[lucy007]

the concentration of a plant neurotoxin was determined using a chromatographic
procedure. A sample of plant material (5.0g) was taken, digested in 100.0 ml of 5%
nitric acid and then rendered alkaline through the addition of sodium hydroxide (25.0
mL, 5M). The resulting solution was then added to 20.0 mL of dichloromethane and
the organic layer separated. The solvent was removed by rotary evaporation to yield a
white powder (250 mg). A 50 mg aliquot of this was then taken and dissolved in 50.0
mL of acetonitrile. The presence of the neurotoxin was identified and the analysis
revealed a concentration of 0.15mg/mL when compared against a standard calibration
set.

iv been asked to express the concentration of the neurotoxin as %w/w in the original plant sample. plz help

[english]

w/w, w/v, as well as v/v are quantitative expressions in parts per hundred, a.k.a. per cent, or percent.

w/w % is (grams of analyte)/(100 grams of solution) x 100

The expression does not necessarily have to be in grams, but the units must be the same in the top and bottom of the ratio.

[sassman]

0.15mg/mL x 50mL x (250mg/50mg) / (5g x 1000mg/g) = the answer in mg neurotoxin/mg plant material