gian planets composition

Hi all,

I was wondering about the chemical composition of giant planets (in
our solar system, as far as I know you can just detect exoplanet by rv
or photometric survey but no clue about their chemistry).

I know that in first approximation you can consider them to have kind
of solar like compositon. But I was wondering if the recent missions -
Galileo on Jupiter and Cassini on Saturn- have provided any specific
measurement. I have been reading an -old- review about the chemical
composition measured by Voyager, and the value of helium was quite low
(although with rather large error bars...)

http://adsabs.harvard.edu/abs/1983prhe.work..139G

Thanks!
S.