Polarization null angle (PNA) method is an accurate alternative to the commonly used polarization intensity ratio method in determination of molecular orientation at interfaces with sum frequency generation vibrational spectroscopy (SFG-VS). Here, the accuracy and sensitivity of PNA method is tested on different experimental configurations. It is found that its accuracy and sensitivity are more sensitive to the incident angle of the visible beam than the IR beam, and the range of the optimal experimental configurations is identified. This development makes better understanding of the polarization measurement in SFG-VS, and should find more applications for interface studies. (c) 2005 Elsevier B.V. All rights reserved.