# Can custom primers be spiked into the Illumina primers within the iSeq 100 reagent cartridge?

No, it is not possible to spike custom sequencing primers directly into the preexisting Illumina primers due to the structure of the iSeq 100 reagent cartridge.

To sequence PhiX pooled with libraries requiring custom primers, use the NextSeq 1000/2000 custom primer kit configurations. Custom primers can be mixed with the appropriate Illumina primers, then loaded into the iSeq 100 reagent cartridge using the custom primer workflow. For further information, search for Knowledge Base articles **Can PhiX be sequenced on the iSeq 100 when using custom primers?** and **Spiking custom primers into the Illumina sequencing primers**.

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| *For any feedback or questions regarding this article (Illumina Knowledge Article #6501), contact Illumina Technical Support* [*techsupport@illumina.com*](mailto:techsupport@illumina.com?subject=Question%2FFeedback%20Regarding%20Illumina%20Knowledge%20Article%20#000006501%20-%20Instrumentation%20\&body=Dear%20Illumina%20Technical%20Support,%0D%0A%0D%0A)*.* |


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