1.4 Icp-aes analysis of nanoparticles  (Page 3/6)

Some people have also used the ICP-AES technique to determine the size of nanoparticles. The signal that is detected is determined by the amount of the material that is present in solution. If very dilute solutions of nanoparticles are being analyzed, particles are being analyzed one at a time, i.e., there will be one nanoparticle per droplet in the nebulizer. The signal intensity would then differ according to the size of the particle. In this way the ICP-AES technique could be used to determine the concentration of the particles in the solution as well as the size of the particles.

Calculations for icp concentrations

In order to performe ICP-AES stock solutions must be prepared in dilute nitric acid solutions. To do this a concentrated solution should be diluted with nanopure water to prepare 7 wt% nitric acid solutions. If the concentrated solution is 69.8 wt% (check the assay amount that is written on the side of the bottle) then the amount to dilute the solution will be as such:

• The density (d) of HNO ₃ is 1.42 g/mL
• Molecular weight (M _W ) of HNO ₃ is 63.01

Concentrated percentage 69.8 wt% from assay. First you must determine the molarity of the concentrated solution, [link] . For the present assay amount, the figure will be calculated from [link] and [link] .

This is the initial concentration C _I . To determine the molarity of the 7% solution will be determined by [link] , i.e., [link] is the final concentration C _F .

We use these figures in [link] to determine the amount of dilution required to dilute the concentrated nitric acid to make it a 7% solution.

Now as we are talking about solutions the amount of mass will be measured in mL, and the concentration will be measured as a molarity, [link] and [link] where M _I and M _F have been calculated above. In addition, the amount of dilute solution will be dependent on the user and how much is required by the user to complete the ICP analysis, for the sake of argument let’s say that we need 10 mL of dilute solution, this is mL _F , i.e., [link] and [link] .

This means that 10.03 mL of the concentrated nitric acid (69.8%) should be diluted up to a total of 100 mL with nanopure water.

Now that you have your stock solution with the correct percentage then you can use this solution to prepare your solutions of varying concentration. Let’s take the example that the stock solution that you purchase from a supplier has a concentration of 100 ppm of analyte, which is equivalent to 1 μg/mL.

In order to make your calibration curve more accurate it is important to be aware of two issues. Firstly, as with all straight-line graphs, the more points that are used then the better the statistics is that the line is correct. But, secondly, the more measurements that are used means that more room for error is introduced to the system, to avoid these errors from occurring one should be very vigilant and skilled in the use of pipetting and diluting of solutions. Especially when working with very low concentration solutions a small drop of material making the dilution above or below the exactly required amount can alter the concentration and hence affect the calibration deleteriously. The premise upon which the calculation is done is based on [link] , whereby C refers to concentration in ppm, and mL refers to mass in mL.