Internal Standards for Pesticide Analysis

[KMP]

Dear All,
I have already run OP and OC standards calibration. I did not use any internal standards.
Just diluted stock standards and run by GC-PFPD and GC -ECD.
Now I want to run my soil and rice samples.
I have internal standards PCB 8 and PCB 138 from Dr.Ehrenstorfer.
These PCB internal standards, can I use for my Organophosphate (OP) and Organochlorine (OC) analysis by GC/PFPD and GC/ECD?
I am confusing a lot. (eg. when I analyze nitrofuran metabolite AOZ, at that time I used internal standard AOZ )
But now PCB 8 and PCB 138 internal standards are represent as internal standards of OP and OC??)
Do I need to use internal standards?
If I want to use in my samples , I need to use in calibration standard curve also?

Please kindly suggest me.

[DSP007]

Good day

What is the precision you need. Plus-minus kilometer, if at all, "no more". Therefore, we can do without the internal standard.
Good standard - chlorobenzene for ECD and tributyl phosphate for PAD - "what the doctor ordered".

[KMP]

Dear DSP007,

Many Thanks for your reply.