Development of an ICP-HRIDMS method for accurate determination of traces of silicon in biological and clinical samples

An inductively coupled plasma-high resolution isotope dilution mass spectrometric (ICP-HRIDMS) method in combination with a microwave-assisted decomposition technique has been developed for the determination of traces of silicon in biological and clinical samples. A 30Si-enriched spike solution was used for the isotope dilution step. Decomposition of the samples was achieved by use either of HNO3 or a mixture of HNO3 and HF. By application of both methods of digestion to the same sample it was possible to differentiate between a poorly soluble silicate fraction and an HNO3-soluble silicon species. Traces of silicon were determined in different reference materials, which are not certified for this element, and in other biological and clinical samples. A concentration range of 1-600 microgram g(-1) was covered by the different samples. For homogeneous samples relative standard deviations of 2-4% were obtained. The detection limit was strongly affected by the blank. In this connection purification of water, used in the analytical procedure, was especially critical. The blank contribution of the ICP-MS instrument could be minimized by applying a nebulizer and a spray chamber made of PFA, a sapphire injection tube, and a silicon nitride torch. Under these conditions detection limits of 0.15 microgram g(-1) and 0.2 microgram g(-1) were obtained for the HNO3 and HNO3-HF digestion methods, respectively, when a sample weight of 0.5 g was used. With regard to expected silicon content this enables determination in almost all biological and clinical samples. The ICP-HRIDMS results were compared with those recently obtained in an interlaboratory study. This isotope-dilution method is an potential option for certification of silicon in reference materials, a method for which is still required.     

A direct solid sampling electrothermal atomic absorption spectrometry method for the determination of silicon in biological materials

A solid sampling electrothermal atomic absorption spectrometry method for direct determination of trace silicon in biological materials was developed and applied to analysis of pork liver, bovine liver SRM 1577b and pure cellulose. The organic matrix was destroyed and expelled from the furnace in the pyrolysis stage involving a step-wise increasing the temperature from 160 °C to 1200 °C. The mixed Pd/Mg(NO₃)₂ modifier has proved to be the optimum one with respect to the achievement of maximum sensitivity, elimination of the effect of the remaining inorganic substances and the possibility of using calibration curves measured with aqueous standard solutions for quantification. For the maximum applicable sample amount of 6 mg, the limit of detection was found to be 30 ng g^− 1. The results were compared with those obtained by different spectrometric methods involving sample digestion, by electrothermal atomic absorption spectrometry using slurry sampling, by wavelength dispersive X-ray fluorescence spectrometry and by radiochemical neutron activation analysis. The method seems to be a promising one for analysis of biological materials containing no significant fraction of silicon in form of not naturally occurring volatile organosilicon compounds. The still incessant serious limitations and uncertainties in the determination of trace silicon in solid biological materials are discussed.     

Possibilities of low-level determination of silicon in biological materials by activation analysis

The capabilities of neutron and photon activation analysis (NAA and PAA, respectively) for low-level determination of silicon in biological materials have been examined. Sensitivities of a variety of modes of NAA and PAA with radiochemical separation have been evaluated. Results are presented for silicon in reference materials CSRM 12-2-03 Lucerne, Bowen's Kale, NIST SRM-1571 Orchard Leaves, and NIST SRM-1515 Apple Leaves. The results were obtained by employing the 29Si(n,p)29Al reaction with fast reactor neutrons and the radiochemical procedure developed for aluminium separation. Possibilities of further improvement of the silicon determination limit down to the microg g(-1) level by employing NAA and PAA with radiochemical separation are outlined.     

Possibilities of low-level determination of silicon in biological materials by activation analysis

The capabilities of neutron and photon activation analysis (NAA and PAA, respectively) for low-level determination of silicon in biological materials have been examined. Sensitivities of a variety of modes of NAA and PAA with radiochemical separation have been evaluated. Results are presented for silicon in reference materials CSRM 12–2-03 Lucerne, Bowen’s Kale, NIST SRM-1571 Orchard Leaves, and NIST SRM-1515 Apple Leaves. The results were obtained by employing the ²⁹Si(n,p)²⁹Al reaction with fast reactor neutrons and the radiochemical procedure developed for aluminium separation. Possibilities of further improvement of the silicon determination limit down to the μg g^–1 level by employing NAA and PAA with radiochemical separation are outlined.     

Lead preconcentration onto C-18 minicolumn in continuous flow and its determination in biological and vegetable samples by flame atomic absorption spectrometry

A procedure for the preconcentration and determination of lead in vegetable and biological samples was developed in the continuous mode coupled to a flame atomic absorption spectrometer. Lead is quantitatively preconcentrated in acetic buffer as its diethyldithiocarbamate chelate onto a C-18 minicolumn, placed in the loop of a proportional injector, eluted by a stream of methyl isobutyl ketone and introduced directly into the nebuliser. A detection limit of 3 microg 1(-1) is obtained using a time-based technique for 2 min preconcentration and an RSD of 3.8% was readily achieved for three measurements of 25 microg Pb 1(-1). The sample throughput is 24 h(-1). Using preconcentration times of 10 min an enrichment factor of 189 can be obtained. The continuous flow system was used for some reference sample analysis and the obtained results reveal that the methodology can be easily applied for vegetable and biological sample analysis.     

聚环氧乙烷凝聚重量法结合ICP–AES法测定玻璃中的二氧化硅

建立聚环氧乙烷凝聚重量法结合电感耦合等离子体发射光谱法(ICP–AES)法测定玻璃中二氧化硅的分析方法。玻璃试样经1 000℃高温下无水碳酸钠熔融,以盐酸浸出后蒸成湿盐状,再用聚环氧乙烷凝聚,过滤并将沉淀灼烧,然后用氢氟酸处理,其前后的质量差即为沉淀的二氧化硅量,滤液中的二氧化硅用ICP–AES法测定,两者相加得试样中二氧化硅的总含量。在选定的条件下,用ICP–AES法测定二氧化硅的线性范围为0.20~50μg/m L,线性相关系数为0.999 5,检出限为0.20μg/m L。测定结果的相对标准偏差为0.45%(n=6),方法的回收率在98.6%~101.9%之间。该方法具有较高的准确度和良好的精密度,测定速度快,可用于玻璃中二氧化硅含量的测定。     

Disposable pipette extraction for gas chromatographic determination of codeine, morphine, and 6-monoacetylmorphine in vitreous humor

The availability of a sensitive and rapid analytical method for the determination of opiates, and other substances of forensic interest, in a variety of biological specimens is of utmost importance to forensic laboratories. Solid-phase extraction is very popular in the pre-treatment of forensic samples. Nevertheless, a new approach, disposable pipette extraction (DPX), is gaining increasing interest in sample preparation. DPX has already been applied to the analysis of drugs of abuse in common biological matrices, such as urine and blood, but has not yet been evaluated on alternative biological samples, such as vitreous humor. The objective of this study was to evaluate the applicability of DPX on the analysis of opiates in vitreous humor. The currently developed method is fast, reliable, and easy to perform. The sensitivity, precision, and accuracy are satisfactory. Recoveries obtained are within the range of 72-91%, whereas the sample volume of vitreous humor required is only 100 μL.     

Grazing-emission X-ray fluorescence spectrometry; principles and applications

In grazing-emission X-ray fluorescence spectrometry (GEXRF), the sample is irradiated at approximately normal incidence, and only that part of the fluorescence radiation is detected that is emitted at grazing angles. This configuration allows the use of wavelength-dispersive detection. This type of detection has the advantages of substantially better energy resolution at longer wavelengths (light elements, L and M lines of heavier elements) and a much larger dynamic range than the energy-dispersive detectors currently used in grazing X-ray techniques. Typical examples are presented of applications that are made possible by this new technique.     

Determination of Impurity Silicon in Anticancer Drug (Ge-132) by Electrothermally Atomised Atomic Absorption Spectrometry with Optical Temperature Control Accessory

The present paper describes the ashing and atomization processes in silicon analysis by electrothermally atomised atomic absorption spectrometry(EAAAS) with an uncoat-ed graphite tube, a pyrolytically coated graphite tube and a tungsten-coated graphitetube. The sensitivity and linear range of three graphite tubes were compared. By using optical temperature control accessory, the signals are enhanced by a factor of 2 and the germanium interferences in the determination of silicon are eliminated. The effects of time constant and carrier gas flow-rate on the determination of silicon were also tested. The sample can be directly analyzed in its aqueous solution without any pretreatment. The measurements of samples containing 0. 2 μg/mL and 0. 4 μg/mL silicon were run ten times and the variation coefficient is 4. 9% and 2.6%, respectively. The recovery tests for carboxyethyl germanium sesquioxide(Ge-132) synthesized and imported were performed, and the recoveries are 97. 0% and 110%, respectively. Keywords     

Microdetermination of silicon in blood, serum, urine, and milk using furnace atomic absorption spectrometry

A simple, direct microanalytical method for quantitative determination of silicon in human whole blood, serum, urine, and milk by furnace atomic absorption technique has been developed. The method employs standard additions and combines the inherent specificity and simplicity of atomic absorption analysis with the greatly increased sensitivity possible with a heated graphite tube atomizer for the determination of silicon in microliter samples. The sensitivity of the method is 1.3 ng. The method is suitable for the direct analysis of silicon with no sample preparation other than dilution with deionized water, thereby minimizing contamination due to sample preparation. The relative standard deviation for 10 μl of blood (1:1), serum (1:1), urine (1:7), and milk (1:1) was 3.45% or less.     

Determination of trace impurities at the p.p.b. level in fused silica by spark-source mass spectrometry

A sample dissolution-concentration technique for the determination of trace elements in fused silica by spark-source mass spectrometry (s.s.m.s.) is described. The fused silica is dissolved by ultra-pure hydrofluoric acid, and most of the silicon tetrafluoride formed is then removed at 80–100° C, leaving behind the impurities in the solution as fluorides. After addition of ultrahigh-purity graphite and internal standards (Tl and Rb), the mixture is dried to give a sample suitable for pressing into electrodes. The method not only concentrates the trace impurities but also reduces the interferences originating from silicon oxide and carbide species in the mass spectra and thus allows the determination of a larger number of elements at p.p.b. levels. More than 30 trace impurities in 6 fused silica boules and J.T. Baker's Ultrex silicon dioxide are determined and compared with data obtained by other methods.     

X射线荧光光谱法快速测定FeSiB非晶合金薄带中硅、硼、铁

提出了以自制的标准样品,采用单点法绘制校准曲线,利用X射线荧光光谱仪测定FeSiB非晶薄带样品中硅、硼和铁的含量。对于4个FeSiB非晶合金薄带样品中硅、硼和铁进行了10次测定,其分析结果的相对标准偏差分别为0.4%~0.5%、1.3%~4.2%和0.2%~0.4%。方法的分析结果与火花源原子发射光谱法、化学重量法和电感耦合等离子体原子发射光谱(ICP-AES)法的测定值吻合较好。方法快速、简便,薄带样品无需制样,适用于FeSiB非晶合金薄带的快速成分分析。     

Determination of oxygen and carbon impurities in polycrystalline silicon by IR spectrometry

The possibility of using infrared spectrometry for the determination of the total oxygen and carbon impurity in polycrystalline silicon of the natural isotope composition and that enriched with the ²⁸Si isotope was studied for samples synthesized by different methods. The results of determining these impurities by the optical method are compared to those obtained by independent methods of analysis. The conditions of IR spectrometric analysis of the silicon synthesized by deposition from the gas phase are determined. It is shown that, for IR spectrometry, the upper boundaries of the analytical range of oxygen and carbon in polycrystalline silicon are 1 × 10¹⁸ and 2 × 10¹⁸ cm^?3; and the limits of their detection are 8 × 10¹⁵ and 5 × 10¹⁵ cm^?3 at a sample thickness of 0.5 and 0.2 cm, respectively.     

X射线荧光光谱法测定萤石中的氟,钙及二氧化硅

提出艇偏硼酸锂和四硼酸锂混合熔剂熔融制样，以Ｘ－射线荧光光谱法定量测定萤石中ＣａＦ２、总钙和二氧化硅。经实际试样和标准试样检测，本法可用实际试样分析，在ＣａＦ２含量为７７－９８％时，其最大误差为０．６０％。     

硅铁中硅、铝、磷的联合测定

采用一次称样、熔样,盐酸酸化后蒸至湿盐状,聚乙二醇聚合后过滤,形成残渣和滤下液。残渣用于以比色法测定硅含量,滤下液则用来分别测定铝(分光光度法)和磷(比色法)。该样品处理方式简化了分析步骤,降低了分析成本,硅、铝、磷的加标回收率在98.9%~103%之间,测定结果的相对标准偏差为0.18%~4.52%(n=6),标准样品的测定值与证书值一致。该方法可满足日常分析要求,特别适用于中小型实验室对硅铁样品质量的监控。     

Determination of chlorine distribution in silicon dioxide by neutron activation

A neutron activation method for the determination of chlorine distribution in silicon dioxide on the surface of Si wafers has been developed. After irradiation of the sample with a standard, successive layers are removed from the oxide surface by chemical etching and the chlorine content in the solutions obtained is determined gamma-spectrometrically. Using a Ge(Li) detector, a lower limit of determination of 1.0·10⁻⁷ g was obtained. This limit can be improved by using a NaI(Tl) detector. The error of chlorine determination is discussed.     

Cyclic injection photometric determination of silicon in oil products

A photometric procedure is developed for determining silicon in oil products involving the preliminary conversion of organic and inorganic silicon into silicate ions followed by their determination by the formation of reduced silicomolybdic heteropolyacid and cyclic injection analysis. The detection limit for silicon is 1 μg/g for a sample weight of 1 g.     

Investigation of element distribution and homogeneity of TXRF samples using SR-micro-XRF to validate the use of an internal standard and improve external standard quantification

Total reflection X-ray fluorescence analysis (TXRF) offers a nondestructive qualitative and quantitative analysis of trace elements. Due to its outstanding properties TXRF is widely used in the semiconductor industry for the analysis of silicon wafer surfaces and in the chemical analysis of liquid samples. Two problems occur in quantification: the large statistical uncertainty in wafer surface analysis and the validity of using an internal standard in chemical analysis. In general TXRF is known to allow for linear calibration. For small sample amounts (low nanogram (ng) region) the thin film approximation is valid neglecting absorption effects of the exciting and the detected radiation. For higher total amounts of samples deviations from the linear relation between fluorescence intensity and sample amount can be observed. This could be caused by the sample itself because inhomogeneities and different sample shapes can lead to differences of the emitted fluorescence intensities and high statistical errors. The aim of the study was to investigate the elemental distribution inside a sample. Single and multi-element samples were investigated with Synchrotron-radiation-induced micro X-ray Fluorescence Analysis (SR-μ-XRF) and with an optical microscope. It could be proven that the microscope images are all based on the investigated elements. This allows the determination of the sample shape and potential inhomogeneities using only light microscope images. For the multi-element samples, it was furthermore shown that the elemental distribution inside the samples is homogeneous. This justifies internal standard quantification.     

Use of alkaline or enzymatic sample pretreatment prior to characterization of gold nanoparticles in animal tissue by single-particle ICPMS

Inductively coupled plasma mass spectrometry in single-particle mode (spICPMS) is a promising method for the detection of metal-containing nanoparticles (NPs) and the quantification of their size and number concentration. Whereas existing studies mainly focus on NPs suspended in aqueous matrices, not much is known about the applicability of spICPMS for determination of NPs in complex matrices such as biological tissues. In the present study, alkaline and enzymatic treatments were applied to solubilize spleen samples from rats, which had been administered 60-nm gold nanoparticles (AuNPs) intravenously. The results showed that similar size distributions of AuNPs were obtained independent of the sample preparation method used. Furthermore, the quantitative results for AuNP mass concentration obtained with spICPMS following alkaline sample pretreatment coincided with results for total gold concentration obtained by conventional ICPMS analysis of acid-digested tissue. The recovery of AuNPs from enzymatically digested tissue, however, was approximately four times lower. Spiking experiments of blank spleen samples with AuNPs showed that the lower recovery was caused by an inferior transport efficiency of AuNPs in the presence of enzymatically digested tissue residues.     

Quantification in grazing-emission X-ray fluorescence spectrometry

In grazing-emission X-ray fluorescence (GEXRF) spectrometry wavelength-dispersive detection can be applied. Much softer radiation and hence lighter elements than in total-reflection X-ray (TXRF) spectrometry can thus be detected. We used simulations to investigate methods of quantification of GEXRF results involving soft characteristic radiation. From these studies, it is concluded that for ultra-thin layers, e.g. the sub-monolayer amounts encountered in semiconductor contamination analysis, calibration plots are linear. For thicker layers, quantification should be performed very carefully because of deviations from linearity due to absorption of radiation and to oscillations in the calibration curve. These oscillations are caused by interference of fluorescence radiation emitted directly towards the detector and radiation reflected at the sample–substrate interface. Suggestions for a judicious choice of measurement conditions are made and the benefits of internal standardisation are discussed.