Isotope dilution mass spectrometry niacin

Isotope Dilution Mass Spectrometry for Niacin in Food... 

The method described here makes use of stable isotope dilution mass spectrometry (IDMS) for quantitative analysis of niacin. Isotopically labelled versions of both nicotinic acid and niacinamide are commercially available at a reasonable cost. The use of an isotopically labelled internal standard has distinct advantages in quantitative analysis, as it can correct for analyte losses and makes possible high levels of accuracy and precision (Fassett and Paulson 1989). Sample digestion and clean-up is based on a previously published LC-UV method (LaCroix et al. 1999, 2002 LaCroix and Wolf 2001). This chapter expands on a previous report of LC-IDMS analysis of niacin (Goldschmidt and Wolf 2007), with material from that report used with permission of the publisher. 

Table 19.1 Ions monitored for determination of niacin by isotope dilution mass spectrometry using positive electrospray ionization. Both natural and labelled nicotinic acid are protonated in positive ion electrospray ionization, giving quasi-molecular ions at mass-to-charge ratios (m/z) of 124 and 128, respectively, which can be monitored directly in selected ion recording (SIR) experiments and selected as the parent ions in multiple reaction monitoring (MRM) experiments. In MRM experiments protonated nicotinic acid can be induced to produce daughter ions at several other m/z values, but the given transitions are the ones with the highest signal intensity.

Table 19.3 Results of niacin determinations for milk samples. Niacin determinations by liquid chromatography-isotope dilution mass spectrometry (LC-IDMS) are compared to expected values for four milk samples. Expected niacin levels for milk are roughly 1 ppm, according to the USDA Nutrient Database for Standard Reference (US Department of Agriculture 2010) and results obtained for two commercial milk samples (Brands F and G) are a little under 1 ppm. The result for sample NFY0409F6 is about 30% lower, but is consistent with results obtained for other milk samples from the same source. In addition, the niaein level for NFY0409F6 was estimated by a standard additions experiment, the result from which is in agreement with the estimate from the normal LC-IDMS procedure. The level obtained for the reference material (RM) RM 8435 whole milk powder, reported on a dry mass basis, is in agreement with the reference value. Data are from Goldschmidt and Wolf (2007), with permission from the publisher.

This chapter is about the determination of niacin in foods using isotope dilution mass spectrometry (IDMS) and liquid chromatography (LC). Niacin, also called vitamin B3, refers to two vitamer forms nicotinic acid and niacinamide. 

Goldschmidt, R.J., and Wolf, W.R., 2007. Determination of niacin in food materials by liquid chromatography using isotope dilution mass spectrometry. Journal of AO AC International. 90 1084-1089. 

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