Sample Preparation for analysis of trace elements in nutraceuticals in compliance with USP chapter.

The global regulation for monitoring these wide range of products is not yet in place. In the USA, nutraceuticals are monitored and regulated as dietary supplements under the Dietary Supplement Health and Education Act (DSHEA, 1994). USP general chapter Elemental Contaminants in Dietary Supplements has been created to limit the amounts of elemental contaminants in finished dietary supplements on the four major elements of toxicological concern: arsenic, cadmium, mercury and lead. The permitted daily exposure limits (PDE; Table1) are derived based on UN recommendation. The latest versions of the chapters were supposed to be implemented by January 1, 2018. 

QLABPro with high-pressure eVHP vessels satisfy all the requirements demanded by USP for microwave power and temperature control. In fact, QLABPro displays and stores temperature profiles for each vessel. The eVHP vessels are capable of handling adequate amounts of sample to provide the required concentration of analytes for analysis.
Though samples can be digested using HNO3 alone, HCl is used for the stabilization of certain analytes, such as Hg, Ag, Ba, and Sb and high concentrations of Fe and Al in solution.
Considering the variations in raw materials, efforts should be made to obtain homogeneous and representative samples. Transfer samples to each vessel liner. Inside a fume hood, add 4 ml HNO3 and 2 ml HCl along the sides of the vessel walls. If sample has components which can froth, make it a point to add small aliquots of acid with little swirling to avoid sample spill over. Let vessel out gas completely or for minimum 10 min. Add an additional 4 ml HNO3 liner from the side wall such that any sample clinging to wall is washed down and brought in contact with acid. Make sure liners are cleaned for any dirt or moisture on outside surface before transferring them to the vessels outer sleeve. Seal the vessels and load them in QLABPro carousel.

Run the digestion program as below:
At the end of digestion program, let the samples cool down to 90°C while still in the system. Inside a fume hood, partly unscrew the OPGuard slowly to release the pressure. Once pressure is released, retighten the valve. Rinse the vessel cap bottom in the liner. After cooling, transfer the contents from the liner to 25 ml standard flask and dilute. Samples are then ready for analysis by the appropriate determinative method. Alternatively, samples can be diluted within the liners using the Vulcan automated reagent handling system. The Vulcan is designed to automate the initial acid addition as well.

Spike recoveries obtained in analysed samples indicate that no target elements are lost during the sample preparation process which demonstrates the microwave and Vulcan digestion method is an excellent choice for sample preparation.

QLABPro
Microwave Digestion System
USP Elemental Contaminants & Nutrients in Dietary Supplements

Notes:
This recipe is a reference starting point for sample digestion using Microwave Digestion System and may need to be optimised for specific sample.
To increase the sample handling capacity and to avoid excess absorption of NO2 in sample, at the end of step-1 of digestion samples can be cooled to 95 °C followed by release of pressure using OPGuard digestion can be performed in two stages. In first stage
Though 12 samples can be processed at a time in QLABPro system it is even capable of handling a minimum of 4 samples as well.

Recipe Name:  MDT Nutraceuticals USP

Sample Type

Nutraceuticals finished product, formulations and raw materials (Herbs, Roots, Bark, etc.)

Element of Interest

Taxological: As, Cd, Pb & Hg

Nutritional: Ca, P, Mg, Fe, Zn, Mn, Cu, I, Cr, Mo, Se & Co

Equipment

QLabPro, eVHP vessel set

Sample Quantity

0.5 gm / ml

Reagents

8 ml Nitric Acid (70%) and 2 ml Hydrochloric acid (35%)

Table 2. Digestion Recipe for Nutraceuticals using QLABPro + eVHP vessel set

Step

Type

Temp. (°C)

Ramp Time (Min)

Hold Time (Min)

1.

Time to Temp.

110°C

7:00

2:00

2.

Time to Temp.

190°C

8:00

15:00

Table 1. Permitted daily exposures (PDE) in dietary supplements according to USP chapter

Element

PDE (µg /day)

Arsenic (inorganic)

15

Cadmium

5

Lead

5

Mercury (total)

15