Hans Vanhoe

The use of internal standards in icp ms

Careful study of the matrix effect in ICP-MS showed that, in all cases studied, the magnitude of the signal suppression or enhancement depends in a regular way on the mass number. Hence, accurate correction for non-spectral interferences is only possible using an internal standard with mass number close to that of the analyte element(s). It is also shown that using an internal standard with mass number close to that of the analyte improves the precision. For both cases, the ionization energy of the internal standard seems to be of no or only secondary importance. To obtain optimal precision and accuracy, the internal standard should be selected as close in mass number as possible to that of the analyte element(s). When a number of elements over a considerable mass range are to be determined, several internal standards have to be used.

Suppression of analyte signal in inductively-coupled plasma/mass spectrometry and the use of an internal standard

Abstract The signal suppression of 9Be, 27Al, 64Zn, 85Rb, 115In and 208Pb in the presence of increasing amounts of sodium chloride is studied. The suppression does not depend significantly on the analyte element considered. The use of 115In as internal standard thus allows correction for the matrix effect. It is shown that the suppressive effect decreases in the order CsCl>NaCl>NH4Cl. The use of the internal standard also significantly improves the precision. The signal suppression is probably due largely to an increasing number of extracted ions resulting in a more pronounced space-charge effect.

Investigation of HfO(+) interference in the determination of platinum in a catalytic converter (cordierite) by inductively coupled plasma mass spectrometry.

The determination of Pt in cordierite is subject to strong interference by spectral overlap from HfO(+) ions with all Pt isotopes. Two mathematical correction methods based on the HfO(+)Hf(+) ratio and a method for the chemical separation of Hf based on adsorption chromatography and isotope dilution were investigated to correct for this interference. Flow infection was used to prevent clogging of the cone orifice. To enhance the sensitivity and thus lower the detection limit, thermospray nebulization was used for sample introduction and the method was compared with pneumatic nebulization. In addition, the memory effects were evaulated for both systems. Analysis of artificial solutions (1 ng Pt ml(-1)) yielded results within 3% of the true value. Th Pt content (ca. 50 ng g(-1)) of a cordierite sample, previously exposed to exhaust gases, could be determined with precisions of about 10-25% and the results agreed with earlier determinations by other workers.

Study of the intensity of M+, M2+ and MO+ signals in ICP-MS as a function of instrumental parameters

In addition to peaks from singly charged ions (M+), signals from oxide (MO+), hydroxide (MOH+) and doubly charged (M2+) ions, which may lead to spectral overlap interferences, are observed in ICP-MS spectra. Using a VG PlasmaQuad ratios of MO+/M+, MOH+/M+ and M2+/M+ were determined for a number of elements, covering a wide range of atomic masses, first and second ionisation energies and chemical properties. The temporal stability of the MO+/M+ and M2+/M+ ratios was investigated. The correlation between the ratios of MO+/M+ and M2+/M+ with the M-O bond strength and the difference between the second and the first ionisation energy respectively is discussed. The influence of several instrumental parameters, associated with sample introduction and plasma operation, on the M+, M2+ and MO+ signals and on the MO+/M+ and M2+/M+ ratios is studied. Simple qualitative explanations are given in order to explain some of the observed results. No quantitative results are given for the MO+/M+ and M2+/M+ ratios as the experiments pointed out that they are influenced to a large extent by several instrumental parameters.

Inductively coupled plasma mass spectrometry of biological samples. Invited lecture

The determination of trace and ultra-trace amounts of elements in biological samples by inductively coupled plasma mass spectrometry is discussed. Most attention is paid to human serum, but other materials are also considered. Matrix effects and their correction using internal standards are discussed in detail, together with the determination of Zn, B, Mo and Sn in serum. An overview is also given of the results obtained on a ‘second generation’ serum reference material.

Determination of strontium in human serum by inductively coupled plasma mass spectrometry and neutron activation analysis: a comparison.

Strontium has been determined in a human serum reference material by ICP-MS and by NAA. By ICP-MS, results for (88)Sr and (86)Sr in both 10- and 5-fold diluted serum were in good agreement. For (88)Sr the precision was better than 3% and the detection limit was 0.05 mug/l. under the conditions used. The results were 25.5 mug/l. in the liquid serum or 0.281 mug/g in the lyophilized reference material. In the NAA the (87m)Sr produced was radiochemically separated by extraction with oxine in chloroform. The precision was about 10% and the detection limit 0.02-0.05 mug/g.

Bismuth in human serum : reference interval and concentrations after intake of a therapeutic dose of colloidal bismuth subcitrate

A sensitive method for the determination of the bismuth concentration in human serum is described. Analyses were carried out by inductively coupled plasma-mass spectrometry (ICP-MS), after a simple dilution of the samples with nitric acid. The detection limit of the applied method is 0.007 microgram/l whereas relative standard deviations varied from 5.7 to 13.6%. Determination of reference values in human serum of healthy adults gave a range from < 0.007 to 0.067 microgram/l (19 persons). Bismuth concentrations in serum were also measured before, during and after the intake of therapeutic doses of colloidal bismuth subcitrate (CBS). About 1.5-2 h after the intake of one tablet of CBS, the bismuth concentration in serum was found to have increased 51-1483 times (two apparently healthy volunteers and six hospitalized patients), showing that the serum bismuth concentrations can increase by several orders of magnitude during the intake of CBS. During the intake of four tablets of CBS per day by two apparently healthy volunteers, bismuth concentrations in serum after an overnight fast were found to be, respectively, 5.56 and 8.1 micrograms/l on day 15 and 4.28 and 13.6 micrograms/l on day 29. After stopping the therapy, the concentration of bismuth in serum slowly returned towards normal over a period of months.

Determination of lithium in biological samples by inductively coupled plasma mass spectrometry

Abstract Lithium was determined in human serum by inductively coupled plasma mass spectrometry. Sample preparation was kept to the minimum: serum samples were diluted and beryllium was added as internal standard. Special attention was given to the choice of the internal standard and to the occurrence of memory effects. To test the accuracy of the method several biological reference materials were analysed, namely a “Second-Generation” Biological Reference Material (Freeze-Dried Human Serum) (University of Ghent), Human Serum SRM 909, Whole Egg Powder SRM 1845 and Mixed Human Diet SRM 1548 (National Institute of Standards and Technology). The results were compared with those obtained by other techniques. For the “second-generation” reference freeze-dried human serum a mean lithium concentration of 15.10 ng g −1 with a standard deviation of 0.54 ng g −1 dry weight was found. Analyses on serum samples from healthy individuals yielded lithium concentrations ranging from 0.22 to 0.97 μg l −1 .

Evaluation of a flow injection system combined with an inductively coupled plasma mass spectrometer with thermospray nebulization for the determination of trace levels of platinum

Abstract In this paper the coupling of a flow injection system to an inductively coupled plasma mass spectrometer using thermospray nebulization for the determination of platinum is evaluated. The results are compared with pneumatic nebulization. The flow injection system provides the possibility of on-line sample dilution and on-line standardization. A comparative study was made between on-line isotope dilution, on-line standard additions and external calibration emphasizing accuracy, precision and flexibility of the method. Several parameters of thermospray and flow injection were evaluated. Sensitivity, background and detection limits were studied as well as the peak integration method to be used with the flow injection system. The detection limits, using flow injection (200 μl loop) and partial integration of the peak, were in the range of 25 ng/l (5 pg absolute) and 8 ng/l (2 pg absolute) for pneumatic and thermospray nebulization, respectively. The optimized procedure was used for the analysis of Pt in corn leaves, mouse liver and a Ca 3 (PO 4 ) 2 matrix.

Determination of trace elements in a human serum reference material by inductively coupled plasma mass spectrometry

A method was developed for the determination of Fe, Co, Cu, Zn, Rb, Mo and Cs in human serum by ICP-MS. Sample preparation was kept as limited as possible: Serum samples were diluted with nitric acid and indium was added as internal standard. The results for Fe, Co, Cu, and Zn were corrected for interferences from polyatomic ions using a suitable blank solution. No interferences occur for the considered isotopes of Rb, Mo, and Cs. A “second-generation human serum reference material” was analyzed, in order to test the accuracy and precision of the analytical procedure. The results obtained are in good agreement with the certified values.