PhosFree Phosphate Assay Biochem Kit (end-point absorbance format)

PhosFree Phosphate Assay Biochem Kit (end-point absorbance format)

Important Notice:

This product is no longer available.  Cytoskeleton recommends that you use CytoPhos Endpoint Phosphate Assay (Cat. # BK054) as a replacement.


Product Uses Include

  • To measure phosphate in a biological solution or buffer
  • To measure ATP or GTP hydrolysis from an enzyme reaction
  • To measure phosphate release from phosphatase catalyzed reactions

The PhosFree™ phosphate assay Biochem Kit™ is an extremely quick and economical way to measure phosphate in solution. There is minimal interference from other common ions and reagents used in molecular biology and biochemistry. The manual is designed to guide you through the process of measuring end-point and kinetic assays. There is special consideration for ATPase and GTPase assays, which can be performed easily with this kit.

The PhosFree™ phosphate assay is specifically developed for measuring phosphate in high protein concentration solutions (>0.5 mg/ml). For measuring phosphate in lower protein concentration solutions, Cytoskeleton, Inc. recommends using the CytoPhos™ phosphate assay (Cat. # BK054).

Kit contents
The kit contains sufficient materials for 1000 assays. The following components are included:

  1. Activator.
  2. Quencher
  3. 1 mM Phosphate Standard in dH2O
  4. PhosFree™ Phosphate Assay Manual

Equipment needed

  1. Spectrophotometer capable of measuring absorbance at 650 nm wavelength.
  2. Small capacity (100-1000 µl) cuvettes or 96-well microtiter plates.

For product Datasheets and MSDSs please click on the PDF links below.   For additional information, click on the FAQs tab above or contact our Technical Support department at

If you have any questions concerning this product, please contact our Technical Service department at

Question 1:  I want to perform both end-point and kinetic assays with some samples.  Can the PhosFree Phosphate Assay Biochem Kit (Cat. # BK050) be used to measure inorganic phosphate production in either end-point or kinetic assay format?

Answer 1:  Yes, the PhosFree Phosphate Assay Biochem Kit (Cat. # BK050) is suitable for end-point and kinetic assays to measure inorganic phosphate production.  The end-point assay determines the level of phosphate in a solution such as a buffer or a sample of urine, which is not expected to change during the time taken to measure the phosphate concentration. The kinetic assay is useful for reactions which hydrolyze ATP or GTP to form ADP or GDP, respectively, and free phosphate over a time course. Finally, even if you decide to perform a kinetic assay, it is useful to use the endpoint method as a rapid method for determining the most suitable enzyme concentration and buffer composition.  The assay’s range is 1 to 50 μM phosphate, so consider this when designing your assay. 


A related decision regarding this kit is whether to perform a high or low protein content assay.  If your test solution has less than 50 μg/ml of protein, then we classify this as a low protein content assay.  If the solution is more than 50 μg/ml, then we classify this as a high protein content assay.



Question 2:  What is the sensitivity of the PhosFree Phosphate Assay Biochem Kit (Cat. # BK050) for detecting inorganic phosphate levels?

Answer 2: The PhosFree Phosphate Assay Biochem Kit (Cat. # BK050) measures phosphate levels down to a level of 0.02 nmole per 20 μl of reaction mix.