Photolysis-assisted, long-path FT-IR detection of air pollutants in the presence of water and carbon dioxide

Seven important air pollutants have been investigated by photolysis-assisted FT-IR spectroscopy. This technique renders invisible the spectra of water and carbon dioxide, which are two of the main concerns in long-path infrared spectroscopy. A cell, equipped with a UV lamp, was used to oxidise the analyte in the air sample and the spectrum recorded was used as a new background for the original sample spectrum. The optimum UV irradiation time and correctness of the concentrations were determined for this technique and compared with those from traditional methods. The signal-to-noise (S/N) ratios of the so-called “shadow spectra” were better than, or at least comparable to, the S/N ratios in the absorbance spectra obtained by using as background an air or an evacuated cell reference and subtraction of the spectra of water and carbon dioxide from a spectral library. The detection limits for the volatile organic compounds investigated have been improved by using this new method in which an appropriate background spectrum can be obtained quickly. The limitations of the method are that it cannot be applied to non-UV reactive compounds, such as methane, and the detection limits can be appreciably degraded when bands due to ozone in the shadow spectra overlap with those of the compounds under investigation.     

New background correction approach based on polynomial regressions for on-line liquid chromatography–Fourier transform infrared spectrometry

In the present study a new approach for the chemometric background correction in on-line gradient LC–FTIR is introduced. For this purpose, the spectral changes of the elution mixture during gradient elution were analyzed applying 2D correlation spectroscopy. The fundamentals of the new background correction algorithm, based on polynomial fits calculated from a reference spectra matrix (Polyfit-RSM method) are explained. The Polyfit-RSM approach was applied on blank gradient runs as well as on LC–FTIR data obtained from the injection of a soft drink sample using acetonitrile:water as eluent. Results found were critically assessed and compared to those obtained by two previous background correction methods which are likewise based on the use of a reference spectra matrix (RSM). The Polyfit-RSM method provided lower noise levels throughout the whole spectral range than other alternative background correction methods, an excellent recovery of analyte spectra as well as chromatograms with a low noise level and also free from baseline shifts. A significant finding, which implies a major advantage for the practical applicability of the algorithm, is that the size of the RSMs can be reduced without affecting the accuracy of the correction method.     

Similarity recognition of molecular structures by optimal atomic matching and rotational superposition

An algorithm for similarity recognition of molecules and molecular clusters is presented which also establishes the optimum matching among atoms of different structures. In the first step of the algorithm, a set of molecules are coarsely superimposed by transforming them into a common reference coordinate system. The optimum atomic matching among structures is then found with the help of the Hungarian algorithm. For this, pairs of structures are represented as complete bipartite graphs with a weight function that uses intermolecular atomic distances. In the final step, a rotational superposition method is applied using the optimum atomic matching found. This yields the minimum root mean square deviation of intermolecular atomic distances with respect to arbitrary rotation and translation of the molecules. Combined with an effective similarity prescreening method, our algorithm shows robustness and an effective quadratic scaling of computational time with the number of atoms.     

Determination of copper, iron, manganese, lead and cadmium in automatically wet-digested animal tissue by graphite-furnace atomic-absorption spectrometry with zeeman background correction

An efficient wet digestion method is described which allows the determination of various elements in animal tissues. Copper, iron, manganese, lead and cadmium in one dilution of the digested sample can be determined by means of graphite-furnace atomic-absorption spectrometry, with Zeeman background correction. Tests with the National Bureau of Standards Bovine Liver SRM as reference gave analytical results, obtained with calibration graphs as well as by the standard-addition method, which agreed well with the certified values.     

Direct chiral resolution of tartaric acid by ion-pair capillary electrophoresis using an aqueous background electrolyte with (1R,2R)-(-)-1,2-diaminocyclohexane as a chiral counterion

Chiral resolution of native DL-tartaric acid was achieved by ion-pair capillary electrophoresis (CE) using an aqueous-ethanol background electrolyte with (1R,2R)-(-)-1,2-diaminocyclohexane (R-DACH) as a chiral counterion. Factors affecting chiral resolution and migration time of tartaric acid were studied. By increasing the viscosity of the background electrolyte and the ion-pair formation, using organic solvents with a lower relative dielectric constant, resulted in a longer migration time. The optimum conditions for both high resolution and short migration time of tartaric acid were found to be a mixture of 65% v/v ethanol and 35% v/v aqueous solution containing 30 mM R-DACH and 75 mM phosphoric acid (pH 5.1) with an applied voltage of -30 kV at 25 degrees C, using direct detection at 200 nm. By using this system, the resolution (Rs) of racemic tartaric acid was approximately 1. The electrophoretic patterns of tartaric and malic acids suggest that two carboxyl groups and two hydroxyl groups of tartaric acid are associated with the enantioseparation of tartaric acid by the proposed CE method.     

Desorption atmospheric pressure photoionization with polydimethylsiloxane as extraction phase and sample plate material

Desorption atmospheric pressure photoionization (DAPPI) is an ambient ionization technique for mass spectrometry (MS) that can be used to ionize polar as well as neutral and completely non-polar analytes. In this study polydimethylsiloxane (PDMS) was used as a solid phase extraction sorbent for DAPPI-MS analysis. Pieces of PDMS polymer were soaked in an aqueous sample, where the analytes were sorbed from the sample solution to PDMS. After this, the extracted analytes were desorbed directly from the polymer by the hot DAPPI spray solvent plume, without an elution step. Swelling and extracting the PDMS with a cleaning solvent prior to extraction diminished the high background in the DAPPI mass spectrum caused by PDMS oligomers. Acetone, hexane, pentane, toluene, diisopropylamine and triethylamine were tested for this purpose. The amines were most efficient in reducing the PDMS background, but they also suppressed the signals of low proton affinity analytes. Toluene was chosen as the optimum cleaning solvent, since it reduced the PDMS background efficiently and gave intensive signals of most of the studied analytes. The effects of DAPPI spray solvents toluene, acetone and anisole on the PDMS background and the ionization of analytes were also compared and extraction conditions were optimized. Anisole gave a low background for native PDMS, but toluene ionized the widest range of analytes. Analysis of verapamil, testosterone and anthracene from purified, spiked wastewater was performed to demonstrate that the method is suited for in-situ analysis of water streams. In addition, urine spiked with several analytes was analyzed by the PDMS method and compared to the conventional DAPPI procedure, where sample droplets are applied on PMMA surface. With the PDMS method the background ion signals caused by the urine matrix were lower, the S/N ratios of analytes were 2-10 times higher, and testosterone, anthracene and benzo[a]pyrene that were not detected from PMMA in urine, were observed in the MS spectrum.     

Fast separations by capillary electrophoresis hyphenated to electrospray ionization time-of-flight mass spectrometry as a tool for arsenic speciation analysis

Fast capillary electrophoresis (CE) hyphenated to time-of-flight mass spectrometry (TOF-MS) of four organoarsenic species (glycerol oxoarsenosugar, sulfate oxoarsenosugar, arsenobetaine, arsenocholine) are presented using short length CE capillaries under high electric field strengths of up to 1.3 kV cm(-1) with small inner diameter (ID). The separation of arsenosugars by CE is demonstrated for the first time. An aqueous formic acid solution was employed as the background electrolyte (BGE) for the separation. Various acid concentrations were evaluated for their influence on migration times, separation efficiency as well as with regard to controlling the charge of the arsenic species. A 0.1 M formic acid/ammonium formate buffer (pH 2.8) proved to be suitable for the separation of the four species. A non-aqueous BGE was tested as an alternative buffer system for fast speciation analysis. Separation of arsenobetaine and arsenocholine could even be achieved within 10 s by pressure-assisted CE. Application of the optimized method for the analysis of extracts of a seagrass and a Wakame algae sample as well as the brown algae homogenate reference material IAEA-140/TM revealed a clear signal for the glycerol arsenosugar.     

Detection of transient events in the presence of background noise

We describe a method to detect and count transient burstlike signals in the presence of a significant stationary noise. To discriminate a transient signal from the background noise, an optimum threshold is determined using an iterative algorithm that yields the probability distribution of the background noise. Knowledge of the probability distribution of the noise then allows the determination of the number of transient events with a quantifiable error (wrong-positives). We apply the method, which does not rely on the choice of free parameters, to the detection and counting of transient single-molecule fluorescence events in the presence of a strong background noise. The method will be of importance in various ultra sensing applications.     

Some characteristics of an intensified photodiode array spectrometer system for use in plasma emission spectrometry

A 1024-element silicon photodiode array with a microchannel plate image intensifier was coupled to a Czerny-Turner spectrometer and basic characteristics of the spectrometer system were studied using an Hg lamp, a hollow cathode lamp and a d.c. argon plasma as emission sources. The intensifier proved to be useful to enhance signals without increasing the electronic background. The signal to dark current ratio of the cooled photodiode array was larger than that of a photomultiplier (HTV R457) in the wavelength region above 380 nm. Effects of entrance slit width, integration time per scan and intensifier gain on signal to background ratios and signal to noise ratio are presented and optimum conditions for emission measurements using the system are described.     

Spektralanalytische Spurenbestimmung in hochreinen Silberhalogeniden unter Verwendung spezieller Auswerteverfahren

A method is given for the quantitative determination of trace elements in silver halides by spectral analysis down to concentrations of 0.01 ppm. A method of evaluation is described, which allows to use reference lines of different wave-lengths and density curves. For a rough estimation or in the case of low impurity concentrations two other methods are used taking the background as reference value.     

Extracting decay curves of the correlated fluorescence photons measured in fluorescence correlation spectroscopy

We have developed a new method to extract the decay curves of the correlated fluorescence photons from the data of fluorescence correlation spectroscopy using time-correlated single photon counting. In this method, a two-dimensional correlation map of photon pairs is generated at an absolute delay time with reference to the excitation-emission delay of each photon. Using a dye-labeled DNA as an example, we have demonstrated that the decay curve of the correlated fluorescence photons is separated from the uncorrelated background signals simply by subtracting a two-dimensional correlation map at sufficiently long delay time without additional prior information.     

Non-dispersive measurements by magneto-optic rotation using a graphite furnace

The signal to background ratio of magneto-optic measurements can be substantially improved by use of a suitable optical masking system. A numerical simulation is used to determine the optimum configuration for such an arrangement. The simulation works well enough to allow experimental non-dispersive measurements to be made at comparable sensitivity to that obtained when a monochromator is used to further limit the atomiser background which reaches the detector. The simulation also allows estimates to be made of the sensitivity reductions caused by the use of standard components whose dimensions are not necessarily optimal.     

Analysis of flavonoids by capillary zone electrophoresis with electrokinetic supercharging

On-line concentration via Electrokinetic Supercharging (EKS) was used to enhance the sensitivity of the capillary electrophoretic separation of the four flavonoids naringenin, hesperetin, naringin and hesperidin. Separation conditions, including the background electrolyte pH and concentration, the length and choice of terminator and the electrokinetic injection time were optimized. The optimum conditions were: a background electrolyte of 30 mM sodium tetraborate (pH 9.5) containing 5% (v/v) of methanol, electrokinetic injection of the sample (130 s, -10 kV) followed by hydrodynamic injecting of 100 mM 2-(cyclohexylamino)ethanesulfonic acid (CHES) (17 s, 0.5 psi) as terminator, and separation with -20 kV. Under these conditions the four flavonoids could be separated with a sample-to-sample time of 15 min and detection limits from 2.0 to 6.8 ng mL(-1). When compared to a conventional hydrodynamic injection the sensitivity was enhanced between 824 and 1515 times which is 7.6-16 times higher than other CE methods for the on-line concentration of flavonoids. The applicability of the developed method was demonstrated by the detection of the four flavonoids in an aqueous extract of Clematis hexapetala pall.     

Electrothermal volatilization of aluminum as 1-phenyl-3-methyl-4-benzoylpyrazolone[5] chelate for gaseous sample introduction in ICP-AES

Based on gaseous compound introduction as 1-phenyl-3-methyl-4-benzoylpyrazolone[5](PMBP) chelate of aluminum by electrothermal vaporization in ICP-AES, a method for determination of trace aluminum was developed. Trace aluminum was vaporized at temperature of 1000 degrees C, and the vaporization behavior of aluminum chelate was detailedly investigated. Under the optimum conditions, the detection limit of aluminum was 0.6 ng ml(-1), and the relative standard deviation for 0.1 mug ml(-1) aluminum was 4.7% (n=8). The proposed method was applied to the determination of trace aluminum in rice flour reference materials, and the results well agreed with the reference values.     

Method validation for the determination of lead in raw cow's milk by electrothermal atomic absorption spectrometry

In this study, lead in raw cow's milk has been determined by validated electrothermal atomic absorption spectrometry (ETAAS) with Zeeman-effect background correction. Maximum pyrolysis and optimum atomization temperatures of lead were determined in the presence of modifiers. Pd + Mg(NO3)2 has been found a powerful modifier mixture for the determination of lead. The analytical parameters of the method such as limit of detection, limit of quantification and the effect of interfering ions have been investigated. The detection limit (3sigma) achieved by the method was calculated to be 0.62 ng/mL for Pb. Repeatability of the method evaluated as the relative standard deviation of 16-17 replicates using 5 ng/mL, under optimum experimental conditions were about 1.5% for synthetic sample solution and about 3% for real sample (N = 5). The described method has been validated by analyzing certified reference material (BCR-CRM 150) and by comparing the results with those obtained by inductively coupled plasma mass spectrometry (ICP-MS). The validated method was applied to raw cow's milk samples produced in 7 different regions of Turkey in 2003-2004. Raw cow's milk contained a mean (range) of 31.4 (2.5 - 313) microg kg(-1) lead with a relative error below 2%.     

Genetic algorithms based on wavelet transform for resolving simulated overlapped spectra

Wavelet transform-based genetic algorithms are proposed for resolving simulated overlapped spectra. Wavelet transform as a derivative method is used for de-noising, for deducting background absorption as well as for peak finding in order to get an estimation of parameters of unresolved spectra. Then genetic algorithms, using the estimations of parameters as input values, are employed to resolve unresolved bands. As a consequence, a good optimized solution was achieved since the reliable estimation of initial values can greatly facilitate the convergence of genetic algorithms and the calculation time is shortened accordingly.     

Determination of atenolol in human urine by emission-excitation fluorescence matrices and unfolded partial least-squares with residual bilinearization

A second-order multivariate calibration method based on a combination of unfolded partial least-squares (U-PLS) with residual bilinearization (RBL) has been applied to second-order data obtained from excitation-emission fluorescence matrices for determining atenolol in human urine, even in the presence of background interactions and fluorescence inner filter effects, which are both sample dependent. Atenolol is a cardioselective beta-blocker, which is considered a doping agent in shoot practice, so that its determination in urine can be required for monitoring the drug. Loss of trilinearity due to analyte-background interactions which may vary between samples, as well as inner filter effects, precludes the use of methods like parallel factor analysis (PARAFAC) that cannot handle trilinearity deviations, and justifies the employment of U-PLS. Successful analysis required to include the background in the calibration set. Unexpected components appear in new urine samples, different from those used in calibration set, requiring the second-order advantage which is obtained from a separate procedure known as residual bilinearization (RBL). Satisfactory results were obtained for artificially spiked urines, and also for real urine samples. They were statistically compared with those obtained applying a reference method based on high-performance liquid chromatography (HPLC).     

On-line determination of trace levels of palladium by flame atomic absorption spectrometry

A preconcentration method is developed for the on-line determination of palladium in complex matrices with flame atomic absorption spectrometry (FAAS). The flow system comprised of a minicolumn filled with polyamine Metalfix-Chelamine resin which is highly selective for Pt(IV), Au(III) and Pd(II). Best preconcentration conditions are established by testing different resin quantities, sample and eluent solution volumes, and adsorption and elution steps flow rates. Sample volumes of 4.7 ml of palladium solutions resulted in an enrichment factor of twenty at the optimum hydrodynamic conditions. This value can be increased by injecting larger volumes of sample solution. The method is sensitive, easy to operate and permitted the determination of sub-mg l⁻¹ levels of palladium with a detection limit of 0.009 mg l⁻¹. The resin was used up to 60 times in consecutive retention-elution cycles without any appreciable deterioration in its performance. The applicability of this method was tested by determining the palladium content in synthetic geological samples as well as in the pellet-type used car catalyst reference material.     

Extension of the smith predictor

An effective means of controlling non-linear systems with time delays by use of a digital computer is presented. A model of the system is required, and an extension of Smith's method is used. The method is demonstrated on an experimental enzyme reactor containing a saturating element and a large delay relative to the time constants of the system. The time optimum control of the experimental system as well as PID control is used to demonstrate the effectiveness of the method.     

催化剂中钨的测定溶样方法的改进

研究了新的溶样方法——微波消解法,并将其与常规光度法相结合测定催化剂中钨。考察了测定条件,研究了消解用酸的种类、用量和不同的消解程序对消解效果的影响,确定了微波消解催化剂的最佳消解程序。将经微波消解处理的催化剂样品用常规光度法测定钨的含量,其相对误差小于2．0%,相对标准偏差小于1．3%。将微波消解法与常压敞口消解法进行对比,测定结果基本一致。微波消解法酸用量减少了约5．0倍,消解速度提高了3．5～6．7倍。该方法具有省时、省酸、样品损失少、无环境污染、测定结果准确可靠等优点。