Xylenol orange(Redirected from Xylenol Orange)
Xylenol orange is an organic reagent, most commonly used as a tetrasodium salt as an indicator for metal titrations. When used for metal titrations, it will appear red in the titrand and become yellow once it reaches its endpoint. Historically, commercial preparations of it have been notoriously impure, sometimes consisting of as little as 20% xylenol orange, and containing large amounts of semi-xylenol orange and iminodiacetic acid. Purities as high as 90% are now available.
3D model (JSmol)
|Molar mass||672.66 g·mol−1|
|Melting point||195 °C (383 °F; 468 K)|
|R-phrases (outdated)||R10, R20, R21, R22, R36, R38|
|S-phrases (outdated)||(S1/2), S26, S27, S28, S62, S63|
|Flash point||> 93 °C (199 °F; 366 K)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|‹See TfM› (what is ‹See TfM› ?)|
Xylenol orange is an indicator of choice for detecting polyvalent metal ions. It (in acetate buffer, at pH = 5.81) has two absorption maxima in its absorption spectrum, at 433 nm and 573 nm. In the unchelated form, the 433 nm absorption dominates. With metal chelation the absorbance at 573 nm increases. Absorbance at 573 nm can thus be used to construct linear calibration curves for the quantification of certain metal ions in solution. Metal complexes of xylenol orange have stability constants (log K ~ 5) lower than that of stronger metal chelating complexes such as those derived from DTPA (log k > 20). Thus xylenol orange has been used for the selective determination of unchelated metal ion contaminant concentrations in lanthanide probes.
- Gay, Craig; Collins, James; Gebicki, Janusz M. (1999), "Determination of Iron in Solutions with the Ferric–Xylenol Orange Complex", Analytical Biochemistry, 273 (2): 143–148, doi:10.1006/abio.1999.4207
- Elshan, N.G.R. Dayan; Patek, Renata; Vagner, Josef; Mash, Eugene A. (November 2014). "Spectrophotometric determination and removal of unchelated europium ions from solutions containing Eu-diethylenetriaminepentaacetic acid chelate–peptide conjugates". Analytical Biochemistry. 464: 24–29. doi:10.1016/j.ab.2014.07.009.
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