Application Notes: General

Semiquantitative elemental analysis by ICP-MS is a powerful tool for quick screening of unknown samples for a wide range of elements.

One problem frequently encountered in LC–MS is the appearance of mass peaks, which appear totally unrelated to the samples run - "ghost" mass peaks. It is impossible to differentiate whether these signals come from an unknown component in the sample co-eluting with a known peak, or from an impurity in the mobile phase or from some residual contamination "bleeding" from the column.

Preliminary studies of biodiesel samples by a high speed LC–MS system using electrospray ionization and a patented cone-wash feature demonstrate that LC–MS reduces the analysis time to 20 minutes and reveals information about higher molecular weight compounds in biodiesel while still detecting many low molecular weight chemicals, including FAMEs, at high sensitivity.

The use of 30 mm UPLC columns coupled with Oasis SPE in µElution format was investigated to increase the speed of quantitative bioanalytical methods while maintaining sensitivity and resolution of closely related analytes.

The analysis of crude oil by means of different atmospheric pressure ionization (API) techniques is described. Crude oil is analysed without any separation prior to API-Fourier transform mass spectrometry. The use of a quadrupole/hexapole device to selectively enhance a certain mass range is demonstrated. Automated generation of molecular formulas from accurate mass measurements enables rapid compound identification.

Solid-phase extraction (SPE) has revolutionized sample preparation. Variations on the technique offer enhanced recovery, greater speciation and reduced solvent and sample consumption over other techniques. Micro-extraction packed sorbent (MEPS) is the miniaturization of conventional SPE from millilitre to microlitre bed volumes that allows SPE to be used with very small samples. The manipulation of the small volumes is achieved with a precision gas tight syringe. With a typical void volume of 7 μL, the volume of solvent eluted from MEPS is compatible with GC and LC inlets making it ideal for integration into an automated sampling system for on-line SPE.

Mixed mode chromatography combines aspects of ion exchange chromatography and conventional reversed-phase (RP) chromatography. The combination of both hydrophobic and ion-exchange properties allows for independent control of retention for ionizable and neutral molecules.

UltraPerformance LC (UPLC) has been widely accepted by chromatographers because of improvements over HPLC in the sensitivity, resolution and speed of separations. As scientists begin to use this technology for impurity and metabolite profiling, they will need to transfer the methods to preparative LC to isolate and purify their compounds for further research. Therefore, it is necessary to systematically transfer UPLC assays not only to HPLC, but, more importantly, to preparative chromatography. In this application, we provide information on how to scale a UPLC impurity/degradant separation to a preparative LC separation.

The exploration of myxobacterial metabolite profiles by LC–MS screening for the presence of new natural products is described. Extracts from fermentations of Myxococcus strains are analysed by UPLC-coupled ESI-TOF mass spectrometry and the obtained data are processed using principal component analysis (PCA). The generation of molecular formulae from accurate mass measurements facilitates rapid compound identification.

Brian De Borba and Jeffrey S. Rohrer, Dionex Corporation

Xiaodong Liu and Christopher Pohl, Dionex Corporation

Eric S. Grumbach, Diane M. Diehl and Jeffrey R. Mazzeo, Waters Corporation

Accurate mass measurements are a key element of chemical characterization. However, the accepted mass accuracy tolerance of 3–5 ppm can still leave significant ambiguity in the proposed chemical formula. Consequently a further input from other analytical techniques such as NMR or MS/MS, along with some judgment based on the synthetic history is often required to arrive at a confident formula assignment.

Column lifetime is a more and more important issue when developing an analytical method for HPLC. Besides sample treatment, column cleaning and storage, operational parameters of the analytical method will have an influence on column lifetime. This question may not always be addressed early enough in the methods development process.

Polybrominated diphenyl ethers (PBDEs) are among the most important and widely used flame retardants. Recent legislation banned certain PBDE congeners.? EU directive 2003/11/EC prohibits the use of Penta-BDE and Octa-BDE for the member states of the European community.? Therefore, analysis of PBDEs have received increased interest as a result of their known toxicity.

On 13 February 2003 the European Union published the new regulation on electric and electronic waste, (WEEE, Waste Electrical and Electronic Equipment) as well as the restriction of the use of certain hazardous substances in electric and electronic equipment (RoHS). Thus both regulations became effective, and in January 2005 they were transferred into national law. According to RoHS, lead, mercury, cadmium, chromium (VI), polybrominated biphenyls (PBB) and polybrominated diphenylethers (PBDE) are forbidden from July 2006. Shimadzu, one of the leading manufacturers of analytical instrumentation offers the complete hardware and software for the secure identification of hazardous substances as well the know-how and competence.

Shimadzu app note - May

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