Quantification of trace elements in human serum fractions by liquid chromatography and inductively coupled plasma mass spectrometry

On‐line coupling of LC and ICP‐MS has been used for fractionation and detection of species of Cu, Fe, I, Se and Zn in human serum. It has been shown that anion exchange chromatography provided better separation capability (both intra‐ and inter‐element) than size‐exclusion chromatography. The mobile phases for ion exchange chromatography consisted of Tris–HNO₃ buffer and ammonium salt (nitrate, acetate or formate). Formate was found to be the best mobile phase counter ion, enabling good chromatographic separation, and is acceptable for mass spectrometry too. The quantitative evaluation of element concentrations adhering to individual fractions was performed by the peak area normalization method. The repeatability of results ranged from 3 to 15% (depending on the element concentration level) and represented the main part of the result uncertainty. The accuracy of Cu and Zn fraction determinations was confirmed by comparison with the isotope dilution technique. Copyright © 2006 John Wiley & Sons, Ltd.     

Quantification of copper and zinc species fractions in legume seeds extracts by SEC/ICP-MS: validation and uncertainty estimation

Fractions of Cu and Zn species in legume samples (common white bean, pea, chick pea and lentil seeds and defatted soybean flour) were analysed by on-line hyphenation of size exclusion chromatography and inductively coupled plasma-mass spectrometry. Samples were extracted by 0.02 mol l⁻¹ Tris–HCl buffer solution, pH 7.5. The extraction efficiency lay in the region 60–90 and 60–80% for Cu and Zn, respectively. Quantification of elements in the individual chromatographic fractions was carried out by isotope dilution (ID) and external calibration (EC) techniques. For ID analysis the chromatographic effluent was mixed with the flow of ⁶⁵Cu and ⁶⁸Zn isotope enriched solution and the isotope ratio values ⁶³Cu/⁶⁵Cu and (⁶⁴Zn+⁶⁶Zn)/⁶⁸Zn were measured. In the case of EC technique calibration solutions of elements were injected to the flow of mobile phase by the second injector. Prior entering detector the effluent was mixed with the flow of internal standard solution (In, 50 μg l⁻¹). Both methods have similar precision, however the behaviour of both studied elements was not the same. The chromatographic analysis itself was the main source of variability in the case of Cu. For Zn species analysis, the extraction process and the manipulation with the extract, played the significant role too. It was probably caused by lower stability of the present zinc chelates. The total amounts of Zn found in all chromatographic fractions represented 85–95% of Zn in sampled extract whereas those of Cu approached 100%. In case of small peaks the results of ID and EC were not the same. The EC results were lower then ID results. The great deal of results uncertainty accounts for the precision.     

Application of infrared spectroscopy to the assessment of authenticity of tea

Diffusion reflectance fourier transform infrared spectroscopy in the mid-IR region was used to assess the authenticity of tea varieties. The differences between the spectra of 12 different tea varieties (seven black, two green, three semifermented grades) were sufficient to allow their discrimination by the soft independent modelling of class analogy classification method or linear discriminant analysis, despite a significant heterogeneity of the samples as revealed by variance analysis.     

掺杂ZnSe/BeTe Ⅱ型量子阱结构中带电激子的磁场效应

报道了n型掺杂ZnSe/BeTe/ZnSe Ⅱ型量子阱(type-Ⅱ QW)在极低温 (5—10 K)条件下的各种光学性质. 磁场中(Farada配置)ZnSe层的反射光谱展示了一个典型的负的带电激子(X^-)的跃迁特征. 对于空间间接光致发光(spacially indirect PL)光谱,它的主发光峰显示了一个反玻尔兹曼分布的非对称性,并且在磁场中(Voigt配置)它的峰值能量随磁场的增加而降低. 这些实验结果显示了该掺杂样品的空间间接PL是来自Ⅱ型QW结构所特有的带电激子的跃迁. 关键词： 光致发光 二维电子气 带电激子 Ⅱ型量子阱     

Multivariate control charts: Control charts for calibration curves

The proposed multivariate control charts for p-dimensional vectors are an extension of the conventional control charts for one variable. The controlling quantity is the Mahalanobis distance of vector x from the central value vector x..: D=(x-x..)^T-1.(x-x..), where is the covariance matrix estimate. The quantity D has Hotelling's T² distribution. A PC program was set up for the automatic graphical construction of such charts. The program draws the sequential chart of the quantity D as well as the position of the vectors x in the p dimensional control ellipsoid in the axes of the principal components. In this way a control chart was developed for the calibration curve in the photometric determination of Fe³⁺ with sulfosalicylic acid. Vector x was formed by absorbance values for the calibration curve points (p=5). The chart can assist in detection of even small disturbances of the calibration curve.     

Diagnosis of tularemia using piezoelectric biosensor technology

A piezoelectric immunosensor for indirect diagnosis of tularemic infection in mouse serum was developed. Francisella tularensis LVS antigen was covalently immobilized on the sensing surface using cystamine and glutaraldehyde for activation and modification of the gold electrode. The normal mouse serum (NMS) and serum prepared from mice immunized by Escherichia coli were used as negative controls providing signal of 28 Hz during a 5 min interaction. The tularemic infectious (immunized) mouse serum (IMS) as sample resulted in the signal above 75 Hz (fifth day after infection). The control sensor containing bovine serum albumin as sensing element provided a signal below 5 Hz with NMS as well IMS. The effects of dilution degree and purification of sera were tested. To improve resolution of the method, sample pretreatment steps such as precipitation with ammonium sulphate and immunoglobulin extraction on CBind™ L and MEP HyperCel columns were tested. R.S.D. of measurements was 2.3% for NMS and 2.4% for IMS, respectively. The developed method allows to indicate the presence of anti-tularemic antibodies shortly (1-3 days) after infection, one analysis is completed in 10 min.     

Computer simulation of the uncertainty of analytical results

Uncertainty is an important quality parameter of any analytical result. Estimating the uncertainty of analytical procedures can be rather difficult in many instances. Computer simulation based on multiple repetition of calculation of the resulting quantity while varying slightly the input parameters is an alternative option. The input parameters for the various computation runs are composed of two terms: the constant mean value and the error, obtained as the product of the standard uncertainty of the parameter in question and a random number with the normal distribution N(0.1). This approach can also serve to optimize measuring procedures, as demonstrated on an example of the determination of lead in biological materials by isotope dilution mass spectrometry. The accuracy of the optimized method was tested by analysis of some CRMs, the robustness of the method was examined, and the detection limit (10 ng/g Pb) and repeatability (4 ng/g Pb) were determined. Received: 30 September 1998 / Revised: 3 December 1998 / Accepted: 8 December 1998