of 1000 p g . y r nil. as conipared to a rtsagcnt I)lank. I3mzaldchyde, how(Yvcar, gave a slight absorption a t 5 0 mp. Higher conccntr:itionP of aldchyde result in yc~llon-, o r a n g , or red Schiff bases. H o w v c r , the absorption spectra of tlw Schiff ~ S P S:tr(x not identical \\.it11 that of the peroxide-reagent coniplcs. Incidcntal nldchyde contamination of t > t h u s in conwntrations as grc~itas 1000 pg. pc'r nil. secnis rather unlikel>-. Foriii:iltlt,h!-tle and glucose
had no eficct in concentrations as high as 1%. CONCLUSION
The reagent will detect low concentrations of peroxide in ethers, probably by reacting with active oxygen. Presence of aldehydes will interfere \\ ith the peroxide-reagent color formation by forming Schiff bases with the reagent. Hom ever, the aldehydes tested do not give highly colored reaction prod-
ucts M hen present in concentrations less than 1000 pg. pcr ml. Therefore the reaction of reagent plus ether t o give a red-blue color n i t h the absorption spectrum previously reported appears to indicate presence of peroxide. Discoloration of the reagent or formation of a color n i t h a different absorption spectrum would indicate the presence of relatively high concentrations of aldehyde, in \\ hich cas? presence of peroxide could not be dctcrmined.
Polarographic Cell for the Continuous Analysis of Flowing Solutions W. J. Blaedel and J. H. Strohl, Chemistry Department, University of Wisconsin, Madison, Wis.
'
cells for the continuous :innl>-sis of flowing solutioils ha,ve lieen &scribed j Blaedel, W. J., Todd, J. \I*., ANAL. CHEM. 30, IS21 (195SjI. Honevcr, most of t h w e devices possess high olimic resistniice, large hold-up and poor response time. or inconvenience in operation. In this paper> D cell is described nhirh has a good i'esponse time and functions un:ittendetl for sevcml hours. A diagram of the cell is given in Figure 1. The outside t'ip, A , of the capillary of the dropping niercury electrode (D.3I.E.) is ground roughly to fit into the cell. The capillary is seated and s c a l d into the cell with epoxy resin. The cell. h:r\-ing B 1.olunic. of about 2 1111.. is equippcd n-itli an inlct tube, B, and tn-o outlet tubes, C and D , terminating a t about the same height. Stopcocks E and F are adjusted so that most of the efflui,nt goes through the upper outlet t,ube, L),with only a small portion : s h g through the lower tube, C. I' 'The upper outlet tube automatically carries off any gas bubbles that may be swept into t,he cell n i t h the influent solution. Kithout such a provision, OLAROGRSPHIC
J
Figure 1. Cell for continuous polaroq r a D h l - analvsi!
occasional gas bubbles accumulate in the top of the cell and eventually interfere with the D.M.E. The Ag-AgC1 reference electrode, G, is immersed in 2 V S a C l (any other convenient concentration may be used) and joined coriductively to the cell through a fine sintered-glass frit, H . The reference solution level, I , is always kept above the level of the solution outlets, C, D , so that a low leakage (about 0.1 ml. per minute) occurs through the frit into the cell, and so that the reference electrode solution never becomes contaminated or diluted with sample solution. Even if the leakage is inadvertently reversed for considerable periods of time, the U shape of the reference electrode tube prevents contamination from reaching the reference electrode The reference electrode solution is chosen to be always denser than the cell solutions, so that the leaking reference solution f l o w smoothly down the face of the frit and is carried off by the effluent stream through the bottom outlet tube. The leaking reference solution therefore does not come into contact with the D.5I.E. and does not require deaeration. \Taste mercury is withdrawn through tube J . In operation, stopcock K is left open and the mercury is permitted to seek its own level in reservoir L. The lower half of the cell is packed with loosely crumpled 26-gage platinum wire, Tyhich helps to isolate the DJ1.E. from the leaking reference electrode solution. The wire packing greatly reduces cycling and turbulence in the solution, nhich otherwise cause fluctuations in diffusion current and give a slow approach to a new steady state when the influent solution changes. The top of the packing should not extend above the mouth of the inlet tube, B; otherwise gas buhbles may be held on this packing instead of passing freely through the cell. The wire should be loosely packed; otheiwise mercury droplets may be trapped in the interstices Glass beads (4-mm. diameter). glass shards, and layers of Teflon film were unsatisfactory packing materials. The inlet and outlet tubes are 2-mm. capillaries The bottom outlet tubing
up to stopcock K is h i m . a d . ; to prevent slugging of the mercury. The reference electrode tubing is 1 cm. in diameter, the top being enlarged so that reference electrode solution need not be added frequently. The whole assembly may be mounted on a board with epoxy resin; the best points of support being a t the stopcocks and the upper end of the reference electrode tube. During operation, the only attentioil required is withdrawal of mercury f i om L and replenishment of the reference electrode solution every few hours. The response time of the cell is described in Figure 2, nhich is a record of diffusion current obtained 1%hen 0.2JI KaCl solution IS alternated 111th 0.001N CdC12-0.2Jf SaCI. The dead regions, A-B and D-€3, are independent of the cell and repreqent the time r e q u i r d for the solution to reach the cell through the inlet tubing and deaerator [Blaedel and Todd, AXAL. CHEW 30, 1821 (1958)j. Flushing of the cell occur5 in regions B-C and E-F. On rising from background, flushing volumes of about 2 and 3 ml. are required for the response to reach 90 and 99% of the
Figure 2.
Cell response
Solution switched from 0.2M NaCI to 0.001 M CdC12-0.2M NaCI. D. Solution switched back to 0.2M NaCI. Flow rates, 2.3 and 0.5 ml. per minute through upper and lower outlet tubes, respectively. Sargent XXI polarograph, sensitivity 0.06 pa. per mm., no damping, 1.25 volts applied cathodic potential (against Ag-AgCI reference electrode in 2M NaCI). D.M.E. characteristics. i = 4.0 seconds, h = 79.0 cm., m = 2 58 mg. per second. A.
VOL. 33, NO. 11, OCTOBER 1961
1631
steady-state value, respectively. On falling toward background, flushing volumes of about 1 and 2 ml. are required for the response to drop to 10 and 1% of the original steady-state value, respectively. These flushing volumes are independent of flow rate in the range 0.5 to 4 ml. per minute. The effect of flow rate on diffusion current is not great. At 4 ml. per minute, the diffusion current of 0.001-41 CdC12 in 0.2111 NaCl is only about 57,
different from the static value. For precise work, the flow rate should not be allowed to vary greatly. For monitoring of the f l o rate, ~ it is convenient to replace stopcock F with a threen a y stopcock, one branch of which voids directly and the other branch of n hich voids-through a flowmeter. When flow of the sample solution through the cell is stopped, the cell will fill slonly with air-saturated reference electrode solution, and the
background current will rise. Holyever, the rise is very slow (0.04 pa. per hour). It is therefore easily possible to stop the flow, if desired, and to run a current-voltage scan on the solution held in the cell. ACKNOWLEDGMENT
Financial support in the form of a research grant from the U. s. Atomic Energy Commission is gratefully acknowledged.
A Simple Method of Temperature Programming for Gas Chromatography Harmon Borfitz, Norwich Pharmacal Co., Norwich, N. Y. N
a search of recent literature, a
1temperature programming procedure
for gas chromatography in which the temperature could be increased while maintaining a constant base line vithout auxiliary and expensire equipment was not found. However, a simple method of temperature programming w s found in these laboratories n-hich has been entirely suitable. The problem consisted of analyzing a mixture of acetic acid, water, methanol, and methyl acetate. Using a PerkinElmer Model l 5 4 D Vapor Fract'ometer, helium gas, and a column of polyethylene glycol (Carbowas 1500) on powdered Teflon, this mixture n-as chromatographed a t 150" C. a t a pressure of 28 p s i . and a gas flow rate of 80 cc. per minute at' 21" C. The methyl acetate and methanol were eluted quickly, both within 20 seconds of each other, but could not be resolved. The water was eluted in the relatively short period of 2.5 minutes with an excellent peak, while the acetic acid had a retention time of 19.5 minutes Ivith a useable peak.
Figure 1.
Attempts to separate the methyl acetate and methanol peaks bj- decreasing the temperature resulted in serious tailing of the acetic, acid peak. However, a t 100" C. the methyl acetate, methanol, and water peaks could all be resolved, with only an insignificant overlapping of the methanol xnd methyl acetate peaks. A known sample n-as then injected into the chromatograph wit'h the initial conditions of 100" C., 28 p.s.i., ant1 a gas flow rate of 116 cc. per minute a t 21" C. Following the elution of the methyl acetate, methanol, and water (total elapsed time of 12 minutes), the oven temperature was quickly brought to 1 3 " C. for the elution of the aretic acid. The 21-minute interral between the elution of the water and the acetic acid proved to be too short a period for the column temperature to equilibrate. Largc changes occurred ill the base line, RS illustrated in Figure 1; nhich in turn c a m d severe tailing of the arctic acid peak.
Effect of increasing temperature with (left) and without (right) interrupting gas flow
A.
Methyl acetate
5. Methanol
1632
Measurement of this peak xould have been extremely difficult. The problem \Ta3 solved 11) simply shutting off the hcliuni supply before the column inlet, in tlik gas sampling valve, after t h the water peak and nllnn-ing about 30 minutes for thc column tctiii)c~r3ta!'c~ to equilibrate (Figure 2 ) . l'he pwnution of shutting off the detector xhilc the gas flo\\- \vas int,crrupted I\-L> not obstarved, hut no difficultics ncw because of this. The nn:il! completed by turning the lielium flow on again, and in the time remaining before t'he elution of the acetic acid (about 15 minutes), the base line n'ns adjusted. The esact tiriie required to elute the acetic acid after restarting the f l o ~was not rwordcd. but it is approximately 27 minutra. This is a simple method of temperature programming which would be applicable to many gas clironiatographp problems without the need of added accessories to maintain :I ronstunt base line.
ANALYTICAL CHEMISTRY
C. D.
Water Acetic acid
