Sodium nitroprusside standard

For a comparison of experimental Mossbauer isomer shifts, the values have to be referenced to a common standard. According to (4.23), the results of a measurement depend on the type of source material, for example, Co diffused into rhodium, palladium, platinum, or other metals. For Fe Mossbauer spectroscopy, the spectrometer is usually calibrated by using the known absorption spectrum of metallic iron (a-phase). Therefore, Fe isomer shifts are commonly reported relative to the centroid of the magnetically split spectrum of a-iron (Sect. 3.1.3). Conversion factors for sodium nitroprusside dihydrate, Na2[Fe(CN)5N0]-2H20, or sodium ferrocyanide, Na4[Fe(CN)]6, which have also been used as reference materials, are found in Table 3.1. Reference materials for other isotopes are given in Table 1.3 of [18] in Chap. 1. 

We close with a plea to investigators to report shift data with respect to a standard absorber, either clean iron foil or sodium nitroprusside or both. The logic behind this request is obvious since anyone who has tried to intercompare results between different papers, knows how frustrating it can be when no common substances were studied. We also suggest that inherently narrow line sources be used—i.e., Cu, Pt, Pd, or Cr. Stainless steel sources are usually so broad that they can often mask important features of the spectrum. Of the host matrices mentioned we prefer Cu since it doesn t give rise to any interfering x-rays and when prepared properly doesn t show any broadening at low temperatures. 

Standard deviation in A and S is 0 005 mm s 8 originally given with respect to sodium nitroprusside. 

Sodium nitroprusside (SNP), hydrocortisone 21-hemisuccinate, desipra-mine hydrochloride, L-arginine hydrochloride, and w-conotoxin GVIA were purchased from Sigma Chemical Company (St. Louis, MO). Acid-washed alumina, sodium octyl sulfate, and catecholamine standards were purchased... 

Hg(N03)2]iH20, 8.5 grams, plus 5 ml 6M nitric acid, is dissolved in water and made up to 500 ml. This solution must he standard-ized. (b) Potassium chloride, O.IN. Dry this salt at 110° for several hours and cool in a desiccator, and weigh out accurately the appropriate amount to prepare 250 or 500 ml of solution dissolve in water, transfer to the volumetric flask, make up to the mark, (c) Sodium nitroprusside, 10 per cent. This solution should be fresh that is, it should not be kept for more than a week, (d) Hexamminecobaltic chloride. Weigh out accurately about 0.9 gram of salt, dissolve in water, and make up to 100 ml in a volumetric flask. 

To standardize the mercuric nitrate, pipette 10 ml of O.lN potassium chloride into a 250-ml Erlenmeyer flask then add 40 ml of water (measured with a graduate) and 3 drops of 10 per cent sodium nitroprusside. Titrate with mercuric nitrate, shaking well between additions as the end point is neared. The end point is marked by a permanent white turbidity and is quite sharp. When the mercuric nitrate has been standardized, titrate the hexamminecobaltic chloride solution by the same procedure, taking care to have the volume of solution in the titration flask the same as in the standardization. The end point arrives somewhat early because of the reaction HgCh + Hg++—> 2HgCl+ but by performing the standardization and titration under similar conditions, with the final mercuric chloride concentrations almost the same, this error, which is small in any case, becomes quite negligible. 

The colorimetric Nesslerization method uses alkaline phenol and hypochlorite to react with ammonia to form indophenol blue in an amount proportional to the ammonia concentration. The blue color is intensified with sodium nitroprusside, and the concentration is measured using a calibrated colorimeter. The titration of basic ammonia is accomplished with standard sulfuric acid using a mixed indicator. Determination of ammonia may also be based upon the indophenol reaction adapted to automated gas-segmented continuous flow analysis. Potentiometric determination of ammonia is performed by ion-selective ammonia electrodes. 

Mossbauer Absorption Spectroscopy. Spectra were acquired at room temperature in a constant acceleration spectrometer using a Co in Rh source. Isomer shifts are relative to the NBS standard sodium nitroprusside. Magnetic hyperfine fields were calibrated with the 515 kOe field of a-FcjO, at RT. Mossbauer parameters were determined by fitting the collected spectra with reference sub-spectra consisting of Lorentzian-shaped lines using a non-linear iterative minimization routine. 

Procedure. To 6 ml. of saturated NaCl add 2 ml. of the solution to be tested. Then add successively 1 ml. of the sodium nitroprusside solution and 1 ml. of the sodium carbonate-sodium cyanide mixture. Read the optical density against water at 520 m/i. Blanks are prepared in the same manner except that 2 ml. of water is used instead of 2 ml. of the solution to be tested. A standard curve is prepared with known amounts of cysteine or of reduced glutathione. 

If the source substance and absorber are different, the spectral absorption line is shifted along the velocity axis that is caused by the additional energy (8.2.9). The energy denominated in units of velocity, is called in TRS the chemical shift (Figure 8.5b). The sodium nitroprusside Na2[Fe(CN)(N0)5]-2H20 is mostly used as the standard (reference) substance in Mossbauer spectroscopy. Indication of the reference substance in scientific publications is obligatory. 

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