# Indexing FAQ for Illumina DNA PCR Free libraries

**If there is no PCR, how indexes and full adapter sequences incorporated during library preparation?**\
There is a proprietary mechanism in Illumina DNA PCR-Free allows for ligation of IDT for Illumina - DNA/RNA Unique Dual (UD) index primers.

**Can Unique Molecular Identifier (UMIs) be incorporated into this workflow?**\
This has not been validated.

**Can UMI anchors (IDT for Illumina - UMI DNA/RNA UD Indexes, Ligation (formerly known as IDT for Illumina - UMI DNA Index Anchors)) be used with the Illumina DNA PCR-Free library prep kit?**\
No, the UMI anchors/index sets cannot be used with Illumina DNA PCR-Free Prep, Tagmentation library prep kit.

**As the protocol uses half the volume in the adapter plate (5 µl of approximate 10 µl fill), why does the protocol say the index plate cannot be reused?**\
This is to prevent cross-contamination and make sure that there is sufficient volume for use.

**Can custom index adapters with the Illumina PCR-Free kit?**

No.

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| *For any feedback or questions regarding this article (Illumina Knowledge Article #3474), contact Illumina Technical Support* [*techsupport@illumina.com*](mailto:techsupport@illumina.com?subject=Question%2FFeedback%20Regarding%20Illumina%20Knowledge%20Article%20#000003474%20-%20Library%20Preparation%20\&body=Dear%20Illumina%20Technical%20Support,%0D%0A%0D%0A)*.* |


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