodine-compounds, on basis of a 10 mL sample volume. A comparison of the analytical characteristics between atomic emission detection (AED) and electron capture detection (ECD) showed a lower sensitivity of the atomic emission detector for halocarbons, but the detection thresholds are low enough to use the method for the determination of volatile halocarbons in trace level concentrations. The ability of the atomic emission detector provides increased selectivity for monitoring individual halogenated compounds under simplified and rapid chromatographic conditions, within a total analysis time of only 30 min. The method was applied with gas chromatographic separation for the analysis of sea water samples. Concentrations for the different elements between 0.05 and 15.28 μg · L^–1 were determined.     

Diode-laser atomic-absorption spectrometry by the double-beam—double-modulation technique

The limitations of absorption measurements in atomic-absorption spectrometry with tunable diode lasers are investigated. It is shown that the double modulation technique (diode-laser wavelength modulation and sample modulation) with detection at the sum or difference frequency suppresses spurious etalon effects, background absorption, residual diode-laser-amplitude modulation and the noise which accompanies these effects, and enables measurement of detection limits determined by the laser excess noise. Detection limits in absorption, defined as absorption equal to the root-mean square value of noise, as low as 1 × 10⁻⁶ AU (absorption units) were achieved for metastable Cl atoms in a modulated low-pressure microwave-induced plasma with a time constant of 1 s. In order to eliminate laser excess noise and signal variations due to changes of optical transmittance, a double-beam arrangement with logarithmic subtraction of sample and reference detector currents was developed. It enables suppression of variations of the laser radiation power outside the detection pass-band and the achievement of a detection limit of about 2 × 10⁻⁷ AU determined by shot noise only.     

LC Determination of Ketorolac in Human Plasma and Urine for Application to Pharmacokinetic Studies

A simple, specific and sensitive liquid chromatographic method has been developed for the assay of ketorolac in human plasma and urine. The clean-up of plasma and urine samples were carried out by protein precipitation procedure and liquid–liquid extraction, respectively. Separation was performed by a Waters sunfire C₁₈ reversed-phase column maintained at 35 °C. The mobile phase was a mixture of 0.02 M phosphate buffer (pH adjusted to 4.5 for plasma samples and to 3.5 for urine samples) and acetonitrile (70:30, v/v) at a flow rate of 1.0 mL min⁻¹. The UV detector was set at 315 nm. Nevirapine was used as an internal standard in the assay of urine sample. The method was validated over the concentration range of 0.05–8 and 0.1–10 μg mL⁻¹ for ketorolac in human plasma and urine, respectively. The limits of detection were 0.02 and 0.04 μg mL⁻¹ for plasma and urine estimation at a signal-to-noise ratio of 3. The limits of quantification were 0.05 and 0.1 μg mL⁻¹ for plasma and urine, respectively. The extraction recoveries were found to be 99.3 ± 4.2 and 80.3 ± 3.7% for plasma and urine, respectively. The intra-day and inter-day standard deviations were less than 0.5. The method indicated good performance in terms of specificity, linearity, detection and quantification limits, precision and accuracy. This assay demonstrated to be applicable for clinical pharmacokinetic studies.

     

Electrothermal vaporization coupled with inductively coupled plasma array–detector mass spectrometry for the multielement analysis of Al2O3 ceramic powders

An electrothermal vaporization (ETV) system useful for the analysis of solutions and slurries has been coupled with a sector-field inductively coupled plasma mass spectrometer (ICP–MS) equipped with an array detector. The ability of this instrument to record the transient signals produced for a number of analytes in ETV–ICP–MS is demonstrated. Detection limits for Mn, Fe, Co, Ni, Cu, Zn and Ga are in the range of 4–60 pg μL^− 1 for aqueous solutions and in the low μg g^− 1 range for the analysis of 10 mg mL^− 1 slurries of Al₂O₃ powders. The dynamic ranges measured for Fe, Cu and Ga spanned 3–5 orders of magnitude when the detector was operated in the low-gain mode and appear to be limited by the ETV system. Trace amounts of Fe, Cu and Ga could be directly determined in Al₂O₃ powders at the 2–270 μg g^− 1 level without the use of thermochemical reagents. The results well agree with literature values for Fe and Cu, whereas deviations of 50% at the 90 μg g^− 1 level for Ga were found.     

Integrated absorption intensities of haloethanes and halopropanes

The infrared absorption intensities of the chlorofluorocarbons C₂Cl_xF_y, (x + y = 6); the hydrofluorocarbons C₂H_xF_yH (x + y = 6); and a number of hydrochlorofluorocarbons, including some members of the propane series, have been measured. Absorption intensities have been obtained by integration over specified ranges of frequencies. The ranges used include the atmospheric window (1250t-833 cm⁻¹), 3500-450 cm⁻¹, 1300-700 cm⁻¹, and those for selected individual absorption bands. Comparisons of the results have been made with published work where available, and attention is drawn to possible sources of error in the measurement of band areas. The spectra of the halopropanes have been included for the range 3500-150 cm⁻¹. A preliminary study has been made of the relation between the number of fluorine atoms in the molecule and the intensity of absorption of the CF stretching vibrations.     

IR dissociation of ammonia clusters

Dissociation spectra of NH₃ clusters have been recorded using a cw CO₂ laser. For the dimer two absorption bands have been found at 979 and 1004 cm⁻¹, which originate from the excitation of two non-equivalent NH₃ molecules. A tunneling motion is held responsible for the observed structure on one of these bands. The symmetry group of the NH₃ dimer is presented considering the tunneling motion solely. Heavier NH₃ clusters dissociate at frequencies between 1020 and 1100 cm⁻¹. The dissociation spectrum of the SiH₄-NH₃ complex shows one peak centered at 972.3 cm⁻¹.     

Direct observation for photophysical and photochemical processes of folic acid in DMSO solution

Using the fast optical technique of laser flash photolysis by a kinetic absorption detector, the photophysical and photochemical processes of folic acid have been observed. By comparison of transient absorptions from photolysis between folic acid and its components, pteroic acid, pterin and 6-carboxypterin, it has been demonstrated that electron-transfer reactions from 4-aminobenzoyl group to the triplet pterin moiety occur through intra- and inter-molecular processes of folic acid. The intermolecular electron-transfer reaction is suggested to be mediated by two tautomers of triplet states of folic acid, lactim and lactam, in different rate constants, 1.4 × 10⁹ and 1.6 × 10⁸ M⁻¹ s⁻¹, respectively.     

Absolute rate constants for the gas-phase reaction of OH radicals with cyclohexane and ethane at 295 K

The absolute rate constants for the gas-phase H-atom abstraction by hydroxyl radicals from cyclohexane and ethane have been determined at room temperature. OH radicals were produced by pulse radiolysis of an H₂O-Ar mixture, and the decay of OH was followed by monitoring the transient light absorption around 309 nm. The rate constants were found to be k = (5.24±0.36) × 10⁻¹² and (2.98±0.21) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ for cyclohexane and ethane, res- pectively. These results are compared with literature data.     

Determination of Three Nonsteroidal Anti-Inflammatory Drugs in Human Plasma by LC Coupled with Chemiluminescence Detection

A simple and sensitive method was developed for the determination of three nonsteroidal anti-inflammatory drugs (NSAIDs)—ibuprofen, naproxen and fenbufen in human plasma. The method involved in column liquid chromatographic separation and chemilumenescence (CL) detection based on the CL reaction of NSAIDs, potassium permanganate (KMnO₄) and sodium sulfite (Na₂SO₃) in sulfuric acid (H₂SO₄) medium. The chromatographic separation was carried out using a reversed-phase C₁₈ column, which allowed the selective determination of the three medicines in the complicated samples. The special features of the CL detector provided lower LOD for determination than that of existing chromatographic alternatives. The results indicated that the linear ranges were 0.01–10.0 μg mL⁻¹ for ibuprofen, 0.001–1.0 μg mL⁻¹ for naproxen, and 0.01–10.0 μg mL⁻¹ for fenbufen. The limits of detection were 0.5 ng mL⁻¹ for ibuprofen, 0.05 ng mL⁻¹ for naproxen and 0.5 ng mL⁻¹ for fenbufen (S/N = 3). All average recoveries were in the range of 90.0–102.3%. Finally, the method had been satisfactorily applied for the determination of ibuprofen, naproxen and fenbufen in human plasma samples.

     

Application of Headspace Liquid-Phase Microextraction to the Analysis of Volatile Halocarbons in Water

The determination of four volatile halocarbons (CHCl₃, CCl₄, C₂HCl₃ and C₂Cl₄) in water by headspace liquid-phase microextraction (HS-LPME) with gas chromatography using a micro electron capture detector (GC-μECD) is described. The effects of the type and volume of the extraction solvent, headspace volume, stirring rate, extraction temperature and time and ionic strength on the extraction performance are investigated and optimized. The developed protocol yields a linear calibration curve in the concentration range from 0.05 to 50 µg L^?1 for the target analytes; the detection limits ranged from 0.003 to 0.146 µg L^?1 and the relative standard deviation (R.S.D.) values below 8.45%. The results demonstrate that HS-LPME followed with GC-μECD is a simple and reliable technique for the determination of volatile halocarbons in water samples.     

3D‐printed Microfluidic Device Based on Cotton Threads for Amperometric Estimation of Antioxidants in Wine Samples

The present work describes the evaluation of microfluidic electroanalytical devices constructed by a 3D printer using ABS (acrylonitrile butadiene styrene) polymer combined with cotton threads as microchannels. Screen‐printed carbon electrodes (SPCEs) were used as electrochemical detector for amperometric determination of gallic and caffeic acid in wine samples. Using optimal experimental conditions (flow rate of 0.71 μL s⁻¹, applied potential of +0.30 V and volume of injection of 2.0 μL) the proposed method presented a linear response for a concentration range of 5.0×10⁻⁶ to 1.0×10⁻³ mol L⁻¹. The detection limits for gallic and caffeic acid were found to 1.5×10⁻⁶ mol L⁻¹ and 8.0×10⁻⁷ mol L⁻¹, respectively, with a sample throughput of 43 h⁻¹. The achieved results are in agreement with those found using the official Folin‐Ciocaulteu method.     

Intensities of lines in the band a 1Δg (v′= 0) − X3Σ−g (v″ = 0) of 16O2 in absorption

Line-strengths in the band a¹Δ_g (v′= 0) − X³Σ⁻_g (v″ = 0) of gaseous ¹⁶O₂ in absorption near 7.9 × 10⁵ m⁻¹ have been remeasured in the laboratory under conditions of pressure less than 101,000 Pa and temperature near 300 K. The band-strength is estimated to be (2.1 ± 0.3) × 10⁻²⁶ m, and the coefficient for self-broadening of individual lines near the band centre is (10 ± 1) m⁻¹ bar⁻¹. No evidence of an underlying continuum was found.     

Measurements of rubidium in standard reference samples by wavelength-modulation diode laser absorption spectrometry in a graphite furnace

An investigation of the capabilities of the WM-LDAS-GF (wavelength-modulation laser diode absorption spectrometry in graphite furnaces) technique for detection of Rb at low pg ml⁻¹ concentrations in samples with complex matrices has been performed. Five reference materials were investigated with respect to their Rb content by the WM-LDAS-GF technique: corn bran (NIST 8433); NIST water; (1643d) riverine water (SLRS-2); estuarine water (SLEW-1); and sea water (NASS-3). Freeze-dried corn bran was found to have a Rb concentration of 440 ± 70 ng g⁻¹. This compares well with the certified concentration of 500 ± 300 ng g⁻¹. The Rb content of the NIST water was assessed to 12.7 ± 1.7 ng ml⁻¹. This compares excellently with the specified (although not certified) level of 13 ng ml⁻¹. None of the three other reference materials has any certified Rb level. The Rb content of riverine water was found to be 3.4 ± 0.8 ng ml⁻¹. Chemical interferences were encountered when estuarine water and sea water were analyzed (loss of Rb as RbCl). Addition of NH₄NO₃ as the matrix modifier increased the Rb recovery values considerably (although not fully to unity). Estuarine water and sea water were found to have Rb contents of 30 ± 10 ng ml⁻¹ and 140 ± 50 ng ml⁻¹, respectively. A detection limit for Rb in deionized water of 10 fg (corresponding to a concentration of 1 pg ml⁻¹ using a 10 μL aliquot) was obtained. This is identical to (and thus verifies) the previously published result by the group of K. Niemax. These results show that the WM-LDAS-GF technique is capable of detecting traces of Rb in samples also with complex matrices.     

Re-examination of primary radical pair recombination in Rp. viridis with QA reduced

Charge recombination in the primary radical pair P⁺H⁻ of the purple photosynthetic bacterium Rp. viridis with pre-reduced secondary acceptor Q_A, has been studied by time-resolved photovoltage measurements and transient absorption spectroscopy with a time resolution of 1 ns. The lifetime of P⁺H⁻ was found to be 2.4–3 ns in intact membranes and ∼5 ns in isolated reaction centers, in contrast to a lifetime of ∼15 ns which has been widely accepted in the literature for reaction centers. The origin of the difference between lifetimes of P⁺H⁻ in membranes and isolated reaction centers is discussed.     

A new far-infrared broadband absorption in non-rigid polar molecules

A new far-infrared broadband absorption has been observed for non-rigid ketone molecules in the frequency range 220 to 340 cm⁻¹. It has been found that the amplitude of this absorption increases with an increase in the flexibility of the molecule. Such an increase in the amplitude of this absorption is accompanied by a corresponding reduction in that of the Poley absorption.     

Absolute infrared band intensities and air broadening coefficient for spectroscopic measurements of formic acid in air

The absolute infrared intensities of the ν₂, ν₃ and ν₆ bands of formic acid have been evaluated in a 480 L White cell system using FTIR and ion chromatography techniques. The values obtained are, respectively; (4.2 ± 0.2) × 10⁻¹⁷ cm molec⁻¹ for the ν₆ band, (4.8 ± 0.2) × 10⁻¹⁷ cm molec⁻¹ for the ν₃ band and (0.57 ± 0.04) × 10⁻¹⁷ cm molec⁻¹ for the ν₂ band. The air broadening coefficient of transitions in the ν₆ band, has been measured using a tunable diode laser spectrometer, equal to (0.101 ± 0.005) cm⁻¹ atm⁻¹ (half width at half maximum). A computer search has been performed to find absorption lines of formic acid suitable for second derivative tunable diode laser measurement of this gas in ambient air.     

Simple Analytical Method for the Determination of Paclitaxel (Taxol ® ) Levels in Human Plasma

Paclitaxel has been widely used for tumor chemotherapy in recent years and it would be useful to assess occupational exposure to the drug, if only to confirm that the procedures and measures for prevention and protection applied in health care structures are effective against this kind of risk. This study is to establish a simple, robust analytical method for routine use in biological monitoring of health workers exposed to taxanes, and extendable to patients receiving these drugs. HPLC equipped with a diode array detector was used. The assay was validated. Intra- and inter-day accuracy and reproducibility were good. Recovery of paclitaxel spiked in drug-free plasma was higher than 87% with SPE using extract-clean normal phase cyanopropyl silica cartridges for plasma clean-up. The calibration curve was linear in the range 10–500 ng mL⁻¹. The method was applied to plasma samples of nurses occupationally exposed to paclitaxel. The experimental analytical method performed well, detecting paclitaxel in plasma at a concentrations down to 10 ng mL⁻¹. This straightforward method for analytical determination of paclitaxel in human plasma is rapid and can measure up to 36 plasma samples per day. It uses more economical equipment than other methods proposed in the literature and its validation parameters are highly satisfactory.

     

Studies of the characteristic frequencies of vapor-phase infrared spectra: II. The characteristic frequencies of ketones and aldehydes

Vapor-phase infrared characteristic frequencies of ketones and aldehydes have been studied. The CO stretching vibrations in vapor phase have higher frequencies than those in condensed phase. The shifts are about 20 cm⁻¹ for ketones and about 10 cm⁻¹ for aldehydes. Both ketone and aldehyde have an absorption band at the range 1300–1100 cm⁻¹, although their intensities are very different. This band was assigned to the CC stretching vibration of C(CO)unit.