ANALYTICAL CHEMISTRY, VOL. 51, NO. 13, NOVEMBER 1979
One other pitfall that was encountered occasionally involved the use of Equation 6, the division of the output by the input in the frequency domain. This was done sequentially starting a t dc and moving to the higher frequencies. The problem occurred when the input contained only very small amounts of those higher frequencies. The division then caused an overflow in the program. This was corrected by dividing only the lower frequencies, with no sacrifice in accuracy because all of the chromatographic information was concentrated in this area of the frequency domain. Once the above problems had been solved, frequency modulated experiments could be run in a routine manner. The concept of information encoding and subsequent decoding, which allows frequency modulated experiments is summarized in Equation 8. It is impressive in its simplicity and conciseness. From this equation any input to a chromatograph can be used to solve for the transfer function of the column, i.e., the spike elution response. Frequency modulation has been shown to expand the scope of potential applications of multiple injection chromatographic experiments by allowing finite concentration systems. Other encoding techniques such as pulse and phase modulation (13) appear to have similar advantages. Work in these areas is currently being investigated.
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Seismograph Service Corporation for the use of the sampling valve, and also thank L. Schooley, M. Trandal, and D. McCaughey of the Electrical and Systems Engineering Departments at the University of Arizona and G. Horlick of the University of Alberta for their consultation in signal processing.
LITERATURE CITED (1) C. N. Reilley, G. P. Hildebrand, and J. W. Ashley, J r . , Anal. Chem., 34,
1198 (1962). (2) R . Annino. and L. E. Bullock, Anal. Chem., 45, 1221 (1973). (3) G. C. Moss, J. P. Kippiing, and K. R. Godfrey, "Application of Statistical Correlation Techniques and Pseudo Binary Sequences to Trace Chromatographic Analysis", in "Gas Chromatography 1972", S. G. Perry and E. R. Adlard, Eds., Applied Science Publishers, London, 1973. (4) H. C. Smit, Chromatographia, 3 , 515 (1970). (5) H. Clough, T. C. Gbb, and A. Littlewood, Chromatcgraphia,5,351 (1972). (6) R . Annino and E. Grushka. J . Chromatogr. Sci., 14, 265 (1976). (7) J. B. Phillips and M. F. Burke, J . Chromatogr. Sci., 14. 495 (1976). (8) R. N. Bracewell, "The Fourier Transform and Its Applications". 2nd ed., McGraw-Hill, New York. 1978. (9) A. 8. Carison, "Communication Systems", 2nd ed., McGraw-Hill, New York. 1975. (IO) G. Horlick and G. M. Hieftje, "Correlation Methods in Chemical Data Measurements", in "Contemporary Topics in Analytical and Clinical Chemistry". Vol. 3, Plenum Press, New York, 1978, p 153. (11) R. Annino, M. F. Gonnard, and G. Gooichon, Anal. &m., 51,379 (1979). (12) P. R . Griffins, "Transform Techniques in Chemistry", Plenum Press, New York, 1978. (13) D. Obst, J . Chromatogr., 32, 8 (1968).
ACKNOWLEDGMENT The authors thank B. Keller of the Seiscor Division of the
RECEIVED for review May 18,1979. Accepted August 20,1979.
Inductively Coupled Plasma Emission Spectrometric Detection of Simulated High Performance Liquid Chromatographic Peaks David M. Fraley, Dennis Yates,' and Stanley E. Manahan' Department of Chemistw, University of Missouri, Columbia, Missouri 652 1 1
Because of its multleiement capability, element-specificity, and low detection limits, inductively coupled plasma optical emission spectrometry (ICP) is a very promising technique for the detection of specific elemental species separated by high performance liquid chromatography (HPLC). This paper evaluates ICP as a detector for HPLC peaks containlng specific elements. Detectbn Umits for a number of dements have been evaluated in terms of the minimum detectable concentration of the element at the chromatographic peak maximum. The elements studied were Ai, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, LI, Mg, Mn, Mo, Na, NI, P, Pb, Sb, Se, Sr, Ti, V, and Zn. In addition, ICP was compared with atomic absorption spectrometry for the detection of HPLC peaks composed of EDTA and NTA chelates of copper. Furthermore, ICP was compared to UV solution absorption for the detection of copper chelates.
One of the major challenges remaining in the area of trace element analysis is the measurement of trace element-containing species (1). In addition, matrix effects and instrumental interferences still cause problems in the analysis of 'Spectroscopy Group Leader, University of Missouri Environmental T r a c e Substances Center. 0003-2700/79/035 1-2225$01.OO/O
elements in some samples by techniques such as neutron activation analysis and furnace atomic absorption. Separation of sample species by high performance liquid chromatography (HPLC) and detection with an element-specific detector can enable analysis of species and help eliminate interferences in elemental analysis. Conventional flame atomic absorption spectrometry (AAS) was one of the first element-specific techniques applied to HPLC (2,3)and was used to detect copper chelates separated by HPLC. Chromium organometallics separated by use of an organic mobile phase were subsequently detected by AAS ( 4 ) . In these investigations the HPLC column outlet was interfaced directly to the AAS nebulizer inlet. Ion-exchange HPLC with AAS detection has been employed for the analysis of Cr(II1) and Cr(V1) complexes ( 5 ) ,Mn(I1) and Mn(VI1) (6), and mixtures of Cu(gly), Cu(EDTA), and Cu(trien) species (7). Gel permeation chromatography has been employed for the analysis of condensed phosphate complexes of Mn(I1) (8) and zinc compounds in plant extracts (9). Affinity HPLC has been employed for the analysis of alkyl and aryl zinc organometallics in lubricating oils ( I O ) , metals bound by amino acids ( I I ) , and alkyllead compounds in gasoline (12). A number of other applications are cited in a review article dealing with the subject (13). Inductively coupled plasma optical emission spectrometry (ICP) is developing as an excellent tool for the analysis of a 0 1979 American Chemical Society
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Table I. Experimental Conditions for AAS and ICP Detectors Employed to Monitor Copper Chelate Peaks parameter AAS ICP instrument Perkin-Elmer 403 Jarrell-Ash 975 Cu hollow cathode plasma source lamp 3247 A 3247 A wavelength 7A 1.7 A spectral bandpass acetylene/air 4in. argon plasma flame single-slot burner sample introduction 2.0 mL/min 2.0 mL/min rate --1.2 kW incident power (rf signal) reflected power
