Acidic potassium dichromate solutions as ultraviolet absorbance standards

Abstract

. The absorbances of five concentrations of potassium dichromate in 0.001 ]l.f perchloric aCid have been determined at eight wavelengths in the ultraviolet on the National Bureau of Standards Institute for Materials Research high-accuracy spectrophotometer. Four of the wavelengths-235, 257, 313, and 3.50 nm-correspond to absorbance maxima or minima in the HCrO,-spectrum and are useful wavelengths for checking the accuracy of the absorbance scale of narrow bandpass speetrophotometers. Although partial dimerization of nCrO,-to Cr207-prod~c.e~ small positive deviations from Beer's law at these wayelengths, the apparent absorptlvltles calculated for each concentration arc reproducible to one part in a thousand. The estimated uncertainties in the absorptivity values are ± 0.7 percent at 0.1 absorbance (A) and ± 0.2 percent ncar A = 1. These uncertainties include all known sources of possible systematic error and the 95 percent confidence level for the mean. The remaining four wavelengths used for measurement arc ncar two predicted isosbestie points in the HCrO,~/Cr207-sp~ctra . The absorptivities at 345 nm arc sufficiently independent of concentratIOn that thiS wavelength can be used for checking absorbance linearity to one part in a thousand over the range A = 0.2-1.~cy words: ~bsorbance linearity; accuracy; acidic potassium dichromate solutions; calibratIOn of ultravIOlet speetrophotometers; liquid filters; transfer standards; ultraviolet absorbance standards.

Ion-selective interpenetrating polymer networks supported inside polypropylene microporous membranes for the removal of chromium ions from aqueous media

“…The Cr(VI) ion was measured at 350 nm in a solution of pH 3.0. The Cr(III) ion concentration was measured at the wavelength 573 nm for an acidic pH, this wavelength is only selective to the Cr(III) [20,21]. At wavelength 300 nm the Cr(III) and Cr(VI) absorb energy, and can cause mistakes in the measurement.…”

Pitfalls in microcystin extraction and recovery from human blood serum

“…[17] after calibration of the spectrophotometer with potassium dichromate in 1 mM perchloric acid [18]. Due to lack of validated coefficients for each of the MC congeners used in this study, all MC congeners were prepared as if they had the same absorption coefficient as MC LR.…”

Note on the Methods for Determination of Chromic Oxide in Shrimp Feeds

“…Furthermore, the absorbance of sample solutions was compared with pure dichromate ion solutions as standards. Acidic potassium dichromate solution is routinely used as a standard to calibrate spectrophotometers (8), but it should be remembered that purity of the hexavalent ion is important for such measurements. In recent years, attempts have been made to replace chromic oxide with other trivalent metal oxides such as yttrium.…”

“…Absorbance at 440 nm was found unsuitable for determining CrO 4 2ion during digestion experiments. Pure acidic potassium dichromate solutions were used as an ultraviolet standard in the absorbance range of 250-400 nm (8).…”