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LITERATURE CITED
Kjeldahl method. The distribution of nitrogen was calculated and then compared with the area % distribution of nitrogen as determined by GC analysis of the total sample. The chromatogram was divided into zones (Figure 6) that corresponded to the boiling points a t which the cuts were taken. The distillation was carried out a t reduced pressure, about 10 mm, and the column overhead temperature a t which each cut was taken was converted to atmospheric boiling point. From the boiling point-retention time calibration curve, the retention time corresponding to each cut point temperature was determined. The area of each zone was planimetered and the areas were normalized to 100%. A base-line or system background correction, as indicated by the broken line in the chromatogram, was determined by making a blank run under the same experimental conditions that were used for the sample. A summary of the comparative analyses is given in Table VIII. The cut point temperatures, the calculated distributions from the elemental analyses, and the GC analyses from three consecutive runs (all a t the same bead voltage) are shown for each cut. The overall standard deviation of the GC analyses is about 8% relative. The overall relative percent difference between the two analyses is also about 8%. Considering the various sources for experimental error, the agreement between the two distributions is reasonably good and indicates that the GC method has potential for development as a "simulated distillation" method for nitrogen compounds.
( 1 ) D. K. Albert, Anal. Chem., 39, 1113 (1967). (2) E. R. Adlard and P. H. D. Matthews, "Selective Nitrogen Detectors for
(3) (4) (5) (6) (7) (8) (9) (10)
(11) (12) (13) (14)
the Determination of Organonitrogen Compounds Separated by Gas Chromatography", in Recent Anal. Dev. Pet. Ind., (Proc. Inst. Pet. Symp.), D. R. Hodges, Ed., John Wiley 8 Sons, New York. 1974, p 59. D. J. David, "Gas Chromatographic Detectors", John Wiley 8 Sons, New York, 1974, pp 114, 194. M. Krejci and M. Dressler. Chromatogr. Rev., 13, 1 (1970). D. F. S. Natusch and T. M. Thorpe, Anal. Chem., 45, 1184A (1973). R. Pigliucci, W. Averill, J. E. Purcell, and L. S. Ettre, Chromatographia, 8, 165 (1975). H. V. Drushei, Anal. Chem., 49, 932 (1977). R. L. Martin, Anal. Chem., 38, 1209 (1966). J. C. Escaller, M. Caude, C. Bollet, and R. Rosset, Analusis, 395 (1977). H. V. Dnshel, "Nibogen Compounds in Fossl Fuels by Gas chromatography with a Chemiluminescent Detector", presented before the Analytical Division, 175th National Meeting. American Chemical Sodety, March 12-17, 1978, Anaheim, Calif. T. A. Gough and K. Sugden, J . Chromatogr., 88, 65 (1973). 8. Koib and J. Bischoff, J . Chromatogr. Sci., 12, 625 (1974). M. J. Hartigan, J. E. Purcell, M. Novotny. M. L. McConnell, and M. L. Lee, J . Chromatogr., 99, 339 (1974). C. A. Burgett, D. H. Smith, and H. 8.Bente, J . Chromatogr., 134, 57
(1977). (15) P. L. Patterson, R. Howe, V. Hornung, and C. H. Hartman, "Selective NRrogen and Phosphorus Detection with Electrically Heated Alkali Beads", presented at the Pittsburgh Conference on Analytkal Chemistry and Applied Spectroscopy, February 27-March 3, 1978, Cleveland, Ohio. (16) R. C. Hall and P. W. Thiede, "Extended Capability for the Detection of Nitroaen and Phosphorous ComDounds". presented at the Pittsburgh Conference on Anaiytical Chemisiry and Applied Spectroscopy, Februa-ry 27-March 3, 1978, Cleveland, Ohio. (17) D. N. Bailey and P. I. Jatlow, Clin. Chem. ( Winston-Salem, N.C.), 22,
777 (1976). -, (18) J. K. Baker, Anal. Chem., 49, 906 (1977). (19) R. F. Admas, F. L. Vandemark, and G. J. Schmidt, J . Chromatogr. Sci.. 15, 63 (1977). (20) G. A. Flanigan and G. M. Frame, Res..IDev., 28, (9), 28 (1977). (21) M. L. Lee, K. D. Bartle, and M. V. Novotny, Anal. Chem.. 47, 540 (1975). (22) C. E. Kennard, S. M. Sonchik, and M. P. T. Bradley, "Detailed Analysis >
CONCLUSIONS In conclusion, this work has shown that (1)with response factors and an internal standard technique, the thermionic detector or NPD can be used for accurate component analyses of petroleum without prior separations; (2) the NPD is applicable to the determination of nitrogen compound distributions in petroleum and results compare favorably with those obtained by microcoulometry or elemental analyses of fractions; and (3) nitrogen compound distribution by boiling point is feasible with the NPD-FID system. Further development of this technique is being done in our laboratory.
(23) (24) (25)
(26) (27)
ACKNOWLEDGMENT I am grateful to R. B. Armstrong of Amoco Oil Company who provided the light vacuum gas oil distillation fractions and to J. J. Miskovich of Standard Oil Company (Indiana) who assisted with the experimental work.
~
of Shale Oil Using Specific Detectors", presented before the Analytical Division 174th National Meeting, American Chemical Society, August 28-September 2, 1977, Chicago, IIi. I. Puskas, E. K. Fields, and E. M. Banas. Div. Pet. Chem., Am. Chem. SOC.,Prepr., 17 ( l ) , 856, (1972). J. A. Lubkowitz, J. L. Glajch, B. P. Semonian, and L. B. Rogers, J . Chromatogr., 133, 37 (1977). American Society for Testing and Materials, "1977 Annual Book of ASTM Standards", Part 24, p 830, Method D2896-73 (1977). M. A . Muhs and F. T. Weiss, Anal. Chem., 30, 259 (1958). American Society for Testing and Materials, "1977 Annual Book of ASTM Standards", Part 24, p 770, Method D2887-73.
RECEIC'ED for review June 13,1978. Accepted August 17,1978. Presented before the Division of Analytical Chemistry, 175th National Meeting, American Chemical Society, Anaheim, Calif., March 12-17, 1978.
Cubic Spline Interpolation for the Calculation of Retention Indices in Temperature-Programmed Gas-Liquid Chromatography Wolfgang A. Halang," Rolph Langlais, and Ernst Kugler Coca-Cola GmbH, Research & Development Department, Kaninenbergstr. 66, 4300 Essen 1, West Germany
Temperature-programmed gas-liquid chromatography (GLCj is extensively used in our laboratories for the analysis of essential oils and other mixtures of volatile oils and substances. The methods applied for the collection, processing, and evaluation of our GLC data have been described earlier (1-3). All GLC retention data are converted into Kovgts indices for further handling and reference. Hence, the indices need to be calculated as accurately as possible. This paper describes the method we employ, which has been
A method is described for the calculation of retention indices based on nonlinear calibration data in temperature-programmed gas-liquid chromatography. It is the method of choice when the indices serve as input for statistical analyses and identification procedures. A comparison of this technique with the polygonal technique is discussed. For easier implementation of the calculation procedure Into existing gasliquid chromatography computer programs, a detailed description of the spline Interpolation procedure is given. 0003-2700/78/0350-1829$01 .OO/O
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analysis. More than a thousand papers dealing with this area of research have appeared. Spline functions distinguish themselves by remarkable properties. For further details we refer to two books (5,6)covering the most important aspects of the subject. In this section we shall present only the topics necessary to apply natural cubic spline interpolation to the calculation of retention indices. Construction of Interpolating Natural Cubic Splines. Given a set of data points ((x,,yJli= 1, ..., n} with x1 < x 2 < ...
