Photoacoustic Spectrometry Research Articles

Photoacoustic spectroscopy use in the analysis of ion-implanted CuInSe2 single crystals

A high-resolution near-infrared photoacoustic spectrometer of the gas–microphone type is used for room-temperature analysis of the defect states in ion-implanted CuInSe2 single crystals. A wide range of ions differing in their masses as well as in their electrical activities in the host crystal (O+, Ne+, Cu+, Xe+, and Li+) have been implanted at various energies and doses to assess the technique sensitivity to detect changes affecting the compound subgap absorption spectrum, which is characteristic of impurities. The detected changes (either by the appearance of new peaks or by a change in the impurity or defect concentrations) are shown to differ from one ion species to another. The depth profiling capability of the technique in analyzing implanted samples is also discussed. The results obtained here are correlated to existing published data. It is shown that photoacoustic spectrometry can be very useful if used to appraise the complex defect structure of ion-implanted CuInSe2.

Application of photoacoustic spectrometry to flow-injection analysis

Photoacoustic spectrometry (PAS) based on pulsed laser excitation has been coupled to flow-injection analysis (FIA) to detect nitrite, nitrate, iron, ammonia, and phosphate ions in water with the aim to verify its potentiality with respect to conventional FIA systems. Excitation has been performed by means of a Nd:YAG laser with a 2nd harmonic generation and a dye laser; a conventional flow-injection cell has been used as photoacoustic cell. Standard solutions and real samples such as ground water, river water, fog and waste water have been analyzed. A good agreement has been obtained between the results of the proposed technique and those of traditional laboratory techniques. The best analytical configuration, in terms of loop length and integration time, has been also defined. The performance as limit of detection (LOD) was comparable for both techniques. The main points to be developed in order to improve the analytical response of PAS-FIA are reported.

Analytical characterization of laser photothermal transient deformation spectrometry

The radiationless relaxation process of excited molecules has developed as the basis for many laser photothermal spectroscopies. For example, laser photoacoustic spectrometry, laser thermal lens spectrometry, laser photothermal deflection spectrometry, laser photothermal refraction spectrometry and laser photothermal interference spectrometry have been applied to analytical chemistry and evolved into a kind of high sensitivity and high space resolution absorption spectrometries.

Qualitative and semiquantitative analysis of annatto and its content in food additives by photoacoustic spectrometry

Photoacoustic spectrometry in the ultraviolet, visible and near-infrared regions was employed to study the absorption behaviour of the colourant annatto and to determine its content in commercial seasoning products via the intensity of an absorption peak compared with the absorption of standard samples with a known content of annatto. Owing to strong absorption and as a consequence saturation of the signal of the pigment in the ultraviolet and visible regions, a peak of weak absorption in the near-infrared region was used, guaranteeing a linear relationship between peak intensity and annatto content for the usually applied low to medium levels of dye contents in commercial products.

In-situ photoacoustic investigation of thallium underpotential deposition on polycrystalline copper electrodes

Photoacoustic spectrometry (PAS) was used as an ancillary in-situ technique for the investigation of underpotential deposition (UPD) of thallium on polycrystalline copper. The PAS signal generated by 605 nm radiation was found to increase upon deposition of Tl on Cu. Since underpotential deposition is generally a monolayer event, the limit of detection obtained for this technique was estimated to be 0.05 of a monolayer. The PAS results support the conclusion that the second UPD peak is due to a second discrete monolayer rather than a filling-in of vacant sites in the first monolayer. The use of PAS to study the thallium system at pH 12 confirmed that removal of Cu2O from the electrode surface occurred at a sufficient rate that it did not interfere with the UPD of thallium.

Sensitive Detection of Aromatic Molecules by Laser Photoacoustic Spectrometry: Signal Enhancement by Fluorescence Quencher

Highly sensitive detection of aromatic molecules has been investigated by pulsed laser excitation. A cylindrical cell surrounded by a piezoelectric transducer has improved the detection limit. Fluorescence quencher, CH3NO, increased the photoacoustic signal of perylene up to three times and the signal-to-noise ratio by about 50%. Typical detection limits of pyrene and perylene were 0.4 ppb in hexane and 6.7 ppb in methanol with nitromethane, respectively.

Laser photoacoustic spectrometry for trace gas monitoring

Spectroscopic methods offer important features with respect to atmospheric trace gas monitoring. Some relevant techniques are briefly discussed. Emphasis is put on various aspects of photoacoustic spectrometry. Its basic principles and important experimental characteristics are outlined. Depending on molecular absorption cross-sections, a detection limit in the low ppbv concentration range is typically achieved without the use of any preconcentration device. In multi-component mixtures this limit may be increased owing to absorption interferences. Two photoacoustic (PA) systems have been developed and some specific applications are presented. A CO-laser PA system operating in the 5–6.5 µm wavelength range was applied to the analysis of motor vehicle exhausts. Apart from nitrogen oxides, CO2 and water vapour, ten different volatile organic compounds (VOCs) including o-, m- and p-xylene were selectively detected at parts per million by volume (ppmv) concentrations. As a second instrument, an automated CO2 laser PA system was implemented in a trailer for in situ measurements. It was applied to the detection of stack gases at a pharmaceutical plant and to air monitoring in urban and rural environments. As an example, ethene, ammonia and ozone were detected at ppbv concentrations in rural air. Finally, new aspects are discussed, in particular the introduction of CO2 isotopes as the laser medium, the design of PA Stark cells and the development of a continuously tunable high-pressure CO2 laser and of a widely tunable mid-infrared laser based on frequency mixing in a non-linear crystal. Although PA spectrometry already represents a valuable alternative to more established spectroscopic and non-spectroscopic schemes, these novel developments should further enhance its potential and versatility.

Equilibria and Kinetics of Gas–Metal Reactions During Sintering of Austenitic Stainless Steel

Reactions involving the removal of oxygen and carbon from AISI 316L stainless steel during sintering have been investigated by monitoring the chemical composition of the sintering atmosphere by mass spectrometry and photoacoustic spectrometry. Thermochemical calculations of reactions and stability of oxides were performed using Thermo-Calc. Compacts of powder with and without the addition of carbon were sintered at 1120°C and 1250°C in hydrogen and in a vacuum. The reduction of oxides is enhanced by carbon addition and a high sintering temperature. Sintering in a vacuum leads to the lowest carbon content. PM/0626

Preservation of solid mercuric dithizonate samples with polyvinyl chloride for determination of mercury(II) in environmental waters by photochromism-induced photoacoustic spectrometry

A novel sample preparation technique has been developed to preserve solid mercuric dithizonate [Hg(HDz) 2] in a matrix of polyvinyl chloride (PVC) for analysis by photochromism-induced photoacoustic spectrometry (PCPAS). This technique, which begins with the extraction of Hg 2+ from water with dithizone, allows for the determination of Hg 2+ in environmental samples. Inclusion of Hg(HDz) 2 within the polymer matrix enhances the PCPAS signal amplitude over that from the bare Hg(HDz) 2 film by almost sixfold. The standard calibration graph of PCPAS signal amplitude as a function of Hg 2+ concentration is linear in the concentration range of 5–100 μg/ml. A lower detection limit can be achieved by using a laser of higher power tuned to a wavelength closer to the maximum absorptivity of the excited Hg(HDz) 2 complex. A study, conducted to monitor the change in PCPAS signal amplitude obtained for the same sample over an extended storage period of 19 days, demonstrates that the PVC protects the integrity of the solid Hg(HDz) 2 sample. Hence, it is potentially feasible to collect environmental samples from a remote area for analysis at a later date.

Large intramolecular energy flow in vibrational overtone spectra of cyclohexene-3,3,6,6-d4

The vibrational structure of CH stretching states in gas-phase cyclohexene-3,3,6,6-d 4 was studied using FTIR spectroscopy in the range 1200-11500 cm -1 and intracavity dye laser photoacoustic spectrometry in the range 12900-16000 cm -1 . The structure was modeled using an effective vibrational Hamiltonian which describes the Fermi resonance couplings of the CH stretching states with suitable low-frequency vibrations. Some conclusions are made on the possible ways of intramolecular vibrational redistribution of the energy (IVR) on the two methylenic groups for wavenumbers below 11 000 cm -1 in connection with the existence of near-infrared circular dichroism in monoterpenes

Hadamard Transform Photoacoustic Spectrometry and Depth Profiling

The Hadamard transform technique has been extended to include photoacoustic detection. The feasibility of Hadamard transform photoacoustic spectrometry in the visible spectral region has been demonstrated. Depth profiling has been illustrated in a layered sample consisting of a thin (20 μm) surface layer of neodymium oxide dispersed in a polystyrene matrix on a thick (2.5 mm) interior layer of holmium oxide dispersed in a polystyrene matrix. Depth profiling may be accomplished by varying the modulation frequency or by phase-sensitive detection at the appropriate modulation frequency.

Kinetic study of the degradation of lubricating motor oil by liquid chromatography and photoacoustic spectrometry

Lubricating motor oil samples were collected throughout one oil change period of 5000 km and analyzed for saturate, aromatic, polynuclear aromatic hydrocarbon (PAH) and polar species using normal-phase high-performance liquid chromatography (HPLC) with ultraviolet light absorption and refractive index detections. The oil samples were also analyzed using a new photoacoustic spectrometry (PAS) method. Fair correlation was established between the HPLC method and the PAS method for determining aromatic concentration. Moreover, the PAS method offers shorter analysis time, comparable reproducibility, and improvement in detection sensitivity over the HPLC method. The analyses data obtained were used to study the degradation kinetics of the motor oil against mileage. The aromatic species were found to increase in concentration with pseudo zeroth-order kinetics, the PAH species rose from zero to some higher amount, whereas the saturate and the polar species remained essentially constant over the mileage period.

Study of photoacoustic phase spectrum of a double-layer film

The photoacoustic (PA) spectrometry of a double-layer film sample was studied and an improved phase-resolved method was developed. Phase-resolved equations for different conditions were derived and were applied to plant leaf samples. For spinach and Chinese ilex leaf samples, the resolved outer layer and inner layer PA signals corresponded perfectly with the experimental PA signal for a single outer layer and inner layer. In addition, the depth profiling method was used to determine the thickness of the outer layer and PA absorptions of a single outer layer, and the results were also in agreement with those of the phase-resolved method applied to plant leaf samples.

Time-resolved thermal lens measurement of thermal diffusivity of soda—lime glass

The time-resolved mode-mismatched thermal lens technique has been used to determine a precise value for the absolute thermal diffusivity of soda—lime glass (70.5 wt% SiO 2, 17.5 wt% Na 2O, 10 wt% CaO and 2 wt% Fe 2O 3). The thermal diffusivity was found to be (4.9±0.3) × 10 −3 cm 2/s which is in good agreement with the value obtained by photoacoustic spectrometry ((5.1±0.1) × 10 −3 cm 2/s). The technique is non-contacting and non-destructive.

Ion-exchanger phase photoacoustic spectrometry for trace analysis of metal ions

Laser-induced photoacoustic spectroscopy has been applied to the determination of chromate, uranyl, and Cr(VI) and Fe(II) ions as coloured complexes that were sorbed on ion-exchanger beads. A simple photoacoustic cell has been constructed; it consisted of a fused silica glass tube and an attached cylindrical piezoelectric transducer. A pulsed laser fight at 532 or 355 nm irradiated the ion-exchanger beads that had been collected in the glass tube of the cell. Since a sample material was effectively concentrated on the ion exchanger, the sensitivity was much higher than that in the corresponding photoacoustic spectrometry in a solution state. The lowest detection limit was 0.21 ng/ml Fe for Fe(II)-DPPS (4,7-diphenyl-1,10-phenanthrolinedisulphonate) complex sorbed on QAE-Sephadex gel. Analytical characteristics of the present method are described.

Application of ion-exchanger phase photoacoustic spectroscopy to flow analysis of trace amounts of iron in water

Ion-exchanger phase photoacoustic spectroscopy has been applied to the flow analysis of trace amounts of iron in water. The reaction product of iron(II) with 4,7-diphenyl-1,10-phenanthroline-disulphonate, introduced into a carrier solution stream in the flow system, was concentrated on a small amount of QAE-Sephadex gel settled in a fused silica glass tube (1.5 mm i.d.) of a photoacoustic cell. The photoacoustic signal produced by pulsed laser irradiation of the gel beads at 532 nm was detected by a cylindrical piezoelectric transducer which was attached outside the glass tube. When 3.7 ml of a sample solution was introduced into the flow system, the sensitivity of this method was 590 times higher than that of the corresponding solution photoacoustic spectrometry and the detection limit of iron was 0.33 ng/ml. Because the coloured complex was desorbed from the cell with a desorbing agent solution, the present method could afford repeated analyses of natural water samples containing iron at ng/ml levels without any preconcentration procedures.

Determination of trace amounts of copper with extraction–photoacoustic spectrometry

A sensitive method for the determination of copper in aqueous solution by pulsed laser-induced photoacoustic spectrometry after extraction is described. The copper is chelated with 1,5-diphenylcarbazide in chloroform and extracted into the chloroform phase. The optimum extraction conditions were found experimentally. By using the stepwise dilution method, the minimum absorbance that could be measured was 8.5 × 10–6 at 6.2 mJ per pulse; this corresponds to 6.9 × 10–3µg l–1 of copper in chloroform. The relative standard deviation for ten measurements of an absorbance of 7.8 × 10–3 at 0.7 mJ is 1.5%. Application of the method to the determination of copper in biological samples is also described. The results obtained were compared with those given by atomic absorption spectrometry.

Concentration of Cobalt on Thin-Layer Chromatography Plate Treated with l-(2-Pyridylazo)-2-naphthol and Its Direct Determination by Photoacoustic Spectrometry

Concentration of Cobalt on Thin-Layer Chromatography Plate Treated with l-(2-Pyridylazo)-2-naphthol and Its Direct Determination by Photoacoustic Spectrometry

PHYSICAL PROPERTIES OF GERMANIUM BASED ALLOYS

The purpose of this paper is to provide a consistent set of data for germanium based alloys using a number of different experimental techniques (optical and photoacoustic spectrometry, Electron Spin Resonance, conductivity and nuclear measurements) in order to know the consequences, both structural and electronic, of carbon incorporation into GeSi network. From correlation between optical and electrical properties information is obtained about the behavior of band tails and the density of states in the gap.

Photoacoustic spectrometric determination of trace phosphorus as molybdenum blue adsorbed on uniform anion-exchange beads

Photoacoustic spectrometry was applied to the determination of phosphorus as molybdenum blue species adsorbed on an anion-exchange resin (10 mg of uniform beads). The photoacoustic intensity of ten resin particles on a glass plate was measured at 760 nm. The calibration graph obtained was linear in the range of 0.05–0.5 μg of phosphorus. The relative standard deviation for ten determinations of 0.3 μg P was 5.0%. The detection limit was 2 ng P ml −1.