Nickel stock solution— Immediately before use, dilute an appropriate quantity of organometallic standard1 with kerosene to prepare a solution containing the equivalent of 1.0 µg of nickel per mL.

Standard solutions— Transfer 0.5, 1.0, 2.0, and 4.0 mL of Nickel stock solution, respectively, to four identical 10-mL volumetric flasks, dilute the contents of each flask with kerosene to volume, and mix. These Standard solutions contain, respectively, about 0.05, 0.1, 0.2, and 0.40 µg of nickel per mL. [note—The calibration range, especially the upper limit, can be adjusted for certain instruments, provided that instrument validation and calibration linearity are achieved.]

Test solution— Transfer about 3 g of Hydrogenated Polydecene, accurately weighed, to a 10-mL volumetric flask, dilute with kerosene to volume, and mix. [note—If necessary, dilute with an appropriate quantity of kerosene to obtain a reading within the calibrated absorbance range.]

Procedure— Place the Standard solutions and the Test solution in an oven, setting the temperature at about 60 during the period of determination, and shake these solutions vigorously before analysis. Use micropipettor and pipettor tips to make all injections. [note—Positive displacement pipets can be used when viscosity may become a problem.] Pretreat the pipettor tip by pipetting and then discarding 20 µL of heptane. [note—The film of heptane remaining on the wall of the tip facilitates a reproducible transfer of the oil sample.] The tip must be pretreated before each injection. Separately inject equal volumes (20 µL) of the Standard solutions and the Test solution into a graphite furnace, and concomitantly determine the integrated absorbances of the Standard solutions and the Test solution at the nickel emission line of 232.0 nm, using a suitable graphite furnace atomic absorption spectrophotometer (see Spectrophotometry and Light-Scattering 851) equipped with a deuterium background corrector, a pyrolytically coated tube with platform, and a nickel hollow-cathode lamp, using kerosene as the blank. Maintain the drying temperature of the furnace at 80 for 1 second, at 120 for 10 seconds, and at 300 for 20 seconds; maintain the ashing temperature at 600 for 20 seconds and at 1000 for 20 seconds; and maintain the atomization temperature at 2500 for 3 seconds and the cleaning temperature at 2600 for 5 seconds. [note—The temperature program may be modified to obtain optimum furnace temperatures.] Plot the integrated absorbances of the Standard solutions versus concentration, in µg per mL, of nickel, and draw the straight line best fitting the four plotted points. From the graph so obtained, determine the concentration, C, in µg per mL, of nickel in the Test solution. Calculate the quantity, in µg, of nickel in each g of Hydrogenated Polydecene taken by the formula: in which W is the weight, in g, of Hydrogenated Polydecene taken to prepare the Test solution: not more than 1 µg of nickel per g is found.

Test solution, System suitability solution, Chromatographic system, and Procedure— Proceed as directed in the test for Content of decene oligomer. Calculate the percentage of each of the short-chain hydrocarbons present by the formula: in which rU is the response of any peak obtained from a peak eluting before the trimer but different from the solvent peak; and rs is the sum of the responses of all the peaks in the chromatogram, excluding the solvent peak: not more than 2.5% of total short-chain hydrocarbons is found.

Test solution— Dissolve about 0.1 mL of Hydrogenated Polydecene in about 10 mL of pentane.

System suitability solution— Dissolve accurately weighed quantities of hexadecane, squalane, and tetradecane in pentane to obtain a solution having known concentrations of about 10 mg per mL, 10 mg per mL, and 1 mg per mL, respectively.

Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector and a 0.52-mm × 16-m fused-silica capillary column coated with 0.1-mm stationary phase G2. The carrier gas is helium, flowing at a rate of about 10 mL per minute. The chromatograph is programmed as follows. Initially, the column is maintained at a temperature of 35, then immediately after injection, the temperature is increased to 50 at a rate of 5 per minute, then increased to 170 at a rate of 12 per minute, then increased to 310 at a rate of 10 per minute, and maintained at 310 for 18 minutes. The injection port temperature is maintained isothermally at about 310, and the detector temperature is maintained isothermally at about 320. Chromatograph the System suitability solution, and record the responses as directed for Procedure: the resolution, R, between tetradecane and hexadecane is not less than 2.0; and the relative standard deviation for replicate injections for each peak is not more than 2.0%. [note—For information purposes only, the retention time for squalane is about 18 minutes; and the relative retention times are about 0.5 for tetradecane, 0.6 for hexadecane, and 1.0 for squalane.]

Procedure— Inject a volume (about 2 µL) of the Test solution into the chromatograph, record the chromatogram, and measure the areas for the major peaks. [note—For information purposes only, the tetramer oligomer has a retention time of about 23 minutes. The trimer, pentamer, hexamer, and heptamer oligomers, if present, have relative retention times of about 0.8, 1.1, 1.3, and 1.4, respectively, relative to the tetramer.] Calculate the percentage of each oligomer present by the formula: in which rO is the response of each oligomer; and rs is the sum of the responses of all the peaks in the chromatogram, excluding the solvent peak: the decene oligomer content is within the limits specified in the accompanying table.