use strict; use warnings;

my $letters = <DATA>;
my @letters = $letters =~ /\w+/g;

my %out;
while(<DATA>) {
  next if /SampleID/;
  chomp;
  my @recs = split /\s+/;
  my $ctr = 2;
  for my $letter (@letters) {
    $out{$letter} .= "$letter\t".(join "\t", @recs[0,1,$ctr++])."\n";
  }
}

for my $letter (@letters) {
  print $out{$letter};
}

__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