Determination of Mercury in Nutraceutical Samples Using a Direct Mercury Analyzer
With the expansion of the global nutraceutical market, the spotlight on the analysis of its raw materials is ever increasing. Testing of nutraceutical products for heavy metals like lead, arsenic, cadmium and mercury has gained utmost importance. Extremely low levels of these heavy metals like mercury, in nutraceuticals make its analysis challenging.
With the expansion of the global nutraceutical market, the spotlight on the analysis of its raw materials is ever increasing. Testing of nutraceutical products for heavy metals like lead, arsenic, cadmium and mercury has gained utmost importance. Extremely low levels of these heavy metals like mercury, in nutraceuticals make its analysis challenging. Analytical chemists have to rely on techniques like CVAA and ICP-MS which involve a time consuming and a labor intensive sample preparation step. Direct mercury analysis, as described by EPA 7473, is an alternative method to traditional techniques that requires no sample prep and with results in as little as ~6min per sample. This makes it significantly faster with comparable or better recoveries than CVAA and ICP-MS.
The nutraceutical industry covers a broad spectrum of products including botanical extracts, vitamins, minerals and dietary supplements. A rise in the level of health consciousness among consumers has lead to an exponential growth of the nutraceutical market. However, the industry has come under scrutiny to ensure control over toxic heavy metals such as mercury. Given the volatile nature of mercury and the industry’s need to test it regularly at low concentrations, sample preparation can often become complicated and confusing.
Traditional techniques used to analyze mercury in nutraceuticals involve a sample digestion step after which they are analyzed on CVAA or ICP-MS. Although effective, sample preparation requires man power, equipment, handling and disposing large amounts of acid and takes hours for completion. Alternatively, the US EPA developed a method 7473 for rapid determination of mercury in solids and aqueous samples without sample prep. This method uses an integrated sequence of thermal decomposition followed by catalytic conversion, amalgamation and atomic absorption spectrophotometry.
INSTRUMENTATION
A direct mercury analyzer (DMA-80 Tri-Cell) from Milestone Inc. was used for this experiment. The instrument was configured to sequentially process up to 40 samples placed on the auto-sampler. The autosampler automatically aligned and accommodated quartz (1500uL) and nickel (500mg) sample boats. All the components of the DMA-80 instrument were contained in a closed system to ensure that the samples were not exposed to outside interferences. Oxygen is used as a carrier gas at 65psi pressure and a flow rate of 7L/hour.
CALIBRATION
The DMA can be calibrated using aqueous standards or Standard Reference Materials (SRM). The DMA-80 used for this experiment had a tri-cell spectrophotometer and covered a dynamic range of 0.0015-1200ng Hg. Each cell was calibrated using different volumes of 1ppm and 0.1ppm stock solutions, prepared from an NIST traceable 1000ppm stock solution (VHG Labs).
EXPERIMENT AND RESULTS
To test the efficiency of the DMA-80, three commonly available nutraceutical samples – Valerian root, Ginkgo Biloba and Glucosamine chondroitin were spiked by a solution having a mean mercury concentration of ~10.2ppb and were run in the instrument to test for spike recoveries. Also, Gingko SRM 3248 was analyzed to test if its mercury concentration falls in the NIST certified range.v
| SAMPLE | CONC (PPB) | EXPECTED CONC (PPB) | RECOVERY % |
| Valerian Root | 4.7447 | -- | -- |
| Gingko Biloba | 2.0537 | -- | -- |
| Glucosamine Chondroitin | 1.5817 | -- | -- |
| Spike | 10.2750 | ||
| Valerian Root Spiked | 15.5589 | 15.0197 | 103.59% |
| Gingko Biloba Spiked | 12.8810 | 12.3287 | 104.48% |
| Glucosamine Chondroitin Spiked | 12.4578 | 11.8567 | 105.07% |
| Gingko SRM 3248 | 0.2609 | 0.271+/-0.034 | 96.27% |
The concentrations mentioned in (Table 1) are mean values obtained after running duplicates for each sample.
The two concentrations obtained for the Ginkgo SRM – 3248 were 0.2544 ppb and 0.2673 ppb. These concentrations were not only in the certified range of mercury concentration but also had an RSD of 0.05% which represented the accuracy and reproducibility of the DMA-80 at low mercury concentrations. The recovery data mentioned in the table above suggests efficient spike recoveries. A nutraceutical testing laboratory is required to analyze different matrices accurately and quickly while keeping operating costs under control. The DMA-80 is an excellent tool as it yields results in ~6min/sample and proves to be proficient, matrix-independent and cost effective while completely eliminating the challenges of sample preparation posed by conventional mercury analysis techniques.