—Use Purified Rayon (General Monograph).

Red-Cell Lysing Agent—
The reagent is available as a solution containing 0.33% potassium cyanide and 0.11% sodium nitroprusside and a quarternary ammonium salt as the surface active agent (5.5%).
[note—The reagent is manufactured by Coulter Electronics Diagnostics, Hialeah, FL and is available from many suppliers under the name of Zapoglobin® (or Zap-oglobin®).]

Direct Red 80,
C45H26N10Na6O21S61373.07 [2610-10-8]—Red powder. Soluble in water; poorly soluble in alcohol. Use a suitable grade.

Red Phosphorus
—See Phosphorus, Red.

Resazurin (Sodium),
C12H6NNaO4251.17 [62758-13-8]—A brownish-purple, crystalline powder. One g dissolves in 100 mL of water, forming a deep-violet-colored solution.
Hydrogen sulfide and other compounds containing the thiol group decolorize solutions of resazurin sodium, forming dihydroresorufin. When the decolorized solution is shaken in the presence of air, a rose color develops as a result of the formation of resorufin.

Retinyl Palmitate,
C36H60O2524.9—Yellow liquid.
Mobile phase— Prepare a mixture of acetonitrile and tetrahydrofuran (55:15).
Procedure— Inject about 10 µL into a suitable liquid chromatograph (see Chromatography621) equipped with a 320-nm detector and a 4.6-mm × 15-cm column that contains packing L1. The flow rate is about 1 mL per minute. The area of the C36H60O2 peak is not less than 93% of the total peak area.

Reverse Transcriptase
—Use a suitable grade.
[note—A suitable grade is available from BD Biosciences, www.bdbiosciences.com.]

Rhodamine B
(Tetraethylrhodamine), C28H31ClN2O3479.01 [81-88-9]—Green crystals or a reddish-violet powder. Very soluble in water, yielding a bluish-red solution that is strongly fluorescent when dilute. Very soluble in alcohol; slightly soluble in dilute acids and in alkali solutions. In strong acid solution, it forms a pink complex with antimony that is soluble in isopropyl ether.
Clarity of solution— Its solution (1 in 200) is complete and clear.
Residue on ignition (Reagent test)— Ignite 1 g with 1 mL of sulfuric acid: the residue weighs not more than 2 mg (0.2%).

Rhodamine 6G,
C28H31ClN2O3479.02 [989-38-8]—Use a suitable grade.

Ribonuclease Inhibitor
—Use a suitable grade.
[note—A suitable grade is available from BD Biosciences, www.bdbiosciences.com.]

Rose Bengal Sodium
(Disodium Salt of 4,5,6,7-Tetrachloro-2¢,4¢,5¢,7¢-tetraiodofluorescein), C20H2Cl4I4Na2O51017.64 [632-69-9]—Fine, rose-colored crystals or crystalline powder. Soluble in water.
[note—Render commercially available material suitably pure by the following treatment. Dissolve 8 g in 200 mL of water, and adjust to a pH between 10 and 11, using short-range pH indicator paper. Add 200 mL of acetone, while stirring gently, then add dilute hydrochloric acid (1 in 10), while continuing to stir, until the pH of the solution reaches 4.0. Add 400 mL more of water, with stirring, and continue the stirring for 5 minutes. Filter the crystals on a filtering funnel, and return the crystals to the beaker used for crystallization. Recrystallize three more times in the same manner, and dry the crystals at 110 for 12 hours. Store in an amber bottle in a refrigerator at a temperature between 2 and 8. Prepare this reagent fresh monthly.]
Chromatographic purity— Dissolve 100 mg of rose bengal sodium, prepared as described above, in 100 mL of water, and apply 10 µL of the solution on suitable chromatographic paper. Develop the chromatogram by ascending chromatography, using a mixture of 1 part of dilute alcohol (1 in 4) and 1 part of dilute stronger ammonia water (1 in 12). Examine the chromatogram in daylight and under UV light (360 nm): no colored or fluorescent spot is visible other than the rose bengal sodium spot.
[note—A suitable grade is available commercially as “Silica Gel H”.]

Ruthenium Red
(Ruthenium Oxychloride,Ammoniated), Ru2(OH)2Cl4·7NH3·3H2O—551.23 [11103-72-3]—A brownish-red to dark purple powder. Soluble in water.