Determination of Total Selenium and Extractability of Selenium in Commercially-Available Dietary Supplements by Inductively Coupled Plasma - Mass Spectrometry (ICP-MS)

Figures & data

Table 1. Microwave digestion parameters.

Time [min]	Temperature 1 [°C]	Temperature 2 [°C]	P [bar]
3	85	50	15
9	145	80	45
4	200	100	45
14	200	120	45

Table 2. ICP-conditions.

Mode	Mass	He gas flow [mL min^-1]	CH4 gas flow [mL min^-1]	rpa	rpq
Std	Ge 73.9219 Se 81.9167				0.25
KED	Ge 73.9219 Se 77.9219 Se 81.9167	4			0.25
DRC	Ge 73.9291 Se 77.9219 Se 79.9165		0.6	0.0	0.45

Carrier gas: Ar: 15 mL min⁻¹. Make-up gas: Ar 1.2 mL min⁻¹.

Definitions: DRC = dynamic reaction cell, KED = kinetic energy discrimination mode, Std = standard mode without physical interference removal; rpa/rpq = Mathieu rejection parameters.

Figure 1. Selenium content determined in SELM-1 for different ICP-conditions. The ⁸⁰Se and ⁸²Se isotopes are measured in DRC (dynamic reaction cell mode), KED (kinetic energy discrimination mode, Std (standard mode). The error bars = standard deviation; certified concentration for SELM-1; red lines: confidence limits for SELM-1.

Table 3. Selenium-content determined in SELM-1 for different ICP conditions: isotopes ⁸⁰Se, ⁷⁸Se, ⁸²Se are measured in DRC (dynamic reaction cell mode), KED (kinetic energy discrimination mode), Std (standard mode), s = standard deviation; s[%] = relative standard deviation.

	^80Se DRC	^78Se DRC	^78Se KED	^82Se KED	^82Se Std
c [µg g^−1]	2080	2082	2009	1998	2023
s	95	84.0	76.9	97.0	98.1
s [%]	5	4.0	3.8	4.9	4.8
Bias [%]	1	1.1	−2.4	−3.0	−1.7
Precision [%]	3.4	3.3	3.1	3.1	3.5

Figure 2. Selenium content in microwave digests of dietary supplements determined with different ICP conditions (DRC, KED and Std) and different istotopes (⁷⁸Se ⁸⁰Se and ⁸²Se) (circles, squares and triangles); declaration = declared selenium content [μg Se g⁻¹] (bars); small bars: standard deviation of the whole procedure; numbers listed in supplementary material.

Table 4. List of ingredients of the supplements containing 153 to 394 µg g⁻¹ declared selenium-concentration [µg g⁻¹Se], the declared source of selenium, additional inorganic ingredients, which could be expected in the microwave digests.

Declaration [µg Se g^−1]	Declaration of selenium source	Inorganic ingredients listed on the label
153*	sodium selenite	iron fumarate, potassium iodide, chromium(III) chloride, sodium molybdate
219*	selenized yeast	zinc, magnesium, titanium dioxide
231	selenized yeast	–
267	sodium selenite	tricalcium phosphate, magnesium, titanium dioxide
268*	sodium selenate	titanium dioxide, magnesium
275	selenized yeast	silicium dioxide, magnesium, dicalcium phosphate
333	sodium selenite	talcum, titanium dioxide, potassium iodide, magnesium
389	sodium selenate	magnesium
394	selenomethionine	calcium phosphate

Supplements with severe effects on ⁸⁰Se DRC are highlighted with an asterisk*, “-” no additional labeled inorganic ingredients.

Figure 3. Extraction efficiency where recovery [%] = selenium in extract (⁷⁸Se KED)/total selenium; tall bars = recovery of one supplement grouped by declared selenium sources; MeSeCys = methylselenocysteine; SeMet = selenomethionine; small bars = standard deviation for the procedure.