Practical Syrinfle Microburet '
PHILIP A. SHAFFER, JR.', PAUL S. FJiRRINGTON, AND CARL NIEMANN G a t e s and Crellin Laboratories of Chemistry, California Institute of Technology, Pasadena, Calif.
A syringe m i o m b u r e t suitable for general 1ahoratory use is described. With t h i s instrument q u a n t i t i e s of liquids of the 02 .der of 0.5 00. can h e deliyered w i t h a precision of +O.l to *O.S%, depending upon the uniformity of the plunger diameter of the svrinee that is employed.
A
LTHOUGH a number of syringe N ~ ~ ~ I~ L ~ ~V T v~r l j ul ~deL scribed ( 1 4 , 8-10),none was sui:able for production in quantity nor in general did any meet the requirements of durs, bility and convenience far general laboratory use. The syringe microburet described herein is the last of % Peries of models developed during the past four years. The development was governed by consideration of not only pkeoision, convenience of use, and resistance to damage under normal laboratory conditions, hut also of the requirements of low cost and ease of production. Over one hundred units of the h a 1 model were constructed and have been in use. They were produced in lots of fifty with 8 hours' labor per unit including tooling and cablibration (7).
~
DESCRlFTION O F INSTRUMENT
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.-
side &meter and 12.5 em. (5 inches attached prerpendicularly near the middle"6f the tube, a n d G t h V-blook a t one end an which the glass syringe is held by four phosphor-bronze clips. Down the center of the tube passes a carefully cut and lapped lead screw which is carried on preloaded ball bearingj to eliminate end play; it ends in a eanaliculated head engraved with suitable divisions. The lead screw drives a oylindrical nut which slides along the inner surface of the tube. The nut is slotted down most of its length from one end in three planes nhioh form a n equilateral prism inscribed in the cylindrical nut; this provides spring contact with the inside of the tube. Another slot normal to the axis of the nut may be narrowed by a mmll smew to compensate for wear of the nut and lead screw. A short, metal post projects radially from the nut through a slot in the tube to support a slide block; the head of the syringe plunger is held in contact with this block by two phosphor-bronze clips.
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Yllr"y'L"""b1.
The tubular construction of the micrometer mechanism has several advantages.. The driving force applied by the lead screw is symmetricdy disposed with respect to the bearing surfaces; this prevents tipping and binding of t h e nut on the lead screw. The delicate parts of the mechanism are protected by the heavy tube. The tube is closed a t both ends, and the leitd-sorew ball hearings are equipped with protective shields; the wiping action of the nut in t h e tube appears to preserve smoothness of operation, despite the fact that a small amount of dirt may e n k r the tubular housing through theslot. The holder is'equipped with two scales, which function like t,hose on the familiar micrometer caliper. One of these is the linear scale extending about 4.4 cm. (1.75inches) along the tube and having graduations spaced 1.25 mm. (0.05 inch) &D&rtwith
is
ct
cylindrical one of Jifty'divisions equallv spaced around the
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Figure 1. M i c m h u r e t
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divisions because the commercially available glass hypodermic Ryringes are not uniform in bore, and i t is therefore not advisable to graduate the syringe holders directly in cubic centimeters. 1
Present address. U. S. Naval Ordnance Test Ststion. Pnmdena. Calif.
492
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which extends through the slot of the main tube holds the head of the syringe plunger. Proper design of the slide is essential for satisfactory operation of the microburet, because very slight forces tending to displace i,he plunger off axis cause the plunger to lack in the barrel. Because of the unevenness of the surface of the molded glass plunger head, s, flat slide block would generally push against the plunger head off center. I n the present ease this difficulty has been removed by soldering a small ball to the driving surfme of the slide on the axis of tho syringe. The ball extends beyond the surface of the slide t o a suffioient extent to prevent contact between the plunger head and the slide a t any other point. The plunger head is held against this ball point by two phosphor-bronze clips, which swing in from each side to engage the head. The hypodermic syringes of corresponding nomind capacity manufactured by several companies differ widely in sieo and necessary t o design the syringe shape. For this reason, it w&~holder of the miomburet for u6e with a specific syringe. The syringe adopted was the soft-glass Beeton-Dickinson Yale 2ec, because i t represented a high quality of workmanship and was available a t the time of development. I n the future it would be desirable t u consider the use of a syringe constructed of Pyrex because of the greater strength and resistance of this mmterial. Steel hypodcrmio needles were umtisfaotory because of. eorrosion by 6ome solutions-e.g. mercuric nitrate-therefore, it was necessary to design glass lips especially for this use. The .glass tip shown in Figure 1is ground with a female Luer taper and is made of Pyrex.
JULY 1947
49 3
OPERATION OF THE INSTRUMENT
By means of the knurled knob controlling the screw mechanism the slide is drawn back, so t,hat t’he syringe can be inserted in t’he V-block wit,hout removing the barrel clips from the \‘-block. A clean syringe is placed in the V-block, a tip fitt’ed on the syringe, and the syringe adjusted, so that the barrel flange is pressed tightly against the V-block before t,he barrel clips are tightened. Care should be taken to avoid deformation of t’he syringe barrel by excessive pressure from t,he barrel clips. Manipulating the plunger by hand approximately 1 cc. of solution is drawn into tjhe syringe, the solution expelled, and a second 1 cc. of solution drawn into t,he buret. With t,he slide plunger clips open, the slide is moved down until it touches the plunger, when the slide clips are closed on t,he head of the plunger. With the syringe inverted the barrel is tapped sharply to dislodge bubbles adhering to the end of the plunger, and the plunger is driven forward with the screw until all the bubbles have been expelled. The buret tip is again placed in the solution, t.he barrel flange held against the V-block, and the plunger withdrawn slowly with the screw mechanism to about 0.5 on the linear scale. The buret tip is removed from the solution and dried with a clean cloth; just before making the initial scale reading a drop of solution is expelled and the excesk liquid removed by touching a clean glass surface to the tip. Tht. initial reading is t,aken and t’he t,itration st’arted promptly. CALIBR4TION OF SYRINGES
Experimental evidence has shown that the volume delivered b> the microburet is equal to the volume displaced by the plunger Therefore the delivery per unit translation was determined by measuring the plunger diameter with a micrometer to the neareqt 0.0001 inch. Measurements weie also taken every centimetet alpng the plunger in order to test uniformity of diameter. Ellipticity of the plunger was tested by making measurements of diameters perpendicular to one another. An eccentricity of 0.0002 out of 0.35 inch and variations of 0.0010 inch along the length was about the maximum accepted. Out of a lot of five hundred syringes purchased in wartime, 40% were acceptable; in a third of the latter the diameter of the plunger varied not over 0.0003 inrh along it. length.
BO =
.___ = 6.4350 X D2(2‘540)3
L)2
The titrations are seen to be reproducible to approximately 0.1%; this corresponds roughly to the limiting accuracy of the end-point estimation. The discrepancy between the volume based on the known normalities and volumes of the standard solutions and the calculated volume approaches 1% at the extreme of the scale for syringes with relatively large variations (0.0006 to 0.0012 inch) of the plunger diameter. These results indicate that an over-all precision of +0.5y0can be expected for selected syringes where variations in diameter range from 0.0004 to 0.0006 inch out of 0.35 inch, while a precision of 0.1 to 0.2% may be attained with the best syringes-i.e., with variations of less than 0.0002 inch. 4CKNOWLEDGMEhT
The authors wish to acknowledge their indebtedness to J. H. fiturdivant for his continued interest and advice and to William Schuelke and Alex Logatcheff, instrument makers in these laboratorie.;, who contributed extremely valuable suggestions and skill-
‘I’ahlr 1.
Thc delivery is calculated from the maximum plunger diametrr measured in inches, D, as follows: C’r. titdivered per 0.5 inch =
Titrations were made using 0.01987 AVsodium t’hiosulfate anti 0.001218 A- potassium biiodate. h pipetted volume of 10.01 cc. of biiodate solution was titrated with t,hiosulfate from the microburet in t,he presence of excess iodide and 0.2 N acetic acid and in an atmosphere of carbon dioxide. A starch end point was used. Thc results of these experimenh are shown in Table I. I n this table the “plunger diameter variation” is t,he maximum variation in the diameter of the plunger as determined by micrometer measurements along the length of the plunger. The “range” indicat,es what portion of the scale (and syringe) was used; the “difference” is tmheactual scale translation required in reaching the. end point, determined to within 0,001 division. The “volume by displacement” is the volume calculated from the scale translation and the micrometer measurements of the plunger diameter: “volume by titration” is the volume calculated from the titration experiment : and “volume differenct.” is the percentage differencc between the t x o ralculatrtl volumes.
S u m m a r y of Titration Delivery Experiments
Syringe H a n d D 4035 Y Plunger diameter (maxinium) 0.3357 inch. Plunger diameter variation 0.0005 inch
Range, Scale Divisionb L.0-1.8
1.5-2.3
8
Ilifferenre, Scale 1)ivision 0.837 0.838 0.839 0.839 0.840 0.840
Volume Calculated Displacement, Cc.
Volume Calculated Titration.
Cr.
Volume Differenee, X
0 6077
0.6105
0.5
0 6090
0.6105
0 3
0 6062
0.6105
0.7
For convenience in calculating, this may be written log Vo = 2 log D
+ 0.80855
Sinw the unit translation as measured by the linear scale is 0.5 inch, the delivery per unit translation is that given above. (Cubic centimeters are used because volumes are calculated from linear measurements. With the small volumes encountered in these operations cubic centimeters can he taken as being equivalent t o the more conventional millilitem.) TEST EXPERIMENTS
L, 8385 Y Plunger diameter (maximum) 0 3482 inch. Plunger diameter variation 0 0006 inch
H and
1,5--22 2.0-2.7
I3 a n d D 8363 Y Plunger diameter (maxiniunl) 0.3553 inch. Plunger diameter variation 0.0002 inch ’
1.0-1.7 1.5-2,2 2.0-2.7
B a n d D 9136 Y Plunger diameter (maximum) 0 3423 inch. Plunger diameter variation 0.0001 inch
Initially an attempt was made to check the calibration of the syringe buret by weight-delivery experiments using mercury, water, and aqueous sulfuric acid (7). Because these methods were not sufficiently precise, a titri- . metric procedure was adopted.
1 .0-1.i
1.0-1.8 1.5-2.3 2.0-2.8
B a n d D 8372 Y Plunger diameter (maximum) 0.3480 inch. Plunger diameter variation 0.0012 inch
1.0-1.7 1.5-2.2 2.0-2.7
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0,777 0.777 0.778 0.779 0.779 0.784 0.784
0.6078
0.6105
0 4
0.6117
0.6105
0.2
0.6105
0.6105
0.0
0.6105
0.6105
0.0
0.6105
0.6105
0.0
0.810 0.810 0.812 0.810
0.6107
0.6105
0.0
0.6115
0.8105
0.2
0.811 0.811
0.6115
0.8105
0.2
0.781 0.780 0,784 0.782 0.788 0.788
0.6079
0.6105
0.4
0.6102
0.6105
0.0
0.6141
0.6105
0.6
0.762 0.754 0.752 0.748 0.752 0.752 0.754 0.752 0.752
494
VOLUME
ful workmanship during the development of the syringe microburet. LITERATURE CITED (1) Chaney, A. L., IND. ENG.CHEW,h . 4 ~ ED., . 10, 326 (1938). (2) Clark, W. G., Levitan, Ii. I., Gleason, D. F., and Greenberg, G., J . B i d . Chem., 145, 85 (1942). (3) Dean, R. B., and Fetcher, E . S., Jr., Science, 96, 237 (1942). (4) Hadfield, I. H., J . Soc. Chem. Ind., 61, 45 (1942). . CHEM.,.&SAL. ED.,7. 180 (1935). (5) Krogh, 4.,1 s ~EXG.
19,
NO. 7
( 6 ) Kiugh, .&.. and Keys, A. B., J . Chem. SOC.,1931, 2436. (7) Office of Publication Board, U. S. Department of Commerce, Report PB 5924 (1946). Sasaki, N., 2 . anorg. allgem. Chem., 137, 181 (1924). Scholander, P. F., Edwards, G. .1.,and Irving. L.. ,J. Biot. Chem., 148, 495 (1943). (lo) Tievan, J . ii.,Biochem. J . , 19, 1111 (1925). COXTRIBUTIOX 1107 from the Gates and Crellin 1,aboratories of Chemistry, California Institute of Technology. Based upon work done for the Office of Scientific Research a n d Development under Contract OEJIsr-325 with t h e California Institute of Technology.
Determination of Mercury in Biological Material F. L. KOZELKA. Uninersity of Wisconsin, Madison, Wis.
A simplified dithizone method for the determination of mercury in biological material is described. The uniqueness of this new method is the quantitative distillation of mercury from the Kjeldahl flask during and subsequent to the digestion without the loss of the metal. This procedure separates the mercury from all the nonvolatile salts of the other metals contained in the specimen. Washing t,he mercury di-
T
HE most dificult thing t o achieve in the detrrniiIiation of mercury is the complete destruction of the organic matter without t,heloss of the metal. The volatility and lack of stability of mercury salts at higher temperatures complicate the deromposition and preparation of the sample for analysis: hence suitable precautions must be taken t o prevent losses through volatilization. To minimize this loss, most of the available mtxthods suggest the use of potassium permanganate or potassium chloratta partially to destroy the organic material, with subsequent concentration of the mercury by precipitat,ion as a sulfide. Kinklei, (b)employed zinc as an entraining agent for mrrcury from nitric. acid extracts of vegetables. The precipitatr containing the mercury was then dissolved in nitric acid and the sinall quantity of' organic matter present was osidized with potassium permanganate. These procedures are time-consuming and an appreciable error may be introduced, particularly when microquantities of mercury are involved either by incomplete entrainnient of thP mercury or the intmdur.t ion of mme mercury with the rragenth employed. -4nother difficulty tsricwuntered in the existing nirbthoda is in the separation of mercury from copper, since both metals combine with dithizone under wsentially the same conditiorib. Winkler (5) employed sodium thiosulfate, while Laug and Nelson (4) used potassium bromide t o effect this separation. Both of these compounds complex the mercury and transfer it from the chloroform phase t o the aqueous phase without affecting the copper dithizonate. In either case the procedure requires several transfers and digestions which are time-consuming for routine purposes. Gettler and Lehman ( 2 ) adapted the potassium permanganate digestion to small quantities of urine and extracted the mercury from the digest lyith dithizone. The technique, however, is applicable only to specimens in which the final digest is small and the quantity of mercury relatively large. Hubbard (3) digested 50-ml. urine specimens with potassium permanganate but substituted di-p-naphthylthiocarbazone for dithizone since they exhibited the same general characteristics. Subsequently, Cholak and Hubbard ( I ) applied this technique t o tissues, employing a preliminary digestion with sulfuric and nitric acids followed by a final digestion with pot'assium permanpxnate. I n preliminary studies in this laboratory the writer observed that the loss of mercury from a digest was markedly increased with a n increase in the chloride ion. and suhsequent wnrk demon-
thizonate with 9 S ammonium hydroxide obviates the necessity of treating the dithizonate extract with potassium bromide or sodium thiosulfate and performing a second digestion and extraction,as required by the pretiously described methods. Consistent reco,eries with an error of less than 2 micrograms are obtainable, which appears to he adequate for toxirolopical or clinical purposes. strated that niercury can be distilled quantitatively from the'digePt by the addition of chlorides as sodium chloride, hydrochloric acid, or chlorine gas. The disadvantage in the use of sodium chloride is the excessive accumulation of sodium sulfate in the digest, too rapid liberation of chlorine, and excessive foaming. The use of hydrochloric acid results in a large volume of the final distillatc and a considerable amount of acid which mupt be neutralized hefore the merrury is extracted. The niajor portion of the mercury is apparently distilled as a mercury aninionium chloridr c,omples, because less than 20L; recoveries can he obtained in the absence of nitrogen. able over a wid? pH range, Snce the mcrcury dithizonate i it can ht, wparated from the excess dit,hizone and othcr contaminants (particularly the traces of copper on the glassware) by washing it in approximately $1 S ammonium hydroxide. The copper dithizonate dissociates in this medium n-ithoiit affecting the nwrc-iiry dithixonatr. *
.
REAGENTS . i N D APPARATUS
dulfuric acid, concentrated, C.P. quality. .Ammonium hydroxide, 9 N,redist,illed. This solution
Table I.
2.5 2.5 5.0
5.0 10.0 20.0 30.0 40.0 50.0
Liver
Kidney
pre-
Recoveries of Know-n Quantities of JIercury from 25 Grams of Tissue Mercury Added Ilzcroorams
Blood
ib
Mercury Recovered Mzcrograms 4.25 4.50 7.00 6.75 11.50 22.00 31.00 41.50 52.25
hrror h'zcrogravra 0.00 +0.25
+0.25 0.00 -0.25 1-0.25 -0.75 -0.25 +0.50
27.0 50.5 245 (1
+0.25
250.0 25 0 50 0 250.0
26.0 52 0 247.5
-0.75 + O 25 -4.25
25.0 50.0
Heagent blank contained .1 75
micrograms
-1.25
-6.75
of niercury
