the initial mixing of the solutions. A sample of reagent grade copper acetate [ C U ( C ~ H , O ~ )HzO ~ ] using a standard curve prepared from lO-3M QTS was analyzed to indicate the application of the method. The copper content of four determinations was 31.0% as compared to 31.83%. The copper complex of o-(ptoluenesu1fonamide)aniline is reported to give a calibration curve over the range of 2 to 16 ppm or 3.2 X 10-5 to 2.5 X lO-5M (2). The copper-QTS complex is linear over a lower range, 10-6 to lO-4M. Billman’s method is less sensitive to interfering ions. The method reported here gives a faster rate of color development for the
complex and the absorbance of the complex is stable for a longer period of time. Obviously, care must be exercised when dilute solutions of copper are handled. Pipetting of the chloroform layer should be done with care so as not to carry along any of the aqueous layer. Glass-stoppered centrifuge tubes are recommended because of the absorption of chloroform into rubber stoppers. RECEIVED for review September 5 , 1968. Accepted December 18, 1968. Presented, ACS Great Lakes Regional Meeting, Milwaukee, Wis., June 1968.
Flame-Luminescence Intensification and Quenching Detector (FLIQD) in Gas Chromatography Walter L. Crider and Robert W. Slater, Jr. U.S. Department of Health, Education, and Welfare, Public Health Service, National Air Pollution Control Administration, Cincinnati, Ohio 45237
PREVIOUS work in our laboratories ( I , 2) has applied the principle of hydrogen flame chemiluminescence in monitoring the concentration of SOz in animal exposure chambers. Brody and Chaney ( 3 ) have applied the same principle in developing a gas chromatography detector specific for sulfur- or phosphorous-containing gases. In these applications, the intensity of sulfur luminescence was found to be an exponential function of sulfur concentration in the flame. Because of this exponential response, it was felt that the sensitivity to sulfur-containing gases in a chromatographic effluent might be increased by pre-establishing a background luminescence with SOz, and thus operate on the more sensitive portion of the response curve. The effect of various levels of background luminescence on the response to carbon disulfide and compounds containing other functional groups was investigated. Detector volume and background chemiluminescent intensity were investigated as parameters that influence instrument response characteristics.
CARRIER GAS
I n SAMPLEVALVE
COLUMN,
2
Apparatus. Figure 1 is a block diagram illustrating the relationship among instrument components. Because an optical filter having a peak transmission at 385 mp was not readily available, one having a peak transmission of 26% at 405 mp was used. The intensity of the sulfur emission band at 405 mp is about 80% of the intensity of the 385 mp band. An RCA 1 P21 photomultiplier tube was supplied with power by a regulated dc power supply having an adjustable range of from 0 to 1500 V and 0 to 10 mA. An electrometer with a full-scale range of from to 0.3 A measures the photomultiplier tube current and drives a recorder. The burner tip, housing, and optical detector assembly as illustrated in Figure 2 were designed in our laboratories and are similar to ones used in previous studies ( I , 2). The burner housing was inverted with the burner tip pointing down from the top and the exhaust port in the bottom. This arrangement allowed the water condensed
+I + He
SOLENOID
VALYE FILTER-SHUTTER
DETECTOR HOUSIUG
t
100 ppm SO2
EXPERIMENTAL
THERMISTOR-CONTROLLED CIR-
I N N2
ELECTROMETER
RECORDER
Figure 1. Block diagram of FLIQD
(1) W. L. Crider, ANAL.CHEM., 37, 1770 (1965). (2) W. L. Crider in “Analysis Instrumentation,” Vol. 4, L. Fowler,
on the cool housing during warm up to drain, thus requiring a shorter time for equilibration to be established. A 5-fOOt column of 0.10-inch Teflon (Du Pont) tubing was filled with 9.1% Squalane on 60-80 mesh Gas Chrom Z. A seven-port gas sample valve with a 1-ml sample loop was used to inject all samples. Reagents. Prepurified grade hydrogen fuel was used. Air was supplied to the burner from a cylinder of compressed dry air. Grade A helium was used as the carrier gas. A cylinder containing approximately 100 ppm SO2 in Nz was prepared in a manner similar to that described by Elfers and Herman (4). All sensitivity and calibration determinations were made using reagent grade chemicals. Operating Parameters. Because a similar burner configuration (with or without shield) gave an optimum response to SOawhen the airflow rate was 470 ml/min and the hydrogen flow rate was 280 ml/min, these flow rates were used through-
R. G. Harmon, and D. K. Roe, Eds., Plenum Press, New York, N. Y . ,1967, p 67. (3) S. S.Brody and J. E. Chaney, J. Gas Chromatogr., 4,42 (1966).
(4) L. A. Elfers and M. Herman, ANAL.CHEM., 39, 1909 (1967). VOL. 41, NO. 3, MARCH 1969
0
531
III
PM TUBE
-
0 I
l
l
1
2
3
4
5
with the shield removed to give a larger luminescent volume. Other operating parameters were the same in both configurations. Except for chlorinated compounds, detector response as a function of sample concentration was determined at the background luminescent intensity giving maximum peak height response for the compound being investigated. The background luminescence for CCll and CHZCI~ calibration was set at the intensity giving maximum peak height response for sulfur compounds, because these two classes of compounds were run simultaneously. The detector responses determined as functions of sample concentration may not reflect the ultimate sensitivity that can be achieved through the use of this detection principle, but serve to illustrate the shape of calibration curves to be expected for the compounds used. The chemical composition of the sample determined whether the background luminescence was intensified or quenched. Consequently, the recorder was usually adjusted so the electrometer response to the background luminescence was midscale and all peaks would be within the range of the recorder.
Figure 2. Burner housing RESULTS AND DISCUSSION
out this study. The helium carrier gas flow rate was maintained at 76 ml/min for all determinations. The SOz flow rate was varied to give the desired background chemiluminescence intensity. Appropriate controls on the recorder were used to suppress the electrometer output at high-intensity background luminescences without loss of sensitivity to small changes in luminescence intensity. The column and sample valve were maintained at room temperature for all measurements. The detector was operated at the equilibrium temperature established by the hydrogen-air flame. A technique similar to the one used by Altshuller et al. (5) that employs plastic bags was used to prepare appropriate sample concentrations in air. Procedure. Detector response characteristics were determined as functions of background luminescence intensity, burner housing volume, sample concentration, and chemical composition of the sample. In determining detector response characteristics as a function of background luminescence, the luminescence was adjusted to a preselected intensity by adjusting the rate of SOz addition to the burner air. Detector response was determined by measuring the chromatographic peak heights of fixed concentrations of several compounds at several background luminescence intensities. The effect of burner housing volume on detector response was investigated for two configurations. The first, as illustrated in Figure 2, was with the borosilicate-glass shield in place to give a small luminescent volume, and the second was (5) A. P. Altshuller, A. F. Wartburg, I. R. Cohen, and S. F. Sleva, Intern. J. Air Water Pollution, 6,75 (1962).
Figure 3 illustrates the types of chromatograms obtained with this prototype detector. These chromatograms show the effect of background luminescence on detector sensitivity and on the response from positive to negative peak as a function of class of compound. As can be seen by examining the air and CS2peaks, the initial response of the detector is rapid, However, recovery of the detector to an equilibrium condition is sluggish and results in an apparent tailing of the peaks. These chromatograms also illustrate the potential specificity that may be obtained with the flame-luminescence intensification and quenching detector (FLIQD). It appears that this detection principle can aid in identifying certain classes of compounds by establishing a certain level of background luminescence or by running the chromatogram at two or more background intensities. Specificity would be established by observing the direction of response (intensification or quenching) of the peaks at these background luminescence intensities. Flame emission detection alone, as in Figure 3 4 does not offer this high degree of specificity because it cannot differentiate between a high concentration of a compound for which it has low sensitivity and a low concentration of a compound for which it has high sensitivity. Figure 4 illustrates detector responses as functions of background luminescence intensity and burner housing volume. From these data it was found that the magnitude of the detector response is increased by factors as large as from 50 to 100 by using flame-luminescence intensification and quenching as compared to flame emission detection. A sub-
Table I. Limits of Detection
Compounds Carbon disulfide n-Propyl mercaptan Carbon tetrachloride Dichloromethane 1,2-Dibromoethane n-Hexane n-Heptane n-Octane Ethyl acetate Methyl ethyl ketone
532
Flame emission, ppm (viv) 0.21
...
FLIQD
Concn., PPm (viv) 0.05 0.86
100
16
100 230
21 76 150 210 250 350 590
... ...
2000 500
...
ANALYTICAL CHEMISTRY
Weight, gram
Rate, g/sec
1.5 X 3 x 10-9 1 x 10-7 7 x 108 X 10-7 5 x 10-7 9 x 10-1 1.6 x 1.2 x 10” 1 . 7 x 10-6
5x 1x 7x 8x 3 x 8X 1x 1x 3 x 2x
10-12 10-10 10-10
10-9
lOW 10-8 10-5 10-8 10-8
Background luminescence, A 5.9 x 3.8 X 3.9 x 3.9 x 1.3 x 1.3 x 1.3 x 1.3 x I ,3 x 1.3 x
10-0 10-8 10-8 10-7 10-7 10-7 10-7 10-7
10-7
r
1
1
lor
100
t'\\ .\\
200
300
400
i ,/I I
-0'
1 x 10.10 0
1
2 3
4
5
6 7 8 9 1011 12131411
RCTENTION TIME. min.
Figure 3. Chromatograms of: 1. air, 2. 1 ppm CS2, 3. 200 ppm CHzCIz, 4. 2000 ppm n-C~H18,and 5. 1000 ppm Br(CHZ),Br at the four background luminescence intensities of: A . zero (flame emission only), B. 2.2 X lop9A, C. 14.3 X A, and D. 69.4 x 10-9 A
1
BACKGROUND LUMINESCENCE INTENSLTY , lo-'
amp
Figure 4. FLIQD response as a function of background luminescence intensity to: I . 200 ppm CHzC12, 2. 1 ppm CSZ,3. 1 ppm CSZ(with glass shield), 4. 1300 ppm wC7H16 (with glass shield), 5. 2000 ppm i-PrOH, 6. 1300 m m n-C,Hla, and 7. 2000 pprn EtAc-
sequent increase in noise level, however, limited the practical sensitivity increase to a factor of 5 to 10. The values presented in the figure illustrate the potential increase in sensitivity that may be achieved by this detection principle. Qualitative evaluation of the raw data obtained during the investigation of the influence of background luminescence on detector response indicates that even though the shielded burner gave a smaller increase in response with increasing luminescence intensity than the unshielded burner, a higher signal-to-noise ratio may be achieved in the shielded burner. Also indicated was that the maximum signal-to-noise ratio for CS2 occurs at a background luminescence intensity of about 6X A rather than at maximum detector response. Maximum signal-to-noise ratios for other compounds studied occurred near the background luminescence giving maximum detector response. Response characteristics of this detection principle as a function of sample concentration were determined at the background luminescence intensity giving maximum detector response for the compounds being investigated. Figure 5 illustrates the response characteristics obtained with the unshielded burner for several classes of compounds. Because these calibration curves were not necessarily determined under maximum signal-to-noise conditions and because peak height rather than peak area was used as a measure of response, these curves cannot be used to accurately estimate the ultimate sensitivity that can be obtained with this detector. This figure does, however, illustrate a fair linearity of response for all the compounds over the range of concentrations used.
2 3 4 5 6 7 SAMPLE CONCENTRATION, P W ( V / V )
8
Figure 5. FLIQD calibration for nine compounds 1, EtAc, 2. MEK, 3. Br(CH&Br, 4. n-Ca14, 5. n-C@ls, 6. CC14, 7. CH2CIz 8. CS2, and 9. mPrSH
Table I lists the limits of detection of several compounds of the experimental apparatus in both the flame emission and flame-luminescence intensification and quenching modes of operation. Data in columns 1, 2, and 3 were obtained by determining sample concentrations and weights that would give peak heights twice the noise level at the elution times obtained under the previously described experimental conditions. Data in column 4 are calculated values for the minimum rate at which those compounds that enter the detector will give a response of twice the noise level. By comparing values in columns 1 and 2, it can be seen that by using the FLIQD at optimum background luminescence, limits of detection for the compounds tested are better by from to those determined by the flame emission mode. The FLIQD has good sensitivity for sulfur and halogenated compounds. Limits of detection for these compounds approach the sensitivity of the flame ionization and argon detectors for these same compounds. For hydrocarbon and oxygenated compounds, sensitivity compares favorably with the thermistor or hot wire detector. ACKNOWLEDGMENT
The authors acknowledge with appreciation the precision workmanship of Bob Dupont in constructing the burner detector housing used in this study. RECEIVED for review July 10, 1968. Accepted October 7, 1968. Mention of products or company names does not constitute endorsement by U. S. Public Health Service. VOL. 41, NO. 3, MARCH 1969
533
