A transpiration-g.l.c. apparatus for measurement of low vapour concentration

M-1272 .J. Chem. Thermodynamics 1981, 13, S-601

A transpiration-g.1.c. apparatus for measurement of low vapour concentration J. L. HALES,

R. C. COGMAN,

and W. J. FRITH

Division of Chemical Standards, National Physical Laboratory, Teddington, Middx TWl I OL W, U.K. (Received 27 November 1980) Equipment is described for measurement of vapour concentration, in which the functions of a transpiration apparatus and a gas chromatograph are combined. The equipment was commissioned by making measurements on 1,2-ethanediol (ethylene glycol) and dibutyl 1,2benzenedicarboxylate (dibutyl phthalate) covering the vapour pressure range 2 x lo-’ to 2000 Pa; good agreement was found with published values. Measurements were also made on a herbicide, butyl 2,4-dichlorophenoxyacetate, and on ethanol,2,2’-{oxybis(2,1ethanediyloxy)}bis(tetraethykne glycol). All measurements were made within the temperature range 283 to 423 K. Two modes of operation are described. of which one discriminates against impurities.

I. Introduction At the present time there is enhanced interest in reliable saturation vapour concentrations in the atmosphere of pesticides, herbicides or potentially harmful chemicals, especially for vapour pressures below 100 Pa. Although the interest continues, it is regretted that the project associated with the work described below has been terminated for economy reasons. The aim of the present work was to develop a convenient method of measurement of vapour concentration (or vapour pressure) with a repeatability of about 5 per cent. Discrimination against impurities, particularly volatile impurities, was of prime importance. The favoured experimental method followed from the work of Friedrich and Stammbach,“) who collected transpired material in a cold trap, which was then transferred to a g.1.c.apparatus and heated. In the present equipment the two stages of transpiration and g.c. analysis are combined, the apparatus being based on a Perkin-Elmer model F-11 gas chromatograph. In the course of the work an alternative method of operation suitable for a higher range of pressures was evolved and this is essentially that described by Franck”’ and by Eggertsen et al.“) The two methods will be referred to as the “collection” method and the “continuous” method. The first method gives a typical chromatographic peak from the (flame ionization) detector while the second, in principle, gives a constant signal corresponding to the concentration of the vapour in the carrier gas. 0021-9614/81/060591+ 11 $01.00/O 37

V 1981 Academic Press Inc. (London) Ltd.

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J. L. HALES, R. C. COGMAN, AND W. J. FRITH

FIGURE 1. Layout of apparatus. Arrows on lines show direction of nitrogen flow. Temperature controlled zones are enclosed by dashed lines. A, Row controller; B, pressuregauge; C, mercury manostat ; D, pressure bleed through needle valve; E, solenoid valve; F, flowmeter; G, red LED; H, light-activated switch; J, timer; K, process timer; L, charcoal filter; M, copper coil ; N, saturator with demountable couplings; 0, sample on inert support; P, stirred oil bath in Dewar flask; R, injection port; S, g.1.c.oven; T, 3 mm column ; U, FID detector; V, heated 1.5 mm line.

2. Experimental The layout of the equipment is shown in figure 1. The controlled flow of dried nitrogen can be diverted through an automatic displacement-type flowmeter F (expansion bulbs and spray traps are not shown). The liquid-filled tube constitutes a cylindrical lens which focusseslight from the red light-emitting diode G on to a lightactivated switch H ; the time interval between the two trigger positions is measured by an electronic timer J. Flow rate of nitrogen is measured at the pressure of the saturator N, a procedure which avoids the need to measure the system pressure. Flow rates are about 0.25,0.5, and 0.75 cm3 s-l. At least two different flow rates are used, with differing collection times, since this gives a sensitive indication of trouble due to leakage, condensation, or inadequate conditioning. COLLECTION

METHOD

(2 x low3 TO 40 Pa)

Nitrogen gas at ambient temperature is passed through the sample saturator N for a preset time, controlled by a process timer K and by a solenoid valve E immediately preceding the saturator. This arrangement allows the sample-saturated gas to proceed via a heated line V to the cold chromatograph column T without the interposition of an elaborate heated valve. The 3 mm diameter chromatograph

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column, containing Porapak P, acts as a trap for the sample and does not need to be cooled below ambient temperature. Column length is between 4 and 20 cm depending on the volatility of the sample. As soon as sample collection is complete, the oven temperature programmer is activated and the column is heated to a temperature appropriate for elution of the sample; the area of the resulting peaked signal from the flame ionization detector U is measured with a Kent Chromalog 1 integrator. The amplifier attenuation was calibrated and the linearity of the integrator was confirmed. Since the column can be left in position for the whole course of measurements, including changes in flow rate and saturator temperature with conditioning procedures (seebelow), the equipment is run as a normal chromatograph so that the detector can be left undisturbed. This procedure discriminates in principle against volatile impurities. Oversaturation of the column produces a plateau with a long “tail” rather than a peak, and since it is desirable for the time of a run to exceed 15 min, this imposes an upper pressure bound (dependent on the compound) for application of the method ; this limit was reached in the “collection” measurements in tables 2 to 4. The lower bound is probably about 10e4 Pa, corresponding to about 20 per cent accuracy for a 5 h run. The integrator count is calibrated for mass of sample by volumetric injection of a solution of known concentration of the substance under study directly on to the cold column packing, via the port R. The column is then taken through the identical temperature cycle to that used with the collected sample. The solvent, here isopropanol, is well separated from the solute even in the shortest column. CONTINUOUS

METHOD

(0.2 TO 2000 Pa)

If an empty tube at elevated temperature is substituted for the packed column, the detector output corresponds to the total vapour content of the gas stream. Measurements are made first with the gas stream passing through the saturator, then by by-passing it. This procedure permits a considerable extension of the upper pressure bound for more volatile compounds, but must be used with caution with less volatile compounds (see below under Discussion, dibutyl phthalate). The best criterion of success is agreement between measurements by both methods at a temperature at which they overlap. The upper pressure bound, which was reached with the two glycols (see tables 2 and 4), relates to unstable vapour production probably influenced by saturator design and packing. Calibration is more difficult involving injection of 10 mm3 of pure sample in 1 mm3 lots into the hot empty tube, with integration of the resulting ill-shaped area. EXPERIMENTAL

TECHNIQUES

A number of important details of technique identified during the work are listed below. Flow lines. Prior to the charcoal filters L, Drallim connectors with rubber gaskets are used on 3 mm copper tubing. The glass filter vesselsL, with 2 cm diameter no. 4

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glass sinters at the exit, are attached to Swagelok couplings with Teflon gaskets. All joints beyond the filters are made with Swagelok couplings and 3 mm tubing, both in stainless steel. The heated line V from the saturator consists as far as possible of vacuum-brazed joints in a 1.5 mm stainless-steel line; the small line diameter minimizes the effect of back-diffusion at the line junction above the oven S, as proved by making blank runs. A stainless foil disk brazed to the line just above the lid of the thermostat P prevents diffusion of bath oil along the line heater. A low-tension nichrome-wire heater, in woven glass sleeving, is wound on the line V in four separate sections. Each section has a variable resistance in parallel so that the temperatures of the sections can be matched roughly with the assistance of thermocouples. Since this matching is upset by the oven running at ambient temperature, the oven fan is switched off during collection. Line temperature is maintained within +2 K by a thermocouple controller and it should be at least 50 K higher than the saturator to avoid any possibility of cold zones. In the early work a cyclic effect, synchronous with the temperature cycling of the heated line, was observed on the plateau obtained with the “continuous” method. The effectwas most pronounced at low temperatures with a 3 mm line and was greatly reduced after the above temperature matching of the new 1.5 mm line. Saturator. The saturator N consists of a tube packed with an inert support 0 mixed with the sample material. The first saturator was made with three turns of 9.5 mm stainless-steel tubing, outer coil diameter 6 cm (to fit inside a 1 dm3 Dewar flask). Later, following leakage problems with the 9.5 mm Swagelok joint, a smaller saturator, having l/6 of the previous volume, was made with one turn of 6.5 mm stainless-steeltubing. The smaller saturator requires about 0.3 g of sample, depending on the type of inert packing. No significant changes in performance were found using different saturators or packings. The stirred silicone-oil bath P is controlled to 20.05 K with a proportional temperature controller made in the laboratory. Temperatures are measured by a calibrated copper-to-constantan thermocouple with a Tinsley Vernier Potentiometer. Calibration. The reproducibility of peak areas on injecting standard solution was poor (t 5 per cent or more) when 1 mm3 plunger-in-needle syringes were used; 10 mm3 plunger-in-barrel syringes are preferred as they give a reproducibility of + 1 per cent; presence of any air bubbles in the glass barrel is immediately evident. Solutions of concentrations of 0.04 per cent by volume (or less) in isopropanol gave significantly lower integrator counts than for those in the range normally used, 0.2 to 10 per cent by volume. Whether this was due to adsorption on the syringe or glassware, or to inadequate conditioning (see below) has not been investigated. Calibrations made early in the day, before there has been any conditioning, usually give low counts; calibrations made immediately after runs with high vapour concentrations can give high counts. Early practice included “normalizing” each “collection” run by injection of isopropanol, whose peak area was measured separately. However, experience showed that the sensitivity of the equipment is sufficiently stable to make this practice unnecessary.Nevertheless any polymerization on the column packing (see below under Materials) causes increased pressure drop

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across the column, with a change in the calibration due to a change in the nitrogento-hydrogen ratio at the FID. At hydrogen flow rates somewhat higher than those recommended for the Model F-11 chromatograph a fairly linear relation obtains between detector sensitivity and nitrogen flow rate, over the range 0.25 to 0.75 cm3 s-i ; a doubling of the nitrogen flow rate increases the sensitivity by about 30 per cent. Column packing. A well-packed g.1.c.column at ambient temperature has proved to be highly effective as a sample trap. However, on injecting a solution of 1,2ethanediol, the most volatile material used, on to a 4 cm column containing Porapak P and leaving at ambient temperature for 1 h before heating, an output peak was obtained showing marked differences from the peak obtained on heating immediately: in the former case the peak had a decreased retention time, distorted shape, and a low integrator count. As a result all measurements on 1,2-ethanediol were made on a 20 cm column for which the above features were far less significant. Ideally the measurements should be linked with g.1.c.estimation of impurities by conventional equipment, to permit optimum selection of packing material ; the use of Porapak P in this work is for convenience, other packings might be superior. Conditioning. As the work proceeded it became evident that low results were being obtained, for two reasons: (a) the 5 min “collection” runs originally used gave insufficient time for equilibration ; 15 min is the lowest permissible time for a run ; and (b) it is essential to condition the flow lines and the packed column or empty tube, prior to each run. Conditioning is achieved by heating the column oven S to its selected peak temperature then diverting the nitrogen stream through the saturator for 20 to 30 min. Next, for “collection” runs, the nitrogen stream is switched back to by-pass the saturator. The FID output now falls to a minimum, indicating removal of volatile material from the column and flow lines, following which the oven is cooled down. Conditions are now correct to commence the run, which usually occupies between 15 and 120 min. The necessity for the above procedure is implied by the work of Leggettt4i on adsorption of TNT. Continuous runs. Estimation of the pleateau height is achieved by linking the switch in the process timer K to the Integrator; 5 min is sufficient to give a reliable count under the plateau. The saturator is then by-passed and the count conducted for the zero setting. For both casesmeasurements are repeated until sensibly constant. Results obtained by the “continuous” method include contributions from any impurities present (excluding water). Volatile impurities in the sample will be concentrated in the vapour and so will be progressively removed. Their contribution to the “continuous” measurement can be estimated if separate peaks are obtained during the “collection” procedure (see below under Discussion. butyl 2.4dichlorophenoxyacetate). AUTOMATIC

SEQUENCE

Because of the relatively large volume of the flow system, arising mainly from the flowmeter F, the build-up of pressure across the column on heating the g.1.c.oven is

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slow. Likewise the cooling down of the oven involves a slow decay of pressure. For this reason an automatic sequencewas devised for resetting the equipment at the end of each run, and of each conditioning period. Although not required for the measurements the pressure gauge B gives a valuable indication of the above pressure changes. The tap of the mercury monostat C will have been opened previously, when the oven was cold, then closed to set the pressure. The automatic sequencecommences after the oven heater is turned off and the oven door opened. It involves (a) a 6 min delay after which the pressure-bleed solenoid valve opens, closing when the mercury contact breaks, (b) a further 6 min delay after which the flowmeter solenoid valve is triggered, (c) the lower light trigger de-energizesthe flowmeter solenoid valve, freezes the timer display, and initiates a flashing warning lamp, signifying readiness to proceed. The sequence unit was assembled from solid-state timers, transistors, and thyristors to effect the required latched operations and triggering of relays. If the oven door latch could be sprung electrically and the oven heater switched off by a heavyduty relay, the conditioning sequencecould be automated as well; the timing would vary with nitrogen flow rate. The demands on the operator would be even less with such an arrangement, while a more sophisticated integrator would take care of drifts in the base-line at high sensitivities, the largest single source of inaccuracy. MATERIALS

For all four materials, the mole fraction of organic impurity was estimated by g.1.c. The sample of ethylene glycol (EG), the samematerial as used by Ambrose and Hall,“’ contained 0.04 per cent of impurities. The sample of dibutyl phthalate (DBP) supplied by Fluka was not purified further ; it contained 1.0 per cent of impurities. The sample of tetraethylene glycol (TEG), a water-white technical grade, was not purified further ; it contained 2.0 per cent of impurities. The sample of butyl 2+dichlorophenoxyacetate (B 2,4-D) was purified by recrystallization from solvents; it contained 1.9 per cent of impurities. EG was found to polymerize steadily on the Porapak P column packing despite an operating temperature of only 373 K. A much smaller amount of polymerization occurred with B 2,4-D, run at 473 K. DBP and TEG, run at 473 and 453 K respectively, showed no signs of polymerization. To avoid accidental contamination when commencing measurements with a new sample in the saturator, it was found advisable (a) to clean the flow line V with solvents, (b) to repack the column used as a sample trap, (c) to clean the FID detector (a detector in a constant-temperature oven would probably offer advantages for this work), and (d) to run the saturator at the highest temperature planned for measurement for a period of several hours, to reduce the level of volatile contaminants; this is particularly important for “continuous” runs. 3. Results The formulae used to calculate the results are

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C,/gcmW3 = (T,,blT)(rn,,lr)(mlg)/l/,,,/cm3),

(1)

(p,/Pa)/(C,/g cmm3) = 8.3145 x lO"(T,,,/K)/(M/g mol-‘).

(2)

where C, is the experimental vapour mass concentration and ps is the experimental vapour pressure, both at T, the saturator temperature, Tarn,,is the ambient temperature, M is the molar mass assuming a monomeric vapour species,I$,,, is the flowmeter volume (here 14.13cm3), tflowis the time for flowmeter operation, t is the time for collection or passageof sample, m is the mass of sample collected or passing, calculated from the integrator count, the flow rate, and the calibration of count per unit mass against flow rate. It should be noted that a formula used by Friedrich and Stammbach,“’ corresponding to our equation (l), erroneously employs T instead of Tamband (one) symbol for saturator pressure (pb) instead of 760 (“tori-“). The assumption in equation (2) of ideal-gas behaviour is acceptable at the very low partial pressures of our test materials (see also under Discussion). Measurements on the four compounds listed above under Materials are shown in tables 2 to 5. The letters s, m, and f under “flow” refer to slow, medium, and fast, relating to the approximate flow rates of nitrogen, where s = 0.25, m = 0.5, and f= 0.75 cm3 s-l. For the results by Franck listed in table 3, s = 0.37. m = 0.51 and f= 0.67 cm3 s- ‘. 4. Discussion Table 1 lists constants for empirical expressions which give the best fit to the experimental measurements listed in tables 2 to 5. It should be emphasized that these measurements are in fact of vapour concentrations calculated from equation (1) and that the vapour-pressure values derived from them by equation (2) might be erroneous if the assumption of monomeric vapour speciesis unwarranted. However, vapour-concentration values back-calculated from the equations in table 1 will be correct. The comparisons between measurementsfrom different sources are shown in the last columns of tables 2 to 5, where 0.01 represents approximately 1 per cent of p,. ETHYLENEGLYCOL

The agreement in table 2 between the results from the “continuous” and the “collection” methods is particularly gratifying. In the light of the above remark about TABLE 1. Parameters in the equation : ln(p,,,,/Pa) = u+b(T/K)~~‘+((T/K)-‘, giving the best fit to experimental measurements in tables 2 to 5, with standard deviations cT(ln(p,/p,.,,); Compound symbol

Formula

EC

C&Oz

DBP

GchA

TEG

C.sH,sOs

B 2,4-D

CI,H,.&W,

a

b

23.1259 27.5178 23.0121 26.5361

-4648.55 - 8739.43 -6135.65 - 7514.03

‘

-

503391 330691 602690 566224

0 i Mw.~lc

0.032 0.029 0.0062 0.0048

)I

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TABLE 2. Literature values and experimental measurements of the vapour mass concentration pressure of ethylene glycol Type

r/b, flow

7-W

Ebulliometric measurements, Ambrose and Hall’“’

374.010 377.019 397.795 419.152

Extrapolations from ebulliometric measurements, Ambrose and HaLIts’

273.150 283.150 293.150 313.150 333.150 353.150 373.150

‘Continuous” measurements, glass beads in large saturator

s m f S

m f S

m f f S

m f S

m f S

m “‘Collection” measurements, 20 cm column, glass beads in large saturator

l/2. s 1. s l/2, m 112,m 1. m l/2. f 1. f l/2. s 1, s l/2, m 112. m

1,m

112. f ‘1, f l/2. s

106CJg cm 3

PJPa 2208 2584 7032 17332

and vapour

Wd’Pa)

~nWp,,t,J

7.700 7.857 8.858 9.760

0.002 0.002 -0.001 -0.010

0.962 2.777 7.378 41.96 187.1 683.0 2112

- 0.039 1.021 1.998 3.737 5.232 6.526 7.655

O.CQO -0.009 -0.013 -0.011 -0.005 O.ooO 0.002

283.00 282.83 283.12 293.16 293.06 293.20 313sxl 313.12 312.92 313.24 333.09 333.19 332.87 347.70 347.72 346.89 373.32 373.30

0.0712 0.0748 0.0700 0.1855 0.1928 0.1827 1.ooo 1.038 1.014 1.051 4.145 4.208 4.435 10.01 10.24 10.17 43.31 41.95

2.698 2.834 2.656 7.285 7.568 7.174 41.91 43.54 42.48 44.12 184.9 187.8 197.8 466.2 476.9 472.6 2166.0 2098 .O

0.992 1.042 0.977 1.986 2.024 1.970 3.736 3.774 3.749 3.787 5.220 5.235 5.287 6.145 6.167 6.158 7.681 7.649

- 0.022 0.045 - 0.050 - 0.026 0.022 - 0.046 0.000 0.029 0.019 0.03 1 -0.013 -0.005 0.069 -0.048 -0.027 0.016 0.019 -0.012

282.90 282.95 282.94 283.17 282.88 283.09 283.24 293.05 293.00 293.08 293.66 293.08 293.15 293.15 313.12

0.0715 0.0714 0.0775 0.0758 0.0746 0.0740 0.0737 0.1848 0.1805 0.1930 0.2011 0.1909 0.1836 0.1826 0.997

2.711 2.706 2.938 2.873 2.825 2.805 2.795 7.254 7.084 7.577 7.911 7.495 7.210 7.170 41.82

0.997 0.996 1.078 1.055 1.039 1.031 1.028 1.982 1.958 2.025 2.068 2.014 1.975 1.970 3.733

- 0.007 -0.013 0.069 0.023 0.037 0.007 -0.011 -0.019 - 0.039 0.020 0.011 0.009 -0.036 -0.041 -0.012

monomeric vapour, the same is true for the agreement of our measurements within the standard deviation with the extrapolation of the ebulliometric measurements reported by Ambrose and Ha11t5’(seefigure 2 of that reference).It would appear that this extrapolation, carried to temperatures 100 K lower than those of the ebulliometric measurements, gives results of about the same reliability as the direct

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TABLE 3. Literature values and experimental measurementsof the vapour massconcentration and vapour pressure of dibutyl phthalate Type

t/h, flow

Effusion measurements, Birks and Bradleyc6’

“Continuous” measurements, Franck”’

S

m f S

“Collection” measurements. 4cm column, glass beads in large saturator

m f S m I s m f 1, s l/2. m 1. m 1. m l/2, s 1. s l/2, m W., m 1, m l/2. s

1. s

112.m

1, m l/2. s 1, s Ditto, small saturator

112,m 2. s 1, m 1, s 1, m

l/2, m “Coliection” measurements, 12 cm column, quartz sand in small saturator

1, m 512. m 112,m 2, m l/2, m

l/2, m 112,m l/2. m 114,m

T/K 293.05 296.15 298.15 303.15 308.15 313.15 316.15 316.65 317.15 359.65 359.65 359.65 378.65 378.65 378.65 398.65 398.65 398.65 417.65 417.65 417.65 313.04 313.07 313.07 313.07 333.33 333.18 333.21 333.21 333.24 353.13 353.11 353.17 353.10 373.08 373.35 373.09 293.00 293.05 303.26 303.28 333.42 293.05 293.15 303.25 303.30 313.22 333.16 353.11 353.07 373.24

lOY,/g cmm3

pslPa

0.001907 0.002733 0.003640 0.006666 0.01180 0.02106 0.02933 0.02959 0.03346 1.53 1.63 1.76 9.42 9.88 10.5 37.8 36.9 34.9 136.0 109.0 103.0 0.002564 0.02398 0.002495 0.02333 0.002430 0.02273 0.002482 0.02321 0.01926 0.1917 0.01742 0.1734 0.01867 0.1858 0.01787 0.1779 0.01850 0.1842 0.1046 1.104 0.1042 1.099 0.1102 1.162 0.1032 1.089 0.4787 5.335 0.5064 5.648 0.5234 5.833 0.0002541 0.002224 0.0002468 0.002160 O.ooO8032 0.007276 0.0008258 0.007481 0.02004 0.1996 0.0002358 0.002064 0.0002348 0.002056 0.0008006 0.007252 0.0008199 0.007428 0.002630 0.02461 0.01835 0.1826 0.1071 1.130 0.1054 1.112 0.5200 5.798

WWPa) - 6.262 - 5.902 - 5.616 -5.011 -4.440 - 3.860 - 3.529 - 3.520 - 3.397 0.425 0.489 0.565 2.243 2.291 2.351 3.632 3.608 3.552 4.913 4.691 4.635 -3.731 -3.758 - 3.784 - 3.763 - 1.652 - 1.752 - 1.683 - 1.727 - 1.692 0.099 0.094 0.150 0.085 1.674 1.731 1.764 -6.108 -6.137 -4.923 -4.895 - 1.611 -6.183 -6.187 -4.926 - 4.902 - 3.705 -1.700 0.122 0.106 1.757

WJpc,,,) -0.107 -0.139 -0.102 -0.102 -0.114 -0.097 -0.094 -0.140 -0.071 -0.236 -0.162 - 0.096 0.113 0.161 0.221 0.118 0.094 0.038 0.216 -0.006 - 0.062 0.044 0.014 -0.012 0.009 0.025 -0.060 0.005 - 0.039 - 0.007 -0.019 - 0.022 0.029 - 0.029 -0.043 -0.006 0.046 0.054 0.018 - 0.027 -0.001 0.057 - 0.028 - 0.042 - 0.029 -0.010 0.049 - 0.006 0.006 -0.006 0.028

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measurements from the present work. By implication, this is true wherever this procedure can be followed, such as the related work on diethylene glycol,“’ with an extrapolation of 140 K. A few of the ebulliometric measurements are listed to demonstrate the agreement outside of our temperature range. DIBUTYL

PHTHALATE

The use of different saturators and different column packings (table 3) did not affect the results within the experimental error. Results obtained from 333 to 373 K using the “continuous” method were between 10 and 35 per cent higher than those obtained by the “collection” method, and have been omitted. The discrepancy is thought to be due to the contribution from volatile impurities, the effect of which would be very much greater for this involatile compound than for the relatively volatile ethylene glycol, at comparable temperatures. The measurements by Birks and Bradley’@are seento be between 7 and 12 per cent lower than ours, a not unreasonable agreement. The considerable scatter of the measurements by Franck”’ which takes place within 24 per cent of our measurements, appears to reflect our experience with the “continuous” method. TETRAETHYLENE

GLYCOL

“Collection” measurements (table 4) at 373 K showed a main peak preceded by two smaller peaks; only the main peak appeared in the calibration runs. The area of the smaller peaks was about 4 per cent of the main peak, and all results obtained by the “continuous” method were corrected accordingly. The rigorous procedure of making additional short “collection” runs at 398 and 423 K was not employed.

TABLE 4. Experimental measurements of the vapour mass concentration and vapour pressure of tetraethylene glycol Type “Continuous” measurements, glass Beads in large saturator

r/h, flow S

s m S

m ‘Collection” measurements, 4 cm column, glass beads in large saturator

l/2, m 1, m 1. s l/2, m l/2. s 114,m 114,m

T/K

106CJg cme3

PAPa

In(pJPa)

W,/p,,~,)

373.60 373.57 373.57 398.23 398.21 424.40 323.24 323.23 348.32 348.28 373.48 373.56 373.49

0.5948 0.6129 0.6033 2.555 2.622 10.209 0.01287 0.01250 0.1054 0.1007 0.5841 0.6094 0.6315

9.512 9.801 9.648 43.56 44.70 185.5 0.1781 0.1730 1.572 1.501 9.338 9.745 10.096

2.253 2.282 2.267 3.774 3.800 5.223 - 1.726 - 1.755 0.452 0.406 2.234 2.277 2.312

-0.018 0.013 -0.002 -0.031 -0.004 0.015 0.012 -0.016 0.023 - 0.020 - 0.029 0.008 0.048

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TABLE 5. Experimental measurementsof the vapour massconcentration and vapour pressure of butyl2.4 dichlorophenoxyacetate r/h, flow

Type Collection” measurements, 4 cm column, quartz sand in small saturator

BUTYL

l/2, m 1, m I. f l/2. m 1. m l/2, f 112,m 1, m 2. m ll2. f I. f 112,m 112,m 112,f

T/K 293.20 293.28 293.13 303.20 303.37 303.30 313.17 313.12 313.14 313.22 313.17 323.12 323.21 323.16

106C,/g cm - ’ 0.0003953 0.0003889 O.OUO3814 0.001401 0.001368 0.001327 0.004145 0.004208 0.004140 0.004220 0.004238 0.01250 0.01196 0.01217

p,iPa 0.003477 0.003422 0.003354 0.01274 0.01245 0.01207 0.03894 0.03953 0.03889 0.03965 0.1212 0.1160 0.1180

Ink/Pa) - 5.662

- 5.678 -5.698 -4.363 -4.386 -4.417 - 3.246 - 3.231 - 3.247 -3.228 - 3.223 -2.111 -2.154 - 2.137

0.016 -0.011 -0.010 0.043 -0.002 - 0.023 -0.015 0.006 -0.013 -0.004 0.007 0.030 - 0.022 -0.001

2,4-DICHLOROPHENOXYACETATE

Measurements made at the lowest flow rate did not agree with those at medium and fast flow rates (table 5), ranging from up to 6 per cent high at 323 K to 20 per cent high at 313 and 303 K. This appears to have been due to concentration of a more volatile impurity which has a slightly lower retention time than that of the main component, resulting in interference. All the results at low flow rates were rejected. Measurements have been published on B2,4-D by Hamaker and Kerlinger,“’ using an effusion method; their results are between 5 and 9 times lower than ours. They also quote effusion measurements by Jensen and SchalP whose results are between 4 and 9 times higher than ours. We are grateful to Mr D. J. Hall for much helpful advice on g.1.c.techniques, also to Dr D. Ambrose for his interest in this work. REFERENCES I. 2. 3. 4. 5. 6. 7. 8.

Friedrich, K.; Stammbach, K. J. Chromatog. 1961, 16, 22. Franck, A. Chem.-Ztg., Chem. Appar. 1969, 93, 668. Eggertsen, F. T.; Seibert, E. E.; Stross, F. H. Ana!. Chem. 1969, 41, 1175. Leggett, D. C. J. Chromatog. 1977, 133, 83. Ambrose, D.; Hall, D. J. J. Chem. Thermodynamics 1%1, 13, 61 Birks, J.; Bradley, R. S. Proc. R. Sot. London Ser. A 1949, 198, 226. Hamaker, J. W.; Kerlinger, H. 0. Adv. Chem. Ser. 1969, 136,39. Jensen, D. J.; Schall, E. D. J. Agric. Food Chem. 1966, 14, 123.