Quantification of nanodiamonds in aqueous solutions by spectrophotometry and thermal lens spectrometry

Spectrophotometry and thermal lens spectrometry were used to study solutions of several commercial detonation nanodiamonds. It was found that the absorption spectra of solutions of all studied nanodiamond samples obey the Bouger-Lambert-Beer law, which ensures the precise determination of the total mass concentration of unknown nanodiamond solutions using a calibration plot. It was shown that the absorption spectra of nanodiamond solutions exhibit both absorption and scattering components, both significantly affecting signal formation. Conditions were proposed for the spectrophotometric determination of nanodiamonds at 250 nm (l = 1.0 cm). The detection limits were from 60 ng/mL to 2 ??g/mL, depending on the nanodiamond type. Limits of detection of SDND nanodiamonds by spectrophotometry and thermal lens spectrometry were calculated for identical conditions of sample preparation and measurements (488 nm, l = 1.0 cm). These were 10 and 0.6 ??g/mL for spectrophotometry and thermal lens spectrometry, respectively (power of excitation radiation 150 mW).     

Tunable thermal lens spectrometry utilizing microchannel-assisted thermal lens spectrometry

A tunable thermal lens spectrometry system was developed for microchip analysis. The system utilized a Xe lamp as an excitation source, instead of a laser. The system can measure the absorption spectrum of a turbid solution without disturbance of the light scattering background.     

Electroinduced thermal lens spectrometry

A new technique for the generation of a thermal lens effect is considered. In this technique, the action of focused radiation from an inducing laser is replaced by an analogous action of electric current, which forms a thermal lens at a certain site of a liquid by the generation of a high local current density in a small liquid volume. The main regularities of this technique for thermal lens signal generation are considered, and an expression is derived to relate the detected signal (a relative change in probing radiation intensity at the detector) and the electrolyte concentration. A cell is proposed for electroinduced thermal lens detection. The dependence of the thermal lens signal on the applied voltage and on the concentration of the test electrolyte is determined for a model electrolyte (NaCl), and sensitivity characteristics are found to be consistent with theoretical estimations made in this work.     

Quantification of boron in water by of spectrophotometry and thermal lens spectrometry using reaction with beryllon III

The conditions for the thermal lens quantification of boron in aqueous solutions with a detection limit of 0.3 ng/mL are found (λ = 532 nm, laser power 40 mW); this value of the detection limit is an order of magnitude lower than that attainable in conventional spectrophotometry. A 1: 1 composition of an aqueous ethylene glycol mixture is proposed, using which as a medium the detection limit for boron was reduced to 0.1 ng/mL. Using spectrophotometry and thermal lens spectrometry, boron was quantified in mineral water; the results agree with the data acquired by the reference method of inductively coupled plasma atomic emission spectrometry.     

Trace level vanadium determination using thermal lens spectrophotometry

Trace level vanadium determination is reported using a dual beam thermal lens spectrometer. The thermal lens was generated using an argon ion beam laser (pump beam) which was focused into a sample cuvette. The thermal lens signal (TLs) was monitored with a He-Ne laser beam and a photodiode detector. Multichannel averager software was developed for processing the transient TLs. The optimal set up, ensuring maximum sensitivity and linear calibration graphs was obtained using experimental design techniques. Under optimized conditions, the detection limits for aqueous and ethanol-water (2+3 v/v) and (4+1 v/v) vanadium complex solutions were, respectively, 0.0071 mg/l, 0.0065 and 0.0039 mg/l.     

Rotational diffusion effects on absorbance measurements: limitations to the magic-angle approach.

Optical absorbance changes are commonly used to characterize intermediates which appear in the bleaching sequence of rhodopsin and in the photocycle of bacteriorhodopsin. Absorbance changes can be caused by an intermediate's rotational diffusion, and when this occurs it can distort absorbance changes due to the structural evolution of intermediates. Linear polarization of an optical probe source at 54.7 degrees (the magic angle) relative to the polarization direction of a linearly polarized actinic source has often been used to eliminate signals due to rotational diffusion. We used Jones calculus to investigate the validity of the magic-angle strategy. Taylor expansion of the result in powers of the absorbances of the bleached ground state and of the intermediates leads to a relatively simple expression which can be used to determine whether rotational contributions are likely under various experimental conditions. This expression shows that in first order no dichroism-dependent term appears in the absorbance measured at magic angle. In second order, however, linear dichroism contributes to signals. For the sequence of rhodopsin intermediates: rhodopsin hv----bathorhodopsin in equilibrium BSI----lumirhodopsin, where BSI is a recently discovered blue-shifted intermediate, we determined the magnitude of the dichroism signals to be, on average, less than 2% of the true absorbance change due to the intermediates themselves (and hence undetectable). Freedom from dichroism artifacts in this case results from the fact that the transition dipoles of these intermediates are similar to that of rhodopsin. Larger and certainly detectable dichroism signals are predicted to occur, even at the magic angle, for later intermediates which have transition dipole moments which differ significantly from that of rhodopsin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Advantages and limitations of coupling isotachophoresis and comprehensive isotachophoresis-capillary electrophoresis to time-of-flight mass spectrometry

Capillary isotachophoresis (ITP) and comprehensive isotachophoresis-capillary electrophoresis (ITP-CE) were successfully coupled to electrospray ionization (ESI) orthogonal acceleration time-of-flight mass spectrometry (TOF-MS) using angiotensin peptides as model analytes. The utility of ITP-TOF-MS and ITP-CE-TOF-MS for the analysis of samples containing analyte amounts sufficient to form flat-top ITP zones (30 microM) as well as for samples with trace analyte amounts (0.3 microM) was studied. Separations were performed in 150 microm internal diameter (I.D.) capillaries for the ITP experiments, and in 200 microm I.D. (ITP) and 50 microm I.D. (CE) capillaries for ITP-CE experiments. The fused-silica columns were coated with poly(vinyl alcohol) to suppress electroosmotic flow that can disrupt ITP zone profiles. The sample loading capacity in both ITP and comprehensive ITP-CE was greatly enhanced (up to 10 microl) compared with typical nanoliter-sized injection volumes in CE. It was concluded that ITP-TOF-MS alone was adequate for the separation and detection of high concentration samples. The outcome was different at lower analyte concentrations where mixed zones or very sharp peaks formed. With formation of mixed zones, ion suppression and discrimination could occur, complicating quantitative determination of the analytes. This problem was effectively overcome by inserting a CE capillary between the ITP and TOF-MS. In such an arrangement, samples were preconcentrated in the high load WTP capillary and then injected into a CE capillary where they were separated into non-overlapping peaks prior to their detection by TOF-MS. The advantage of this comprehensive arrangement, which we have described previously, is that there is no need to discard portions of the sample in order to avoid overloading of the CE capillary. The whole sample is analyzed by multiple injections from ITP to CE. Thus, this method can be used for the analysis of complex samples with wide ranges of component concentrations.     

Sensitive spectrophotometric determination of aluminium using thermal lens spectrometry

The determination of Al³⁺ in solution using a continuous-wave mode mismatched thermal lens spectrometer is reported and two spectrophotometric procedures are compared. The reagent investigated were bromopyrogallol red—tetradecyltrimethylammonium bromide (BPR—TDTA) and chrome azurol S—cetylpyridinium chloride (CAS—CPC). The CAS—CPC system gave a superior detection limit (0.17 μg 1^?1) to the BPR—TDTA system (1.15 mg 1^?1) owing to the higher reagent blanks and concomitant laser noise in the latter system.     

Optimisation of thermal lens microscopic measurements in a microchip

The thermal lens optical scheme-design was optimised for microscopic measurements in microchannels. The efficient pathlength of the sample, irradiated volume, and the diameter of the thermal lens were estimated. Experimental time curves of development of the thermal lens and periodical oscillations of the signal due to convectional heat transfer are in good agreement with the theoretically expected behaviour. Noise sources (laser noises, instrumental flicker noise, convection, and flow noise) were studied. The possible effect of probe laser power on transient and steady-state thermal lens measurements were estimated. The effect of solvent absorption on the performance characteristics is shown. Under the optimum optical scheme-design, the limits of detection of ferroin and Sunset Yellow FCF at 488.0 nm are 1×10⁻⁸ and 4×10⁻⁹ mol dm⁻³, respectively (corresponding quantities in the detection volume are 3×10⁻²¹ and 1×10⁻²¹ mol). The total linear calibration range is n×10⁻⁸ to n×10⁻⁴ mol dm⁻³, the repeatability R.S.D. for this range is 3-7%. The optimised instrument was also used for the determination of characteristic rate constants of formation and dissociation of ferroin at the level of n × 10⁻⁸ mol dm⁻³. Some analytical applications are discussed.     

Measurement of thermal energy recovery using thermal lens spectrometry in fluorescence quenching experiments

This paper describes some limitations of the pulsed-laser thermal lens method in measuring the heat produced by non-radiative relaxation of excited fluorescent molecules. Simultaneous measurements of the fluorescence intensity and thermal lens signal have been carried out for fluorescein dianion in water and perylene in ethanol. It is shown that complete fluorescence quenching of fluorescein and perylene by potassium iodide and nitromethane, respectively, does not result in full recovery of the thermal energy. The results depend on either the operating mode of the excitation laser or the solvent composition.     

Sandwich-type flow-through fiber-optic cells for optical absorbance measurements

The sandwich cell described by Pavon et al. and a similar sandwich cell, except with angled (45 degrees, confocal) single strand optical fibers and a conventional Z-type cell of 6-mm path length have been studied with respect to their performance for absorbance detection. Both sandwich cells show less susceptibility by one order of magnitude to artifact absorbance signals from RI changes than the Z-cell. The light throughput in the sandwich cells increase by an order of magnitude when an inert metallized reflector is used and this improves S/N. The overall light throughput is substantially greater for the angled entrance single strand fiber optic cell rather than the cell with the bifurcated fiber optic. Attainable limits of detection with these cells appear to be related to the pathlength for the cell dimensions studied.     

Laser induced thermal lens spectrometry for cobalt determination after cloud point extraction

A new approach, employing cloud point extraction (CPE) in combination with thermal lens spectrometry (TLS), has been developed for the determination of cobalt. The CPE and TLS methods have good matching conditions for combination because TLS is suitable for low volume samples obtained after CPE and for organic solvents, which are used for dissolving the remaining analyte phase.1-(2-Pyridylazo)-2-naphthol (PAN) was used as a complexing agent and octylphenoxypolyethoxyethanol (Triton X-114) was added as a surfactant; then the pH of solution was adjusted. After phase separation at 50 °C based on the cloud point extraction of the mixture, the surfactant-rich phase was dried and the remaining phase was dissolved using 20 μL of carbon tetrachloride. The obtained solution was introduced into the quartz micro cell and the analyte was determined by thermal lens spectrometry. The He-Ne laser (632.8 nm) was used as both the probe and the excite source.Under optimum conditions, the analytical curve was linear for the concentration range of 0.2-40 ng mL⁻¹ and the detection limit was 0.03 ng mL⁻¹. The enhancement factor of 470 was achieved for a 10 mL sample. Relative standard deviations were lower than 5%.The method was successfully applied to the extraction and determination of cobalt in tap, river and sea water.     

A single and simple mathematical expression of the signal for cw-laser thermal lens spectrometry

Since the discovery of the thermal lens effect, several theoretical models have been put forward for cw-laser thermal lens spectrometry and different expressions of the thermal lens signal have been derived for various optical configurations including single-beam or dual-beam situations. This review focuses primarily on the successive mathematical expressions reported so far for both steady-state and time-resolved measurements, with the aim of comparing them in order to propose a single and convenient relation that accurately accounts for the sensitivity and the temporal behaviour of the thermal lens efrect.     

近场激光热透镜光谱分析法测定铌

采用氦-氖激光器(632．8nm)观测了铌(V)与2-(5-溴-2-吡啶偶氮)-5-二乙氨基苯酚(5-Br-PADAP)和酒石酸所形成的紫蓝色三元配合物的激光热透镜效应，建立了近场激光热透镜光谱分析法测定铌的新方法。铌(V)质量浓度在0-500ng/mL范围内与热透镜信号强度呈良好的线性关系，检出限为5ng/mL。该方法已应用于钢样及铌矿样中铌的测定。     

Near infrared thermal lens spectrometry for the real-time monitoring of supercritical fluid extraction

A commercially available supercritical fluid extractor provided with carbon dioxide was coupled to a dual-beam thermal lens spectrometer with a pumpprobe coaxial configuration, pumped by a pulsed Nd-YAG laser operating at the fundamental wavelength of 1064 nm. As a preliminary step, several compounds were studied in batch regime using carbon tetrachloride as solvent, in order to observe the influence of overtones and combinations involving distinct chemical bonds on thermal lens spectrometry (TLS). Several factors related with supercritical fluid extraction (SFE) under hydrodynamic conditions were studied in order to establish their influence both in the extraction yield and thermal lens signal magnitude obtained. The advantages and limitations of the hyphenated SFE-TLS technique proposed are discussed, and the possibility of on-line detection in SFE with a pulse thermal lens spectrometer was demonstrated.     

Abnormal signals in thermal lens spectrophotometry: Determination of the triplet lifetime of erythrosine

Thermal lensing of erythrosine with pulsed laser excitation may exhibit abnormal signals. It is shown that a non-thermal signal is superimposed to the     

Recent applications of thermal lens spectrometry in food analysis and environmental research

This review summarizes the most recent achievements related to the application of thermal lens spectrometry (TLS) in food analysis and environmental research. All the applications are associated with the use of an appropriate analytical procedure providing sufficient selectivity, that cannot be achieved by TLS itself. Several selective reagents, biosensors and chromatographic separation procedures (IC, HPLC), used for this purpose, and their performance in combination with TLS, are described. Heavy metals and related species, pesticides, carotenoids, fatty acids, and their determination in samples such as water, fruit juices, oils and marine phytoplankton were given most consideration. The main advantages of novel analytical methods include improved sensitivity and selectivity, simplicity, minimized need for sample preparation and handling as well as reduced time of analysis.     

Real-time thermal lens absorption measurements with application to flow-injection systems

Flow-injection methods are shown to reduce effectively the blank-related uncertainties in trace-level spectrophotometry. When thermal lens detection is used with efficient, real-time data processing, sensitive determinations are possible with response times adequately fast for flow-injection monitoring. Absorbance detection limits of 8.5 × 10^?7 in a 1?cm pathlength flow cell were obtained for injections into carbon tetrachloride solvent. Thermal lens detection of iron with 1,10-phenanthroline as reagent produced detection limits of 37 pg of iron in the 100-μl injection volume. The advantages of flow injection for minimizing problems with photochemically unstable analytes in thermal-lens measurements are demonstrated.     

激光热透镜光谱分析法同时测定铜、钴和镍研究

基于2-(5-NO2-吡啶-2-偶氮)-1-羟基-8-氨基萘-3，6-二磺酸与铜(Ⅱ)、钴(Ⅱ)和镍(Ⅱ)反应酸度的差异及热透镜信号强度的加和性，建立了激光热透镜光谱法同时测定铜、钴和镍的新方法。测定铜、钴和镍的线性范围依次为0～200ng/mL、0～200ng/mL和0～100ng/mL，检出限依次为2ng/mL，2．5ng/mL和1ng/mL。方法已用于合成样品及人发样中铜、钴和镍的同时测定。     

Use of poorly absorbing materials and low-contrast photometric reactions in thermal lens spectrometry

The capability of thermal lens spectroscopy as a highly sensitive method applicable to indicator reactions, the products of which appear poorly absorbing and/or insufficiently contrasting and, which there-fore cannot be utilized in traditional spectrophotometric analysis, are considered in a study of a number of model systems (phenanthrene, unsubstituted dibenzo-p-dioxin, polysaccharides, lyposaccharides, and other materials). It is shown that, in thermal lens spectrometry, the sensitivity of determination in such reactions can be increased by significantly increasing the sensitivity of thermo-optical measurements due to the formation of colloidal reaction products and the exploitation of the kinetic behavior of such reactions. Along with the increase in the sensitivity of absorbance measurements due to the thermo-optical effect itself, these factors also favor a gain in sensitivity in comparison to the spectrophotometry by 1–2 orders of magnitude.