Spectroscopy

[bucket]

I have a few questions regarding the calculations for analysing AAS data.
Consider this example in the book.

A batch of oysters is tested for lead.
A 1.50g portion was heated in 10ml nitric acid.
The mixture was filtered and sprayed into the AAS flame.
The absorbance was found to be roughly 3.5, which correlated to the concentration of 9ppm.

Answer:
(why?)

was present in the 1.50g of oyster:
Concentration (why do we divide this?)
                   
60ppm is in the 1.50g sample (i'm completely lost)

[doboman]

the concentration is ppm...either \mu g, g/L, \mu/g
since we have the sample in ml(10 ml) we use microgram/ml

we get 9\mu/mL...so in 10ml, we have 90\mu

in the 10ml, we have 1.5g lead, therfore we can say, 90\mu/1.5g
it tells us to find it in \mu/g
hence we divide by 1.5g

[Mao]

right:

to answer your first question:

ppm, or parts per million, literally means parts per million.
In the sense of an aqueous solution, since one litre of water is one kilogram, and one millionth of a kilogram is a milligram, 1 ppm = 1 mg/L, which is also 1 microgram per millilitre (divide top and bottom by 1000)
in the sense of mass/mass, it is 1mg/kg, or 1 microgram/gram

This 9ppm is the concentration of lead, however, this is per millilitre. Since we had 10 mL of solution, it is appropriate to calculate all the lead, hence 9ppm x 10 = 90 microgram/mL

Since this 90 microgram is present in 1.5g of oyster "extract", to find how many micrograms are in 1g of oyster, 90/1.5 = 60 microgram/gram.

to our convenience, microgram just happens to be one millionth of a gram, hence it can be said to be 60 ppm w/w (weight per weight).