I haven't used Chemistry::MolecularMass previously (in fact, I wasn't aware of its existence until now); however, looking at its documentation, it would appear another (completely untested) solution would be: 

use Chemistry::MolecularMass;
my $mm = Chemistry::MolecularMass::->new();
$mm->replace_elements(H => 0);
my $no_H_mass = $mm->calc_mass($your_formula);

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-- Ken

In reply to Re^3: How to avoid an alphabet and integer next to it in a string? by kcott
in thread How to avoid an alphabet and integer next to it in a string? by piscean

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