Filter dataframe based on presence of sample in a seperate list

I am wanting to filter a dataframe with 1212 so it only contains that samples listed in a seperate list. The list has multiple values and I can't work out how to do this.

df = RNASeq2

RNASeq2Norm_samples Substrng_RNASeq2Norm
   1    TCGA-3C-AAAU-01A-11R-A41B-07    TCGA.3C.AAAU
   2    TCGA-3C-AALI-01A-11R-A41B-07    TCGA.3C.AALI
   3    TCGA-3C-AALJ-01A-31R-A41B-07    TCGA.3C.AALJ
   4    TCGA-3C-AALK-01A-11R-A41B-07    TCGA.3C.AALK
   5    TCGA-4H-AAAK-01A-12R-A41B-07    TCGA.4H.AAAK
   6    TCGA-5L-AAT0-01A-12R-A41B-07    TCGA.5L.AAT0
   7    TCGA-5L-AAT1-01A-12R-A41B-07    TCGA.5L.AAT1
   8    TCGA-5T-A9QA-01A-11R-A41B-07    TCGA.5T.A9QA
   .
   .
   .
   1212

list = intersect_samples

intersect_samples: "TCGA.3C.AAAU""TCGA.3C.AALI""TCGA.3C.AALJ""TCGA.3C.AALK" ... 1097

I have tried this code but returns all the original 1212 samples:

RNASeq_filtered <- RNASeq2[RNASeq2$Substrng_RNASeq2Norm %in% intersect_samples,]

Yet if I try

RNASeq_filtered <- RNASeq2[RNASeq2$Substrng_RNASeq2Norm %in% "TCGA.3C.AAAU",]

it will return the correct row