Shimadzu Europa
Analysis of heavy elements in cannabis and medicinal plants by USN-ICP-OES

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  • Published: Jan 18, 2016
  • Source: Shimadzu Europa GmbH
  • Categories: Atomic
thumbnail image: <font size=3>Shimadzu Europa</font><br />Analysis of heavy elements in cannabis and medicinal plants by USN-ICP-OES

Authors: Dan Davis, Keith Long, Johan Leinders
Shimadzu Europa GmbH, Albert-Hahn-Str. 6-10, 47269 Duisburg
www.shimadzu.eu, shimadzu@shimadzu.eu

Introduction

It is a fact that metals and heavy metals are present in our daily environment. They are present in the soil, in water, in plant life, in animals and in us humans.

Plants have the tendency to concentrate metals by absorbing them from the soil in which they are grown. Some metals and elements are beneficial, even essential for life. Other metals are highly toxic and have a negative effect even in the lowest of levels. Because of this toxicity, a correct quantification of these elements is required and their limits are based upon daily consumption.

In this advertorial we will investigate the preparation and the analysis of heavy metals in cannabis and medicinal plants using an ICP-OES in combination with an ultrasonic nebulizer (USN-ICP-OES).

Shimadzu’s ICPE-9800 series enables use of the ultrasonic nebulizer in combination with the patented “mini-Torch”. This combination results in an extremely low-cost alternative to the widely used ICP-MS technology.

Throughout the measurements, spike and recovery tests were performed at the target values to ensure accuracy and sensitivity of the technique.

Figure 1. Shimadzu’s ICPE-9800 Series ICP-OES.

Table 1. Metal analysis target based on daily intake of 5 g.

Sample preparation

For the sample preparation, 0,5 g of plant material (in our case cannabis flower) was added to a close vessel digester and 2 ml of nitric acid, 2 ml of 30% H2O2 and 4 ml of H2O2 were added. The sample was ramped to 900 W over a period of 15 minutes and kept at this power for an additional 20 minutes. After that the sample was allowed to cool to room temperature and 0.5 ml HCl acid was added along with Yttrium as an Internal Standard as well as a mercury stabilizer. The solution was brought to 25 ml total volume with demineralized H2O.

Figure 2. Digestion / preparation procedure.

Analytical conditions

Measurements were conducted using the calibration curve method with an Internal Standard. The main measurement parameters are shown in Table 2.

Table 2. Measurement conditions.

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The standard solutions were prepared by diluting commercially available standard solutions for atomic absorption measurements. 100 ml of the stock calibration solution was prepared at As 320 ppb, Pb 192 ppb, Hg 64 ppb and Cd 128 ppb, all stabilized with 1.0% nitric acid.

Add 50 ml of the stock solution to a 100 ml volumetric flask and add 0.5 ml of HCl, 100 µl of 100 ppm Yttrium internal standard and the mercury stabilizer. Bring the total volume to 100 ml. This is Calibration Solution 4. Add 25 ml of the stock solution to a 100 ml volumetric flask, add HCl, Yttrium internal standard and mercury stabilizer and bring to 100 ml. This is calibration solution 3. Add 12.5ml of the stock solution to a 100 ml volumetric flask and add HCl, Yttrium internal standard and mercury stabilizer. Bring to a volume of 100 ml. This is calibration solution 2. Calibration solution 1 is blank with HCl, Yttrium internal standard and mercury stabilizer.

Table 3. Calibration solutions.

Results and Conclusions

Figures 3, 4, 5 and 6 show the calibration curves generated for each of the analytes. All calibration curves achieved a good linear correlation of 0.9999 or better, proving that the instrument is capable of measuring the specified target range shown in Tables 1 and 3.

                 Figure 3. As calibration curve.                                                                            Figure 4. Cd calibration curve.

                 Figure 5. Hg calibration curve.                                                                              Figure 6. Pb calibration curve.

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Figures 7 and 8 show the signals of each analyte of the unknown samples and spikes for As, Cd, Hg and Pb. There is a good signal distinction at each of the target analysis levels indicated in Table 1.
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Figure 7. Peak profile As & Cd.

Figure 8. Peak profile Hg & Pb.

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The results in Table 4 show that all of the analytes were within the target analysis and the sample spikes achieved recoveries of 100% (+/- 10%) of their theoretical values. These recoveries show that the system is capable of achieving good sensitivity and accuracy at the desired elemental concentration levels. The results also show that USN-ICP-OES is a suitable alternative to much costlier techniques like ICP-MS.
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Table 4. Results of samples and spikes.

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Additionally the ICPE-9800 series incorporates a vertically mounted “Mini-torch” that achieves the same sensitivity as conventional torches but consumes only 50% of the amount of argon gas leading to substantial cost savings over the lifetime of the instrument. The vertical orientation of the torch allows it to handle highly dissolved solids without fouling, thereby extending the time between maintenance operations and making for a highly sensitive, robust ICP-OES system for analyzing of heavy metals in cannabis samples.

About the ICPE-9800 series

Analytical service- and quality control laboratories will benefit from the new ICPE-9800 series of simultaneous ICP optical emission spectrometers Shimadzu has released. The systems combine higher throughput with reduced operating costs and feature easy-to-use software, a sophisticated design and the Eco mode which brings savings of 50 percent or more in power and argon gas consumption, independent of sample matrix, whether aqueous or organic samples are aspirated. The vacuum optical system does not require any purge gas, thereby eliminating gas consumption when plasma is switched off.

ICP optical emission spectrometers are used in a variety of fields involving environmental samples, drinking water, foods, pharmaceuticals and petrochemical materials. All-wavelengths acquisition allows users to add elements and wavelengths post-analysis without time-consuming reanalysis of samples.

The ICPE-9800 series consists of the ICPE-9810 which provides axial view plasma observation in a direction coaxial to the plasma, and the ICPE- 9820 which in addition to axial view provides radial view plasma observation in the perpendicular direction. This dual view capability allows measurements to switch automatically between high-sensitivity axial view and high-accuracy radial view, enabling analysis of elements across a broad concentration range with a single method.

Literature

SSI Application Note SSI-ICP-002 [PDF file]: Analysis of the "Big Four" Heavy metals in Cannabis using USN-ICP-OES.
Dan Davis, Keith Long, Justin Masone, Patricia Firmin; Shimadzu Scientific Instruments.

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