Interferences in ICP

Several authors [386,387] have discussed the spectroscopic and nonspectroscopic (matrix) interferences in ICP-MS. ICP-MS is more susceptible to nonspectroscopic matrix interferences than ICP-AES [388-390]. Matrix interferences are perceptible by suppression and (sometimes) enhancement of the analyte signal. This enhanced susceptibility has to be related to the use of the mass spectrometer as a detection system. In fact, since both techniques use the same (or comparable) sample introduction systems (nebulisers, spray chambers, etc.) and argon plasmas (torches, generators, etc.), it is reasonable to assume that, as far as these parts are concerned, interferences are comparable. The most severe limitation of ICP-MS consists of polyatomic... 

Table 6.3. Spectral interferences in ICP-MS of the five most abundant cadmium isotopes relevant for the cadmium determination in Mo-Zr alloys additional Cd isotopes 106Cd 1.25%, 108Cd 0.89%, 116Cd 7.49% ...

Discuss in detail the origins and effects of interferences in ICP atomic emission and ICP mass spectrometry, and describe how they may be minimized or eliminated in practice. Explain why some of these interferences are common to both methods. Illustrate your answer with suitable examples where appropriate. 

Fig. 3. Example ofthe constitution of isobaric interferences in ICP-MS. Shown is the situation with the low-resolution ICP-MS instrument for the detection of bromine.

Anderson, T.A. and Parsons, M.L., ICP emission spectra III the spectra for the group IIIA elements and spectral interferences due to group IIA and IIIA elements, Appl. Spectrosc., 38, 625,1984 Parsons, M.L., Forster, A., and Anderson, D., An Atlas of Spectral Interferences in ICP Spectroscopy, Plenum Press, New York, 1980. 

D. R. Bandura, V. I. Baranov, S. D. Tanner, Reaction chemistry and collisional processes in multiple devices for resolving isobaric interferences in ICP-MS, Fresenius J. Anal. Chem., 370 (2001), 454D470. 

There are troublesome spectral interferences, spectral line overlapping in ICP-OES, and polyatomic interferences in ICP-MS. 

Table 2 Typical isobaric interferences in ICP-MS elemental analysis...

Knapp, G., Maichin, B., Baumgartner, U. Interferences in ICP-OES by organic residue after microwave-assisted sample digestion. At. Spectrosc. 19, 220-222 (1998)... 

ICP emission spectrometry is renowned for presenting few interferences. Undoubtedly the most serious potential interference in ICP emission spectroscopy is spectral superposition. 

Analyte Atomization and Ionization By the time the analyte atoms and ions reach the observation point in the plasma, they have spent about 2 ms in the plasma at temperatures ranging from 6000 to 8000 K. These times and temperatures are two to three times greater than those attainable in the hottest combustion flames (acetylene/nitrous oxide). As a consequence, desolvation and vaporization are essentially complete, and the atomization efficiency is quite high. Therefore, there are fewer chemical interferences in ICPs than in combustion flames. Surprisingly, ionization interference effects are small or nonexistent because the large concentration of electrons from the ionization of argon maintains a more-or-less constant electron concentration in the plasma. 

Interferences in ICP-MS are of two classes spectroscopic interferences and matrix effects. Spectroscopic interferences occur when an ionic species in the plasma has... 

High-resolution mass analyzers, such as double-focusing analyzers, can reduce or eliminate many spectral interferences in ICP-MS. 

For additional discussion of interferences in ICP-MS. see K. E. Jarvis, A. L. Gray, and R. S. Houk, Handbook of Inductively Coupled Plasma Mass Spectrometry, Ch. 5. New York Blackie. 1992 G. Horlick and Y. Shao. in Inductively Coupled Plasmas in Analytical Atomic Spectrometry, 2nd ed., A Montaser and D. W. Golightly, Eds., pp. 571 -596 New York VCH-Wiley. 1992. 

Fig. 92. Spectral interferences in ICP-OES as recorded in wavelength scans obtained by displacement of the entrance slit. 3 kW Ar-ISh ICP, Baird 1000 1 m spec-trometer, sample 0.5534 mg of airborne dust sample HBW 2 per mL (-), 19 mg/mL of HBO3, 19 mg/mL of HF, 4.9 N HNO3...

Tab. 16. Minimally required resolving power (R) in order to avoid spectral interferences in ICP-MS (extracted from Ref. [499]).

G. (1988) Matrix interferences in ICP MS some effects of skimmer orifice... 

Possible problems of interferences in ICP-MS were highlighted as well as the need to carry out a preconcentration step. Spectral interferences may occur for copper, leading to high results caused by spectral overlap from unidentified polyatomic species at mass 65. The existence of this species in natural samples was stressed in the certification of an estuarine water reference material by a mass spectrum obtained by high resolution ICPMS, although its exact composition could not be determined. 

An atlas of spectral interferences in ICP spectroscopy. Plenum Press, New York. 

---