Jörg Bettmer

Size characterisation of Au nanoparticles by ICP-MS coupling techniques

In modern nanotechnology the properties of nanoparticles (NPs) in different application fields is mainly dependent on their size and their size distribution. This paper aims to develop a reliable method for the size characterisation of Au NPs. Basing on the combination of two different separation techniques (liquid chromatography and gel electrophoresis), coupled on-line to inductively coupled plasma-mass spectrometry (ICP-MS), we study the separation of Au NP standards. Separations by liquid chromatography show size dependent retention behaviour with good reproducibility (RSD < 1%). The results are compared with complementary methods like dynamic light scattering (DLS) and transmission electron microscopy (TEM) and show good agreement. Furthermore, the on-line coupling of gel electrophoresis and ICP-MS results in a distinct peak tailing for the analysis of these NPs, which is found to be related to the chemical structure of the NP’s surface. It can be demonstrated that NPs with a covalently bound surface do behave in a different way.

Determination of phytic acid and its degradation products by ion-pair chromatography (IPC) coupled to inductively coupled plasma-sector field-mass spectrometry (ICP-SF-MS)

We developed a method for the determination of phytic acid (IP6) and its degradation products (IP1-IP5) by ion-pair chromatography coupled to a double focussing inductively coupled plasma-sector field-mass spectrometer (ICP-SF-MS). For the detection of the phosphorus species a mass resolution (m/Δm) of 4000 was needed in order to separate the 31P+ signal from the interfering clusterions. The separation of the six phosphorus species was enabled by a gradient elution using tetrabutylammonium hydroxide (TBA) as ion-pair reagent. Calibration data were reported and a detection limit of 230 ng g−1 for IP6 could be obtained. The method was firstly proved for a hydrolyzate of commercially available phytic acid and then applied to various real samples like nuts, cereals, legumes, beer etc. In all samples different pattern of inositol phosphates could be detected. The compositional comparison of inositol phosphates in a malt and a beer sample showed that during the brewing process IP6 is completely degraded to IP2 and IP3.

DNA quantification approach by GE-ICP-SFMS and complementary total phosphorus determination by ICP-SFMS

Quantification of DNA is still a great challenge for scientists in many fields. Here, we present the on-line coupling of gel electrophoresis (GE) and inductively coupled plasma-sector field mass spectrometry (ICP-SFMS) for quantitative purposes. GE conditions are chosen for optimised separations depending on the target analyte composition in terms of DNA chain length. In particular, agarose concentrations are varied in the range 0.6–2.2%, which corresponds to a separation range of DNA from 100 base pairs (bp) to genomic DNA (approximately 3 Mbp). Separated DNA compounds are directly transported at a flow rate of 100 μL min−1 to a Micromist nebuliser which is followed by ICP-SFMS with 31P detection at a mass resolution of 4000. For their quantification different approaches are tested using external calibration by PO43− standards as well as by a commercially available QuantLadder standard. Precisions lower than 3% can be achieved in any analysis: however, the indicative values for DNA concentrations given by the manufacturers cannot be found in all the samples. As to our best knowledge no certified quantitative DNA reference material exists, unfortunately we could not prove the accuracy of the developed method. Despite this, we then applied the GE-ICP-SFMS coupling to the analysis of genomic DNA in order to confirm its practicability for the separation and detection of these large biomolecules.

Development of a new method for the separation of vanadium species and chloride interference removal using modified silica capillaries-DIN-ICP-MS

Abstract A new on-line method for the separation of vanadium (IV) and vanadium (V) as well as for the removal of ClO+ mass spectral interference on vanadium determination by quadrupole-ICP-MS has been developed. The sample introduction system consists of a modified fused silica capillary coupled to a direct injection nebuliser (DIN), between the solvent delivery system and the ICP. Fused silica capillaries were treated with different anion and cation exchanger reagents and were tested for the retention of Cl− and the separation of vanadium ions at μg l−1 levels. A suitable strong anion exchanger functional group (3-aminopropyltrimethoxy silane) was selected. Chlorine anions were retained in this anionic capillary and the separation between V(IV) and V(V) was possible in the pH range 2–4. The selections of instrumental ICP-MS conditions for the minimisation of the ClO+ interference were carefully considered. Factors affecting the chromatographic separation such as sample pH, sample flow rate, effect of methanol in the mobile phase and length of the capillary for the separation were optimised. The proposed methodology provides a simple and rapid method for vanadium speciation. A relative detection limit of 12 l−1 (i.e. absolute detection limits of 120 pg) for V(IV) based on peak height measurements was obtained. The relative standard deviation for V(IV) was 2.4% for a 10 μl injection (n=6).

Determination of phosphorylation degrees in caseins by on-line gel electrophoresis coupled to ICP-SFMS

The determination of the phosphorylation degree of proteins is essential in many biochemical fields. Besides mass spectrometric techniques elucidating the protein structure, ICP-MS has entered this research area as it provides excellent quantification capabilities. In this work the separation of the proteins has been carried out by gel electrophoresis on-line coupled to an ICP equipped with a double-focusing sector field-MS (ELEMENT 2). Based on the simultaneous detection of 32S+ and 31P+, this work presents an alternative approach to determining the phosphorylation degree of caseins. For the example of α- and β-casein the results obtained were in excellent agreement with the expected values, and therefore the described method might be very useful and serve as an alternative in the analysis of phosphorylated proteins.

On-line Chloride Interference Removal for Arsenic Determination in Waste Water and Urine by ICP-MS Using a Modified Capillary

The determination of arsenic in environmental samples like waste waters from industrial effluents and in biological samples like urine is very important due to the toxic nature of some of its species at moderate levels of exposure. The objective of this study was to evaluate the capability of modified anionic capillaries to remove chloride for ICP-MS determination of arsenic, which causes spectral interference due to formation of 40 Ar 35 Cl + . Also high chloride content gives non-spectral interferences. The results indicate that arsenic at a concentration higher than 1 µg L m 1 in a matrix with a chloride content up to 600 mg L m 1 can be accurately determined using a 3-aminopropyltrimethoxysilane (APTMS) modified capillary connected to a microconcentric nebuliser (MCN). The interference level of chloride is considerably reduced due to its retention in the capillary. The method has been successfully applied and validated for waste water and by recovery tests for urine (diluted 1 : 15) samples.