loq the percent purity of the drug substance on an anhydrous solvent and salt free basis can be determined for each sample preparation as follows msp sample mass spectrometric purity of the main uv peak of the sample expressed as a decimal fraction the msp is calculated by dividing the sum of the percent contributions to the sample of the full length target oligonucleotide and its major impurity by the uv purity of the sample the uv purity is determined on the first preparation of each sample and is defined as the decimal fraction of the peak area of the main uv peak divided by the total uv area an average assay value can be calculated for each sample in calculating the value the number can be rounded and reported to one decimal place in some embodiments the agreement between the assay and impurity profile values for the drug substance can be determined by subtracting the sum of the full length oligonucleotide and major impurity material from the average assay value it is desirable that the two values agree to within an absolute value of u00b1 4 0 in some embodiments the method can be used to support a drug product label claim the label claim of each drug product preparation can be determined as follows msp sample mass spectrometric purity of the main uv peak of the sample expressed as a decimal fraction the msp is calculated by dividing the sum of the percent contributions to the sample of the full length target oligonucleotide and its major impurity by the uv purity of the sample the uv purity is determined on the first preparation of each sample and is defined as the decimal.