Isotope dilution-mass spectrometry interferences

The large number of tin isotopes (10) means that there is significant choice for ICP-MS analysis, however, a significant number suffer from interferences or low abundances. As a result °Sn is the most commonly employed isotope for analysis using miz 120. The use of ICP-MS detection also allows the primary method of isotope dilution mass spectrometry (IDMS) to be employed. This involves the... 

A logical approach which serves to minimise such uncertainties is the use of a number of distinctly different analytical methods for the determination of each analyte wherein none of the methods would be expected to suffer identical interferences. In this manner, any correspondence observed between the results of different methods implies that a reliable estimate of the true value for the analyte concentration in the sample has been obtained. To this end Sturgeon et al. [21] carried out the analysis of coastal seawater for the above elements using isotope dilution spark source mass spectrometry. GFA-AS, and ICP-ES following trace metal separation-preconcentration (using ion exchange and chelation-solvent extraction), and direct analysis by GFA-AS. These workers discuss analytical advantages inherent in such an approach. 

Determination of oxidized amino acids in urine is usually performed by isotope dilution gas chromatography-mass spectrometry (L9). DOPA is estimated by HPLC separation of acid protein hydrolysates with fluorescence detection (excitation 280 nm, emission at 320 nm) (A15). Other methods are based on borate-hydrochloric acid difference spectroscopy (this method suffers interference from tyrosine and tryptophan) (W2), derivatization of DOPA with nitrite and subsequent coulometric determination (W3), and fluorometric detection after derivatization with ethylenediamine (A15). 3-Hydroxylysine is quantitated by HPLC with 9-fluorenylmethyl chloroformate precolumn derivatization (M25) of amino acids obtained by gas-phase hydrolysis of proteins (F21). Other general methods to detect amino acid damage are mass spectometry methods applied to protein hydrolysates, such as tandem mass spectrometry (F6). 

Mohamed R, Hammel Y, LeBreton M, et ah. Evaluation of atmospheric pressure ionization interferences for the quantitative measurement of sulfonamides in honey using isotope dilution liquid chromatography coupled with tandem mass spectrometry techniques, J. Chromatogr. A 2007 1160 194-205. 

Chemical separations may be specific for the analyte of interest (see Chapter 3), such as liquid or gas chromatography, or scavenging (such as by precipitation) to remove the major interfering substances. Addition of carrier, as practiced in radioanalytical chemistry to assist in purifying radionuclides, usually is not appropriate for mass spectrometric analysis. Such addition undermines the isotopic ratio measurements that are often at the heart of this procedure, and also overloads the system for ion generation and peak resolution (but carrier addition is used for accelerator mass spectrometry). Addition of tracers, known as isotope dilution, is often employed for yield determination (see Section 17.2.9). Interferences are distinctly different in radiometric and MS analyses of radionuclides, and may be the deciding factor in selecting one method versus the other. 

See also Atomic Absorption Spectrometry Interferences and Background Correction. Atomic Emission Spectrometry Principles and Instrumentation Interferences and Background Correction Flame Photometry Inductively Coupled Plasma Microwave-Induced Plasma. Atomic Mass Spectrometry Inductively Coupled Plasma Laser Microprobe. Countercurrent Chromatography Solvent Extraction with a Helical Column. Derivatization of Analytes. Elemental Speciation Overview Practicalities and Instrumentation. Extraction Solvent Extraction Principles Solvent Extraction Multistage Countercurrent Distribution Microwave-Assisted Solvent Extraction Pressurized Fluid Extraction Solid-Phase Extraction Solid-Phase Microextraction. Gas Chromatography Ovenriew. Isotope Dilution Analysis. Liquid Chromatography Ovenriew. 

The application of isotope dilution analysis to ICP-MS-based hyphenated techniques, for example HPLC-ICP-MS, can be divided into two diflerent modes the spedes-unspecific mode and species-specific mode. The two modes are illustrated in Figure 4.6. Because IDA-ICP-MS relies on the measurement of isotope ratios by mass spectrometry, the traditional interference to the accuracy and precision of IDA should all be considered and some biases need further correction in this case, such as spectral interferences, dead time of detector, mass discrimination, and statistic and stability of ion counting. 

Park, C. J., Cho, K. H., Suh, J. K., and Han, M. S. (2000) Determination of cadmium in sediment reference materials by isotope dilution by inductively coupled plasma mass spectrometry with correction of tin isobaric interference using mass bias equations. J. Anal. At. Spectrom., 15, 567-70. 

---