I suspect that toolic has the right idea. Your basic code is fine; I've tried it on my system and it works for me:

#!/usr/bin/perl -w
use strict;
use Data::Dumper;
# open a filehandle
# file being read from

while(<DATA>){
    my @fields = split /,/;
    my $field1 = $fields[0];
    my $field2  = $fields[1];
    print "$field1\t$field2\n";
}
__DATA__
"-0.500, 4.502e-6"
"-0.499, 4.474e-6"
"-0.498, 4.458e-6"
"-0.497, 4.445e-6"
"-0.496, 4.433e-6"
"-0.495, 4.421e-6"
[download]

gives for output

"-0.500  4.502e-6"

"-0.499  4.474e-6"

"-0.498  4.458e-6"

"-0.497  4.445e-6"

"-0.496  4.433e-6"

"-0.495  4.421e-6"
[download]

So the best bet is that you do, as your title says, have some invisible characters hiding in there. So follow toolic's advice and you'll smoke them out.

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