Simple Varia ble-Temperature Sample Inlet for Beckman GC-2 Gas Chromatograph SIR: Lowry ( 1 ) in a recent paper in this journal described a device (solid sample injector) he designed to overcome tailing and poor resolution which he found while analyzing fatty acid esters with a Beckman GC-2 gas chromatograph hydrogen flame accessory. This same problem was encountered in this laboratory (Figure lil) and may be characteristic of these instruments. The solution offered below requires no custom fabrication, uses commercially available components, and can be installed in a short time. The temperature of the stock inlet was found to be about 210" C., apparently not a sufficiently high temperature to ensure adequate vaporization. h t tempts to increase the temperature of the standard sample inlet with insulation were unsuccessful. The standard inlet was replaced by a special preparative inlet (Beckman No. 45429). This unit is designed to vaporize large samples for evenha1 fraction collection, and is heated by a highdensity 550 W cartridge heater operated a t 110 volts for short periods through a tinier. The temperature rise of the heater is about 10" C.jsecond. Operation of the heater for 12 to 14 seconds prior to injection of the sample yields an inlet temperature of about 260" C., and the chromatogram seen in Figure 1B. Although the separation was excellent and tailing was practically nonexistent the effectiveness of this procedure was
Figure 1. Chromatograms of fatty acid methyl esters Operating conditions: column, 6 ft. X '/a inch, 20% DEGS on Chromosorb W. Column temperature, 175OC. Flow rate, 50 ml. He/minute. Split ratio, 1 :1. Air pressure, 7 P A . ; hydrogen pressure, 4 p.r.i. Samples, 0.2 PI. 10% sohtion fatty acid methyl esters in acetone (purchased from Applied Science Co., College Park, Po.). Attenuation, X2000
nullified by the appearance of a "peak" next to the solvent peak, which would prevent analysis of fatty acid esters shorter than palmitate. Occasionally, unknown peaks would appear in other positions in the chromatogram. These "peaks" apparently represented traces
of impurities deposited in the special inlet which were vaporized each time the inlet reached its maximum temperature. All attempts to remove these impurities both by solvent extraction and by repeated heating were unsuccessful. Excellent results were finally obtained by disconnecting the special inlet heater from the timer and operating the cartridge heater continuously through a variable resistance (Powerstat). -4 setting of 18 volts kept the inlet temperature betaeen 260 and 270" C. and yielded Chromatograms of which Figure 1C is typical. This system has been successfully used to chromatograph methyl esters of fatty acids prepared from lipoproteins, fish, and fish products. The long-chain polyunsaturated fatty acids in the latter show no deconiposition due to the new inlet as shown by comparison with chromatograms obtained from other instruments. In effect, this modification provides the GC-2 with a variable-temperature injection heater, which undoubtedly mould prove useful in other applications as well. LITERATURE CITED
(1) Lowry, R. R., ANAL.CHEY.36, 1407,
1964.
THOMAS F. KELLEY
Bio-Research Institute 9 Commercial Ave. Cambridge, Mass. 02141
Determination of Va na dyl Porphyrins by De meta lation with Hydrogen Bromide-Formic Acid SIR: Although the Groennings' method (10) has been widely applied in the quantitative determination of metalIoporphyrins in fossil fuels, decomposition occurs in varying degrees depending upon the conditions imposed and the types of porphyrins involved ( 1 4 ) . EXPERIMENTAL
An amount of 0.00.5 tc 0.2 pniole of a model vanadyl porphyrin, dissolved in 10 to 15 nil. of benzene or toluene, is placed in a 50-nil. round-llottonied flask together with 25 nil. of 9 i - t % formic acid (Distillation Products, Rochester, S . Y . ) . The flask is attached to a Claisen head with ground glass joints. A gas-inlet tube, with the appropriate ground glass joint, t o introdurr S2 or HRr is arranged so that a capillary reaches near tlic hott,oni of the flask. h T-unit) with appropriate stopcocks is 2374
ANALYTICAL CHEMISTRY
at'tached to the gas line using Teflon t,ubing and t,hen connected to N2 and HBr tanks. h water-cooled condenser is att'ached t'o the other Claisen head opening. Gases leaving the unit' t'hrough the top of the condenser are carried int,o a trap cont,aining mineral oil to inhibit backflow of the atmosphere and then into a water trap to dissipate HUr. The unit is thoroughly flushed with K2 (about 20 minut,es) while the reaction flask is heated to 50" C. and maintained at that temperature. Then K2 flow is stopped and anhydrous HI3r (Mathescn Coleman & I3ell) is introduced a t a rate sufficient t o iiiainhin observable agitation in the rraction flask for a period of 2-3 hours. The rate of input is decreased after t,he reaction mixture is saturated. The system is then flushed with S2 again for 20 to 30 minutes while the reaction mixture is allowed t,o cool to room temperature.
This operation is necessary t o inhibit Br2 formation resulting from atmospheric oxidat'ion cf HBr. The benzene or toluene phase is separated from the,acid layer, and the former is washed once with 15 ml. of 97+7, HCOsH. The combined acid solutions are neutralized with anhydrous XH3. Water is added to the resulting mixture to dissolve precipitated salts. This solut,ion is then treated in the manner described by Groennings ( I 0 ) . The purified porphyrin or porphyrin aggregate is analyzed spectrophotometrically (I3eckinan DK-2) by integration of the area under the Soret band (13).
Formyl fluoride was prepared by the method of Olah and Kuhn ( l a ) . MesoIiorphyrin IX dimethyl ester was prepared ( 2 ) and nietalated ( 6 ) wit'h vanadyl sulfate. Etioporphyrin I was obt,ained by the two-step synthesis (7, 8) from 3-ethy1-2,4-dimethS-]pvrrole (9)
