Methods for the determination of total carbon (TC), total nitrogen (TN), and total phosphorus (TP) in cattail (Typha domingensis) using cold and thermal neutron prompt gamma activation analysis (CNPGAA and TNPGAA) have been developed in the CNPGAA and
TNPGAA facilities at the National Institute of Standards and Technology (NIST), and evaluated through the analysis of Standard
Reference Materials (SRMs) in previous studies. There are major issues that impact the sensitivities of C, N and P using CNPGAA
and TNPGAA including the effects of hydrogen content in samples, sample thickness and Compton scattering. However, interference
from chlorine (Cl) in cattails has a major impact on the detection of P. This paper compares the effects of hydrogen content,
sample thickness and Compton scattering on the sensitivities of C, N, and P between CNPGAA and TNPGAA and provides a resolution
to the Cl interference on P in cattail.