A METHOD FOR THE DETERMINATION OF SMALL AMOUNTS OF LACTIC ACID.

BY S. W. CLAUSEN. (From the Department of Pediatrics, Washington University School of

Medicine, St. Louis.)

(Received for publication, February 25,1922.)

INTRODUCTION.

For quantities of lactic acid greater than 10 or 20 mg. the titra- tion method of von Ftirth and Charnass (1) is available. For much smaller quantities, the only methods hitherto proposed have been calorimetric (2). With the disadvantages of calorimetric methods in mind, study was made of a titration method which gives satisfactory results with as little lactic acid as 0.2 mg.

Chemical methods for determining lactic acid are based upon the following (3) reaction:

CHaCHOHCOOH -+ CHs COH + CO +H,O (A)

It is not the purpose of this paper to review the literature dealing with these methods. It should be pointtid out that the reaction has been carried out under two sets of conditions. In one case (4), dilute KMn04 is added to the boiling acidified solut.ion, and the resulting acetaldehyde distilled off and determined. In the other case (5), the reaction is carried out at a higher temperature in the presence of concentrated sulfuric acid. Under these cir- cumstances, either the aldehyde or the carbon monoxide may serve as a measure of the lactic acid present.

Two questions arise in connection with these methods. First, as to the specificity of the reaction: It will be shown that many other substances-especially the other cz-hydroxy-acids-yield aldehydes or ketones when subjected to either process. The sepa- ration of lactic acid from such interfering substances is by no means easy. This question will be discussed further in connection with the application of the proposed method to biological material.

263

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264 Determination of Lactic Acid

The second question is concerned with the quantitative aspect of the reaction. In the present paper, it will be shown that either process can be adapted to the determination of small quantities of lactic acid.

The features of the method here presented are: a modification of the Ripper aldehyde titration with bisulfite; and the application of aeration to the transference of aldehyde from the reaction mix- ture to a solution of sodium acid sulfite.

EXPERIMENTAL PART.

Titration of Acetaldehyde.

The method of Ripper (6) is based on the following reaction:

CH,COH + NaHS03 $ CH3 CHOH SOa Na (B)

In slightly acid or neutral solutions, the reaction very rapidly proceeds practically quantitatively to the right; and the excess of bisulfite may be titrated without including that “bound” in the double compound. This method of titration gives concordant results with O..l and 0.01 N solutions; but when 0.001 N concentra- tion is used, the results are erratic. This may be due in part to the instability of such dilute bisulfite. It is not due to the instability of the double compound. For, if after the end-point is reached in a titration of excess bisulfite, a small amount of sodium bicar- bonate is added, the bound sulfite may then be titrated; and the results are theoretical. The figure so obtained is practically, if not quite, independent of the quantity of bisulfite originally used. These facts form the basis of the modified method.

Preparation of Materials.

Acetaldehyde was prepared by distilling paraldehyde with a small amount of dilute H&Oh. The vapor was led through a reflux condenser filled with water at about 30” and received in a flask of ice water. The product was redistilled in the same appa- ratus three times. In this manner a 20 per cent solution was obtained. Dilutions to 0.1, 0.01, and 0.001 N were made as needed.

Sodium acid suljite was prepared by leading SO2 gas into a saturated Na2C03 solution as long as COz was given off. The

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S. W. Clausen 265

color becomes pale greenish yellow, and the odor of SO2 is obvious. Dilutions were made only as needed.

Iodine was prepared in the usual way. A stock 0.1 w solution was diluted to make 0.01 or 0.001 N as needed. All solu- tions contain 2 per cent KI. The solutions were frequently checked against 0.1 or 0.005 N Na, &OS containing a little NaOH, which, in turn, were checked against standard 0.1 N KI03HIOa (3.2496 gm. per liter).

Method in Detail.

The solution of aldehyde to be analyzed is added to a consider- able excess of bisulfite, whose exact amount need not be known.

TABLE I.

Titration of acetaldehyde by the Ripper method and by the modified method. Results are given in terms of cc. of standardized iodine. Acetal- dehyde solutions prepared by diluting an approximately 0.05 N solution.

Acetsldehyde.

10 CC. 0.05 N 10 “ 0.05N 10 “ 0.005 N 10 “ 0.005 N 20 “ 0.0005 N 10 “ 0.0005N 5 “ 0.0005 N

Titer by Ripper method. Titer byEe;fo2.d Ripper

8.05 cc. 0.1 N iodine. 7.93 cc. 0.1 N iodine. 8.03 “ 0.1 N “ 7.83 “ 0.1 N “ 8.09 “ 0.01 N “ 8.08 “ 0.01 N “ 8.10 “ 0.01 N “ 8.08 “ 0.01 N “

14.90 “ 0.001 N “ 16.25 “ 0.001 N “ 8.42 “ 0.001 N “ 8.10 “ 0.001 N “ 3.00 “ 0.001 N “ 4.05 “ 0.001 N “

After 10 minutes, the excess of bisulfite is oxidized by adding 0.1 N

iodine, and the end-point is adjusted to a definite blue to starch. Sufficient saturated sodium bicarbonate solution is then added to discharge the blue color. The bound sulfite can now be titrated with accurately standardized iodine. The end-point is deter- mined by a blank control. It will be seen that 2 atoms of iodine correspond to 1 molecule of aldehyde. Three points deserve attention; if the first end-point is exceeded, no great inaccuracy is introduced, because of the very slow velocity of reaction (B) to the left. The second end-point, though perfectly clear-cut, is not permanent, owing to secondary reactions, such as the forma- tion of iodoform. This side reaction is much more rapid if the alkalinity is too high; as may happen if the bicarbonate used con-

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266 Determination of Lactic Acid

tains much carbonate, or if too much bicarbonate be used. The titration of the double compound is somewhat slow. The method appears to be satisfactory for dilute solutions as may be seen by comparison with the standard Ripper titration (Table I).

Among the advantages of ihe method may be mentioned the fact that a large excess of bisulfite may be used, thereby making possible the aeration procedure for catching acetaldehyde. Among the disadvantages must be mentioned errors introduced by volatile substances, such as phenols, which react with iodine in weakly alkaline solution. Both the modified method and the original method yield values for acetone which are always low. This is due to the fact that the hydrolytic dissociation constant for acetone sodium bisulfite (7) is relatively large (3 X 105) as compared with that for aldehyde sodium bisulfite, (2 X 10m6). It can be shown theoretically and by experiment that if a con- siderable excess of bisulfite is present, the fraction of acetone bound is constant for any given concentration of bisulfite and hy- drogen ion concentration. The error introduced by the presence of acetone can therefore be determined after removal of the alde- hyde by Shaffer’s method (8) on an aliquot of the solution to be analyzed.

Isolation of Acetaldehyde from Reaction Mixture.

Owing to its great volatility, acetaldehyde is liable to be lost when distilled. It was found, however, that the method of aeration lends itself readily to the transfer of acetaldehyde from one solution to another. This can be understood from a considera- tion of the distribution coefficient. At 100”, the ratio of the con- centration of aldehyde in air and in water is 1: 60; at 4”, the ratio falls to 1:1,760. If a slow stream of air be led through a small volume of the aqueous solution in a tube heated to loo”, and then through a large volume of ice water in two tubes in series, the transfer may be nearly quantitative. In one experiment, a liter of air passing through 5 cc. of solution at 100’ removed 99 per cent of t,he aldehyde, transferring 96 per cent to 20 cc. of ice water in the first receiver and 3 per cent to a like volume in the second. If an excess of bisulfite is present in the receivers the aldehyde is so rapidly combined that subsequent losses do not occur, even if very large volumes of air pass. An ordinary aspiration pump is

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S. W. Clausen 267

used. No cooling of the receivers is necessary. In all the experi- ments to be reported, the receivers consist of 20 X 200 mm. Pyrex tubes; the aeration tubes are of glass drawn to thick-walled capil- laries, so that air passes through the fluid in a stream of small bubbles. Rubber tubing does not appear to hold back more than traces of aldehyde. The tube leading from the warmed reaction vessel is made of glass 40 cm. long and serves as an air condenser. Although the first receiver becomes warm from condensed water vapor, the catches of aldehyde are good (see Table II).

TABLE II.

Analysis of lithium lactate solutions by the permanganate method. The largest part of the acetaldehyde is found in the first receiving tube.

0.1 N lithium lactate.

cc. 0 1 1 1

0.001 i-4 lithium lactate.

cc. 0 2 2 2

field of aldehydc in termr of 0.01 N I.

Receiver 1. Receiver 2.

0.05 0.00 18.00 0.75 18.65 0.20 19.00 0.10

Geld in terms of 0.001 N I

Receiver 1. Receiver 2.

0.25 0.05 3.68 0.16 3.57 0.22 3.53 0.25

18.70 18.80 19.05

3.58 3.59 3.63

Theory.

20.00 20.00 20.00

Theory.

4.00 4.00 4.00

Yield.

pe7 cent

Yield.

per cent mo.

89.50 0.18 89.8 0.18 90.8 0.18

Determination of Lactic Acid in Pure Solutions.

Two lactic acid standards are used. Both were prepared from a commercial brand of lactic acid. i-Lithium lactate was prepared by adding the calculated quantity of L&CO3 to 50 per cent lactic acid, filtering, concentrating, and recrystallizing three times. Owing to high solubility, the yield was small, and the product was probably not pure. It possesses the advantages of having no water of crystallization. For most of the experiments, i-zinc lactate was used. It was prepared by adding the calculated amount of zinc chloride in solution to lactic acid previously neu-

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268 Determination of Lactic Acid

tralized with NaOH. The product was recrystallized four times. It was free of chloride and its ZnO content was 27.32 per cent; theoretical for Zn (C3H603) 3 Hz0 is 27.36 per cent. A 0.1 N

solution contains 14.88 gm. per liter. The reaction is carried out in a Pyrex glass tube 20 X 200 mm.

A straight inlet tube drawn to a capillary extends nearly to the bottom. The outlet %ube is joined directly to a 40 cm. air con- denser which, in turn, leads to the two receiving tubes. A rapid current of air is maintained by an aspiration pump. Usually four set,s of analyses are run simultaneously. Rubber stoppers are used.

TABLE III.

Lactate used corrected for I used corrected for blank error in pipettes. and titer.

2.0 CC. 0.001 N 3.95 CC. 0.001 N

4.0 “ 0.001 N 7.85 “ 0.001 N 8.0 “ 0.001 N 16.00 “ 0.001 N 2.0 “ 0.005N lg.80 “ 0.005N 4.0 “ 0.005 N. 40.00 “ 0.005N 8.0 “ 0.005N 80.10 “ 0.005N 0.980 ” 0.05N 9.86 “ 0.01 N

1.995 “ 0.05N lg.32 “ 0.01 N 3.990 “ 0.05N 39.10 “ o.olN

9.950 “ 0.05N 97.0 “ o.olN

rhmry. Yield.

cc. per cm1 ma.

4.00 98.8 0.18 8.00 98.2 0.36

16.00 100.0 0.72 20.00 99.0 0.9 40.00 100.0 1.8 80.00 100.1 3.6

9.82 100.5 4.5 19.95 96.9 9.0 39.90 98.0 18.0 99.50 97.5 45.0

Analysis of zinc lactate by heating with &SO‘. Receivers in cases of 0.05 N zinc lactate contained 20 cc. of 0.1 N NaHSO,.

Two methods for carrying out the reaction were tried. The first is a micro adaptation of the von Fiirth-Charnass procedure. The reaction tube, containing 5 or 10 cc. of 1 per cent HzSOl and the lactic acid to be estimated, is placed in a water bath heated to 95’; the receivers each contain 20 cc. of 0.02 N NaHSOa. While a fairly rapid air current is passing, 0.005 N KMnOa is added through the inlet tube, drop by drop; only as rapidly as it is de- colorized. Water is added to preserve the original volume. After about 3 hour, the permanganate no longer fades, and the reaction is complete. The air current is run for 10 minutes longer. The contents of the receiver are then transferred to a flask and the bound aldehyde is determined by the above described

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S. W. Clausen 269

titration. The yield (Table II) is about 92 per cent of the theo- retical, a figure corresponding closely with that found by von Fiirth and Charnass for larger quantities of lactic acid. A factor, 0.05, was consequently used to calculate mg. of lactic acid from CC. Of 0.001 N I.

When larger quantities of lactic acid than 10 mg. are determined the results of this method are liable to be low. Attention was therefore directed to a second procedure, that of Meissner and Schneyer, for the formation of acetaldehyde from lactic acid. 50 per cent sulfuric acid is allowed to react at 140’ with the solu- tion to be analyzed. The volume of the reaction mixture varies from 5 to 10 cc.; the tube is heated in a fusible alloy bath to 140”. The air current should be rapid. After an initial lag of 10 minutes, the aldehyde catch steadily increases and reaches a theoretical amount in 50 minutes. An hour is allowed for the reaction. It will be seen from Table III that the results with pure lactate solu- tions are satisfactory for 0.18 to 45 mg. of lactic acid. The blank, although fairly large, is constant.

Application to Biological Material.

Before applying these methods to biological material, it seemed important to study their results with various known substances. Table IV shows the yield of a bisulfite-binding product in terms of cc. of N iodine for a gram-molecule of each substance tested. It is seen that ar-hydroxy-acids in general give considerable yields aa does glucose; glyceric aldehyde, gluconic acid, pyruvic acid, smaller yields; citric acid under.the conditions of the test, yields acetone, which binds bisulfite. Amino-acids give very small yields. /3-Hydroxybutyric acid gives only a small yield, as do creat- inine and uric acid. Charring occurred during the H&304 diges tion only in case of glucose and gluconic acid but never with pure a-hydroxy-acids. Amino-acids and urea do not interfere.

Another source of error must be pointed out. Many substances react with acetaldehyde in the presence of acid. Among these substances are the phenols. 1 mg. of phenol added to 1 mg. of lactic acid decreased the yield of aldehyde by the H&O4 method by more than 50 per cent. Charring results in 50 per cent H&30*, although neither pure phenol nor lactic acid are so charred.

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270 Determination of Lactic Acid

It is evident that the methods are not specific for lactic acid but apply to other cr-hydroxy-acids. Certain other compounds may be regarded as interfering substances. The problem of

TABLE IV.

Yield of bisulfite-binding substance from various compounds treated according to proposed methods for lactic acid. Results expressed in terms of cc. of N 1 solution Per mol of substance. Theoretical for a hydroxy-acid should be 2,000. -

Substance analyzed.

Alanine ....................................... a-Aminobutyric acid .......................... Asparticacid .................................. &Hydroxybutyric acid (synthetic). ........... Citric acid .................................... Creatinine .................................... Cystine ....................................... Gluconicacid ................................. Glucose ....................................... Glyceric acid .................................. Glycocoll..................................... Glycollic acid ................................. Hippuric “ ................................. Histidine dihydrochloride ..................... Leucine ....................................... Malicacid .................................... Oxalic “ .................................... Phenol ........................................ Phenylalanine ................................. Pyruvic acid .................................. Succinic “ .................................. Tartaric “ .................................. Urea .......................................... Uricacid ......................................

T --

N I per mol.

KMnO, H&O, method. method.

cc. cc.

0 4 32 0

0 0 100 35 360 151 100 50

0 2 202 270

1,000 1,080 16.5 95.6 0 9

36 365 0.0 40 0 9 7 0

255 1.012 0 0

76 10 32 0

7.5 7.6 0 0

27 370 0 0

220 52

separating lactic acid from such substances is by no means easy. One of the methods most frequently used is that of ether extrac- tion from an acid aqueous solution. Extraction from solid dehy- drating media (9), such as N&SO+ or such as plaster of Paris, has also been advocated. Other solvents, such as amyl or butyl

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alcohol and ethyl acetate (10) have also been advocated, because the distribution coefficient (11) of lactic acid between these and aqueous solutions is more favorable to rapid extraction. These solvents, of relatively high boiling point, do not adapt themselves as readily to any automatic extractor as does ether. For this reason, the use of ether was adopted. The theory of continuous liquid extractors has been well presented by Pinnow (ll), and needs very little comment. Practical points deserving emphasis are that the rapidity of extraction varies directly (a) with the dis- tribution coefficient (ratio of concentrations of extractable sub- stance in ether and in aqueous solution) ; (b) with the rate of flow of ether; and (c) inversely with the volume of solution to be ex- tracted. The latter point has not received due attention; con- sequently, we find in the literature that very long periods of time, up to 60 hours, are sometimes necessary for “complete” extraction. Most chemists, impressed by the “salting out” a.ction of ammon- ium sulfate, have added this salt to the solution to be extracted, thus raising the distribution coefficient.

As the method described above for lactic acid is applicable to very small quantities, such as those found in 2 or 3 cc. of urine, it seemed desirable to devise a liquid extractor designed for such volumes of fluid. Its construction and operation may be ex- plained best by reference to Fig. 1. K is a 300 cc. Kjeldahl flask containing 50 cc. of ether, warmed in a water bath. H is a Hop- kins condenser. F is a funnel made from a test-tube; its end should be slightly bent, and its opening about 0.5 mm. E, the extraction tube, blown from a test-tube, has a side opening 0 for ether outflow, and a small bulb at the lower end. The narrow lower portion should contain about 2 cc. in a column about 10 cm. deep. A copper wire, W, holds E, and is carried between a cork, C, and the flask, K. As ether condenses and enters F, it gradually displaces the fluid in the stem; which should be of sufficient length to give such a head of pressure as to carry a rapid stream of ether in drops through the liquid in E, until a steady outflow takes place through 0. Soon after starting operation of the apparatus, bubbles of vapor may fill the stem of F, and pre- vent flow. In this case it is only necessary to make momentary the air pressure at the side tube of the Hopkins condenser. The ob- structing bubbles of vapor then collapse. After flow has begun,

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272 Determination of Lactic Acid

the apparatus works very smoothly. It is usually run with the water bath at 60-70”. Liquids to be extracted are saturated with ammonium sulfate. It is convenient in practice to add about 1.3 gm. of the crystals (from a small graduated testAube) to 2 cc. of fluid in E.

In studying the performance of this apparatus, 2 cc. quantities of solutions of various acids were placed in E and saturated by addi-

FIG. 1.

tion of 1.3 gm. of (NH&S04. From time to time, extraction was interrupted and the ether extract was titrated in the flask with 0.1 or 0.01 N NaOH, using phenolphthalein as indicator. The resulting figures were compared with the amount of acid known to be present at the outset, or with the total amount extractable. Results are tabulated in Table V.

It is evident that 99 per cent of lactic acid is extractable from 2 cc. of solution in 3 hour; that in this period, about 5 per cent of

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ci.tric acid, 60 per cent of glycollic acid, 100 per cent of /3-hydroxy- butyric acid, and 90 per cent of pyruvic acid are extractable. Only a trace of H&SO4 is extractable; pyruvic acid (12) can be rendered unextractable by the presence of bisulfite; glucose is not extractable. It is thus possible to free lactic acid from some of the known substances that interfere with its estimation. It must be emphasized at this point, that biological fluids probably contain substances other than lactic acid which are extractable by ether and which yield bisulfite-binding compounds. Some of these, such as the other cu-hydroxy-acids, may even yield crystallized

TABLE V.

Extraction of various acids in 3 hour period, using continuous ether extractor. Results expressed in terms of 0.1 N acid.

Acid.

Malic ..................................... Gluconic .................................. Glyceric ................................... Pyruvic ................................... Glycollic .................................. Tartaric ................................... Citric ..................................... 8-Hydroxybutyric. ........................ Lactic .....................................

-

_ _

-

-7

Taken. Extracted. ?ercentage extracted.

cc. cc. per cent

1.8 0.3 16 2.2 0.05 2

12.52 2.0 16 10.33 9.30 89.5 6.45 3.90 60.5 7.30 0.15 2

22.35 1.05 4.6 20.0 20.0 100 20.45 20.32 99.2

zinc compounds closely resembling zinc lactate. Moreover, phe- nols are extracted, and, as has been pointed out above, seriously lower the yield of acetaldehyde. One may, therefore, speak only provisionally of the total amount of ether extractable substances yielding aldehydes in terms of lactic acid. With this reservation in mind, the investigation was undertaken of the “lactic acid” content of urine and of blood.

Determination of “Lactic Acid” in Urine.

Since urine ordinarily contains very small amounts of lactic acid, and relatively large amounts of other carbon compounds, ether extraction was always employed before applying either’ the KMn04 or the HzS04 method. It is quite certain that many other carbon compounds are thus extracted; such as phenols and fatty acids. This is evident from the fact that the ether extra&

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274 Determination of Lactic Acid

reduce a very large amount of KMn04 and char slightly when heated to 150’ with H2S04. These facts throw some doubt upon the figures obtained.

As a measure preliminary to ether extraction, it is necessary to remove albumin if present. This is accomplished by means of tungstic acid. To 5 cc. of urine are added 0.5 cc. of 10 per cent sodium tungstate, and 0.5 cc. of N sulfuric acid. After precipita-

TABLE VI.

Analysis of urine. Results expressed as mg. of lactic acid per 100 cc. and as lactic acid per kilo per 24 hours.

Diagnosis.

-

CllSC

1 2 3 4 5 6 7 8 9

10 11 12 12 12 13 14

Pneumonia, acute ..................... Epilepsy (no recent attack) ........... Cardiac decompensation .............. Normal (1) ........................... Bronchitis, chronic .................... Scabies ............................... Pneumonia, convalescent .............. Chicken pox .......................... Scarlet fever, convalescent ............

“ I‘ ‘I ........... “ “ “ ...........

Athrepsia ............................. “ ............................ “ ............................ “ ............................ “ ............................

-

Lactic acid ,actic acid Blood per 100 cc. lactic acid of urine.

per k. per day. per 100 cc.

38 13 23 11 11

5 10 11 14

6 8.3 6.5

11.7 11.3 19 8

ma.

1

2.4 4.1 5.4 4.4 4.1

I 2.3 1.6 5.9 2.9 6.4 3.4 2.9 4.2 6.4

w.

32 24 33 32 25 15 30 44 31 23 32

32.5

Con, the urine is filtered, 2 cc. are placed in the extraction tube. It has been found possible to separate phenols from lactic acid by a very simple procedure. 2cc. of albumin-free urine in the extrac- tion tube are treated with a few drops of a strong phosphate buf- fer solution of pH 7.0, and extracted for 15 minutes. All the free phe’nols are then removed; 1.3 gm. of ammonium sulfate and a few drops of concentrated sulfuric acid are then added, and the lactic acid is extracted with a fresh supply of ether for 3 hour. To the ether are added about 10 cc. of water, 1 drop of 0.5 per cent phenolphthalein, and sufficient 0.1 N NaOH just to give an alka- line reaction. The ether is removed by distillation. The con- tents of the flask are transferred quantitatively to a small beaker,

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S. W. Clausen 275

and evaporated on a water bath nearly, but not quite, to dryness. The material is then washed with a small quantity of water into the reaction tube of the lactic acid apparatus, 10 cc. of 1: 1 H2SOd (by volume) or 5 cc. of concentrated HzSOd are added, and the determination is carried out as usual. Table VI shows figures for a few urines analyzed in this way. That lactic acid added to urine (containing albumin) may be recovered, is demonstrated both by direct titration of the ether extract and by the conversion to aldehyde. Blanks are fairly large, but constant. Although the ether contains large amounts of bisulfite-binding substances, these seem to be removed by the two evaporations. Acetone, preformed or split from acetoacetic acid, is also removed by evaporation. A source of error might arise in case of urines con- taining considerable 8-hgdroxybutyric acid. This error is greater if the KMn04 method is used.

Determination of “Lactic Acid” in Blood.

The removal of protein from biological material deserves special note. Mondschein (13) has shown that under certain conditions lactic acid is not uniformly distributed between pre- cipitated protein and filtrate. Van Slyke and Baker (14) ca.11 attention to the fact that casein has the power to adsorb consider- able amounts of lactic acid and to the fact that at the isoelectric point of casein, such adsorption becomes negligibly small. Folin and Wu (15) find (empirically) that uric acid is adsorbed by pro- tein precipitates, if the acidity of the medium is too high; the tungstic acid precipitation as elaborated by these workers avoids that difficulty. It also gives a filtrate satisfactory for the deter- mination of lactic acid. This is indicated by the figures for re- covery of lactic acid added to blood.

Recovery of lactic acid added to blood before precipitation of piotein; 1 cc. of zinc lactate solution, diluted to correspond to final dilution of blood filtrate gave a liter of 51.2 cc. of 0.001 N I.

Zinc lzwtate. 0.001 N I. Recover~dof lactic Recovery.

ce. CC. cc. per c-ml

0 16.8 1 67.5 50.7 99.0 2 114.0 97.2 93.5

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276 Determination of Lactic Acid

One of the most time-consuming steps in the usual methods for determination of lactic acid in blood has been the ether extraction. This is due, as has been indicated above, to the large volume of filtrate extracted. This difficulty can be obviated by evaporating the filtrates to a small volume. It must be remembered, however, that evaporation should be done under diminished pressure, in neutral or slightly acid solution, because at loo”, loss of lactic acid will occur if the solution is acid; and if the solution is alkaline, glucose readily yields compounds extractable by ether and yielding bisulfite-binding substances. In solutions too acid, glucose yields formic acid. It is likely that in blood filtrates the chief interfering substance from which lactic acid is separable by ether,

TABLE VII.

Comparison of lactic acid determinations in the same blood by the KMnO, and the HlSOd method.

C.W?. I KMnOd

per 100 co. I ,zEo.

Normal child ................................... Burn, child .....................................

“ “ .................................... Rabbit 1.. .....................................

“ 2 ....................................... “ 3 .......................................

27; 42.8 36.3

112.0 54.0 04.5

w.

21.0 33.1 28.5 98.0 49.0 43.0

is glucose. Any method which would remove the glucose from solution would probably be satisfactory. A method proposed by Van Slyke (16) has been used for this purpose. To 10 cc. of the Folin-Wu filtrate, representing 1 cc. of blood, are added 2 cc. of 10 per cent CuSOl and 2 cc. of 5 per cent suspension of Ca(OH)t. After being shaken at intervals for 3 hour the mixture is centri- fuged, and 5 cc. duplicates of the filtrate are used for analysis. The blank in this case is determined by treating 10 cc. of 0.1 per cent glucose in the same way as the Folin-Wu filtrate. Results on ether extracts of evaporated blood filtrates agree well with those obtained on the copper hydroxide filtrate.

Blood lactic acid (in a case of cardiac failure): Determination on ether extract of blood filtrate, mg. per 100 cc.

of blood.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 Determination by copper-lime method, mg. per 100~~. of blood. 161

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S. W. Clausen 277

It is of interest to compare the results obtained by means of the KMn04 method with results of the H&S04 method (Table VII). The results of the oxidation method tend to be slightly higher. Probably the H&SO4 method gives results nearer the truth. It must be emphasized again that neither method is specific for lactic acid, but determines a group of substances. The same criticism

TABLE VIII.

Determinations of lactic acid in blood of convalescent children at rest in bed.

CW2.

Empyema .................. Nephritis ................... Diphtheritic paralysis. .... Nephritis .................. “Normal” ................. Cardiac .................... Chorea ....................

“ ................... Typhoid ................... Harelip............, ....... Tuberculous hip ........... Pulmonary tuberculosis .... Chorea .................... Bronchitis ................. Epilepsy ................... Feeding .................... Diabetes ...................

“ ..................

Maximum ................ Minimum ................ Average .................

KMnO, method.

mg. 100 cc.

25.9 32.3 27.9 35.6 21.8 26.7 20.5 29.0 27.0 25.4 28.0 34.0 27.2 25.4 34.0 29.1 28.0 20.0

35.6 20.5 28.1

HaSO4 method. ClW?e.

Pneumonia.. . . . . . . . . . . . . Epilepsy.. . . . . . . . . . . . . . . . “Normal”.. . . . . . . . . . . . . . Bronchitis.. . . . . . . . . . . . . Scabies.. . . . . . . . . . . . . . . “Normal”.. . . . . . . . . . . . . . Convalescent scarlet fever

“ I‘ “ I‘ ‘I “

Maximum .............. Minimum ............... Average ................

n&7.100 ce.

29.1 24.0 32.1 25.3 14.7 30.7 31.2 23.2 32.0

32.1 14.7 26.9

applies to methods proposed by others for lactic acid. The zinc salt (17), which is often isolated, weighed, and analyzed, frequently contains impurities, which may even prevent its perfect crystal- lization. If purified, loss inevitable occurs. Methods (18), de- pending upon measurement of the CO evolved when H2S04 acts upon lactic acid, are of less value because many other substances yield CO under like circumstances. Polariscopic methods (19) are

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278 Determination of Lactic Acid

of value only when the presence of other optically active com- pounds can be excluded, and when large amounts of material are at hand.

It should be pointed out that pathological bloods containing acetone bodies (13) may yield too high results. In order to take account of the interfering action of acetone (preformed or derived from P-hydroxybutyric or acetoacetic acid), the method proposed by Shaffer and further studied by Hubbard was employed. After the final titration with 0.001 N iodine, the solution is transferred to a 300 cc. Kjeldahl flask, and about 1 gm. of sodium peroxide is added. The flask is joined to a condenser. In the receiver is placed 40 cc. of 0.02 N NaHS03. After heating the Kjeldahl flask 15 minutes in a boiling water bath, direct heat is applied and dis- tillation is carried out for 4 or 5 minutes. It can be shown that acetaldehyde is completely oxidized, and that all the acetone may be recovered. After half an hour, the contents of the flask are titrated in the usual way. The blank thus obtained is subtracted from the original quantity of 0.001 N iodine. In normal cases it varies from 0 to 0.2 cc., and in most cases may be disregarded without great inaccuracy.

A summary is given of the findings in the blood of convalescent children (Table VIII).

SUMMARY.

1. A modification of the Ripper method for the titration of acetaldehyde is developed.

2. Aeration is applied to the transference of acetaldehyde from one solution to another.

3. The von Fiirth-Charnass method for the estimation of lactic acid is adapted to quantities from 0.2 to 10 mg.

4. A method is developed, using 50 per cent sulfuric acid at 14O”C., for the estimation of from 0.2 to 45 mg. of lactic acid.

5. It is shown that methods such as these need special criticism when applied to biological material.

6. A method is elaborated for urine, which gives a provisional normal figure for the lactic acid content from 5 to 13 mg. per 100 cc.

7. A method is elaborated for blood, which gives a provisional normal figure from 15 to 32 mg. per 100 cc.

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S. W. Clausen 279

BIBLIOGRAPHY.

1. von Fiirth, O., and Charnass, D., tfber die quantitative Bestimmung der Milchsiiure durch Ermittlung der daraus abspaltbaren Alde- hydmenge, Biochem. Z., 1910, xxvi, 199.

2. Chelle, L., and Mauriac, P., Sur la transformation du glucose en acide lactique dans I’autoglycolyse du sang, Compt. rend. Sot. biol., 1914, lxxvi, 852. Harrop, G. A., Jr., A method for the estimation of lactic acid in blood, Proc. Sot. Exp. Biol. and Med., 1919-20, xvii, 162. Herzog, R. O., Zum chemischen Nachweis einiger physiologisch aktiver Stoffe, Lieben-Festschrift, 1906, 440; abstracted in Biochem. C&r., 1907, vi, 47. Polonowski, M., Note sur le dosage colorimetrique de I’acide lactique dans l’urine, Compt. rend. Sot. biol., 1920, lxxiii, 475. Ryffel, J. H., A new method for the estimation of lactic acid in urine, J. Physiol., 1909-10, xxxix, p. v.

3. Deniges, G., Reactions analytiques de quelques fonctions organiques fondies sur leur transformation en derives aldehydiques et cetoniques, Ann. chim. phys., 1910, xviii, 149.

4. Boas, I., Eine neue Methode der qualitativen und quantitativen Milchsaurebestimmung im Mageninhalt, Deutsch. med. Woch., 1893, xix, 940. Jerusalem, E., uber ein neues Verfahren zur quanti- tativen Bestimmung der Milchsiiure in Organen und tierischen Fltissigkeiten. I. Bestimmung der Milchsiiure in wiisserigen Losun- gen, Biochem. Z., 1908, xii, 361; II. Bestimmung der Milchsiiure in tierischen Fltissigkeiten, Biochem. Z., 1908, xii, 379. von Fiirth, O., Berichtigung betreffend die Mitteilung von Ernst Jerusalem, “uber ein neues Verfahren zur quantitativen Bestimmung der Milchsiiure in Organen und tierischen Fhissigkeiten; I and II,” Biochem. Z., 1910, xxiv, 266. Mondschein, J., Quantitative Bestim- mung der Milchsiiure neben &Oxybuttersliure, Biochem. Z., 1912, xlii, 91.

5. Meissner, R., tfber die quantitative Bestimmung der Milchsiiure in Organextrakten als Kohlenoxyd, Biochem. Z., 1915, Ixviii, 175.

6. Ripper, M., Eine allgemein anwendbare, massanalytische Bestimmung der Aldehyde, Monatsch. Chem., 1900, xxi, 1079.

7. Kerp, W., Zur Kenntnis der gebundenen schwefligen Sauren, Die schwefligen Siiure und ihre Verbindungen mit Aldehyden und Keto- nen, Berlin, 1904, pt. 1,40.

8. Shaffer, P. A., A method for the quantitative determination of &oxy- butyric acid in urine, J. Biol. Chem., 1908-09, v, 211. Stepp, W., and Engelhardt, W., Uber die quantitative Bestimmung von Aceton und Aldehyd in ein und derselben Fliissigkeit, Biochem. Z., 1920, cxi,8.

9. Schneyer, J., Biochem. Z., 1915, lxx, 294. 10. Ohlsson, E., Eine neue Methode zur Extraktion der Milchsiiure, Skand.

Arch Physiol., 1915, xxxiii, 231; abstracted in Physiol. Abst., 1916-17, i, 384.

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Determination of Lactic Acid

11. Hoffman, F. A., and Vollhardt, M., Die Anwendung des Teilungskoeffi- cienten bei der Milchsaurebestimmung im Magensaft, Arch Ezp. Path. u. Pharm., 1891, xxviii, 423. Pinnow, J., Verteilungskoeffici- ent und Extraktionsgeschwindigkeit einiger organischer Siiuren, 2. anal. Chem., 1915, liv, 321-45.

12. Czapski, L., Zur Methodik der Bestimmung von Milchsiiure neben Brenztraubensaure, Biochem. Z., 1915, lxxi, 167.

13. Mondschein, J., Uber die quantitative Bestimmung von Milchsaure bei Gegenwart von Eiweisskorpern, Biochem. Z., 1912, xlii, 105. Wolf, C. G. L., The determination of lactic acid, J. Physiol., 1914, xlviii, 341. Riesenfeld, G., Beitrage zur Technik der Milchslurebes- timmung und der Ermittlung des maximalen Milchsiiurebildungsver- mogens von Muskeln, Biochem. Z., 1920, cix, 249.

14. Van Slyke, L. L., and Baker, J. C., Free lactic acid in sour milk, J. Biol. Chem., 1918, xxxv, 147.

15. Folin, O., and Wu, H., A system of blood analysis, J. Biol. Chem., 1919, xxxviii, 81.

16. Van Slyke, D. D., Studies of acidosis. VII. The determination of &hydroxybutyric acid, acetoacetic acid, and acetone in urine, J. Biol. Chem., 1917, xxxii, 455.

17. Kondo, K., Uber Milchsaurebildung im Muskelpresssaft. II. Mit- teilung, Biochem. Z., 1912, xlv, 63; Uber Milchsliurebildung im Blute. III. Mitteilung, 88; Uber Milchsaurebildung im Blute. II. Mit- teilung, 81. von Noorden, K., Jr., Uber Milchs;iurebildung im Blute. IV. Mitteilung, Biochem. Z., 1912, xlv, 94.

38. Maver, M. E., The Schneyer method for the determination of lactic acid in urine, J. Biol. Chem., 1917, xxxii, 71.

39. Hoppe-Seyler, F., and Araki, T., Ueber die Einwirkung der bei SLuer- stoffmangel im Harne ausgeschiedenen Milchs;iure auf polarisirtes Licht und die Rotationswerte activer Milchsiiuren im Allgemeinen, Z. Physiol. Chem., 1895, xx, 365.

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S. W. ClausenAMOUNTS OF LACTIC ACID

DETERMINATION OF SMALL A METHOD FOR THE

1922, 52:263-280.J. Biol. Chem. 

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