I would expect very low concentrations of gold in beverages. So I suggest an ICP-MS method to determine gold in your samples. Depending on the properties of the fluid (e.g. fruit particles,...) maybe a digestion step prior to analysis is necessary.

Thank you for the answers. The biggest problem should be the high orange juice concentration... (11%)

Digestion by acid is necessary for juice before you analyzed the samples by ICP-MS. You can try to add 1 ml juice (if there is too much solid in the juice, you have to filter or crash the samples first) into 4 ml concentrated HNO3 in a 15ml tube, Kept the tube with samples and acid in 95 degree or higher, you may find the solution clear. Clear solution is OK for ICP-MS detection ( please adjust the acid concentration before analysis). BTW, I do not think you can find significant gold in juice unless the plants grew in high gold soil.

I (partly) agree with Zhen Chen digestion is the key for ICP-MS analysis. but filtration of your samples prior to analysis may influence your results since gold could be in nanoparticular form and be connected to any other particular matter in your juice (and thus beeing filtered) you might also add 2 mL hydrogen peroxide to the 4mL of nitric acid and increase the temperatur to about 200 °C at 20 bar. It usually increases the digestion efficiency of organic matter

I forgot to mention that I expect a limit of detection of ~1 ng gold in 1 L juice by using the method described above.

Which of these methods can detect the gold, even it´s surrounded by a layer, that hides the gold inside? AAS? ICP-MS?

Why can they detect it? (please tell me, what these analysis methods differ from others)

Hi Use ICP=MS or CytoViva hyperspectral

The ICP-MS will quantify the amont of gold in the sample. The CytoViva hhyperspectral has a very detection to determine the gold in the sample, but need to form a hyperspectral library of the gold first

the method you choose depends on the amount of gold in the sample. ICP-MS is the most sensitive one one of the methods mentioned before. But the most important step is sample preparation and although I have not seen you sample I think you MUST use a digestion step prior to analysis.

BTW: You have an exellent analytical chemistry departmernt at TUM. Maybe one member of the Schuster group is willing to do the analysis for you. I guess they would do it by AAS. http://www.fganalytik.ch.tum.de/

Thanks Markus's comment, I generally agree with you. For the gold is "surrounded" by a layer, do Danial mean gold nanopartilces? If so , you may need some new developed ICP-MS technique to do that. A recent article on analytical chemistry may help, please find it on http://pubs.acs.org/doi/pdf/10.1021/ac201952t.

If the samples are gold nanoparticles, actually as Zheng said, you will need ICP-MS. I have used Cytoviva hyperspectral and it works very well. try and see as well.

For Clarence, I have no experience on Cytoviva hyperspectral, but according to the introduce of Cytoviva http://cytoviva.com, it seems that the system works quite well on nanoparticle.

Info about ICP-MS: http://www.cee.vt.edu/ewr/environmental/teach/smprimer/icpms/icpms.htm

Info about Cytoviva hyperspectral: http://www.cytoviva.com/product_hyperspectral_imaging.htm