Flow injection method for the rapid determination of chemical oxygen demand based on microwave digestion and chromium speciation in flame atomic absorption spectrometry

The present paper describes a new flow injection method for the determination of Chemical Oxygen Demand (COD). This method consists of a first digestion step, where the sample is heated by microwave radiation, a second one where an anionic exchange resin retains the Cr(VI) that has not been reduced by the organic matter of the sample and a third one where Cr(VI), after being eluted, is determined by flame atomic absorption spectrometry. The microwave power applied, the sulphuric acid concentration, the liquid flow in the digestion step and the sample volume were the variables studied. The recovery and precision obtained with this method are similar to those obtained using a standard semi-micro method, whereas the throughput is much higher (up to 50 determinations per hour). As regards sensitivity, by changing the sample loop volume and the concentration of dichromate, one can analyze samples with Chemical Oxygen Demand values between 25 and 5000 mg/l. The limit of detection is about 7 mg/l COD. An interesting feature of the new method, which is not shared by most other flow injection methods of Chemical Oxygen Demand determination, is that there is no matrix effect in the determination step.     

Structural and chemical characterisation of titanium deuteride films covered by nanoscale evaporated palladium layers

Thin titanium deuteride (TiD_y) films, covered by an ultra-thin palladium layer, have been compared with the corresponding titanium and palladium films using a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The TiD_y layers were prepared under ultra-high vacuum (UHV) conditions by precisely controlled deuterium sorption at 298 K on a Ti film evaporated onto a Si(100) substrate. Both Ti and TiD_y films were then covered in situ by a nanoscale Pd layer. It was found that a 10- to 12-nm-thick Pd layer protects the TiD_y films efficiently against extensive air interaction. The morphology of both the surface and bulk Pd/TiD_y (Ti) films have been observed using SEM and cross-sectional TEM analysis, respectively. A polycrystalline bulk morphology in both Ti and TiD_y films accompanied by a fine-grained Pd surface was observed. High-magnification cross-sectional TEM images reveal the TiD_y film to be plastically deformed leading to an increase in the roughness of the top Pd layer. Complex structures, including Moiré patterns, have been identified within the Pd/TiD_y interface. The chemical nature of this interface has been analysed after partial sputtering of the Pd top layer using XPS. Besides TiD_y and Pd, TiO and PdO were found to be the main chemical species in the interface region of the Pd/TiH_y film. The XPS valence-band spectra of the Pd/TiD_y interface reveal electronic features characteristic of a Pd–Ti bimetallic structure.     

Determination of vanadium and titanium in steel by inductively coupled plasma atomic emission spectrometry with modified use of a tungsten boat furnace atomizer for atomic absorption spectrometry

For electrothermal sample introduction, a commercially available tungsten boat atomizer for atomic absorption spectrometry (AAS) was transferred to a vaporizer for inductively coupled plasma atomic emission spectrometry (ICP-AES). The modification retained as much of the original design of the atomizer as possible, so that the apparatus could be switched easily between conventional tungsten boat furnace (TBF)-AAS and TBF-ICP-AES. By using this system, a procedure for the determination of vanadium and titanium in steel was investigated. The detection limits (S/N=3) of vanadium and titanium were 3.9 and 1.5 ng ml^?1, respectively. The relative standard deviations for five replicate determinations were ca. 3% for both elements. The calibration graphs were linear up to 100 μg ml^?1 vanadium(V) and 10 μg ml^?1 titanium(IV). Results of analyses of some low-alloy steel samples are given.     

A novel titanium dioxide-polydimethylsiloxane plate for phosphopeptide enrichment and mass spectrometry analysis

The phosphorylation of proteins is a major post-translational modification that is required for the regulation of many cellular processes and activities. Mass spectrometry signals of low-abundance phosphorylated peptides are commonly suppressed by the presence of abundant non-phosphorylated peptides. Therefore, one of the major challenges in the detection of low-abundance phosphopeptides is their enrichment from complex peptide mixtures. Titanium dioxide (TiO₂) has been proven to be a highly efficient approach for phosphopeptide enrichment and is widely applied. In this study, a novel TiO₂ plate was developed by coating TiO₂ particles onto polydimethylsiloxane (PDMS)-coated MALDI plates, glass, or plastic substrates. The TiO₂-PDMS plate (TP plate) could be used for on-target MALDI-TOF analysis, or as a purification plate on which phosphopeptides were eluted out and subjected to MALDI-TOF or nanoLC-MS/MS analysis. The detection limit of the TP plate was ∼10-folds lower than that of a TiO₂-packed tip approach. The capacity of the ∼2.5 mm diameter TiO₂ spots was estimated to be ∼10 μg of β-casein. Following TiO₂ plate enrichment of SCC4 cell lysate digests and nanoLC-MS/MS analysis, ∼82% of the detected proteins were phosphorylated, illustrating the sensitivity and effectiveness of the TP plate for phosphoproteomic study.     

A rapid method of sample preparation for determining arsenic in water by stripping voltammetry

A procedure was developed for sample preparation for the further determination of arsenic in potable and natural water and process solutions by stripping voltammetry (SV). To minimize the losses and simplify the procedure, arsenic(III) was oxidized by the ozonation or UV irradiation of the solution in the presence of sulfite, chloride, or hydroxide ions, which increased the oxidation efficiency. The time required for 100% oxidation does not exceed 60 s for an arsenic concentration of no more than 1 mg/L. The reduction to arsenic(III) was performed photochemically in the presence of sodium sulfite for 5 min. Further stripping voltammetric determination was performed in the same solution using a gold-plated carbon electrode. The developed procedure is rapid, simple, and easy-to-automate.     

Characteristics of a novel UV-TiO2-microwave integrated irradiation device in decomposition processes

The efficiency of oxidation in wet decomposition procedures for organic materials can be of great importance to the quality of the analytical data from various measurement techniques. A novel, microwave-assisted, high-temperature/high-pressure UV-TiO₂ digestion procedure was developed for the accelerated decomposition of various biological samples. The technique is based on a closed, pressurized, microwave digestion apparatus (MW). UV irradiation is generated by immersed electrodeless Cd discharge lamp operated by the focused microwave field in the single polymer vessel. To enhance oxidation efficiency, a photocatalyst TiO₂ was added to the microwave heated Teflon bomb. Measures of digestion completeness were provided by the appearance of carbon content and determination of trace and minor elements, enabling a comparison of different digestion procedures and sample types. Compared with other digestion systems, unusually low residual carbon contents were obtained. For the organic compounds and biological samples digested, the residual carbon content was 1-2%, corresponding to a decomposition efficiency of 98-99%. The potential of the MW-UV-TiO₂ system was illustrated by the decomposition of four certified reference materials (serum, urine, milk, arsenobetaine solution) and subsequent determination of trace and minor elements. Recoveries between 92% and 107% were found.     

Determination of Na, K, Ca and Mg in biodiesel samples by flame atomic absorption spectrometry (F AAS) using microemulsion as sample preparation

This study proposes a procedure for determining sodium, potassium, calcium and magnesium in biodiesel samples by flame atomic absorption spectrometry (F AAS). The sample was prepared as a microemulsion without surfactant. The optimized composition of the microemulsion was 10% (w/v) biodiesel, 75% (v/v) n-propanol, 1% (v/v) concentrated nitric acid and 14% (v/v) of aqueous solution formed by 0.2% (v/v) of nitric acid and 0.5% (v/v) of ionization suppressor. Analyte signals in the samples as microemulsion were found to be stable for a period of 15 days. Analytical curves were obtained using organometallic standard solutions. The limits of detection (LOD) found for the proposed procedure were 0.1 µg g^− 1, 0.01 µg g^− 1, 0.04 µg g^− 1, and 0.004 µg g^− 1 for Na, K, Ca and Mg, respectively. The reference method established by ABNT (Brazilian Association of Technical Norms) NBR 15556:2008 was used to verify the accuracy of the proposed procedure. No significant statistical difference was found between the results obtained with the proposed and the chosen reference procedure. The proposed procedure showed no matrix influence when recovery tests were performed (89%-103%). The results found in this study show that the proposed procedure is a good alternative for determining Na, K, Ca, and Mg by F AAS in biodiesel samples.     

A rapid sample preparation method for mass spectrometric characterization of N-linked glycans

A rapid method for analysis of glycans of glycoproteins is presented. This method comprised deglycosylation, sample cleanup and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analysis of glycans. The enzymatic deglycosylation of N-linked glycoproteins was enhanced in terms of speed and reproducibility using an enzyme-friendly surfactant. The released glycans were desalted using a micro-scale solid phase extraction (SPE) device packed with a hydrophilic interaction chromatography (HILIC) sorbent. Hydrophilic glycans were well retained by SPE, while salts and surfactants were removed from the sample. The glycans were eluted using 25-50 microL of solvent and analyzed directly without derivatization using MALDI-MS. MALDI quadrupole time-of-flight (Q-Tof) instrumentation was utilized for glycan profiling and structure characterization by tandem mass spectrometry (MS/MS). The presented method allows sensitive analysis of glycans benefiting from optimized deglycosylation reactions and efficient sample cleanup.     

A novel sample preparation method of matrix-assisted laser desorption/ionization time of flight mass spectrometry for polystyrene

A novel sample preparation method of matrix-assisted laser desorption/ionization mass spectrometry for polystyrene was reported. Compared to the conventional dried-droplet method, the efficiency of ionization and signal intensity of mass spectra were improved. The mechanism was also analyzed.     

A novel one-step chemical method for preparation of copper nanofluids

This paper presents a novel one-step method for preparing of copper nanofluids by reducing CuSO(4).5H(2)O with NaH(2)PO(2).H(2)O in ethylene glycol under microwave irradiation. Nonagglomerated and stably suspended Cu nanofluids are obtained. The influences of CuSO(4) concentration, addition of NaH(2)PO(2), and microwave irradiation on the reaction rate and the properties of Cu nanofluids were investigated by transmission electron microscopy, infrared analysis, and sedimentation measurements. It is found to be a fast, efficient one-step chemical method to prepare Cu nanofluids.     

Determination of tin and titanium in soils, sediments and sludges using electrothermal atomic absorption spectrometry with slurry sample introduction

Fast-heating programmes for determining titanium and tin in soils, sediments and sludges using electrothermal atomic absorption spectrometry (ETAAS) with slurry sampling are developed. For titanium determination, suspensions are prepared by weighing 5-40 mg of sample and adding 25 ml of a solution containing 50% (v/v) concentrated hydrofluoric acid. For tin determination, suspensions are prepared by weighing up to 300 mg of sample and then adding 1 ml of a solution containing 25% (v/v) concentrated hydrofluoric acid. Palladium (30 μg) and ammonium dihydrogen phosphate (7% w/v) are used as matrix modifiers for titanium and tin, respectively. Prior mild heating in a microwave oven is recommended for titanium determination. Calibration is carried out using aqueous standards. The tin and titanium contents of a number of samples obtained by using the slurry approach agree with those obtained by means of a procedure based on the total dissolution of the samples using microwave oven digestion. The reliability of the procedures is also confirmed by analysing several certified reference materials.     

Multiple response optimization for Cu, Fe and Pb determination in naphtha by graphite furnace atomic absorption spectrometry with sample injection as detergent emulsion

The present paper reports the optimization for Cu, Fe and Pb determination in naphtha by graphite furnace atomic absorption spectrometry (GF AAS) employing a strategy based on the injection of the samples as detergent emulsions. The method was optimized in relation to the experimental conditions for the emulsion formation and taking into account that the three analytes (Cu, Fe and Pb) should be measured in the same emulsion. The optimization was performed in a multivariate way by employing a three-variable Doehlert design and a multiple response strategy. For this purpose, the individual responses of the three analytes were combined, yielding a global response that was employed as a dependent variable. The three factors related to the optimization process were: the concentration of HNO₃, the concentration of the emulsifier agent (Triton X-100 or Triton X-114) in aqueous solution used to emulsify the sample and the volume of solution. At optimum conditions, it was possible to obtain satisfactory results with an emulsion formed by mixing 4 mL of the samples with 1 mL of a 4.7% w/v Triton X-100 solution prepared in 10% v/v HNO₃ medium. The resulting emulsion was stable for 250 min, at least, and provided enough sensitivity to determine the three analytes in the five samples tested. A recovery test was performed to evaluate the accuracy of the optimized procedure and recovery rates, in the range of 88-105%; 94-118% and 95-120%, were verified for Cu, Fe and Pb, respectively.     

Determination of selenium, zinc and cadmium in antidandruff shampoos by atomic spectrometry after microwave assisted sample digestion

Microwave assisted pre-treatments for atomic spectrometric determination (inductive coupled plasma-optical emission spectrometry, ICP-OES or flame atomic absorption spectrometry, FAAS) of metallic elements, usually present in antidandruff shampoos, are proposed. They are based on the digestion of the sample with HNO₃ into a closed reactor, which is irradiated at 800 W for a few minutes. Selenium was determined by ICP-OES. The limit of detection was 0.11 mg l⁻¹; the relative standard deviation (R.S.D.) for the selenium content in the samples was in the 0.6–3.6% range. The results obtained were in agreement with the label contents and the recovery of the proposed method was in the 100–106% range. Zinc and cadmium were determined by FAAS. The limit of detection for zinc determination was 0.078 mg l⁻¹; the R.S.D. for zinc contents was in the 0.8–8.6% range. A limit of detection of 0.09 mg l⁻¹ was obtained for cadmium determination; the R.S.D. for cadmium contents was in the 0.7–2.7% range. The determinations were performed after two different sample mineralization pre-treatments — dry ashing (in an electric furnace) and wet mineralization (in a microwave oven). Both methodologies provided comparable results for zinc and cadmium determination in shampoos. The proposed microwave assisted digestion procedures allow a precise and accurate determination of selenium, zinc and cadmium in commercial antidandruff shampoos, and the sample pre-treatment is less time-consuming than the classic methods.     

A rapid method for the determination of mercury in air by flameless atomic absorption spectrometry.

A rapid method for the determination of total gaseous mercury in the atmosphere is described. A simple, inexpensive sampling device is used; the collection time for mercury levels above 5 ng m^?3 is less than 25 min; less than 10 min is then needed to determine the mercury by flameless atomic absorption. For subnanogram levels longer sampling periods are used, but air polluted with mercury can be monitored in a few minutes. Data obtained for different samples are presented.     

Simple method for the determination of Cu and Fe by electrothermal atomic absorption spectrometry in biodiesel treated with tetramethylammonium hydroxide

A simple analytical procedure for the determination of Cu and Fe in biodiesel samples by electrothermal atomic absorption spectrometry is proposed. An aliquot of the sample is simply mixed with tetramethylammonium hydroxide (TMAH) and heated to 90 °C for 5 min. Pyrolysis and atomization temperatures were optimized through pyrolysis and atomization curves. The high pyrolysis temperature adopted, of 1000 °C, certainly helped minimizing potential interferences. Even though, calibration should be carried out with aqueous standard solutions in the presence of the TMAH. The detection limits (3 s, n = 10), in the sample, were quite low 15 ng g⁻¹ and 24 ng g⁻¹ for Cu and Fe, respectively. Seven biodiesel samples, produced from different raw materials, including vegetable seed, frying oil and animal fat were analyzed. Accuracy was validated by applying the recovery test to two samples, enriching the samples with two concentration levels (recoveries from 105% to 120%). The precision, expressed by the relative standard deviation was less than 3% for Cu and less than 7% for Fe. Copper could be quantified in two and Fe in three of the seven samples. The biodiesel sample from fodder turnip was especially rich in the analytes in comparison to the other samples.     

Rapid on-line sample dissolution assisted by focused microwave radiation for silicate analysis employing flame atomic absorption spectrometry: iron determination

An on-line automated flow injection system with microwave-assisted sample digestion was used to perform silicate rock dissolution in acid medium for iron determination. For this purpose, a continuous flow system was built up by using an automatic flow injection analysis (FIA) system coupled to a flame atomic absorption spectrometer (FAAS), including a focused microwave oven unit. Inside the microwave cavity was inserted a polytetrafluoroethylene (PTFE) reactor coil (300 cm length and 0.8 mm i.d.) where the dissolution takes place. Chemical and flow variables as well as iron determination parameters were studied. In the flow system, a slurry of the rock sample (50 mg in 200 ml of acid mixture HF+HCl+HNO₃) is pumped through the reaction coil and the microwaves are turned on. After elapsed the time required to complete the sample dissolution, the mixture is pumped again in order to fill the sampling loop (500 μl). Then, by changing the valve position, a water carrier stream pushes the sample solution through the flame atomic absorption spectrometer nebulizer. To achieve an accurate determination of the rock certified materials, the slurry sample was irradiated during 210 s at 90 W power. Working in that condition, a detection limit of 0.80 μg ml⁻¹ (which corresponds to an Fe₂O₃ content of 0.46%) and an analytical throughput of 10 h⁻¹ were achieved. The relative standard deviation (R.S.D.) of the method varied between 1 and 11% when applied to the rock certified materials.     

流动注射在线萃取色谱分离原子吸收光谱法测定痕量铂

研究了流动注射在线分离富集原子吸收光谱法测定痕量铂的方法。以自制的GDX501-TBP萃取树脂为微型分离柱，在优化后的分离富集条件下，进样时间为60s，洗脱时间为45s。在线分离测定时间为3min，方法检出限为0．25μg/L，线性范围10—600μg/L，加标回收率为97．8％-103．6％，相对标准偏差3．49％-4．25％。方法已用于矿物管理样中铂的测定。     

A spectrophotometric method for estimation of titanium alkoxide,a catalytically active form of titanium in oligomer/ polymers

A spectrophotometric method was developed for the selective estimation of titanium in alkoxide form in the presence of TiO₂. Polymers like polybutylene terephthalate have been synthesized by using homogeneous catalyst such as titanium tetra-isopropoxide (TTIP). These types of catalysts are susceptible to moisture and convert to inactive TiO_2. Hence, it is essential to have analytical method for selective estimation of alkoxide form of titanium. In this study, we have used O-cresol to convert TTIP to tetra O- cresyl titanate, a colored compound, which was quantitatively analyzed by spectrophotometric technique. Polymer matrix was used in standard solution to compensate the effect of matrix during UV-VIS measurements. Method validation was successfully carried out for linearity, reproducibility, recovery, specificity and the observed acceptable results as per ICH guidelines. 2-sample t-test was performed to check the variation observed between two analysts and the observed p-value indicated the results were statistically similar to each other. Mechanism of color formation was established by synthesis of colored complex called tetra O-cresyl titanate. The structure was supported by ICP, CHNS and NMR analysis. The method is simple and easy to implement at manufacturing plant for initial monitoring of active catalyst concentration in polymer/oligomer samples.     

Preparation of carbide isolates of new high-speed steel for analysis by atomic absorption spectrometry

The paper presents results of the investigation of a new high-speed steel's (HSS) carbide isolates, using atomic absorption spectroscopy (AAS). Because of the presence of metallic residues, two stage preparation of isolates was applied: electrolytic winning of the carbide isolates, followed by additional treatment with phosphoric acid. The chemical compositions so obtained were of enhanced accuracy and served as input data for computing the matrix's chemical composition. This indirect approach reduced the errors connected with the phases mutual contribution, such as occur in the case of HSSs and steels of similar multi-phase microstructure when bulk specimens are investigated with energy dispersive XRF. The extent of the carbides' dissolution in the matrix and hence the matrix's saturation during hardening, as well as the character of secondary precipitation while tempering, were assessed. These findings are of importance in respect of both phenomena during heat treatment and the investigated steel's properties.     

Application of multivariate techniques for optimization of direct method for determination of lead in naphtha and petroleum condensate by electrothermal atomic absorption spectrometry

A direct method is proposed for the determination of lead in naphtha and petroleum condensate by electrothermal atomic absorption spectrometry (ET AAS) using palladium as a permanent modifier. The procedure includes the dilution of 3 mL of sample (naphtha or petroleum condensate) to a final volume of 10 mL with xylene, and direct injection of 30 μL of this solution into the graphite furnace. The optimization of the instrumental conditions was performed using multivariate techniques. Firstly, a 2³ full factorial design was performed for preliminary evaluation of the factors: pyrolysis time, pyrolysis temperature and atomization temperature. This experiment showed that in the studied levels only the factors pyrolysis time and atomization temperature were significant. Then, a 3² full factorial design was performed for the determination of the critical conditions of these variables. The method allows the determination of lead using the standard calibration technique with a calibration curve from 2.6 to 30 μg L⁻¹ (correlation coefficient higher than 0.998). A limit of detection (3σ) of 0.8 μg L⁻¹ and a characteristic mass of 35 pg were obtained in the presence of palladium as modifier. The precision expressed as relative standard deviation (RSD) was 1.5 and 0.8% for lead concentrations of 3.0 and 30 μg L⁻¹ (n = 10). Recovery studies demonstrate that lead can be determined in naphtha and petroleum condensate using calibration with organic standard solutions. This method was applied for the determination of lead in three petroleum condensate and two naphtha samples. The concentrations found for the petroleum condensate was between 2.7 and 5.7 μg L⁻¹, while the naphtha samples did not contain any detectable lead.