Analytical characterization of laser excited atomic fluorescence of bismuth

The possibilities of direct determination of Bi traces by laser excited atomic fluorescence spectrometry were investigated. Practically all one-color excitation-detection schemes were examined. For the resonance fluorescence at 306.8 nm, the main source of background was a molecular fluorescence of residual water vapors. The background characteristic OH rotational lines of O-O band of ²Σ - ²Π transition were registered in the excitation spectra. From the relative intensities of the rotational components, the gas temperature of the analytical volume above the open graphite cup of the atomizer was estimated as 680 ± 120°C. A detection limit (LOD) of about 1 pg/ml was achieved for the resonance scheme. For the excitation wavelength shorter than 230 nm, broadband fluorescence of unidentified species in the 300-400 nm spectral range was the main source of background. The best LOD of 0.05 pg/ml was realized for the 223.1/ 299.3 nm excitation-detection scheme. This LOD is the best one for the one-color LEAFS technique. Possible ways of further increasing the LEAFS sensitivity of Bi traces detection are briefly discussed.     

Lamp-based native fluorescence detection of proteins in capillary electrophoresis

The potential of a recently developed lamp-based fluorescence detector for the analysis of underivatised proteins by capillary electrophoresis (CE) was investigated. Fluorescence detection (Flu) was achieved using optical light guides to deliver excitation light from a Xenon–Mercury lamp to the capillary detection window and to collect fluorescence emission and lead it to a photomultiplier. The performance of the detector was evaluated by monitoring the native fluorescence of the amino acid tryptophan and the proteins α-chymotrypsinogen A, carbonic anhydrase II, lysozyme and trypsinogen upon excitation at 280 nm. The test compounds were analysed using background electrolytes (BGEs) of sodium phosphate at pH 3.0 and 11.3. The results were compared to experiments of CE with UV absorbance detection. For tryptophan, a linear fluorescence response was obtained with a dynamic range of over 4 orders of magnitude, and a limit of detection (LOD) of 6.7 nM. This LOD was a factor of 200 more favourable than UV detection at 280 nm, and a factor of 20 better than detection at low-UV wavelengths. All tested proteins showed linear fluorescence responses up to 250 μg/mL. LODs were typically in the 10–20 nM range. These LODs were a factor of 25 lower than for UV detection at 280 nm, and comparable to UV detection at low-UV wavelengths. Overall, Flu yields much more stable baselines, especially with a BGE of high pH. The applicability of CE–Flu is demonstrated by the analysis of a degraded protein mixture, and of an expired formulation of the protein drug human growth hormone, indicating that protein degradation products can be selectively detected.     

Highly sensitive fluorescence detection with Hg-lamp and photon counter in microchip capillary electrophoresis

A microchip capillary electrophoresis system with highly sensitive fluorescence detection is reported. The system was successfully constructed using an inverted fluorescence microscope, a highly sensitive photon counter, a photomultiplier tube (PMT) and a capillary electrophoresis microchip. This system can be applied to the fluorescence detection with various wavelengths (300-600 nm). Different fluorescence reagents require different excitation wavelengths. The wavelengths of UV light (300-385 nm), blue light (450-480 nm) and green light (530-550 nm) are employed to excite Titan yellow, fluorescence-5-isothiocyanate (FITC) and Rhodamine 6G, respectively. The detection limit (S/N = 3) of FITC is 7 × 10⁻¹⁰ M, which is 2-3 orders of magnitude lower than that obtained with the lamp-based fluorescence and PMT detection system and approaches the data gained by the laser-induced fluorescence detection. The linear relationship is excellent within the range of concentration 1.3 × 10⁻⁹ to 6.5 × 10⁻⁸ M FITC. It offers a new method to widen the application of the lamp-based fluorescence detection.     

Evaluation of a tungsten coil atomization-laser-induced fluorescence detection approach for trace elemental analysis

The analytical utility of a tungsten (W)-coil atomization-laser-induced fluorescence (LIF) approach has been evaluated for trace level measurements of elemental chromium (Cr), arsenic (As), selenium (Se), antimony (Sb), lead (Pb), tin (Sn), copper (Cu), thallium (Tl), indium (In), cadmium (Cd), zinc (Zn) and mercury (Hg). Measurements of As, Cr, In, Se, Sb, Pb, Tl, and Sn were performed by laser-induced fluorescence using a single dye laser operating near 460 nm whose output was converted by frequency doubling and stimulated Raman scattering to wavelengths ranging from 196 to 286 nm for atomic excitation. Absolute limits of detection (LODs) of 1, 0.3, 0.3, 0.2, 1, 6, 1, 0.2 and 0.8 pg and concentration LODs of 100, 30, 30, 20, 100, 600, 100, 20, and 80 pg/mL were achieved for As, Se, Sb, Sn, In, Cu, Cr, Pb and Tl, respectively. Determinations of Hg, Pb, Zn and Cd were performed using two-color excitation approaches and resulted in absolute LODs of 2, 30, 5 and 0.6 pg, respectively, and concentration LODs of 200, 3000, 500 and 60 pg/mL, respectively. The sensitivities achieved by the W-coil LIF approaches compare well with those reported by W-coil atomic absorption spectrometry, graphite furnace atomic absorption spectrometry, and graphite furnace electrothermal atomization-LIF approaches. The accuracy of the approach was verified through the analysis of a multielement reference solution containing Sb, Pb and Tl which each had certified performance acceptance limits of 19.6-20.4 μg/mL. The determined concentrations were 20.05 ± 2.60, 20.70 ± 2.27 and 20.60 ± 2.46 μg/mL, for Sb, Pb and Tl, respectively. The results demonstrate that W-coil LIF provides good analytical performance for trace analyses due to its high sensitivity, linearity, and capability to measure multiple elements using a single tunable laser and suggest that the development of portable W-coil LIF instrumentation using compact, solid-state lasers is feasible.     

Determination of aluminum in highly concentrated iron samples: Study of interferences using high-resolution continuum source atomic absorption spectrometry

High-resolution continuum source atomic absorption spectrometry (HR-CS AAS) has been used to investigate spectral and non-spectral interferences found with a conventional line source atomic absorption spectrometer in the determination of aluminum in pharmaceutical products containing elevated iron and sugar concentrations. A transversely heated graphite furnace was used as the atomizer in both spectrometers. The two most sensitive aluminum lines at 309.3 nm and 396.2 nm were investigated and it was found that an iron absorption line at 309.278 nm, in the vicinity of the aluminum line at 309.271 nm, could be responsible for some spectral interference. The simultaneous presence of iron and the organic components of the matrix were responsible for radiation scattering, causing high continuous and also structured background absorption at both wavelengths. The aluminum and iron absorption could not be separated in time, i.e., the iron interference could not be eliminated by optimizing the graphite furnace temperature program. However, an interference-free determination of aluminum was possible carrying out the measurements with HR-CS AAS at 396.152 nm after applying least squares background correction for the elimination of the structured background. Analytical working range and other figures of merit were determined and are presented for both wavelengths using peak volume registration (center pixel ± 1) and the center pixel only. Limits of detection and characteristic masses ranged from 1.1 to 2.5 pg and 13 to 43 pg, respectively. The method was used for the determination of the aluminum contamination in pharmaceutical formulations for iron deficiency treatment, which present iron concentrations from 10 to 50 g l^− 1. Spike recoveries from 89% to 105% show that the proposed method can be satisfactorily used for the quality control of these formulations.     

Simultaneous multi-element analysis in a commercial graphite furnace by diode laser induced fluorescence

A powerful and compact experimental arrangement for simultaneous multi-element measurement by laser induced fluorescence is presented. The analytes are excited in a commercial graphite furnace atomizer by cw semiconductor diode lasers and the fluorescence is detected by a simple photodiode without interference filters or a polychromator. In preliminary measurements, detection limits of 1 pg ml⁻¹ (10 fg absolute) and 2 pg ml⁻¹ (20 fg) for lithium and rubidium, respectively, have been obtained.     

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.     

A Fluorescence Quenching Method for the Determination of Nitrite with Indole

A new fluorescence quenching method has been developed to determine nitrite in water and food samples. The method is based on the reaction between nitrite and the fluorescent indole to form a compound which has no fluorescence in acidic medium. The fluorescence intensity was measured in 1 cm quartz cell with excitation and emission wavelengths of 285 and 350 nm, respectively. The relationship was obtained between the fluorescence intensity and nitrite concentration in the range 0.01–0.6 μg ml⁻¹. The detection limit was 2.5 ng ml⁻¹. The proposed method was applied to determine nitrite in water and food samples. The mechanism involved in the reaction was studied.     

Multi‐residue analysis of 44 pharmaceutical compounds in environmental water samples by solid‐phase extraction coupled to liquid chromatography‐tandem mass spectrometry

A solid‐phase extraction combined with a liquid chromatography‐tandem mass spectrometry analysis has been developed and validated for the simultaneous determination of 44 pharmaceuticals belonging to different therapeutic classes (i.e., antibiotics, anti‐inflammatories, cardiovascular agents, hormones, neuroleptics, and anxiolytics) in water samples. The sample preparation was optimized by studying target compounds retrieval after the following processes: i) water filtration, ii) solid phase extraction using Waters Oasis HLB cartridges at various pH, and iii) several evaporation techniques. The method was then validated by the analysis of spiked estuarine waters and wastewaters before and after treatment. Analytical performances were evaluated in terms of linearity, accuracy, precision, detection, and quantification limits. Recoveries of the pharmaceuticals were acceptable, instrumental detection limits varied between 0.001 and 25 pg injected and method quantification limits ranged from 0.01 to 30.3 ng/L. The precision of the method, calculated as relative standard deviation, ranged from 0.3 to 49.4%. This procedure has been successfully applied to the determination of the target analytes in estuarine waters and wastewaters. Eight of these 44 pharmaceuticals were detected in estuarine water, while 26 of them were detected in wastewater effluent. As expected, the highest values of occurrence and concentration were found in wastewater influent.     

Direct laser photo-induced fluorescence determination of bisphenol A

Classical photo-induced fluorescence methods are conducted in two steps: a UV irradiation step in order to form a photo-induced compound followed by its fluorimetric determination. Automated flow injection methods are frequently used for these analyses. In this work, we propose a new method of direct laser photo-induced fluorescence analysis. This new method is based on direct irradiation of the analyte in a fluorimetric cell in order to form a photo-induced fluorescent compound and its direct fluorimetric detection during a short irradiation time. Irradiation is performed with a tuneable Nd:YAG laser to select the optimal excitation wavelength and to improve the specificity. It has been applied to the determination of bisphenol A, an endocrine disrupter compound that may be a potential contaminant for food. Irradiation of bisphenol A at 230 nm produces a photo-induced compound with a much higher fluorescence quantum yield and specific excitation/emission wavelengths. In tap water, the fluorescence of bisphenol A increases linearly versus its concentration and, its determination by direct laser photo-induced fluorescence permits to obtain a low limit of detection of 17 μg L⁻¹.     

The application of electrodeposition on a tungsten wire to furnace atomic absorption spectrometry

This work utilizes electrolytic separation and preconcentration of analyte metals on a thin tungsten wire electrode prior to their determination by furnace atomic absorption spectrometry (AAS). Only a very basic electrolysis system operating at constant applied voltages is needed. Following the deposition step, the wire electrode is inserted into the central region of a miniature CRA 90 furnace and electodeposited metals atomized. Tungsten wire melts in the furnace environment at approximately 2500°C and this restricts the range of metals which can be determined by this technique. So far, elements characterized by relatively low atomization temperatures, such as Cd, Zn, Ag, Pb and Cu, have been studied. Sensitivity improvements ranging from 1.5 to 15-fold over the conventional furnace AAS have been achieved with deposition times between 30 and 300 s. No appreciable background absorption has resulted during the atomization step following depositions from NaCl solutions, confirming very efficient separation. The technique has been successfully applied to the determinations of Pb in blood digest and in seawater. Apart from the analytical applications, the wire deposition approach to furnace atomization offers some more fundamental advantages over systems operated in the conventional manner. It can be used to study the atomization behaviour of elements in metallic form in relation to the atomization of their different compounds. Moreover, by rapidly introducing the wire into the furnace preheated to a constant temperature, very fast atomization is achieved with corresponding improvements in analytical sensitivities. The rapid wire introduction technique also lends itself to studies of the removal of sample vapour from furnaces.     

High-performance liquid chromatography with fluorescence detection for the simultaneous determination of 3,4-methylenedioxymethamphetamine, methamphetamine and their metabolites in human hair using DIB-Cl as a label

This paper describes a highly sensitive HPLC method for the simultaneous determination of 3,4-methylenedioxymethamphetamine (MDMA), 3,4-methylenedioxyamphetamine (MDA), amphetamine (AP) and methamphetamine (MP) in human hair samples. The amphetamines investigated were derivatized with the fluorescent reagent, DIB-Cl to yield highly fluorescent DIB-derivatives, which were then analyzed by HPLC with fluorescence detection at excitation and emission wavelengths of 325 nm and 430 nm, respectively. The separation was achieved on an ODS column with an isocratic mobile phase composed of acetonitrile-methanol-water (30:40:30, v/v/v). The limits of detection for the four compounds obtained by the proposed method ranged from 11 to 200 pg/mg. The method was successfully applied to the determination of MDMA and MDA in hair samples obtained from MDMA abuser.     

Enhanced Fluorimetric Determination of Europium(III) With Thenoyltrifluoroacetone and 4,7-Diphenyl-1,10-Phenanthroline by Gadolinium(III)

Abstract

A sensitive fluorimetric method was developed for the determination of trace amount of europium in rare earth oxides. In the presence of gadolinium, the fluorescence of the europium complex with thenoyltrifluoroacetone and 4,7-diphenyl-1,10-phenanthroline was increased by a factor of about 2; the excitation and emission wavelengths were 346 and 613nm, respectively;the fluorescence was linear up to 1.59ng/ml of europium;and the detection limit was found to be 0.6pg/ml of europium. A general mechanism of fluorescence enhancement was proposed.     

Determination of trace levels of metal ions in water samples by inductively coupled plasma mass spectrometry after on-line preconcentration on SO3-oxine CM-cellulose

Summary A method utilizing a miniature chelated ion-exchanger column of SO₃-oxine CM-cellulose has been developed to increase the sensitivity for multielement measurements by inductively coupled plasma mass spectrometry (ICP-MS). This matrix/analyte separation and preconcentration technique has been used to preconcentrate Mn, Co, Ni, Cu, Cd, and Pb from natural water samples. The multielement detection limits are in the low ppt (pg/mL) range. This FIA-ICP-MS method has been applied to the determination of various trace levels of metal ions in riverine reference material SLRS-2 and open ocean seawater reference material NASS-3.     

钯作基体改进剂FIA－HG－GFAAS法测定锗及其机理研究

采用钯，钯－镁作基体改进剂，ＦＩＡ－ＨＧ－ＧＦＡＡＳ法成功地测定了锗。灵敏度、精密度和分析速度都得到很大的提高。峰值吸收的特征质量８．０ｐｇ，检出限１０．９ｐｇ，相对标准偏差０．３４％，同时探讨了基体改进剂钯的稳定作用机理及锗在石墨管中的原子化机理。     

Comparative study of conventional and multivariate methods for aluminum determination in soft drinks by graphite furnace atomic absorption spectrometry

In the present study, conventional and multivariate methods were used to optimize conditions for direct determination of aluminum in soft drinks by electrothermal atomic absorption spectrometry. For the conventional method, the optimized experimental parameters were: pyrolysis and atomization temperatures and chemical modifier. A multivariate study was performed using factorial design and the optimized parameters were the same employed in the univariate method including pyrolysis time. For the conventional method, the optimal conditions obtained were: pyrolysis temperature of 1600 °C, atomization temperature of 2700 °C, and Zr as permanent modifier. For the factorial design in the multivariate optimization, the Pareto´s chart showed that the atomization temperature, the modifier, and the pyrolysis temperature presented a significant effect on the integrated absorbance and the interaction between pyrolysis temperature and pyrolysis time also had a significant effect on the signal. Better results were obtained using Zr as modifier. The surface response indicates that the lowest pyrolysis (1100 °C) and atomization temperatures (2350 °C) provide higher absorbance for aluminum in soft drinks. Characteristic mass of 23.4 and 19.4 pg and LOD of 17.9 and 11.3 μg L^− 1 was obtained to conventional and multivariate methods, respectively. The calibration was accomplished with standard addition in a range of 60–200 μg L^− 1 for conventional method and of 38–200 μg L^− 1for multivariate method with R higher than 0.99 for both conditions. Recoveries in both studies were nearly 100% with adequate precision for GFAAS analysis. For the Al concentrations level found in soft drinks, both experimental conditions are adequate as good results were obtained in recovery studies. The Al concentrations in different soft drinks range from 147.9 to 599.5 μg L⁻¹. Higher concentrations were found in soft drinks sold in Al cans than in PET bottles, indicating that contamination can occur.     

Simultaneous amperometric determination of lignin peroxidase and manganese peroxidase activities in compost bioremediation using artificial neural networks

High-performance liquid chromatography (HPLC) and fluorescence derivatization were applied for a nanogram-level N-nitrosodimethylamine (NDMA) analysis of water samples. For the analysis of N-nitrosodimethylamine, samples were first denitrosated by a mixed solution of hydrobromic acid and acetic acid to produce dimethylamine, which was derivatized with dansyl chloride for HPLC fluorescence detection. Fluorescence detection was optimized with excitation and emission wavelengths of 340 and 530 nm, respectively. pH adjustment after denitrosation was necessary to maximize fluorescence intensity with pHs in the range of 9-12. A dansyl chloride concentration of 500 mg l⁻¹ was found to be optimal for measuring a fluorescence signal. An instrumental detection limit of 0.1 ng of NDMA was possible with fluorescence derivatization. The NDMA in water samples was extracted by continuous solid-phase extraction using Ambersorb 572. Although the determination of NDMA was variable at lower concentrations (less than 200 ng l⁻¹), it was observed that the NDMA detection limit with this method could be lowered to a concentration of 10 ng l⁻¹. Another benefit of this method can be found in its selectivity for NDMA. Unlike gas chromatographic (GC) methods, this method generates a distinct peak for NDMA without interference even in the complex matrix of wastewater effluents. The HPLC with fluorescence derivatization method may be applicable for determining NDMA in water and wastewater samples for various research purposes and for screening environmental samples.     

Analytical carbon furnace atomic emission: Temperature measurements and excitation mechanism

Atomic emission has been observed from 20 elements in an electrically heated graphite furnace. Two-line temperature measurements carried out on iron indicate an excitation temperature of ca. 2450 K when the temperature of the furnace walls is ca. 2420 K. Calibration curves have been obtained for Al, Mo and Cr, each showing a useful working range. The detection limit for Al was 5 pg, and for Cr and Mo was 140 pg. Bismuth was found to give a poor detection limit (10 ng). Time resolved traces of background emission and line emission intensity shows the validity of using the two-line method to measure the excitation temperature of iron. A thermal excitation mechanism of emission is proposed.     

用ETV-ICP-MS研究Cr、Ni、Zr、Nb、Yb在石墨炉中的蒸发/原子化机理

本文以电热蒸发电感耦合等离子体质谱（ETV-ICP-MS）为手段,探讨了Cr、Ni、Zr、Nb和Yb在石墨炉中的蒸发/原子化机理;比较了不同化学改进剂存在条件下,Cr、Ni、Zr、Nb和Yb的蒸发行为和在石墨炉原子吸收（GFAAS）中的原子化行为;考察了石墨炉温度和ICP功率等实验参数对上述元素发射强度及轮廓的影响.结果表明,Pd和Mg化合物的存在对Cr、Ni、Zr、Nb和Yb的蒸发/原子化行为没有明显的化学改进作用;然而,以聚四氟乙烯（PTFE）为化学改进剂时,可显著改善Cr、Ni、Zr、Nb和Yb的蒸发行为,避免难熔碳化物的形成,降低待测物的蒸发温度;对Cr和Ni的GFAAS信号强度略有增强;但是,由于Yb、Nb和Zr氟化物的离解键能很高,难以离解/原子化,PTFE的存在反而降低了Yb、Nb和Zr在GFAAS中的信号强度.     

Two-color excitation system for fluorescence detection in DNA sequencing by capillary array electrophoresis

Two computer-controlled galvanometer scanners are adapted for two-dimensional step scanning across a 96-capillary array for laser-induced fluorescence detection. 488 nm and 514 nm laser lines from the same Ar(+) laser were alternately coupled for two-color excitation in each capillary. The signal at a single photomultiplier tube is temporally sorted to distinguish among the capillaries and the excitation wavelengths. Based on the differences in absorption spectra for the dyes, the peak-height ratios in the 488 nm and 514 nm excitation electropherograms were used for peak identification for multiplexed capillary electrophoresis. Successful base calling for 24-capillary DNA sequencing was achieved to 450 bp with 99% accuracy. Advantages include the efficient utilization of light due to the high duty-cycle of step scan, good detection performance due to the reduction of stray light, ruggedness due to the small mass of the galvanometer mirror, low cost due to the simplicity of components and flexibility due to the independent paths for excitation and emission.