[Python] Drop NaN values from dataframe imported from excel

I am trying to import my data from excel in to python using Pandas. I then want to plot the data. At the moment I am struggling with blank values in my data. Source data looks like attached image. When I run the code as below the data printed contains 'Nan'

import pandas as pd
df = pd.read_excel('CSTRS Chem Eng Practicals_2.xlsx', sheet_name='Flow Rates')
df = pd.DataFrame(df)
df = df.values
Time2 = df[4:,0]
Conc1 = df[4:,2]
Conc2 = df[4:,4]
Conc3 = df[4:,6]
Conc4 = df[4:,8]
Conc5 = df[4:,10]
print (Time2)
print (Conc1)


If I use df.notna() then I get this error message 'AttributeError: 'numpy.ndarray' object has no attribute 'notna'' Can anyone suggest a way to remove the NaN values so I am able to plot the data

Thanks

I have tried df.notna() and I have also tried slicing the data and neither works

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