use strict;
use warnings;

my @col1 = split ' ', <DATA>;
<DATA>;
my @rows = map { my @row = split; \@row } <DATA>;

my $i = 2;
for my $col (@col1) {
	print "$col\t$_->[0]\t$_->[1]\t$_->[$i]\n" for @rows;
	$i++;
}

__DATA__
               A     C     F
SampleID        Time    ObsConc ObsConc ObsConc
5        24      2.27E+06        687.02  32521.94
5        168     1.92E+06        525.02  22198.44
5        12      2.94E+06        896.39  41331.61
5        -0.5    2.23E+06        942.34  40616.49
5        8       4.03E+06        1371.32 45863.69
6        24      1.02E+06        1057.89 46341.04
6        168     3.14E+06        4987.32 42166.08