as the polystyrene. This eliminates all interference caused by the rough cut surface of tlie polymer. When glycerol is used in the roll-out bath, a glycerol-potassium mercuric iodide solution (n% 1.59) meets all requirements and is a good mounting medium.
K i t h all three considerations met, a sharp knife, and a little experience, a cross section can be prepared on many impact-grade polymers in as little as 5 minutes. d typical photomicrograph produced by this technique is shown in Figure 1.
LITERATURE CITED
(1) Claver, G . C., Merz, E. H., Ofic. Dig.
Federation Paint a n d Varnish Prodicction C h b s 28, 858-68 (1056). ( 2 ) Llcrz, E. H., Claver, C:. C., Barr, J . Polymer Sei. 27, 325-41 (1956). ( 3 ) Richard$, 0 . IT.. "Effective r s e and Proprr Carr of the Microtome," Aiiiierican Optical eo.: Buffalo 15, S . T., 1949.
Rapid Detection of Traces of Peroxide in Ethers Patrick R. Dugan, Mircobiological and Biochemical Center, Syracuse University Research Corp., Syracuse, N. Y
Thc reagent is an aromatic amine. and therefore n ill form Schiff bases with aldehydes: if they are present in tlie ethers. EXPERIMENTAL Solutions containing from 0.1 to 1% of a variety of aldehj des n ere p r e p a r d Reagents. . ~ ~ , ~ ~ - T ) i m c t h ! - l - ~ - p l i ~bj~ n ~di-solving lin absolute CH,OH: enedianiinc sulfate n a s prepared h>2 ml. of each n a ' reacted nith 2 ml.-sf dissolving 0.3 gram in 10 nil. of reth(3 rc,agent. distilled w a t w in a 100-nil. volumetric flask, arid brought t,o tlic mark with RESULTS AND DISCUSSION frtsh C.P. absolutcx nictlianol. Procedure. T K O millilitcrs of tlic h d w p rcd-blue reaction product' was reagcnt \vas n i i r d ivith from 2 to !5 obscricd whcn the reagcnt iyas mixcd nil. of tctrahydmfuran ( T H F ) in a with T H F ; h o w v e r . no color changc test tulw and allocvetl t'o stnnti for 5 del-eloprd \\-hen t'he T H F had first niinutcs in rubtlucd light a t roo111 h c n distillrd over sodium, a proccw t e in p era t1.1 re. A c. o nip arisoi i t ul)r n-(Ire uscd for the r e m o d of pcroxides (and preparcti in thi. sun(' nianiicr by adding 2 nil. of tt.ti,ahydi,ofurati n-hicli also aldchytics) . had hccn clistill(~t1 o v r r d i u m in Srvrral grades of diethyl ether w u e p l a c ~of the 2 nil. of st,ot-kT H F . examined. In all cases in which tlic TTVO millilitcrs of tlic rcngcmt n-cw rrducing agcnt, sodium dicthyldithioalso added to 2 ml. of mvh of scvcral carhamate, had been addcd to the ether, samplcs of dicthyl et'liw, isopropyl no color change could bc drtccted. ether, and diosanc whirh had bem Honevcr, the typical colortd coniplcs stored in thc laboratory stock room. rcw1tc.d whrn ethcr n h i c h had not 1m.n stabilized n-ith sodium diethyldithiooarbamatc was used. Table I. Comparison of Absorbance Values of Lauroyl Peroxide to Benzoyl 'l'he color complex \vas formed n-hcn Peroxide a t 570 Mp with Respect to Active Oxygen Content 2 nil. of dioxanr n-hich had hren stored 1,aaroylfor scvcral months in a partially filled Peroxide Benzoyl bottlc was employcd; but no color Concn.,a pg./hIl. Lauroyl Peroxide Benzoyl Peroxide Ratio drvrloped when 2 nil. from a freshlj10 0.051 (89% T ) 0 . 1 0 2 ( i 9 % 2') 0.50 opcncd lmttle was uscd in the reaction. 20 0 . 1 0 2 ( i 9 7 0 2') 0.195 (645; 2') 0.52 30 0.155 (70% T ) 0.285 (52% 2') 0.54 If the absorbance (or %I") of the 40 0.211 (6170 2') 0.446 (3670 7') 0.48 colored solutions as previously rcport'cd Av. 0 . 5 1 is compared to the ratio of the active Active oxygen content, yo 3.8 6.8 ;zv. 0.56 osygcn content of benzoyl and lauroyl 0 hlicrograms per ml. of 2 nil. added to reaction t h e . peroxide, the absorbance values of the colored complex from both peroxide reactions appear nearly equal (see Table II. Absorption of Reaction Product of Aldehydes with Reagent 1 at Selected Table I). W a v e Lengths vs. Reagent Blank It is therefore suggested that the % Concentration of Aldehyde in Absolute CHdOHa amount of active oxygen can be de0 1 0 3 0 5 0 7 1 0 termined on the basis of this reaction 545 5iO 590 535 570 590 545 570 590 545 570 590 E i m O and that the amount of active oxygen Aldehyde mp mp mp nl9 in9 mp mp mp mp mp mp mp mp mpmM in ethers can possibly be quantitated Formaldewithout knowing the specific chemical hyde S o effect KO effect K-Propionstructure of the peroxide. aldehyde 100 108 97 65 TG 65 50 61 50 32 44 33 . . . . . . The method is a rapid qualitative K-T'alerindication of peroxide content in ethers aldehyde 113 118 110 . . . . . . , . . 98 106 100 . . . . . . 80 92 85 and possibly other solvents, and may A'-Hep< be an aid in controlling accidents aldehyde 112 119 108 104 112 104 96 106 96 86 99 89 77 90 80 Benzaldecaused by peroxide-induced explosions. hyde 65 94 99 Comparison of O/oT values a t 570 S o effect No effect Glucose mp (Table 11) shows that the aliphatic a i'alues at 545, 5i0, and 590 m M represent minima, maxima, minima, respectively, of aldehydes tested decolorized the reagent absorption peak a t which peroxide color is determined. somewhat when added in concentrations for detecting microgram quantities of benzoyl and lauroyl peroxides [AiV.AL. CHEM. 33, 696 (1961)] was developed to detmninc, the prtsence of these perosides as they migrated from polymers. 1rliic.11 had been formed using peroxidc ental)-sts in polymcrization, into various solvents. The publication referretl Fpccifically to cictection in benzene and mineral oil. I t has since been dctcrminctl in this laboratory that thc reaction is suitable for dctecting tracm of pcroxidc in diethyl ether, isopropyl cther. diosanc! and tetrahydrofuraii. Because the method is so rapid and simple, and because peroxide formation in ethers in general can be hazardous: particularly when ethers are evaporated in an anhydrous condition (Soller, C. B.,"Chemistry of Organic Compounds," p. 139, Saunders Publishing Co., Xew York, 1950), i t should be a useful tool in the hands of invcstigators
A
METHOD
1630
ANALYTICAL CHEMISTRY
working with ethcrs as w l l as tho-e concernd with quality control.
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
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