Not sure what you mean by quartile but maybe it's 1/4 of the sorted data. If so, try this:
vec = sort(yourOriginalVector);
numElementsPerQuartile = numel(vec)/4;
stDev(1) = std(vec(1 : numElementsPerQuartile));
stDev(2) = std(vec(numElementsPerQuartile + 1 : 2 * numElementsPerQuartile));
stDev(3) = std(vec(2*numElementsPerQuartile + 1 : 3 * numElementsPerQuartile));
stDev(4) = std(vec(3*numElementsPerQuartile + 1 : end));
bar(stDev);
grid on
ylabel('Standard Deviation')
