How to calculate the fourier transform of a signal in form of a time series with given sampling interval?

I have a signal in form of a column matrix say [2 4 5.6 7.8 5 9 6.7 3 3 2 1] and the sampling interval is 5 Hz. How can I compute the amplitude spectra of this signal and plot the same from the matlab prompt? As every time i use the fft command it assumes 1 sample per second. Every example I went through on the internet had the signal in the form of a function of time ( time vector was predefined) but here I can't relate my time series as any function of time.