Present-day methods for the determination of trace elements in oil and its fractions

The development and use of instrumental methods for the determination of a wide range of trace elements in oil is considered. Special attention is paid to methods of the direct introduction of samples into spectrometers. It is shown that preliminary sample preparation is in certain cases necessary for the determination of trace elements in oil. The main methods of sample preparation of oils, including methods of extraction of a series of trace elements from crude oil (extraction, membrane, sorption, etc.), are described.     

Determination of Phosphorus in Crude Oil and Middle Distillate Petroleum Products by Inductively Coupled Plasma–Optical Emission Spectrometry

A method for the precise and accurate determination of phosphorus in crude oil and middle distillate petroleum products was developed using inductively coupled plasma–optical emission spectrometry to rapidly determine phosphorus as a control method. The presence of phosphorus is undesirable in petrochemical products as it complexes with other metals generating residues that interrupt normal operation of refineries. The presence of phosphorus may be due to some anti-fouling additives or the crude oils processed. Consequently, it is necessary to control the phosphorus present at trace levels in the crude oil and in process streams that present various densities and viscosities. The instrumental power, nebulizer flow, pump rate, read time, and the sample preparation conditions were optimized. The desired level of quantification for the petrochemical industry was achieved allowing the simultaneous analysis of diverse liquid petroleum products.     

Determination of trace element pathways in a petroleum distillation unit by instrumental neutron activation analysis

The concentrations of 11 trace and minor elements (Na, Al, S, Cl, Ca, V, Mn, Ni, As, Br, I) have been measured by instrumental neutron activation analysis in a sample of crude oil from Venezuela, and in 7 of its distillates and in the final residue produced in a primary distillation unit. Concentrations range from 0.5 ppb to 2.0%. The elements have been classified in 4 categories on the basis of their distributions among the fractions analyzed. The results on concentrations have also been used to establish elemental balances in the distillation unit studied operating under steady-state conditions. Only S and V have been found to give rise to losses by emission.     

Group-type fractionation of petroleum and alternative fuels by column liquid chromatography

The present paper introduces an instrumental procedure based on column liquid chromatography for the total analysis of petroleum heavy ends and similar samples. The procedure avoids the precipitation of asphaltenes and asphaltols. One sequence of eluents fractionates the sample into 8 fractions: 5 non-polar (hydrocarbons), one intermediate (resins), and 2 polar fractions (asphaltenes and asphaltols). Quantitative results from gravimetric measurements and UV-Vis and FTIR spectra of fractions obtained from petroleum heavy ends are presented, as well as those from GC/MS data obtained from one fraction obtained from liquefaction of biomass. The method presented is easy to set up and operate, requires minimum operator attention, is reliable (no precipitation), reproducible, and inexpensive.     

Trace elements distribution in Antarctic sediments by neutron activation analysis

In the present investigation iron and trace elements were determined by instrumental neutron activation analysis in a number of sea bottom sediment samples, collected in the Ross Sea and close to the Italian Station at Terra Nova Bay in Antarctica. Full listing of results is presented and discussed as well as the evaluation of precision and accuracy. In order to find correlations and similarities among the sediment samples, the analytical data were submitted to statistical treatment. In addition rare earth element patterns were obtained. Typical trends were observed with no evident Eu negative anomaly and a depletion of heavy rare earth elements.     

Importance of quality control in a gas chromatographic method to characterize crude oils

A quality control scheme has been developed to achieve reproducible capillary GC characterization of crude oils and petroleum condensates. The method uses an internal standard to quantify the amount of non-eluted material in the crude oil sample. Correlation between the gas chromatographic results and actual distillation was 2 %. After repeated use, however, weekly analysis of the same standard crude oil did not give the correct composition. This was a result of discrimination, which worsened with time, as a result of leaks in the septum or the graphite ferrules. More reproducible results were obtained by performing frequent analyses of quality control samples to ensure that the gas chromatographic system was operating properly. The use of quality control charts was a convenient way of ensuring correct operation and identifying the need for corrective action on the gas chromatographic system.     

Multielement standards for instrumental neutron activation analysis of biological materials

Standards for instrumental neutron activation analysis (INAA) of biological materials are proposed. The standards are multielement solid solutions in phenol-formaldehyde resole resin (PFR) moulded as pellets weighing 30 to 50 mg. The concentrations of trace elements in the standards are selected so that, firstly, they are commensurable with their concentrations in the biological materials and, secondly, that the analytical lines of each of the elements incorporated in PFR are resolved with the aid of modern equipment. The principal standard contains 21 trace elements from among those of greatest interest for INAA of biological materials. This standard is recommended for work on high-resolution equipment. At the same time, standards of simpler trace element composition have been prepared and studied which can be used in work on simpler equipment or in solving particular problems in determination of certain groups of chemical elements.     

Nuclear activation methods for the characterization of fossil fuels

A review is presented on the use of neutron activation analysis (NAA) for the analyses of coal, oil shale, tar sands and petroleum. Fast NAA has been widely used for the determination of oxygen, and to a limited extent, of other elements such as nitrogen and silicon. Reactor NAA followed by instrumental counting, and in specific cases, after radiochemical separations is discussed. Thermal and epithermal neutrons are both used. Limited use of the²⁵²Cf source has been made in fuel analysis. A complementary technique to NAA is the photon-activation analysis with linear accelerator. It can determine over thirty elements, many of them not possible to do by NAA. Round-robin analyses of standard coal, fly ash, or oil shale samples indicate nuclear activation methods are comparable in accuracy and precision to X-ray fluorescence or atomic spectrometric methods for most elements.     

Dimethylbenzothiophenes and methyldibenzothiophenes in crude oils from different sources

A method is presented for the identification and quantification of C₂-substituted benzothiophenes in crude oil. The method will enable analysis of the pattern of these compounds, for example as a basis for differentiating crude oils from one another (fingerprinting) and for investigation of their suitability as indicators of oil maturity. Here results are reported for five crudes from Iraq, Venezuela, Saudi Arabia, the former Soviet Union, and the North Sea. The aromatic fraction of the crudes was oxidized and the dioxides of the heterocycles separated according to the number of carbon atoms in the side chains. The final separation was by capillary GC with atomic emission or flame ionization detection. A fluorinated analog was synthesized and used as internal standard. The concentrations of 2,3-, 2,4-, 2,7-, and 3,7-dimethylbenzothiophene ranged between 11 and 272 ppm. Three other dimethylated benzothiophenes present in lower amounts were also identified.     

石墨消解-ICP-MS法同时测定铜精矿中4种有害元素

为弥补标准检测方法的不足,建立了石墨消解-ICP-MS法同时检测铜精矿中Pb、Cd、As 和Hg等4种有害元素。确定了样品前处理和仪器分析条件。用铜精矿标准样品和参考样品分别进行7次重复实验,Pb、Cd和As的检测结果均在标准值范围内,Hg的检测结果与参考值基本一致。7次重复检测结果的变异系数符合GB/T 27417-2017《合格评定 化学分析方法确认和验证指南》要求。选择5种不同物相铜精矿作为待测样品,通过与标准方法比对,两种方法检测结果的绝对差符合标准方法的再现性要求,说明本方法适用于不同种类的铜精矿。本方法操作简单,可同时测定多种有害元素,实用性强。     

Spatially resolved ultra-trace analysis of elements combining resonance ionization with a MALDI-TOF spectrometer

A combined setup for spatially resolved mass analysis of trace amounts of elements and macromolecules is presented. Using a MALDI-TOF mass spectrometer, a laser spectroscopic setup for resonant ionization of neutral atoms has been implemented. This allows for an efficient and selective detection of trace elements by means of resonance ionization mass spectrometry (RIMS). The instrumental scheme is described, and methodological developments are presented. In a first application pure, laser desorption/ionization with TOF-MS was used to measure mass distributions of cosmic nanodiamonds. For further applications regarding the spatially resolved ultra-trace analysis of elements in solid samples, an implanted target was used to characterize both laser desorption/ionization and laser desorption/resonance ionization for the detection of trace elements within. A perspective of the setup is given and future investigations are outlined.     

Solid-phase spectrophotometric determination of trace amounts of vanadium at sub-ng/ml level with 4-(2-pyridylazo)resorcinol

Solid-phase spectrophotometry has been applied to analysis for trace amounts of vanadium. Vanadium was sorbed in a styrene-divinylbenzene-type anion-exchanger Dowex 1-X8 as a vanadium-4-(2-pyridylazo)resorcinol complex. Resin phase absorbances at 562 and 800 nm were measured directly which allowed the determination of vanadium in the range of 0.1-2.4 ng/ml with a RSD of 1.5%. The method has been applied to the determination of vanadium in different samples, namely toadstool tissue, mussel tissue, petroleum crudes and swamp water.     

Trace elements in Nigerian oil sands and extracted bitumens

The Nigerian oil sands are very extensive with an estimated in place reserves of bitumen/heavy oil of over 30 billion barrels. Instrumental Neutron Activation Analysis (INAA) has been used to determine the trace and minor elements in the raw oil sands and bitumens. About 43 trace elements in the raw oil sands and 30 in bitumen extracts were determined. The results are compared with values of Canadian bitumens and some Nigerian conventional light crude oils. In general, the Nigerian bitumens has higher hydrocarbon concentration than the Athabasca bitumen but slightly lower than in the Nigerian crude oils. The sulphur, vanadium and nickel contents of the Nigerian bitumens and crude oils are appreciably lower than those of Athabasca bitumen, thus indicating that the extraction and refining of Nigerian tar sand oil would pose less technological and environmental problems than the Athabasca syncrude.     

Aspects of proficiency testing studies of trace elements in environmental samples with a focus on laboratory performance

Four proficiency tests of environmentally significant elements in soil and water are described. The effects of sample matrix, analyte, sample preparation procedure, extraction method efficiency and instrumental technique on laboratory performance were assessed. Participants’ performance was evaluated using z scores and E _n scores. One study included dried sediment and sediment digest as test samples. By testing both dried sediment and sediment digest in the same study, differences in laboratories’ results due to the extraction method or instrumental technique were evaluated. Cadmium and nickel were the elements with the most unsatisfactory z scores for dried sediment compared to sediment digest. The second study had as test samples river water and river water fortified with biosolid. For an evaluation of the efficiency of participants’ extraction method, the results reported for the analysis of river water were compared to the results for analysis of the same river water fortified with biosolid. No consensus could be found between participants’ results for Cr and Ni in this study as the extraction method employed by them produced results that were too variable. The last two studies included saline and fresh water samples. The analysis of fresh and saline water samples with similar analyte concentrations assisted laboratories in developing their methods for trace elements in saline water. For Cr, Pb and Se, the assigned values were reference values traceable to SI, measured using isotope dilution inductively coupled plasma mass spectrometry. Saline water containing low concentrations of analytes presented difficulties to some laboratories. Arsenic and selenium were the analytes most difficult to analyse in all types of environmental samples.     

An electrochemical enrichment procedure for the determination of heavy metals by total-reflection X-ray fluorescence spectroscopy

An electrolytic separation and enrichment technique was developed for the determination of trace elements by total-reflection X-ray fluorescence spectroscopy (TXRF). The elements of interest are electrodeposited out of the sample solution onto a solid, polished disc of pure niobium which is used as sample carrier for the TXRF measurement. The electrochemical deposition leads to a high enrichment of the analytes and at the same time to a removal of the matrix. This results in substantially improved detection limits in the lower picogram per gram region. The deposited elements are directly measured by TXRF without any further sample preparation step. The homogeneous thin layer of the analytes is an ideal sample form for TXRF, because scattered radiation from the sample itself is minimized. The proposed sample preparation method is useful particularly for the analysis of heavy metals in liquid samples with for TXRF disturbing matrices, e.g. sea water.     

原油及重油的快速分析技术进展

近年来,随着我国原油加工量的不断增加,加工难度的不断增大,原油快速评价问题日益受到重视.原油评价是指在全面分析原油的物理及化学性质的基础上,对原油的可加工性能及加工过程中可能出现的问题进行综合分析的过程.目前飞速发展的计算机技术及仪器分析技术,为原油快评技术奠定了良好的基础.该文以不同分析方法进行分类,介绍了近红外光谱(NIR)、中红外光谱(IR)、核磁共振波谱(NMR)及其他分析方法在原油和重油快速分析领域的技术进展.     

Determination of some trace elements in different organs of normal rats

In our biological investigations some trace elements have been determined by instrumental radioactivation analysis in organs of normal rats. The results of trace element distribution of Cr, Zn, Br, Sb, Fe, Co, Sc, Ag and Na in liver, spleen, brain, lung, kidney and heart of normal rats are presented in the paper.     

Characterization of trace elements in high viscosity materials by total reflection X-ray spectrometry

This paper proposes the use of radiation scattered by the sample instead of the internal standard method for quantifying impurities in high viscosity materials using X-ray fluorescence with total reflection geometry. The method has been performed for checking trace elements in gels of polymers. Advantages include no sample preparation and a minimum amount of sample (10 μl). The method is also insensitive to instrumental variations, sample amount and particle size of the sample. The ratio of coherent to incoherent scattering intensities of X-ray was also investigated to estimate the content of C plus O in these polymers.