852
ANALYTICAL CHEMISTRY
Acidity IO 00 500
IO
20
Rp.m. AlkaWty (as Ca CO,) 30 4 0 50 6 0 7 0
bonk acid). The increasing solubility of glass a t higher p H values limits the reliability of this application.
43
80
CONCLUSIONS
400
45
- 300
m 0
‘0
z
X
f-m o
47
100
50
2
60 70 18
0
Figure 2.
2
4
6
8 IO 12 d. 0.02 N \SO,
14
16
Extrapolations for typical rain water samples
Numbers (38 to 48) refer to laboratory sample numbers
Further consideration will show that both weak and strong acid concentrations in the same sample can be determined by titration first with 0.02N sulfuric acid and extrapolating to zero (H+)for mineral acidity. This may then be followed by backtitrating with excess increments of 0.02N sodium hydroxide and extrapolating to zero (OH-) per liter. The difference between the end points represents the weak acid acidity (exclusive of car-
The procedure described for the determination of alkalinity has been found to be sensitive and accurate to fO.05 p.p.m. alkalinit!: or mineral acidity when present in extremely low concentrations. A discussion has been provided on the titration of strong baseweak acid mixtures and the estimation of respective concentrations of strong acid and weak acid in acidic samples. This procedure was devised for analysis of rain water. I t is equally applicable for analysis of steam condensate and impurities in deionized water. Alkaline steam condensate samples should be collected with a known quantity of acid in order that ammonia is not volatilized before and during the titration. The procedure may also be adapted to analysis of .air pollution samples. It is limited to low concentrations and by the care and technique of the analyst. It can be made more sensitive and accurate by use of a more sensitive pH meter and a more accurate measurement of titrant volume. LITERATURE CITED
(1) Am. Public Health Assoc., New York, “Standard Methods for the Examination of Water and Sewage,” 9th ed., 1946. RECEIVED for review September 1 4 , 1954.
Accepted December 29. 1954.
Correction Factors for Comparing Activities of Different Carbon-1 4labeled Compounds Assayed in Flow Proportional Counter M. L. KARNOVSKY, 1. M. FOSTER, L. I. GIDEZ, D. D. HAGERMAN, C. V. ROBINSON, A. K. SOLOMON, and C. A. VILLEE, Biophysical Laboratory and Department o f Biological Chemistry, Harvard M e d i c a l School, Boston, Mass.
A comparison has been made of the activities of several organic compounds counted as such or as barium carbonate obtained after combustion. In the windowless gas-flow counter, under the conditions specified, the relevant correction factors are much smaller than those reported in the literature for end-window Geiger counters.
I
K experiments with carbon-14 it is frequently necessary to
compare the activities of different substances. For example, a comparison might be desired of the activity of a labeled substrate with the activity of carbon-14 dioxide derived from it metabolically or by chemical degradation. Correction factors have been reported to be necessary in making such conversions of the activities of organic substances (counted as such) to equivalent activities determined by counting the carbon-14 as barium carbonate. The following factors have, for example, been reported in experiments in which end-BTindow Geiger Muller counters were used: Glucosephenylosazone Pyruvic-2,4-dinitrophenylhydrazone Wax
1.34 1.26 1.29
(5) (1) (8)
Over the past several years, the authors have made similar measurements on a windowless gas-flow proportional counter. With this counting technique and using thin samples mounted on stainless steel planchets, correction factors are found under routine conditions of counting in this laboratory to be significantly lower than correction factors previously reported. APPARATUS
The counter, used for these studies and described previously ( J ) , is of the flow proportional type and uses a gas mixture of
argon with 5% carbon dioxide. The dimensions are shown in Figure 1. The counter couples directly (without a cable) into the scaler-amplifier unit (Model 162, Nuclear Instrument and Chemical Corp., Chicago, Ill.) which is operated a t about 1650 volts with a 5-mv. input sensitivity. The efficiency for thin carbon-14 samples is about 40%. THEORETICAL
If a series of planchets of various thicknesses is made up from a single batch of material and counted, a curve obtained for counts us. sample thickness is similar to that illustrated in Figure 2. This curve is characteristic of the sample material and can be used t o make relative corrections between planchets of a given compound by correcting all counts to the same weight of sample. To determine the ratio of activities between an organic compound and barium carbonate, the self-absorption curves must be known for each and the relative scales of the curves-Le., the correction factor-must be determined. One wav to do this is to burn thk organic compound to obtain barium carbonate with the same activity per carbon. Self-absorflion curves may then be obtainedfor ANOJE the organic compound and for the barium carCAThODE bonate derived from it. E These curves may be related to each other in scale by adjusting the counts per minute in E SAMPLE each case for the weight fraction of carbon in :1 OLANCHET Tf each compound. Ratios of counts obi 1-9 mm-1 tained from barium car1-14 3 mm.bonate and those from -1 19 mm.the organic compound may be calculated from Figure 1. Windowless proporthese curves for various tional flow counter
T ~
L
i ,
‘I
* V O L U M E 27, N O . 5, M A Y 1955
a53
Table 1. Specific Activity Counts per Minute per Millimole Carbon of Organic Substances and Barium Carbonate Direct Count, Original Compd Derivative Planchets Planchets (a) counted (b) counted
Gubetance Glucose Pyruvate Glycerol
*
a
e fL
8
...
199333 f 4267 198167 f 4080
...
2 Triolein 1
3371 f 118 17131 f 193
...
1
2
...
Barium Carbonate from Original Compd. , Derivative Planchets Planchets (C) counted (d) counted
20 b 166
3424 i 57 16177 f 342
2d 4
209500 1240 213300 i 3255
+
897 5 25 2 939 f 12 3d 51600 =k 900 2 ... 56400'; Probability level for comparing columns from which ratio is calculated. Glucose phenylosazone. Pyruvic-2,4-dinitrophenylhydrasone. Formaldimedon. Ratio in this case is c / a .
I600 -
1200 IO00 -
800-
0
6oot1
400v1 '0
1435
2
204500';
10 mgl12
8 I
6
4I
,
mg / cm
I
I
I
I
I
I
0
2
4
6
8
IO
12
Self-absorption curve for barium carbonate
...
...
6
j-
1200 IOOOk
!
8OOC 600
GLXOSAZOLE
coo-
.
f'
200
PYS-r C--2.4-O
mg rng
cm
1TkiPnEhY_hY:FLZC+ "'9
rI
6
oc
*
iC mg
I
C F 2
I
4
6
8
2
C
12
1600-
160Cr
1400
4CCf
-
2
i
IO
8
8
4
y 7 - 1
.
4 : '*
.
ZCG'
ccc-
f"
I
E
8co-
::F; 60CL
LIPIDE
'0
mg I
0
4
i' FORNALDIMEOCN
2
,
,
,
4
6
8
I cm
,
mg,
IO
12
rng / cni
,
,
,
14
16
18
20
2
l
I
2
6
1 . 0 2 f0.04 0.94 f0.02 1 . 0 5 i. 0 . 0 3 1.08 f 0 . 0 3 1 09
2 0.03'
Pa 0.70 0.02
