Determination of Hydrogen Cyanide in Combustion Gases by a FourChannel Continuous Analyzer Desmond Alan Reilly Imperial Chemical Industries Limited, Organics Division, Hexagon House, Blackley, Manchester M93 DA, England
A continuous analyzer has been developed for the determination of hydrogen cyanide in gases arising from the combustion of polyurethane foams and other furnlshlng and constructlonal material. It is based on the formation of a red color when cyanide is heated with alkaline sodlum picrate, followed by spectrophotometricanalysis. Concentratlonsfrom Q to 200 ppm by volume can be measured. Of the other compounds llkely to be present In fire atmospheres, aniline, acetonitrile, nitric oxlde, and hydrogen chloride do not interfere while Interference from formaldehyde, acetaldehyde, acrolein, acetone, and sulfur dioxide is slight. The trolley mounted equipment is mobile and transportable and has been used extensively in our own laboratories and In fire trlals on another slte.
In recent years much public attention has been directed towards the dangers to life and health arising during the accidental combustion of furnishing and structural materials, particularly those containing polyurethane and polyisocyanurate foams. A substantial literature has appeared describing the analysis and toxicology of the products of small scale pyrolyses and combustions of individual products. It has, however, been increasingly realized that to gain information on the contribution of a single component of a composite structure such as a chair, it is desirable to burn the whole chair or even a whole roomful of furniture. As part of a program of medium and large scale fire trials, there was a need for continuous measurement of hydrogen cyanide concentrations in fire atmospheres. In the absence of a suitable commercial instrument, a four-channel continuous analyzer has been developed based on the reduction of sodium 2,4,6-trinitrophenate (sodium picrate) to give a red colored compound in which one of the nitro groups is reduced to -NH2 (I,2). Four separate gas samples are drawn into the analyzer through stainless steel lines which are heated to prevent condensation and possible loss of hydrogen cyanide. After filtration, each gas sample stream is mixed with a metered flow of aqueous sodium picrate in which the hydrogen cyanide is absorbed. Each picrate solution is then separated from the gas and pumped through a heated glass coil to complete the reaction and finally passed through a continuous colorimeter, the signal from which is displayed on a potentiometric recorder. This method was chosen because it uses only one reagent and avoids the stepwise addition of several reagents necessary with other methods. The reagent pumping arrangements are thus simpler.
CONSTRUCTION AND USE OF THE ANALYZER Apparatus. 1) A 15-channel peristaltic pump from Chem-Lab Instruments Ltd., Hornminster House, 129 Upminster Road, Hornchurch, Essex R M l l 3XJ, England. 2) Two high temperature oil filled hezting baths from Chem-Lab Instruments Ltd. The original 4O-foot glass coils were replaced with 50-cm coils, 0.75-mm id., with 2-mm i.d. short end pieces. 3 ) A four-channel colorimeter from Chem-Lab Instruments Ltd., with 15-mm path length flowthrough cells and with wavelength se322
lection by 500 nm interference filters. The de-bubblers fitted on the cell inlets are replaced by larger ones (Catalogue No. LK 116-0202-04 C4). 4) Two Kipp and Zonen two-pen, flat bed, potentiometric chart recorders. 5) Four Capex Mark 2 compressor/vacuum pumps from Charles Austen Pumps Ltd., 100 Royston Road, Byfleet, Weybridge, Surrey KT14 7PB, England. 6) A Duplex 4 compressorhacuum pump from Charles Austen Pumps Ltd. 7) Four Gapmeter Flowmeters type GSD, 60-600 cm3/min air from Flowbits, Freepost, Basingstoke RG21 ZXD, England. 8) Four short scale Gapmeter Flowmeters with needle valves, type GSXV, 0.5 to 5 l./min air from Flowbits. 9) Four high vacuum control valves, Model OSID from Edwards High Vacuum, Manor Royal, Crawley, Sussex, England. 10) Four Gelman 47-mm stainless steel, in-line, filter holders. The nylon hose connectors were replaced with specially made brass ones. 11) Gelman glass fiber filters type GF/A, 47-mm diameter. 12) Elkay solvent flexible maniford pump tubing. The following types were used: LK 116-0533-13,0.065, blue, 1.37; LK 116-0533-14, 0.073, green, 1.69; LK 116-0533-09,0.040, white, 0.56 (catalogue No., i.d. in inches, color code, and nominal pumping rate in cm3/min, respectively). All from L. K. Laboratory Supplies, 46 High Street, Alton, Hants GU34 ZEL, England. 13) Elkay solvent flexible tubing, catalogue number LK-0537-05. 0.020-inch i.d. and LK 0537-15,0.081-inchi.d. from L. K. Laboratory Supplies. 14) Tubing connectors made from slightly oversize sleeves of plastic tubing. 15) Four circular self clamping band heaters, approx. 59-mm diameter, 25 mm wide, 100 W a t 25 V. These were used to heat the Gelman filter holders and were made by Injection Services and Supply (Birmingham) Ltd., Middlemoor Lane West, Aldridge, Staffordshire, England. 16) Stainless steel tubing, thick walled, lh-inch diameter. 17) Chrome1 alumel thermocouples. 18) .Insulated nichrome heating wire, 3 W per yard. 19) Sleeve connectors from silicone rubber tubing 5-mm and 6.3-mm i.d. 20) Stainless steel sample lines. These were produced in 3-m lengths. Each was wound with 4.5 m of nichrome heating wire and then covered with asbestos tape. A chrome1alumel thermocouple was placed in each length next to the tube. Where necessary 3-m lengths were joined by quarter inch brass in line couplings. All the heaters were connected in parallel to a 50-V ac supply. Temperatures of 120 to 140 "C were obtained. 21) Glassware as specified in Figures 1and 2. Reagents. 1. Dry Picric Acid. Because of the explosion risk, this material was normally stored under water. The solid was filtered off, spread thinly on a pad of filter paper, and allowed to dry for two days a t laboratory temperature away from sunlight or sources of heat with occasional gentle stirring. Material surplus to requirements was returned to water. 2. Sodium Picrate Reagent. Dry picric acid, 12 g, and 200 g of anhydrous sodium carbonate were dissolved in 4 1. of hot water, the solution being cooled to room temperature. To avoid deposition of heavy metal picrates, used reagent was flushed down the drain with copious volumes of cold water. 3. Standard Potassium Cyanide Solution. About 7.0 g of potassium cyanide was dissolved in 100 cm3 of water. This was standardized by titration with 0.1 M silver nitrate in the presence of sodium hydroxide and sodium iodide. The end point was marked by the first appearance of a faint permanent turbidity caused by precipitation of silver iodide after conversion of the cyanide to sodium argentocyanide NaAg (CN)*. 4 . Standard Hydrogen Cyanide Solution. About 10 cm3 of liquid
ANALYTICAL CHEMISTRY, VOL. 49, NO. 2, FEBRUARY 1977
24/29 socket
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N, ' ,
;
heated glass line
,
',,
24 29ioint
sampletiowmeter
F
r
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Figure 2. Gas mixer and separator
by pass
k mixer
+
to waste
channel 1 blue
c h a m i 2 greal
dotted lines represent airconnectiow behind theboard
Figure 1. Sampling system
hydrogen cyanide was poured from a i-pound steel bottle which had been cooled in ice, into 250 cm3 of methanol. This operation was carried out with great care in a fume cupboard while wearing a suitable respirator. The solution was standardized by titration with 0.1 M silver nitrate as described for the previous reagent. Assembly of the Analyzer. The sampling system was attached to a vertical wooden board 60 cm X 105 cm set 59 cm from the front of a horizontal board 75 cm X 105 cm, thus leaving a shelf 15 cm wide behind the vertical board. The front vertical and horizontal surfaces were faced with Formica laminated plastic. The sampling systems for the four separate analysis channels were mounted side by side on the front of the vertical board (Figure 1).The inlet filter holder containing a glass fiber filter was joined to the outlet of the stainless steel line by a silicone rubber sleeve so that there was metal to metal contact inside the sleeve. The filter holder sat in a specially made bracket attached to the top of the board. The central part of the filter was surrounded by a circular band heater inside which was tucked the end of a thermocouple. The whole filter was insulated with asbestos tape. Its outlet yas connected by a glass tube to the inlet of the gas mixer. This condecting tube was wound with 4 m of heating wire connected to a 25-V supply and insulated with asbestos tape. Details of the gas mixer and separator were as in Figure 2. Gas and liquid connections to this unit are shown in Figure 1.Liquid connections to the processing units of the analyzer are shown in Figure 3. The layout of the processing units was as shown in Figure 4. The wooden structure to which the sampling and processing systems were attached was placed on the upper part of a two-tiered wheeled trolley. The lower part accommodated the Duplex 4 pump, electrical transformers, and the reagent waste bottle. Electrical connections were to multipoint sockets on the back oT the vertical board and the whole system could be plugged into a single 13-A, 240-V mains outlet. Preparation of the Analyzer for Use. About 2 h before beginning the calibration procedure, all units including the heated sampling system are switched on. The oilbath is adjusted to 90 "C. The reagent inlet tubes are dipped into the supply bottle and the by-pass air flow adjusted t o 1.0 l./min and the sample air flow to 100 cm3/min. When the system has been run until there are no air bubbles in the colorimeter cells, the electrical zero of each recorder pen is first set to 5% of full scale and the optical zeros are then set to the same value by adjusting the shutter in each colorimeter channel, the recorder being set to read 0.2 V full scale, and the gain setting on each colorimeter channel to 2.0. The rate of reagent uptake is measured for each channel by noting the volume removed from a graduated vessel, e.g., a 50-cm,' cylinder in 30 min. The rate is usually in the region of 1.3 cm3/min. It declines with the age of the pump tube and is checked a t frequent intervals. The pump tube in reagent channel 1 (Figure 3) should be replaced when the reagent uptake falls below 1.25 ml/min. Calibration. The analyzer is then calibrated with sodium picrate
I
channel 3 white peristaltic pump
towaste
Figure 3. Liquid flow system
dl bath
I
pehtaltic
pump
~
Figure 4. Layout of analyzer units
reagent to which known concentrations of potassium cyanide have been added. The volume of the potassium cyanide solution (Reagent 3) which, when added to 100 cm3 of the picrate reagent is equivalent to 100 ppm (v/v) of hydrogen cyanide in the gas stream, is calculated as follows. Assuming a temperature of 20 O C (at the flowmeter) a pressure of 1atm, and a gas flow of 100 cm3/min, then, for a concentration of 100 ppm (v/v) the rate of hydrogen cyanide input will be 11.25 pglmin. If the measured flow of sodium picrate reagent = A cm"min, then the equivalent micrograms of hydrogen cyanide per 100 cmi of reagent = (11.25 X 1OO)lA and the volume of potassium cyanide solution required to give this concentration is (11.25 X 1OO)lBpl where B is the micrograms of hydrogen cyanide equivalent to 1pl of the potassium cyanide solution. This volume of potassium cyanide solution is added to 100 cm6of sodium picrate reagent and the inlet tube of one channel dipped in this mixture. When each channel is showing a steady reading, its colorimeter gain control is adjusted to give a recorder deflection of 65% of full scale, Le., a net deflection of 60%. By using appropriate volumes of potassium cyanide solution, and running these in a similar manner, additional calibration points are obtained corresponding to 12.5,50,200 ppm (v/v) of hydrogen cyanide. It is only necessary to do a full calibration once for each channel. Subsequently it is sufficient to fix the zero and 100 ppm (v/v) points to make the analyzer response coincide closely with the graph in Figure 5 (lower curve). Normal Use of t h e Analyzer. During a run, the flowmeter readings are carefully monitored and adjusted if needed. Occasionally rapid jerking of the recorder pen is observed. This may be due to air bubbles in the colorimeter cell and can be cured by squeezing its exit tube for a few seconds, and then releasing it sharply. Sometimes the same thing happens but is associated with an accumulation of liquid in the separator. It is caused by blockage of the exit tube from the separator and its is cured by stopping the peristaltic pump, removing ANALYTICAL CHEMISTRY, VOL. 49,
NO. 2, FEBRUARY 1977
323
6 '001
'3
standards externally heated
70
60 standards heated in analyser
50
50
Figure 5.
160
150 200 equivalent ppm HCN added as KCN
Calibration graphs
the blocked tube, and blowing it clear before replacing it. At the same time, surplus liquid in the separator is drained off. During use, the filter on the air inlet becomes contaminated with soot. Though this does not appear to have any adverse effect on the recovery of hydrogen cyanide, the precaution is taken of renewing the glass fiber element of this filter after every second run.
EXPERIMENTAL BASIS OF ANALYZER DESIGN Reagent Composition. A reagent weaker in picric acid than that recommended by Louden and Antrobus (1) is used because their reagent tends to deposit crystals on standing especially when used out of doors in cold weather. As a precaution against this, the reagent is normally filtered before use. Design of Absorption System. It is necessary to secure maximum absorption of hydrogen cyanide in the picrate reagent and to minimize buildup of reagent a t any point in the system, with consequent blurring of the response to changes of hydrogen cyanide concentration. The air and liquid are carried through the absorber in the same direction, as past experience suggests that countercurrent operation may cause buildup of liquid at the point where air leaves the liquid. The gas/liquid separator is in principle a larger version of an AutoAnalyzer de-bubbler with a big air chamber to minimize splashing of liquid into the air exit line. Care is taken to ensure that the base of this chamber slopes down to the liquid exit point so as to prevent the accumulation of a pool of reagent. Speed and Sharpness of Response to Hydrogen Cyanide. The lines carrying reagent from the gashiquid separator to the heating bath and from that to the colorimeter and also the glass coils in the heating bath are made as narrow and short as possible in order to minimize the time to first response and the time from that to the attainment of a steady reading. The shortest times consistent with a near complete reaction of the cyanide are 160 s for first response and 75 s to climb the step. In earlier tests using longer and wider lines times of up to 13 and 3 min, respectively, were obtained. Checking of t h e Calibration Based on Potassium Cyanide. One channel of the analyzer was calibrated with potassium cyanide as described above. Known concentrations of hydrogen cyanide in air were produced by continuous injection of the solution of hydrogen cyanide in methanol (Reagent 4) into a metered air stream (3).These concentrations were supplied to the analyzer at a point immediately downstream of the inlet filter which was removed. The mean recovery of hydrogen cyanide was 94 f 7% (see Table I). Checking of Possible Loss of Hydrogen Cyanide in the 324
Sampling System. The response of the analyzer was again checked with known concentrations of hydrogen cyanide in air but this time the mixture was passed through a 12-m sampling line and the filter before reaching the analyzer. T o simulate real test conditions, this was done when the instrument has previously been used in a rather dirty fire and the sampling line and filter were contaminated with soot. The results are shown in Table 11. The mean recovery of 97% is probably not significantly different from the 94% reported in Table I and indicates that there is little or no loss of hydrogen cyanide in the sampling system. Interferences. Ashida and co-workers ( 4 ) have criticized the use of the picrate method for the determination of cyanide because of interference from aldehydes, ketones, and other, unspecified, reducing compounds. In the combustion products of polyurethane and polyisocyanate foams, those species most likely to interfere are formaldehyde, acetaldehyde, acrolein, acetone, aniline, nitriles, sulfur dioxide, and nitric oxide. Known concentrations of these compounds were prepared by continuous injection or by aspiration or were taken from a cylinder in the case of nitric oxide. Results are shown in Table 111. The compound showing most inteference was acrolein and even this had little effect. In the very few determinations of acrolein carried out in fires, the maximum values obtained were in the region of 3 ppm (v/v). Check of Completeness of Color Development. In this type of analyzer it is not particularly important to have a chemical reaction going to completion. Provided that operating flow rates can be held constant, satisfactory results can be obtained with partial reactions. However, the reason for the sharp curvature of the calibration graph which is concave to the concentration axis a t its upper end (Figure 5) was felt to merit investigation. A series of calibration standards was made by adding known quantities of potassium cyanide to the picrate reagent as above. Then 20 cm3 portions of these were heated for 10 min in a boiling water bath so that the color was fully developed. After cooling, these were run through the analyzer which was run as normal except that the oil bath was unheated. The net recorder deflections were compared with those obtained with similar solutions put through the analyzer with the oil bath at 90 OC but without any preliminary heating of the calibration solutions. The results are given in Table IV. They indicate that the analyzer in its normal mode of operation achieves about 79 f 3%conversion of the cyanide and that the curvature of the calibration graph is probably due to nonlinearity of the colorimeter response at higher levels. In a further set of tests, waste reagent streams from the colorimeter cell were collected while running potassium cyanide standards corresponding to 50,100, and 200 ppm. The absorbances of these were measured in 5-mm cells in a Unicam SP800 recording spectrophotometer. An approximately linear plot of absorbance vs. concentration was obtained confirming the curvature of the analyzer response to cyanide to be due to nonlinearity of the flowthrough colorimeter response at high absorbances. The externally measured absorbance corresponding to 100 ppm is 0.740 in a 5-mm cell. This corresponds to 2.220 in the 15-mm cell of the flowthrough colorimeter. Check of Reproducibility. After setting up the calibration of one channel of the analyzer with potassium cyanide, four different known concentrations of hydrogen cyanide were supplied to the sample inlet. Six readings were taken a t each level. The results of this are shown in Table V. The response of the recorder a t the 300-ppm level was very sluggish,possibly due to the very low proportions of the incident light being transmitted through the colorimeter cell a t this level. It is probably unsafe to attempt to use the analyzer to measure concentrations of hydrogen cyanide greater than 200 ppm.
ANALYTICAL CHEMISTRY, VOL. 49, NO. 2, FEBRUARY 1977
Table I. Validity of Calibration Based on Potassium Cyanide Test No.
ppm HCN (v/v) supplied by injection apparatus ppm HCN (v/v) indicated by KCN calibration % Theory
1
2
3
4
5
6
7
8
18.8
37.6
75.2
150
150
75.2
37.6
18.8
17
35
70
135
152
72
37
17
90
93
93
90
101
96
98
90
Table 11. Recovery of HCN through the Sampling System Test No.
ppm HCN (v/v) supplied to inlet of sampling line ppm HCN (v/v) indicated by KCN calibration % Theory
Table IV. Check on Completeness of Color Development 1. mg HCN per 100 cm3
1
2
3
76
76
38
73
75
36
96
99
95
2. 3.
4.
Table 111. Effect of Interfering Compounds on the Determination of Hydrogen Cyanide
Compound Formaldehyde Acetaldehyde
Apparent ppm (v/v) HCN/100 ppm of Apparent pprn ppm of ppm (v/v) (v/v) compound supplied HCN found supplied 0 0
190 760 50
2 4 6 14 3
100
Acrolein Acetone Aniline Acetonitrile Sulfur dioxide
200 400 26 104 200 800 400 420 15
10 2 5
0 0 2
4 4 3 3.5
12 10 1
0.54
1.08
2.16
25
50
100
200
24
45
70
85
18
37
61
81
19
41
76
160
76
82
76
80
Table V. Reproducibility of Readings a t Different HCN Concentrations Calculated ppm HCN ppm HCN found
0.6
0 0
120 1500 5000
7 7 6 5 3
1000
0
0
~~
6.
0.27
0 0
4 7 80 150
50
Nitric oxide
5.
reagent, added as KCN Equivalentcalculated ppm (v/v) HCN in air stream Net recorder deflection after external heating to produce full color development Net recorder deflection after heating in analyzer ppm (v/v)HCN corresponding to readings in line 4, assuming the color to be fully developed % Conversion of cyanide, i.e., (line 5 figure x loo)/ line 2 figure
~~
The coefficient of variation a t the 46- and 92-ppm levels is quite good and is adequate a t the 176-ppm level. This last concentration is so high from a toxicological point of view that one would not be concerned with the precise measurement of small concentration differences. Application of the t-test to the readings taken a t 176 ppm show that there is no significant difference between this value and the mean of the observed readings. For the readings taken at 46 and 92 ppm, this difference is significant. The negative bias so revealed could be a combination of reading errors of the two flowmeters involved, one in the analyzer and the other in the apparatus used to generate concentrations of HCN in air.
DISCUSSION The investigation has shown that the process of absorbing a gas in a solution, heating, and measuring the color produced can be adapted t o the continuous monitoring of hydrogen
Mean ppm HCN found Standard deviation Coefficient of variation, (std dev X 100)/mean (Mean ppm found - ppm calcd) X loo/ ppm calcd (estimate of bias)
176 200 157 163 176 197 197 181.7 18.9 1.7 10.4
46 44 43 45 44.5 45 44.5 44.3 0.75 1.7
92 85.5 88 85.5 84 87 87 86.2 1.44
-3.7
-6.3
+3.2
300 320 320 320 320 304 320 3i7.3 6.5 2.1 +0.6
cyanide concentrations in dirty atmospheres without loss in the sampling system. Once the analyzer is set up and calibrated, it is stable and needs little or no adjustment of the controls to produce the predetermined response to the calibration solution. Interference from other components of typical fire atmospheres is slight and can probably be neglected although in the absence of information about typical levels of aldehydes, ketones, and sulfur dioxide, it is difficult to be completely certain on this point. The analyzer is used routinely in our own laboratories. It is robust, mobile, and fairly simple to operate. It has survived road journeys of 120 miles without damage. Measurements of hydrogen cyanide concentrations have been made in fires involving loads as small as a single cushion of flexible polyurethane foam and as large as a whole roomful of furniture. ANALYTICAL CHEMISTRY, VOL. 49, NO. 2, FEBRUARY 1977
325
ACKNOWLEDGMENT
(3) J. C. Gage, J. Sci. Instrum., 30, 25 (1953). (4) K. Ashida, F. Yamauchi, M. Katoh, and T. Harada, J. Cell. Plast. 10 (4), 181-185 (1974).
T h e a u t h o r acknowledges t h e help given by P. Maddison i n t h e construction of t h e analyzer a n d in its commissioning in field trials.
RECEIVED for review J u n e 14,1976. Accepted November 9, 1976. T h i s work was partly supported by a g r a n t from t h e
LITERATURE CITED
Products Research Committee (U.S.A.) in association with t h e International Isocyanate Institute Inc. of New York.
(1) C. Louden and H. Antrobus, Ana/yst(London),64, 187-189 (1939). (2) A. Chaston Chapman, Analyst (London),35, 470-477 (1910).
Chlorine-Selective Detection for Liquid Chromatography with a Coulson Electrolytic Conductivity Detector John W. Dolan and James N. Seiber* Department of Environmental Toxicology, University of California, Davis, Calif. 956 16
The design and operation of a liquld chromatography/Coulson electrolytic conductivity detector (CECD) analytical system are described. Vydac totally porous reversed phase column effluent (aqueous methanol) was introduced to the CECD quartz combustion tube through a stainless steel inlet. The conductivity response of pyrolysis products formed In the presence of hydrogen was monitored with slight modifications of the standard CECD cell operation. The system showed high selectivity to organochlorine compounds relative to hydrocarbons, with a linear range of lo5 and minlmum detectability of 5-50 ng for lindane. The CECD detectability was better than that of the UVSe4detector and its selectivity greater than that of the UV22. detector, when CI-containing aliphatlc pesticides were examined. This was reflected in the successful CECD analysis of uncleaned extracts of lettuce and river water fortified to sub-ppm levels with aldrin and dieldrin and the corresponding failure of the UV detector at either 254 or 220 nm in the same analyses.
High performance liquid chromatography ( H P L C ) has become increasingly useful for analysis of low levels of chemicals in biological a n d environmental samples. F o r example, H P L C represents a potential alternative t o gas-liquid chromatography (GLC) for t h e residue analysis of pesticides lacking sufficient volatility or thermal stability for GLC determinations ( 1 ) . T h e utility would likely be extended were there available element-selective detectors for H P L C comparable t o those in current use with GLC. Electrochemical (2-5), spray impact (6), alkali-flame ionization (7), electron capture ( 8 ) ,a n d other experimental detectors offer some selectivity which may be useful in pesticide residue analysis. B u t among those commercially available, only the ultraviolet (UV) a n d fluorescence photometric detectors have provided t h e sensitivity and detectability needed for practical applications in this field (1, 9, 10). Selectivity with t h e photometric detectors is limited t o those compounds or their derivatives having UV absorbance or fluorescence properties n o t possessed by sample interferences; these requirements are n o t m e t by m a n y pesticides a n d their conversion products of current environmental importance. T h e Coulson electrolytic conductivity detector (CECD) is a n example of a n element-selective detector widely used in the GLC determination of pesticides (11,12).In the reductive mode of t h e CECD, with n o pyrolysis catalyst, compounds 326
containing C1 or Br respond with little or no interference from chemicals which lack these heteroatoms. T h i s selectivity, which may b e extended to S- a n d N-containing compounds through appropriate choice of pyrolysis gas, catalyst, and effluent scrubber, reduces the need for time-consuming cleanup of environmental samples prior t o determination (13). We have adapted t h e CECD t o monitoring t h e effluent from HPLC. Our system was aimed at providing selective detection of poorly UV-absorbing organochlorine pesticides resolved by reversed phase chromatography. We examined t h e system’s design a n d optimization, its response t o some representative pesticide standards, a n d its applicability t o analysis of a few environmental samples fortified with aldrin a n d dieldrin. A U V detector was used for comparison with t h e CECD, t o aid in evaluating t h e latter’s performance with HPLC. GLC/ CECD was also used t o compare C E C D performance with t h e two modes of chromatography.
EXPERIMENTAL Materials. Pesticides and other chemical standards, generally of 99% or greater purity, were obtained from manufacturers. The following Mallinckrodt solvents were used: Nanograde acetonitrile and hexane, absolute diethyl ether and methanol, and reagent grade isopropanol and petroleum ether. Ion exchange resin (AG 501-X8(D), Bio-Rad Laboratories, Richmond, Calif.) was used to deionize the recirculating CECD water supply. HPLC Components. The HPLC system was assembled in this laboratory from several components. Single piston or dual piston pumps, 5000 psi, with pulse dampers (Laboratory Data Control, Riviera Beach, Fla.) were used at various times with similar results. Injection was through a Valco valve (Laboratory Data Control) fitted with a 12.5- or 30-pl sample loop, or a Rheodyne Model 70-10 valve (Rheodyne, Berkeley, Calif.) fitted with a 20-pl sample loop. A 5 cm X 4 mm i.d. guard column packed with 37-40 pm Vydac reversed phaqe packing (Separations Group, Hesperia, Calif.) was placed between the injector and column during analysis of environmental samples. A 25 cm X 3.2 mm i.d. reversed phase column of 10-wm nominal particle size (Vydac 201 T P reversed phase, Separations Group) was used in all analyses. The mobile phase, approximately80% methanol in deionized water pumped at a flow rate of 0.5 ml/min, was adjusted slightly in composition to effect solute elution within 20 min of injection. A Spectrometer I variable wavelength detector (Laboratory Data Control) was used for UV detection. CECD Interface and Components. A Coulson electrolytic conductivity detector furnace, cell, and deionizer (Tracor, Austin, Texas) were used with the modifications noted below. In the final configuration of the LC/CECD system (Figure l), effluent from the analytical column entered a 1.59-mm o.d., 0.18-mm i.d. No. 304 stainless steel tube (the inlet) extending 6 cm into the furnace. The inlet tube, a 1.59-mm0.d. stainless steel sidearm allowing
ANALYTICAL CHEMISTRY, VOL. 49, NO. 2, FEBRUARY 1977
