Described herein is a buffer concentration for highly efficient ligation of two oligonucleotides. The embodiments herein have led to the development of an optimized ligation step used in the sample preparation for sequencing reactions. Further, embodiments herein describe a high-throughput method for sequencing using barcodes or the purpose of multiplexing several samples simultaneously and novel methods for making targeted DNA libraries for re-sequencing on massively parallel next-generation sequencing platforms and for alternatives to gel-purification for recovering the desired templates from small RNA libraries for next generation sequencing.