A COMPARISON OF T H E METHODS OF ANALYSIS FOR LEAD IN
URINE*
WILLIAM R. V. MARRIOTT
From the Laboratories of the Collis P. and Howard Huntington Memorial Hospital, Pasadena,
California, and the William G. Kerckhoff Laboratories of Biological Sciences at the
California Institute of Technology, Pasadena, California
The analysis for lead in tissues and excreta has been discussed by Kehoe1 who
lists four points which condition the value of any lead determination: the accuracy of the analytical method employed, the amount of lead present in the
sample, the care with which the samples for analysis are collected, and the
amount of additional information available for properly interpreting the analytical results. Because of the difficulty of adequately satisfying these requirements, Kehoe suggested that one should not place too much reliance on a lead
determination in order to diagnose lead poisoning. However, Gant 2 has found
that while many various symptoms are of value for diagnosing lead poisoning,
in every case a lead analysis of blood or urine is necessary to confirm the diagnosis. In view of this, the selection of a satisfactory and accurate lead determination is desirable. The classical method of Fairhall 3 is a very long procedure and has been shown by Kehoe4 to give low and unreliable results. In recent
years, numerous methods have been devised for determining very small amounts
of lead in biological material. The object of this paper was to try and evaluate
several different methods on the basis of accuracy and applicability to the
average clinical laboratory. Many methods which require very special technic or apparatus were not considered. Others were omitted because they had
been improved upon, or because they were too detailed for general clinical
procedure.
The method of comparison was to add known amounts of lead in the form of lead nitrate
or lead acetate solution to equal volumes of pooled urine. Along with the analysis of the
samples, a determination was made on the original urine, and a blank run on the reagents.
Pyrex glassware was used throughout, except where specially noted, and in place of silica
dishes, 350 ml. Pyrex Vicor evaporating dishes were used for ashing. All glassware was
cleaned with cleaning solution, and before using rinsed with dilute nitric acid, then with
distilled and redistilled water. While there was no noteworthy discrepancy in the values
when water direct from a Barnstead Still was used in place of redistilled water, for security
against contamination, this water was redistilled in Pyrex. All the reagents used were
of the C. P. Reagent type and in most cases no further purifaction was carried out.
Following the instructions given with the various methods followed, the hydrochloric
and nitric acids, the ammonia, the carbon tetrachloride and the ether were redistilled.
Later these reagents were tried without special purification, and no significant differences
were found in blank determinations. However, if large blanks are obtained, the offending
reagents should be treated and the lead in them removed.
Certain modifications were made in the methods. For ashing, since a muffle furnace
was not available, the urine was evaporated on a water bath. When the volume was re* This investigation was carried out with the aid of The Clinic Research Fund.
488
LEAD IN URINE
489
duced to 50 ml., 5 ml. of concentrated HNO3 were added and 5 ml. more of HNOs were added
at 25 ml. When the dish was dry, the nitrated organic material was decomposed on a hot
plate at 250°C, and the carbon residues oxidized by adding concentrated H N 0 3 to the
cooled dish and reheating until white ash was produced. Overheating was avoided. One
half a ml. of concentrated HNOs was added at a time and from 1 to 3 ml. were needed. To
dissolve the ash obtained by this procedure, it was found advisable to add some tartaric
acid to the hydrochloric acid. If this were not done, some of the lead might be left behind
as an insoluble phosphate. If one gram of tartaric acid is added to 20 ml. of 20 per cent
hydrochloric acid, satisfactory results are obtained. The 20 per cent hydrochloric acid
was prepared by adding equal volumes of concentrated HCl (Sp. gr. 1.19) and distilled
water, and distilling in a Pyrex still. The distillate from this constant boiling mixture,
except the first and last portions, contains 20 per cent HCl by weight. When methods other
than ashing were used to prepare the urine, they were followed as the procedure directed.
The dithizone solution was always the same strength, except when used for titration
(see below) and made by purifaction of Eastman dithizone. The yellow oxidation product
of dithizone was removed by extracting a solution of 10 mg. dithizone in 100 ml. CCU with
several 100 ml. portions of 0.05 per cent NH4OH. The dithizone goes into the aqueous
phase and leaves any lead and the yellow oxidation product in the CCI4. The combined
NH4OH solutions were acidified with concentrated HCl added drop by drop, and the dithizone taken up in 70 to 95 ml. of CCI4. The CCI4 solution was shaken with a few ml. of
25 per cent hydroxylamine solution and stored in an amber colored bottle in the ice box.
The layer of hydroxylamine solution prevents the oxidation of the dithizone and this solution will keep for several weeks. In the methods using titrations, the dithizone must be
kept away from the air and strong light as much as possible, to prevent oxidation. For
the titration, this dithizone was diluted till 1 ml. was equal to about 0.01 mgiri. of lead.
The sodium diethyldithiocarbamate was made to 2 per cent in water, and any lead removed by shaking with ether and discarding the ether after separation. The diphenylcarbazide solution was made by adding 0.1 gm. of the reagent to 500 ml. of water, boiling a
few minutes, cooling and adding 500 ml. more of water. The solution was stored in a dark
bottle in the ice box, where it is stable for several months.
Stock lead solutions, which are quite stable, were made, and these diluted when used.
For a lead acetate solution, 0.1831 gm. of Pb (CH 3 COO) 2 -3H 2 0 were dissolved in 100 ml.
of 1 per cent acetic acid (1 ml. = 1 mgm. of lead). For a lead nitrate solution, 0.1599 grams
of Pb (NOs)2 were dissolved in 100 ml. of 1 per cent nitric acid (1 ml. = 1 mgm. of lead).
For titrations, a 5 ml. buret was used which was graduated in 0.01 ml., and solution added
by 0.1 of a ml. The stopcocks were lubricated with glycerol and Lubriseal was used at the
edges. The colorimetric readings were made on a spectrophotometer, and green light of
0.525 m/j was found to be the most satisfactory for both dithizone and diphenylcarbazide.
The results obtained with a spectrophotometer were much more reproducible than those
obtained in tests with a colorimeter. The spectroscopic data obtained with an Applied
Research Laboratories spectrograph, and the light intensities'measured by a photo-electric
comparator.
The technics and results of the methods used are as follows:
Method of Lentonoff and Reinholds
For 100 ml. of urine. Ash, cool, add 5 ml. 20 per cent HCl containing tartaric acid and
evaporate to one third the volume. Add 5 ml. 50 per cent citric acid, 1 drop phenol red, and
concentrated NH4OH till indicator turns pink. Filter into a 25 ml. or possibly a 15 ml.
centrifuge tube, wash dish four times with 1 ml. portions of 0.1 N NH4OH, add washings,
and add 25 per cent acetic acid till indicator just turns orange yellow. It is important to
have the pH right at this step to insure the complete precipitation of lead chromate, as
given below. Add exactly 1 ml. standard lead acetate containing 0.10 mgm. Pb, wash
sides of centrifuge tube with 1 ml. 40 per cent ammonium acetate, and add 1 ml. 30 per cent
K 2 Cr04, stir well with narrow stirring rod, whichis left in the tube, and let stand over night.
490
WILLIAM R. V. MARRIOTT
Remove stirring rod, wash sides of tube and stirring rod with 3 ml. 0.4 per cent NH 4 OH,
centrifuge (10 min. 2400 R.P.M.), decant the supernatant fluid, invert tube on filter paper
to drain, wipe mouth of tube. Wash the lead chromate with 10 ml. 0.4 per cent NH 4 OH,
centrifuge 10 min., decant, drain. Repeat washing. Dissolve the precipitate in 3 ml. of
10 per cent hydrochloric acid, add 10 ml. of diphenylcarbazide solution (0.01 per cent in
water). Prepare standards by adding 10 ml. of color reagent (diphenylcarbazide) to 3 ml.
of standard lead chromate solution (0.01 and 0.02 mgm. per ml.), made from stock solution.
Stock solution is prepared by dissolving 39 mgm. of PbCrCh in 100 ml. of 10 per cent hydrochloric acid; 1 ml. equals 0.25 mgm. of lead and is stable in the ice box for 3 months. After
10 minutes, compare the unknown with the standard in the colorimeter. Since the unknown
lead is precipitated as double chromate salt, which has twice as much chromate as there is
lead, results must be multiplied by 0.5. Then to find the amount of lead in the urine the
reagent blank, including the 0.1 mgm. of lead added in the procedure, is subtracted. For
a colorimeter the calculation then becomes: mgm. of lead per 100 ml. = (reading of
standard/reading of unknown X 0.01 (or 0.02) X 3 X 0.5) — (0.1 mgm. added lead + amount
of lead in reagent blank).
Method of Thompsett and Anderson"
For 100 ml. of urine. Ash, cool, dissolve in 5 ml. HC1 containing tartaric acid, add 10-20
ml. water, wash into 500 ml. separatory funnel, using water to a total volume of 100 ml.
Add 100 ml. 20 per cent sodium citrate and make alkaline to litmus with concentrated NH4OH. To extract the lead, add 10 ml. 2 per cent sodium diethyldithiocarbamate
in water, and 25 ml. ether. Shake and remove all the ether which contains the lead. Wash
the ether in a separatory funnel with two 25 ml. portions of water. Transfer ether to small
Kjeldahl flask or large tube. Remove ether by heating on water bath and digest organic
residues over small flame with 1 ml. concentrated H2SO* and 1 ml. concentrated HCIO4
till almost dry (caution). Add 10 ml. water, 1 ml. glacial acetic acid, 5 ml. concentrated
NH4OH, and water to 25 ml. Add 1 ml. S0 2 water. This was prepared by allowing S0 2 ,
made by adding concentrated H2SO4 to copper wire, to bubble into 10 cc. H 2 0 for several
minutes. Then add 5 ml. 1 per cent KCN, 5 ml. CCU, 0.5 ml. dithizone solution in CCI4,
shake, and separate lead out in CCI4 phase. Wash CCI4 with four separate 10 cc. portions
of 1 per cent KCN to remove excess dithizone, and finally with 10 ml. of water. Make CCI4
volume 10 ml. Compare color to standards made by adding 0.005, 0.010, 0.015 mgm. of lead
in solution to a solution made as from "Add 10 ml. water . . ." on, and extracting lead with
dithizone in CO4. To calculate: mgm. of lead per 100 ml. of urine = (reading of
standard/reading of unknown X standard) — reagent blank.
Method of Kench1
For 100 ml. of urine. In a 350 ml. Kjeldahl flask, add to the urine 100 ml. N/2 H2S04
and digest over a small flame, adding few drops of 30 per cent H 5 0 2 till clear. Dilute digest
with water to 300 ml., add 5 ml. 20 per-cent sodium citrate to keep iron and other metals in
solution, concentrated NH4OH till alkaline to litmus, 5 ml. 10 per cent KCN. Use 25 ml.
ether and 10 ml. of 2 per cent sodium diethyldithiocarbamate to extract the lead, as in
previous method, and repeat extraction, pooling ether carbamate solutions. Wash ether
phase with water, remove ether by evaporation, digest with 1 ml. concentrated H2S04 and
a few drops 30 per cent H 2 0 2 (caution). Dilute with 4 ml. water, add 0.2 ml. concentrated
acetic acid to convert lead to acetate, concentrated NH4OH till alkaline to litmus (about
3 ml.). Wash into a 50 ml. separatory funnel, add 5 ml. 1 per cent KCN, 5 ml. CCI4,0.5 ml.
dithizone, and separate the lead out in the CO4 phase. Wash CO4 phase with 1 per cent
KCN, make CCU volume 10 ml., compare color with standards containing 0.005, 0.010,
0.015 mgm. of lead, prepared in a similar way to the unknown, starting at "dilute with 4 ml.
water, etc."
To calculate: mgm. of lead per 100 ml. of urine = (reading of standard/reading of unknown X standard) — reagent blank (as in the Thompsett and Anderson method).
LEAD IN URINE
491
Method of Ross and Lucas'
100 ml. urine in a large test tube with ground glass stopper. Adjust to approximately
pH 4.5 (brom cresol green) with glacial acetic acid. Add 10 ml. saturated ammonium
oxalate solution, 2 ml. 10 per cent CaCl2, precipitating calcium oxalate which carries down
the lead, let stand overnight, centrifuge, decant supernatant fluid, drain by inverting over
filter paper, wash precipitate with water, centrifuge, decant and drain. Digest precipitate
over small flame with 2 ml. concentrated HCIO < then a few drops of 30 per cen t H 2 0 2 (caution
in adding H 2 0 2 ). Use hood with fan, or suction of fumes from tube. Add 5 ml. water, 3 ml.
10 per cent citric acid, 2 drops brom thymol blue, and about 1.5 ml. concentrated NH4OH
till just alkaline. Transfer to a 50 ml. separatory funnel, add 4 drops 20 per cent NaCN,
0.5 ml. dithizone in CC14 and 3 ml. CC14. Shake and remove the CC14 which contains the
lead, wash CCI4 in separatory funnel with 10 ml. 0.5 per cent NH4OH + 2 drops 20 per cent
NaCN to remove excess dithizone, then with water, make CCU volume up to 10 ml., read
color, compare to standards prepared in a similar way, starting after the digestion step.
Calculations are the same as for Thompsett and Anderson method.
Method of Horwitt and CowailV*
For 100 ml. urine. Ash, cool, add 15 ml. 20 per cent HC1 containing tartaric acid, heat on
hot plate till almost dry, add 15 ml. 20 per cent HC1 and wash into 500 ml. separatory funnel.
Add 50 ml. 20 per cent sodium citrate, 5 ml. concentrated NH 4 OH, 2 drops phenol red, concentrated NH4OH till indicator turns pink (pH 8.0). Add 3 ml. 10 per cent KCN, 0.5 ml.
dithizone in CCI4 and 3 ml. CC14 and remove the CC14 woich contains the lead. Wash
CCU with 1.5 vol. of 0.5 per cent KCN and then with water. Read color and calculate as
in Ross and Lucas method, or carry out titration. To titrate, first remove lead from CCU
by shaking with 2 volumes 0.5 per cent HC1, which dissolves the lead. Wash HC1 solution
with few ml. CCI4. Aad 0.5 ml. 0.5 per cent KCN to the combined CCI4 fractions and
titrate the free dithizone with standard lead acetate till color leaves the KCN layer. Remove the pink colored CC14 and continue titration with lead solution, adding 0.5 ml. portions of fresh CC14 at same time and remove colored CCI4 at intervals. Add lead solution
from buret till last drop gives faintest pink CC14. Fresh CCI4 stays colorless with further
addition of lead solution. Calculation: mgm. lead per 100 cc. urine = (ml. of standard
lead solution) X (amount of lead per ml. of standard lead solution) — reagent blank.
Dithizone titration, Wilkins ei al.10
For 100 ml. urine, ash, etc. as above, up to the addition of the dithizone. In this method,
dithizone is added and the pink colored lead dithizone complex formed is soluble in C O 4.
The colored CCI4 is drained off at intervals, and fresh CCI4 added, 1 ml. at a time,
as dithizone isAslowly added. Titration is continued until the CCI4 layer stays colorless.
Dithizone solution is made so that 1 ml. equals 0.010 mgm. of lead, standardized against
known amount of lead in blank solution.
The calculation is mgm. of lead per 100 ml. = (ml. of dithizone) X (amount of lead 1 ml.
of dithizone equals) — lead in reagent blank.
Method of Shiels11
For analysis, 50 ml. of fresh or preserved urine are taken, and 25 ml. deleaded by making
acid with 2 ml. 10 per cent acetic acid and adding 5 ml. 5 per cent CaCl2, then with stirring
adding an excess of saturated ammonium oxalate until no more precipitate occurs. The
solution is filtered by suction through filter paper. To 20 ml. of the deleaded urine and 20
ml. of untreated urine in 100 ml. separatory funnels, 20 ml. of extractive solution are added,
consisting of 1.3 per cent KCN and 1.0 per cent ammonium citrate (1.0 per cent citric acid
made just alkaline with NH4OH). Add 1 to 2 ml. of dithizone solution in CCI4 or CHC18,
containing 5 to 20 mgm. dithizone. Titrate with standard lead solution into deleaded
urine until color matches the untreated urine CCI4 phase. Determination of exact end
492
WILLIAM R. V. MARRIOTT
point is extremely difficult. If bismuth is present in the urine, it greatly interferes and
must be removed by first extracting at pH 4 with dithizone.
Lead per 100 ml. = 5 (amount of lead added by the titration) — reagent blank.
Fairhall method, Myers^ Oustafson, Throne modification™
One liter or more of fresh or preserved urine used, for each liter add 50 ml. concentrated
NH 4 OH, stand overnight, separate precipitate by decanting and filtering with suction.
Ash precipitate and filter paper in "Coors" crucible over bunsen burner (do not overheat!),
destroy carbon traces with 1 ml. concentrated HNO3. Dissolve ash in 7 ml. of 20 per cent
HC1 + tartaric acid by boiling gently. Filter HC1 solution and 5 ml. portions of water,
used for washing crucible, into a 250 ml- conical flask, final volume 35 ml. Make solution
basic to methyl orange by 5 ml. 20 per cent NaOH and acid with 20 per cent HC1, add 1 ml.
acid excess. Saturate with H2S and stand overnight. Separate sulfide precipitate by
filtering and wash with three 15 ml. portions of boiled distilled water, and then dissolve in
15 ml. hot concentrated H N 0 3 and evaporate solution to 5 ml. Wash into a small flask
using 50 ml. of water. Make solution alkaline to phenolphthalein with 20 per cent NaOH,
and acid with 10 per cent acetic, and add 1 ml. excess 10 per cent acetic acid. Heat solution
and add 1 ml. 1 per cent K 2 Cr04, and let stand overnight. Separate chromate precipitate
on filter, and wash with three 10 ml. portions of hot water. Dissolve precipitate off the
paper with 2 ml. 20 per cent HC1, catch the dissolved lead chromate in precipitation flask,
and wash filter with small portions of water till volume is about 40 ml. Add 5 ml. 10 per
cent KI solution and titrate with approximately 0.005 N Na 2 S 2 0 3 solution, made freshand
standardized against K2OO4. Use starch for end point.
To calculate: 1 ml. of 0.005 N Na 2 S 2 0 2 = 0.34 mgm. Pb. Mgm. of lead in total specimen
= (ml. of Na2S2Os) X (normality of Na 2 S 2 0 3 X 100) X 0.68 mgm.
Spectroscopic method—Cholak13
Ash 100 ml. urine, dissolve residue in 2 ml. concentrated HN0 3 , add 3 to 4 ml. water, wash
into a graduated centrifuge tube with water to volume of 8 ml. Add 1 ml. bismuth solution
(0.1 mgm. Bi per ml.), and make final volume 10 ml. with water. Dry some of solution on
hollow end of electrode. Arc and photograph the spectrum. On dry plate read intensities
of lead line 2833.2 A and bismuth line 2898.1 A, and plot ratios of intensities against lead
in a series of known standards. From this graph find lead in unknowns. The original
article must be consulted for details.
DISCUSSION
The results obtained by the various methods tried are given in charts 1 and 2.
I t will be seen that the error does not change greatly from method to method.
However, since the increase in lead excretion which accompanies lead poisoning
is often quite small, these small differences of error among the methods become
important. Also of importance is the ease with which a determination can be
done and the error still kept small enough for the results to be of value. Because
of this, special consideration should be given to the procedures followed to obtain
these results. No method is satisfactory unless the urine samples are collected
directly into lead-free glass containers, such as Pyrex glass.
For the determination of lead in urine, the spectroscopic method seems to be
the best. It is the fastest and quite accurate. The dithizone methods, such as
Horwitt and Cowgill, and the method of Lentonoff and Reinhold are as accurate
as the spectroscopic, but are longer, and because of more elaborate procedure it
is easier to make an error in them. The modified Fairhall method and the
Lead
found
Error
Error
Lead
found
4
Error
.001
.0035
.007
.008
.012
.018
.0245
+ .0015
-.0005
-.0015
-.0005
+ .001
-
.004
.007
.010
.013
.016
.024
.028
+ .001
+ .001
-.001
+ .002
+ .001
.012
.018
.022
.025
.002
.007
Lead
found
5
Error
HETHOD
Lead
found
6
.0024
.004
.004
.0056
.010
.010
.012 .000
.0126 +
.000 .016 + .001
+ .001 .020 .000 .021 + .001 .016 +
.0224 +
.000
- . 0 0 2 .030 .000 .030 .000 .028 +
.002
.003
.006
.007
.000 .010 + .001
.008
.012 + .001 .011 - . 0 0 1
Lead
found
3
Error
Lead
found
7
Error
.002
.0004
.0028 .019 + .004
.0024
.005
.0026
.004
.004
.0042
.008
.008 - . 0 0 2
.012 - . 0 0 1 .011 + .0018 .010 + .001
.0155 + .0065
.012 + .002
.0105 + .0005
.000 .019 + .001 .017 + .001 .016 -.001 .018 .000 .0179 + .0037 .015 + .001
.013
.015 + .001
.000 .022 + .001
.024 + .001 .0212 + .002
.0165 -.0015 .023
.0225 -.0005 .030 + .002 .025 -.001 .028 + .001 .030 + .002 .0246 + .0004 .026 + .002
.0235 -.0005
.034 -.002
.0306 + .0014
.026 -.002
Error
.004
.0015
.008
.003
.006 + .001
.0065 -.0015 .015 + .002
.014 + .001
Lead
found
2
Error
Lead
found
9
Error
1
.0205 -.006 .030 + .001
.0220 -.0045
.001
.004
Nil
.006 .000
.0016 -.0034 .009 .000
.0071 -.0029 .015 + .001
.019 .000
.023 - . 0 0 1
.0371 -.0129
.0106 -.0009 .014 .000
.0097 -.0018
.0139 -.0026 .018 - . 0 0 1
.023 - . 0 0 1
.001
.004
.005 - . 0 0 1
.0049 -.0016 .009 .000
.0052 -.0013
.0015
Lead
found
i
1. Lentonoff, Reinhol d. 2. 1Tiompsett, Arjiderson. 3. Kench. 4. Ross, Lucas. 5. Horwitt, Cowgill. 6. Dithizone titration. 7. Shiels
(50 ml. of urine iised). S. Fairh all (1(300 ml. (jf urirle used) 9. Spectroscopic.
Reagent blank
Urine blank
0.002
0.005
0.005
0.006
0.006
0.010
0.010
0.015
0.020
0.020
0.025
0.025
Reagent blank
Urine blank
0.002
0.005
0.010
0.015
0.020
0.050
LEAD ADDED TO
TABLE 1
Results obtained with various methods when lead was added to pooled urine
All values are expressed in mgm. of lead per 100 ml. of urine
CO
3H
t-4
3
w
H
494
WILLIAM E. V. MARRIOTT
method suggested by Shiels give results which are too inaccurate for one to place
any confidence in them. The various methods of preparing the urine, if done
carefully, seem to be about the same. However, ashing is the most convenient
unless the laboratory is especially set up to do one of the others. In dissolving
the ash, tartaric acid should always be added to the HC1 (1 gm. for 20 ml. 20
per cent HC1), in order to make certain that all of the lead goes into solution.
Otherwise, some of the lead in the form of phosphate may remain unaffected by
the HC1. High temperatures should be avoided in ashing as some lead may be
volatilized and lost. The method of first extracting the lead with sodium diethyldithiocarbamate and ether, such as Thompsett and Anderson, and Kench, seems
to be a needless step, since as good results can be obtained by one of the methods
using only dithizone. Also, this extra step is long and introduces another place
TABLE 2
Comparison of the methods
Values in mgm. of lead per 100 ml. of urine
HEINE SAMPLE
METHOD OF ANALYSIS
Lentonoff, Reinhold...
Thompsett, Anderson.
Kench
Ross, Lucas
Horwitt, Cowgill
Dithizone titration....
Shiels
Fairhall
Spectroscopic
.005
.008
.007
.007
.007
.008
.009
.0047
.007
.005
.007
.007
.007
.006
.0074
.0075
.0037
.006
.001
.003
.003
.002
.004
.0034
.0025
.001
.002
.004
.004
.004
.005
.005
.0042
.006
.004
Samples: 1. 24 hour specimen, girl with lead poisoning in past, 2. 24 hour specimen,
same girl, next 24 hours. 3. 24 hour specimen, normal adult male, 4. 24 hour specimen,
adult male, mild chronic nephritis.
for error. The colorimetric procedures are fast and accurate. Titration with
dithizone is a short cut, but less accurate. The oxidation of the dithizone in the
buret, and the fact that it is impossible to titrate to any closer than the nearest
0.2 or 0.3 ml. increases the possible error considerably. The titration using a
lead solution is more satisfactory than the dithizone titration, but longer. In
both the dithizone and the spectroscopic methods, the presence of large amounts
of bismuth (over 1 mgm. per 10 ml. urine) is a cause of error. In the dithizone
methods, the bismuth may first be extracted at pH 4, then the lead at pH 8.
For the spectroscopic method, the bismuth may be removed as the oxychloride,
or no internal standard added to the unknown and the average intensity of the
bismuth line in the standards used. While the general opinion is that bismuth
is seldom present in large enough amounts to interfere, one should continually
remember that it is a possible cause for high lead values. The method devised
by Lentonoff and Reinhold is relatively simple, yet it gives surprisingly good
LEAD IN URINE
495
results and can be recommended for the average laboratory. Bismuth does not
seem to interfere. However, there are drawbacks to this method. It is necessary always to allow the solution to stand overnight so that all the lead chromate
will be separated out. This increases the time when only a few analyses are
being done. Also, the handling of the lead chromate precipitate is very much
open to error, particularly, if as sometimes happens, a very granular phosphate
precipitate also separates out.
As can be seen from what has been said, there is no simple and foolproof way
to determine lead in urine. The spectroscopic method comes the closest to
offering this, but a great outlay for expensive equipment is required. The other
methods mentioned are capable of giving very good results, but are rather long
and unless done very carefully, open to considerable error. For clinical laboratory work, the Horwitt and Cowgill, or the Lentonoff and Reinhold methods are
perhaps the most satisfactory. In doing any of these tests, a blank should be
done on the reagents and the values obtained subtracted from the total amount
found.
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Clin. P a t h . , 5, 13 (1935).
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(3) FAIRHALL, L. T . : Lead studies. J.
Ind. H y g . , 4, 9 (1922); J. Biol.
Chem., 60, 485 (1924).
(4) K E H O E ,
R.
A.,
THAMANN,
F.,
AND
CHOLAK, J . : Normal absorption and
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(5) L E N T O N O F F ,
T.
V.,
AND R E I N H O L D ,
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280 (1940).
(6) T H O M P S E T T ,
S.
L.,
AND A N D E R S O N ,
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amounts of lead in urine. Biochem.
J., 34, 1245 (1940).
(8) R o s s , J. R., AND LUCAS, C. C : A new
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(9) H O R W I T T , M . K., AND C O W G I L L , G.
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