. Chemical Instrumentation
Topics in..
Edited by GALEN W . EWING, Seton HoII University, So. Orange, N. J. 07079
These articles are intended to serve the readers of THIS JOURNAL by calling attention to new developments in the theory, design, or availability of chemical laboratory instrumenlalim, or by presenting useful insights a n d ezplanations of topics that are of practical importance to those who use, m leach the use of, modem instrumentation a n d instmmental techniques. The edilor invites cmespondence from prospective contributors.
XLIV. Automation of Organic Elemental Analysis by the lote VELMER 0. FISH, Lehigh University, Bethlehem, Pennsylvania Editor's N o t e T h e preseut article was presented by Dr. Fish in July 1968 ns part of a Workshop on Instrumental Analysis a t the Center for Professional Advancement, Hopatcong, N. ,I. At t h a t time he agreed to publish the paper in this Column, and gave me a copy of his manuscript. Dnfortonatoly this copy did not contain the illustrations, and since Dr. Fish's denth, they cannot he locxt,ed. I have becn able t o reconstrnct what they must have been, with the exception of x final cartoou suggesting the conceivable rapid "melei mt~rphosis"of an a n n l y t as the result of overdoing autnmntiou. I have added the appendix to Dl.. Fish's paper. G.W.E. The automatioll of estnblished techniqnes in the art of organic elemental annlynis has been neither abmpt nor complete. Rather in most case3 our presentpmition has been attained h y st,epwise modificnlion of the origird system. We shordd like l o consider this process as applied t o the determinntinu of carhon a d hydrogen with the eventual inclusion of nitrogen alld oxygen.
The firs1 step in aut,omation was a n adaptation of exist,ing combnstion systems to a micro or a t lemt semimicro scale. This was an essential step sinre most of our present. automabed techniques opcrnto optimally whelr applied t o milligrnms or less 01 sample. An early earbon-hydrogen combustion system is shown in Figme 1, and consists of the following units: (1) A supply of purified oxygen andlor sir from whieh has been removed carbon dioxide, water, and m y organic substances whieh might produce them. The regulation of the rate of gas flow may also be included irl this portion. (2) The seeorid major partion deals with the combustion of the sample and removal of d l interfering products of that combostion. Thus the products which are allowed to flow from this porbion are carbon dioxide, water, oxygen, nitrogen, and possibly a t,raee of "ot,her" materials. (3) The next seetion allows the separation of the desired products, water and carboll dioxide, from each other and from all other mat,esials present. (4) The final stage of the procednre consists of measusiug and recording the response of a detector, in this ease a suitable halnnce, to tho water mtd carbon
Figure 1. A monvolly operated micro-combustion apparatus of the Pregl type. A, bubble tube b ertobli~ho mesure head; 8, Rowmeter; C. electric weheater; D, %rvbbina tube to remove tracer of CO. and H?O from tne oxygen; L gor-heateo movaole &eve rurrovnotng rilm como~ltion tube; F, main frmo
,.....-
ofter
Horumi. Thb is similor in ~rincipleto the apparatus of Figure 8. (Continued on page AS481
but iodine is determined photometrically.
Chemical Instrumentation any analysis of a n orgenic cornpormd including the functional groups. Ahant all that is roqrtired is an adaptation of some detector system which is sensitive t o the prodncta of a reaction, and 8. recorder. The development of requisite sensitivity and scan time in recorders has made instn~ments available which are adequate for most detector systems. Further improvements are of course possihle if the output of the detector
INTROOUCTION PORT
FLOWMETER
COMBUSTION TUBE
1000.C FURNACE MAGNESIUM OXIDE
OXYGENOUT
[--SILVER
MANGANESE DIOXIDE
CALCIUM HYORIOE
WOOL
SILICA
Figure 1 I. Flow diagram o f Aminco Model 10-010. W a t e r from the combustion ir held on silico gel while COX is meowred on the thermal conductivity cell, then is demrbed b y a movable heater, and reduced t o Hz b y colciuh hydride. The H. is then meowred b y the some detector. Fluorine is removed b y MgO, hologenr and sulfur b y A v e r wool, and nitrogen oxides b y MnOz. Figure 10. Amencon In5trument Company Model 10-010 Carbon and Hydrogen Analyzer.
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Chemical Instrumentation system is tied in with an appropriately progrrtmmed computer which will then deliver the desired information. Snch systems are in use, and have recently heen described ( 1 4 ) . There remains one major obstacle in the realization of a completely automatic system. I n most cases the sample must he selected, prepared, weighed, and int,roduced into the instrument manually. Even this problem has been solved in cases of ges or liquid samples which may he metered directly into the analyzer.
OTHER ELEMENTS Commercid instruments are available for the automated determination of carbon, hydrogen, nitrogen, and oxygen in organic materials. The other elements often found in such samples are ns~ially determined by some well established procedure involving mainly the efforts of the analyst. However conditions may demand some degree of automation in order to inereaye the efficiency of the laboratory. There are obvious extremes in the complexity and expense involved. It might well be economical t,o purchase and coordinate a mass spectromet,er and a computer in order to resolve problems involving stable isotopes, stn~ctoralisomers, or even to yield the empirical formule, directly from the output of a CHN rtndyzer. On the other hand the need for a. specific determination or a means of
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praews control may reqnire some d e g m of automation. For a prncticsl example, one might consider the chlorination of wax where the critical information necessary may be the percent, of chlorine. In order to obtain a reliable value qnickly one must find a snhstitute far the Carius tube, the Parr bomh, or even the Schiiaiger elosed-flask system which may be too slow. One may w e very smnll samples and micro reaction equipment like that employed in (,he hot,-flask method of Iiirsten, el al. ( 1 6 ) which, with potenti
