José Alvarado

Analysis of human blood serum and human brain samples by total reflection X-ray fluorescence spectrometry applying Compton peak standardization

Abstract The method of using the Compton peak as internal standard in total reflection X-ray fluorescence (TXRF) determination is established for trace element determination of Fe, Cu, Zn, Se and Pt in human serum and of Cu and Zn in homogenized brain samples. A new method of spectrometer sensitivity calibration using spiked matrices with known amounts of trace elements is tested against established methods of matrix matching as well as internal element addition. The analytical results with the proposed procedure are compared to a certified international standard and to values with Atomic Absorption Spectrometry (AAS) obtaining analytical results of comparable accuracy and precision. The method is adequate for routine clinical analysis as it has the advantages of requiring very small amounts of material and simple preparations, which avoids the chemical digestion stage.

Pollution effects of the Tuy River on the central Venezuelan coast: Anthropogenic organic compounds and heavy metals in Tivela mactroidea

Bivalve samples were collected at seven sampling stations located between the town of Machurucuto and the Bay of Higuerote, Venezuela, covering approximately 70 km of coastline. Samples were collected both east and west of the Tuy River mouth, which has a plume known to move in a north-westerly direction. Petroleum hydrocarbons, both aliphatic (n-alkanes and UCM) and polyaromatic (PAHs), were detected and quantified in the samples. These hydrocarbons were found to be primarily derived from fossil fuels. Halogenated organics consisted mostly of polychlorinated biphenyls (PCBs) and some chlorinated pesticides, primarily of the DDT group. Heavy metals such as Pb, Cu, Ni, Zn, Cr and Cd were analysed in the samples. The results clearly show the influence of the Tuy River plume on the water quality of the coastal zone, particularly that located west of the river mouth. One sampling station, located just east of the river mouth, also showed significant influence from the river plume.

Liquid-phase microextraction with in-drop derivatization combined with microvolume fluorospectrometry for free and hydrolyzed formaldehyde determination in textile samples.

A new miniaturized methodology based on the combination of headspace single drop microextraction and microvolume fluorospectrometry is proposed in this work for the determination of free and hydrolyzed formaldehyde in textile samples. The proposed method is based on the extraction and in-drop derivatization of free and hydrolyzed formaldehyde using the Hantzsch reaction. The effect of experimental variables affecting the performance of the proposed method, such as fluorescence parameters, nature of the extractant phase composition (including acetylacetone concentration, pH, ammonium acetate concentration and presence of an organic solvent), sample temperature, NaCl concentration and microextraction time was carefully investigated. Under optimized conditions, instrumental detection and quantification limits were 26 and 87 μg L(-1), respectively, whereas procedural detection and quantification limits were 1.0 and 3.5 mg kg(-1), respectively. Repeatability, expressed as relative standard deviation, was 4.6% (n=9). The method was successfully applied to the determination of free and hydrolyzed formaldehyde in several textile samples, the found results being in good agreement with those obtained with the EN ISO 14184-1:1998 method.

Determination of copper, iron and zinc in spirituous beverages by total reflection X-ray fluorescence spectrometry ☆

Abstract The concentration of copper in traditional homemade alcoholic distillates produced in Venezuela (Cocuy de Penca) were determined by total reflection X-ray fluorescence (TXRF) using vanadium as internal standard. The results were compared to those obtained by flame atomic absorption spectrometry (FAAS). Three preparative methods of addition of vanadium were compared: classical internal standard addition, ‘layer on layer’ internal standard addition and in situ addition of internal standard. The TXRF procedures were accurate and the precision was comparable to that obtained by the FAAS technique. Copper levels were above the maximum allowed limits for similar beverages. Zinc and iron in commercial and homemade distilled beverages were also analyzed by TXRF with in situ addition of internal standard demonstrating the usefulness of this technique for trace metal determination in distillates.

Determination of Organic Nitrogen by the Kjeldahl Method Using Microwave Acid Digestion

Abstract Essential aminoacids, vegetables, milk products, seafood, and canned meat were analyzed by the Kjeldahl method to determine their organic nitrogen content. The samples were brought into solution in two different ways, by conventional and by microwave wet acid digestion. The main goal of the study was to assessthe efficiency of the microwave method of sample treatment in regard to the speed of the dissolution process and to the precision and accuracy of the nitrogen determination. The experiments indicate that, in most cases, the precision of the results obtained using the microwave treatment is better than the one obtained by the conventional procedure; the accuracy of both methods of analysis is comparable and the time employed for the sample digestions using microwave heating is shorter.

Comparison of conventional and microwave wet acid digestion procedures for the determination of iron, nickel and vanadium in coal by electrothermal atomisation atomic absorption spectrometry

Certified coal standards and Venezuelan coal samples were submitted to conventional and microwave wet acid digestion procedures to assess and compare the efficiency of both decomposition methods. Several acid mixtures and heating power and time settings were investigated in order to achieve the optimum sample treatment conditions. The resulting solutions were analysed by electrothermal atomisation atomic absorption spectrometry to determine their Fe, Ni and V content. The results obtained showed total recovery of the analytes and good accuracy and precision of the measurements. Sample treatment time was reduced from 11–12 h per sample using conventional heating, to 8–10 min per sample using the microwave-heating source.

Radioisotope X-ray fluorescence analysis of vanadium in petroleum coke samples

Radioisotope X-ray fluorescence spectrometry, RIXRF, was used for the determination of vanadium in Venezuelan petroleum coke samples using a simple standardless method and fundamental parameter approach. The values obtained by this method were in agreement with values measured by graphite furnace atomic absorption spectrometry, GFAAS.

Organic compounds and heavy metals in the atmosphere of the city of Caracas, Venezuela — I: Atmospheric particles

Aliphatic and aromatic hydrocarbons, fatty acids and heavy metals (Pb, Cu, Ni, Zn, Fe and Cd) were analyzed in atmospheric particulate matter in the city of Caracas, Venezuela. Samples were taken from 6 stations within the metropolitan area of Caracas, characterized as industrial (one), urban (two), suburban (two) and rural (one). In addition, the concentration and composition of the organic compounds was monitored over a 5 month period at an urban site to determine seasonal and temporal variabilities.In general terms, the concentrations of pollutants decreased from industrial and urban sites to suburban to rural. A similar trend was observed for preliminary toxicity tests carried out on the particulate extracts. The concentration levels of most of the pollutants were high for the industrial and urban sites, and comparable with those of other major cities worldwide.

Electrochemical determination of arsenic in natural waters using carbon fiber ultra-microelectrodes modified with gold nanoparticles.

We have developed an anodic stripping voltammetry method that employs carbon fiber ultra-microelectrodes modified with gold nanoparticles to determine arsenic in natural waters. Gold nanoparticles were potentiostatically deposited on carbon fiber ultra-microelectrodes at -0.90V (vs SCE) for a time of 15s, to form the carbon fiber ultra-microelectrodes modified with gold nanoparticles. Cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy coupled to an X-ray microanalysis system were used to check and confirm the presence of gold nanoparticles on the carbon fiber ultra-microelectrodes. Arsenic detection parameters such as deposition potential and deposition time were optimized allowing a detection range between 5 to 60µgL-1. The developed modified electrodes allowed rapid As determination with improved analytical characteristics including better repeatability, higher selectivity, lower detection limit (0.9μgL-1) and higher sensitivity (0.0176nAμgL-1) as compared to the standard carbon electrodes. The analytical capability of the optimized method was demonstrated by determination of arsenic in certified reference materials (trace elements in water (NIST SRM 1643d)) and by comparison of results with those obtained by hydride generation atomic absorption spectrometry (HG-AAS) in the determination of the analyte in tap and well waters.

Peak-area measurements in electrothermal atomisation inductively coupled plasma atomic emission spectrometry

A commercial inductively coupled plasma atomic emission spectrometer has been utilised in combination with an electrothermal atomisation system for sample introduction into the plasma and its operation has been modified so that transient signals from the analytes can be integrated. Good signal to background ratios were achieved by ensuring that the time interval of the analyte peak was accurately selected. This arrangement has provided results which are essentially independent of the heating rate of the electrothermal atomiser and of the length of tubing used to transport the analyte vapour to the plasma. Chemical matrix interferences, normally observed during electrothermal atomisation atomic absorption measurements and in ETA-ICP-AES when the peak height is used, are greatly reduced under peak-area measurements in the ICP.