We're biotinylating proteins and want to know how many biotins are conjugated to our proteins. The HABA assay is an accurate assay for quantitating the number of biotins conjugated to a protein. However, HABA is time consuming and tedious. We have considered chromogenic biotin (biotin with a PEG spacer and a chromogenic moiety; there are a couple of companies that make or distribute the products) as an alternative to HABA, but I have been unable to find any published studies comparing HABA to chromogenic biotin. Does anyone know of any studies that compare the two methods directly? If so, can you provide a reference or a link to a study?