FOR loop standard deviation of multiple images

I want to construct a FOR loop to calculate the standard deviations of multiple images all stored within one 4x5 matrix. Then I would like the standard deviations to be stored within the vector B. I keep getting an error message and the code I have right now is:

if true
for E = 1 : 5
  for D = 1 : 4
      B(1i) = std2(ca{D,E});
  end
end
  % code
end