= G. N. Bowers Jr
{c}
\b[G. N. Bowers Jr] is an author of research on <spectrophotometry> and <reference materials> used for <measurement calibration> in biochemical analysis. In a 1980 study, Bowers and colleagues specified high-purity <4-Nitrophenol> for standardizing measurements of <alkaline phosphatase> activity. Some commercial samples met their specifications; others required <recrystallization> or <sublimation>. This makes purity a practical part of the measurement, rather than an assumption about a reagent label.<High-purity 4-nitrophenol: purification, characterization, and specifications for use as a spectrophotometric reference material by G. N. Bowers Jr and others>[Abstract; purification and intended use in clinical enzymology]{ref}
The same study reported a <molar absorption coefficient> of $(18380\pm90)\,\mathrm{L\,mol^{-1}\,cm^{-1}}$ at a <wavelength> of $401\,\mathrm{nm}$ and a <temperature> of $25\,{}^\circ\mathrm{C}$, for $35\,\mu\mathrm{mol\,L^{-1}}$ <4-Nitrophenol> in $10\,\mathrm{mmol\,L^{-1}}$ <sodium hydroxide>. The stated solution conditions belong with the coefficient: it is not automatically the value for a different <wavelength> or reaction mixture.<High-purity 4-nitrophenol: purification, characterization, and specifications for use as a spectrophotometric reference material by G. N. Bowers Jr and others>[Abstract; numerical molar absorptivity and measurement conditions]{ref}
For an illustrative <Beer-Lambert law> calculation using the central reported coefficient, an <absorbance> $A=0.3676$ through a path length $\ell=1\,\mathrm{cm}$ gives a <molar concentration>
$$
c=\frac{A}{\varepsilon\ell}=\frac{0.3676}{18380\times1}\,\mathrm{mol\,L^{-1}}=20\,\mu\mathrm{mol\,L^{-1}}.
$$
This chosen example shows how characterizing a <reference material> connects an optical reading to an amount of substance in solution.
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