Hi piscean.

I don't know much about chemistry, but I think I found a library that will help you.

Chemistry::File::Formula - Molecular formula reader/formatter

http://search.cpan.org/~itub/Chemistry-Mol-0.37/File/Formula.pm

I plugged the library into a basic script and it seems to parse the elements out in the way you need.

From here you should be able to parse each key/value in the formula hash and base your calcuation on the elements you need.

I hope this helps.

use strict;
use warnings;
use Data::Dumper;
use Chemistry::File::Formula;

while(<DATA>)
{
    chomp;
    my %formula = Chemistry::File::Formula->parse_formula("$_");
    
    print "-" x 16, "\n";

    print Dumper \%formula;

    print "-" x 16, "\n";
}


__DATA__
C6H5OH
C6H9
Hg
[download]

Output:

C:\monks\calc_mass>perl calc_molecularmass.pl
----------------
$VAR1 = {
          'H' => 6,
          'O' => 1,
          'C' => 6
        };
----------------
----------------
$VAR1 = {
          'H' => 9,
          'C' => 6
        };
----------------
----------------
$VAR1 = {
          'Hg' => 1
        };
----------------

C:\monks\calc_mass>
[download]

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