The ionic composition of interstitial and intravascular fluids is the same. Proteins, however, are kept with the vascular compartment, at least to a degree, by the vascular wall, which is a semi-permeable membrane. The concentration of proteins is much higher in the plasma sector than in the interstitial sector.
Detection of marijuana using swab drug test can vary from person to person taking into account the different conditions like general health, different fluid intake, metabolism, etc.
First, you need to know that marijuana can be found in the mouth swab tests within 24 hours of the consumption. If you had the drug before 24 hours of your mouth swab drug test, you are likely to pass the test. If the duration is 48 hours, then you definitely have an increased chance to pass the test.