The phrase "a three step purification" is correct and usable in written English.
It can be used when describing a process that involves three distinct stages of purification.
Example: "The experiment involved a three step purification to isolate the desired compound from the mixture."
Alternatives: "a three-stage purification" or "a tri-step purification".
For instance, a two step purification approach was already sufficient for shorter constructs, e.g., the catalytic domain of ColG (Eckhard et al. 2008), whereas a four-step approach was necessary for the full-length collagenases to meet our purity requirements.
Methods of PAI-2 expression in E. coli have generally utilised a one or two step purification procedure, usually involving metal affinity chromatography and/or ion exchange chromatography.
While this level of expression is one of the highest reported so far for the total CD81 receptor using mammalian cell, previous studies on the expression of soluble CD81-LEL in Escherichia coli using a GST-LEL fusion tag reported expression level of up to 3 mg/L, and achieved a purification of >95% using four step purification procedures [10].
b The commassie blue staining results of Her-S-Fab after two step purification.
The four step purification protocol for laccase resulted in 4.2~fold purification (Table 1) with 11% laccase recovery.
Four step purification procedure involving ammonium sulphate fractionation, dialysis, DEAE-cellulose ion exchange and G-100 Sephadex gel permeation chromatography was gradually employed for the purification of MnP.
Human neutrophils were isolated in LPS-free conditions by means of one step purification on polymorphprep gradient dextran sedimentation as previously described [18].
Four step purification procedure involving ammonium sulphate fractionation, dialysis, diethyl amino ethyl (DEAE) cellulose ion exchange and G-100 Sephadex gel filtration chromatography was employed for the purification of MnP.
The two steps purification of each protein followed the same procedure as described previously (Zhang et al., 2012).
Three steps, antibody purification, enzymatic activity, and mass spectrometric detection of specific cleavage products, combine to minimize cross reactivity.
