Most chromatographers may not realize it but if fittings and tubing are not properly seated and a perfect connection is accomplished, a small but important dead volume can occur that does not get swept.
This extra volume can cause band broadening or ghost peaks or may decrease the sensitivity of your run by increasing baseline noise.
To attain a proper seat for good results, the tip of the tubing (tubing must be properly cut) that the fitting and ferrule are holding must make a perfect alignment with the Inlet of the receiving port.
Click HERE for HPLC fittings ordering information and pictures.