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Octadecyl Silane —This reagent is formed in situ by reaction of the column support with a suitable silylating agent such as octadecyl trichlorosilane.

Octanophenone, C14H20O—204.31—Colorless liquid.
Assay—
MOBILE PHASE— Prepare a filtered and degassed mixture of acetonitrile and water (7:3).
PROCEDURE— Inject about 20 µL into a suitable liquid chromatograph (see Chromatography 621) equipped with a 254-nm detector and a 4.6-mm × 15.0-cm column that contains packing L1. The flow rate is about 2 mL per minute. The area of the C14H20O peak is not less than 99% of the total peak area.
Refractive index 831: 1.5043 at 20.

Octoxynol 9— See Nonionic Wetting Agent.

(p-tert-Octylphenoxy) nonaethoxyethanol, C34H62O11—646.85—Use a suitable grade.
[NOTE—A suitable grade is available commercially as “Tergitol Nonionic NPX,” and as “Triton N101,” from reagent suppliers.]

(p-tert-Octylphenoxy)polyethoxyethanol —Use a suitable grade.
[NOTE—A suitable grade is available commercially as “Triton 100” from reagent suppliers.]

Octyl Sulfate, Sodium Salt, C8H17O4SNa—232.27—White powder.
Solubility— A 2-g portion dissolves in 100 mL of water.
Melting range 741 : between 195 and 197, with decomposition.

Odorless Absorbent Paper —See Filter Paper, Quantitative.

Olefin Detector Tube— A fuse-sealed glass tube so designed that gas may be passed through it and containing suitable absorbing filters and support media for the indicator in a stabilized form of permanganate.
Measuring range: 0.06 to 3.2 Vol.–% Propylene, 0.04 to 2.4 Vol.–% Butylene.
[NOTE—Available from Draeger Safety, Inc., www.draeger.com.]

Oligo-deoxythymidine —Polymeric length: 18. Use a suitable grade.
[NOTE—A suitable grade is available from BD Biosciences, www.bdbiosciences.com.]

Orange G (the sodium salt of azobenzene-betanaphthol disulfonic acid), C6H5N:NC10H4(OH)(SO3Na)2-2,6,8—452.37—Orange to brick-red powder or dark red crystals. Readily soluble in water, yielding an orange-yellow solution; slightly soluble in alcohol; insoluble in ether and in chloroform. The addition of tannic acid TS to its 1 in 500 solution causes no precipitation (acid color). The addition of hydrochloric acid to a mixture of 500 mg of zinc dust and 10 mL of its 1 in 500 solution produces decolorization. When filtered, the colorless filtrate, on standing exposed to air, does not regain its original color (presence of azo-group). When heated, orange G does not deflagrate (distinction from nitro colors). The addition of barium or calcium chloride TS to a concentrated solution of orange G produces a colored, crystalline precipitate. The addition of hydrochloric acid to its 1 in 500 solution produces no change; the addition of sodium hydroxide TS to a similar solution produces a yellowish red to a Bordeaux color but no precipitation. Orange G dissolves in sulfuric acid with an orange to yellowish-red color. No change in color results upon diluting the solution cautiously with water.

Orcinol (5-Methylresorcinol), C7H8O2·H2O—142.15—White to light tan crystals.
Assay— Transfer about 60 mg, accurately weighed, to a 100-mL volumetric flask, dissolve in methanol, dilute with methanol to volume, and mix. Transfer 5.0 mL of this solution to a 50-mL volumetric flask and dilute with methanol to volume, and mix. Using a suitable spectrophotometer, 1-cm cells, and methanol as the blank, record the absorbance of the solution at the wavelength of maximum absorbance at about 273 nm. From the observed absorbance, calculate the absorptivity (see Spectrophotometry and Light-scattering 851): the absorptivity is not less than 13.2, corresponding to not less than 98% of C7H8O2·H2O.
Melting range 741: between 58 and 61.

Orthophenanthroline —See 1,10-Phenanthroline.

Osmium Tetroxide (Osmic Acid; Perosmic Anhydride), OsO4—254.23—Use ACS reagent grade.

Oxalic Acid, H2C2O4·2H2O—126.07—Use ACS reagent grade.

3,3¢-Oxydipropionitrile, O(CH2CH2CN)2—124.14—Clear, colorless to slightly yellow liquid. Refractive index: about 1.446 at 20.
Boiling range: between 174 and 176 at 10 mm of mercury.