1562
ANALYTICAL CHEMISTRY
are measured by volume and seldom a t a uniform temperature They are measured in United States, Imperial, and metric volumes; weight-volume measurements are in units of density, specific gravity, and API (Baum6 type) gravity and with a t least t v o different temperaturec sales. RIaterials are frequently shipped between areas in which different units of measurement prevail and standard coefficients and conversion factors should mean much i n simplifying and unifying petroleum accounting practices through the norld. The new and extended tables are expected t o meet these exacting requirements
CONCLUSIONS
Analytical standardization is far from a dull activity, if the program is product,ive of new and bett’er laboratory practices. To add to its interest, the work involved in having technical people accept scientific data and technical facts as well as realize that the term “st,andardization” itself implies a measure of give and take if progress and uniformity are to be achieved, demands high statesmanship on t’he part of those sponsoring and fostrring standardization in the interests of commprw or trade. RECEIVED June 20, 1961.
4th Annual Sammer Symposium-Standards
Standards of Unstable Materials LLOYD E. WEST, Color Control Division, Eastman h-odak G o . , Rochester, .V. Y . Solutions for processing color film are unstable, but standard samples of such solutions are none the less needed as a check upon the analyst, his equipment, and the methods. Some decomposition occurs during the preparation of the solutions; thus even primary standard chemicals do not fulfill the usual requirements for standard solutions. Some decomposition occurs with standing. The decomposition rate is determined and extrapolated. The standard deviation of’ individual anal) ses is calculated and used as the basis for control limits. The quality of the analyst’s results are appraised by plotting the average and range of three successive analqses. Beckman Type E glass electrodes gradually become sluggish with use. The electrodes are checked with a calcium hydroxide-calcium chloride buffer and results plotted. Electrodes are used as long as the results remain within tolerance limits.
T
I n some instances t,he contaminants have not been identified. Specially selected product.ion-quality chemicals arc thrrcafole used for standards. Frequently, the most critical constituents of the proccssing solutioni are the organic chemicals. As some of t,hese must be i n solution a t concentrations approaching t,heir limit of soluhilit y, relat,ively long acirring is necessary to obtain true solutions. The precautionary measure of the addition of sodium sulfite minimizre but does not prevent aerial oxidation during preparation of thew solutions. After preparation, these solutions decompose th time, according to the temperature and the available oxygen. The pH of a processing solution is important for photographir purposes. The purit,ies of production-quality chemicals such as sodium carbonate, sodium sulfite, and sodium sulfate art’ surh that the p H of the resuking solutions is frequently found t o 1 x 3 out of control and must be adjusted before use. In spite of th(8 buffering action in these solutions, sniall amounts of free alkali in the starting chemicals are reflected in the final p H measurements. I n some solutions the resulting pH is a function of time of stii,riny
HE Eastman Kodak Co. processes Kodachronie and Koda-
color film for customers by continuous processes which are 3ut)jec.t to many variables. I n Kodachrome processing, for example, there are nine solutions with washes in between. Each processing solution contains approximately twelve chemicals, and most solutions contain strong reducing agents. Some are subject to aerial oxidation, t o interactions with other chemicals, and t o changes brought about by reactions with the film being processed. Chemical analyses are routinely run on these solutions t o ascertain that t.he chemical concentrations remain a t the operating level. I n one processing laboratory alone approximately one thousand analyses are reported every 24 hours. As a check on the reliability of the methods, the analysts, t,he rcagrnts, and the instruments, it is desirable t o analyze periodically stable primary standard solutions of composition comparable to those used in processing. However, primary standard processing solutions cannot be prepared because of aerial oxidation of the chemicals during the dissolving operation and the interaction of chemicals in the processing soluti’on. As stable primary standards are not available, procedures have been established for utilizing the unstable instead, Some of these procedures are described below. If they are t o be similar in composition to the processing ~ o l u tions, the standards cannot be made with reagent grade chemicals, because some of the processing chemicals are not 100% pure. Some of the trace impurities have photographic effects, which may be very different from those of the pure materials.
.
GRAMS PER LITER
Figure 1. pH, Hydroquinone, and Elon Histograms of Standard Sample
V O L U M E 2 3 , N O . 11, N O V E M B E R 1951 61-
series from colorless to dark brown, were analyzed and found to contain varying amounts of the various constituents, as shown in Figure 2.
54-
32I -
o;
1563
r
I
Il3r
80
The hydroquinone, Elon, sulfite, and pH of sample 1, the colorless sample, agreed closely with most of the 50 other bottles that had been analyzed up to this time. Sample 2, which was yellox in color, had a hydroquinone content of less than 0.5 gram, u hich is a drop to only one tenth of the amount originally present. There was a large drop in sulfite concentration and rise in pH, but little change in the Elon. Sample 3 showed a large drop in the Elon content and sulfite, and an incrrttse in pH. Sample 4 showed still further decomposition, the pH having dropped to a lower level than in sample 3. OH
OH
50
10.9
SODIUM HYOROOUINONE MONOSULFONATE
~+YOROOUINONE
10.8
d
10.7
'
40
I
I 2
Colorless
Yellow
10.6
SAMPLE
I 3 Lt. Brown
I 4 Dk. Brown
+ ZNozSO3+O2
-
Figure 2. Effect of Air upon Developer Stability
+ NazSO4+NaOH
*
SODIUM HYDROOUlNONE DISULFOHATE
*
forming the corresponding mono and disulfanotes
For Elon, substitute H'
'CH3
Oxidatioii of Hydroquinone and Elon
Figure 4 .
Such unprctiictal)lr tltwnlposition makes a zjample u8elrss as a standard saniplr. -4partial underst,anding of the decomposition that occurred may he obtained from Figure 3. These ultr~violet absorption rurvw of t h r w of t,hr samplrs indicate a gradual shifting of the p ~ a kabsorptiorls during darkening and decomposition.
Wovelength
Figure 3.
in millimicrons
Absorption of Developer
during the preparation of the solution. Thus, a solution cannot lie prepared and used as a primary Ftandard in the usual senw of the n Old,
7
BUILD-UP OF DECOMPOSITION PRODUCTS IN STANDARD SAMPLE
Z
050
E
030
0 10 I
FIRST DEVELOPER
The first developer through which certain color film is procwsed is an Elon-hydroquinone developer similar to the type used for black and white film. This contains hydroquinone, Elon (monomethyl-p-aminophenol sulfate), sodium sulfite, and other chemicals, and has a pH in the range of 10 to 11. Although such a solution cannot be preparrd and used as a primary standard, it can be used as a check upon methods of analysis, the analysts, the equipment, etc. Fifty-liter volumes of such a solution are prepared and placed in 250-nil. bottles, which are stored in a refrigerator. Periodically a sample is removed and the various constituents are determined. The distribution of data obtained from a given batch of developer analyzed over a period of several months is shown in Figure 1. Histograms indicate a bimodal distribution of the data on pH, hydroquinone, and Elon. During the course of the study it was noted that a few samples, stored in glass-stoppered bottles, had darkened in color. Four of these samples, in a color
0
2
4
I
6
14
I6
18
20
22
24
DAYS
Figure 5. Stability of Coupler and Build-C'p of Decomposition Samples stored at room temperature
Curve 1 shows characteristic absorption of hydroquinone :rut1 Elon. Curve 2, peaking at 300 mp, indicates the presence of a decomposition product, hydroquinone monosulfate. Curve 4 represents disu1fon:tten. Figure 4 indicates some of the reactions that are occurriiig i n the solution. Hydroquinone reacts with sulfite arid oxJ.g:isri t)o produce sodium hydroquinone monosulfonate and sotliui~r Iiydroxide; the latter accounts for the rise of pH. Further ositixtion consumes more sulfite and more oxygen to produce the tlisulfonate. The corresponding changes for Elon are analogous to the changes for hydroquinone and are indicated by the boxes shown on Figure 4. Oxygen is consumed in these reactiom. The author attributes the decomposition of these solutions primarily to leakage of oxygen around the glass stoppers, as in no
.
ANALYTICAL CHEMISTRY
1564 instance did a Sam le in a tightly closed rubber-stoppered bottle show appreciable &composition. COLOR DEVELOPER
The Kodachrome processes have three color developers, each of which has a developing agent and an organic coupler. These materials, in the presence of a silver halide, produce dyes in the exposed film. The stability of a given coupler is shown a t the top of Figure 5. The concentration of this coupler, in grams per liter, is determined by a method of analysis based upon the ultraviolet absorption of this material. The decomposition rate is not linear and does not fit a first-order reaction. The total decrease in concentration is approximately 0.4 gram in 3 weeks. The plots are examined a t the time each analysis is made. If, in the aupervisor’s opinion, the result does not fall nearly enough in line with the extrapolated degradation rate, he asks the analyst to reanalyze the same sample. The x’s indicate such instances.
tory, upon this standard sample, all fell within the 2u control limits. I n Figure 7 coupler B decomposition rate is shown. This rate is neither linear nor in accordance with a firsborder reactionthat is, if the logarithms of the concentrations are plotted against time, a straight line does not result. The use of this sample as a standard sample is based upon the visual inspection of the plotted results. If an analysis is noted to be markedly out of line, from the general direction of the extrapolated decomposition rate, it is reanalyzed w
ii P
i
32’0
0 LL
31.0
0
VI
E -
j 2
-
300 WEEKS
I
2
3
4
5
6
I -
Figure 8.
Iodine Equivalent of Processing Solutions Analysts A. B, C, etc.
c
e
c
ILIO0
c
u 0 1.00I
0 90
2
(
1
3
1
4
5
1
6
1
1
WEEKS
Figure 6. Decomposition of Coupler A in Standard Sample Samples stored a t 40’ F.
This method of analysis for the coupler involves an extraction. The decomposition products, or a t least part of them, as there are several, may be obtained by making use of the absorbancy measurements before and after extraction. These are plotted on the lower portion of Figure 5.
a
2 0-
... *e
w
-I
I
*e
1.8-
00 0
*.
1.6-
a.
*
00
0
1.4-
4 z
1.2-
4.0.e..* 0.8
I
I
Z
I
3
1
4
1
5
1
6
1
7
1
8
1
9
WEEKS
Figure 7.
Decomposition of Coupler B in Standard Sample
Thp stability of this solution can be improved by keeping the samples in a refrigerator rather than a t room temperature. I n Figure 6 it is noted that the decomposition rate is less than that in the previous figure. I n this case the loss of coupler during 3 weeks of storage a t 40” C. was only 0.15 gram per liter, whereas in Figure 5 the drop was 0.40 gram per liter. These data fit a linear rate of decomposition over the 6-week period. The standard deviation of these analyses has been calculated by the use of ranges of three successive analyses. Twice this valuenamely, the 2u limits-is shown by broken lines. Thus, it is apparent that during this time interval the results from the labora-
To be of most value, a standard sample should be run objectively. If the analyst is aware of the correct answer, he may be influenced in the values he reports. A recent practice has therefore been to have a series of three standard samples available a t all times. The supervisor or monitor asks the analyst to run one of these, but the analyst is not told the correct answer. T o make this program operate on a continuing basis, batches of the three standards are scheduled so that the supply does not become exhausted simultaneously. Therefore, a new standard sample is considered as a temporary standard sample during the collec,tion of cross-over data. APPRAISAL OF ANALYSTS
Figure 8 indicates the results obtained by various analysts on one of the standard samples over a 6-week period. The decomposition rate fits a straight line; all but one point fall within control, using 2a limits. These results are of great value in giving the supervisor of the laboratory assurance that his reagents are satisfactory and that the analyst is performing work of satisfactory quality. These results have recently been used periodically to appraise the general quality of the work done by the individual analyst. The top graph of Figure 9 shows average results of three successive analyses by individual analysts of any of the three standard samples mentioned above. Each analyst’s averages are plotted as deviations from the standard value. The standard value is obtained from graphs such as the one shon n in Figure 8. The lower graph of Figure 9 shows the range of the individual analyst’s three successive analyses. The average range is shown to be 0.35 ml. The standard value \vas 31.0 ml. One analyst has one value above the 2u upper control limit. This record is revien ed periodirally to appraise the precision of the analyses being reported by each analyst, whereas the accuracy of the analyses is indicated by the upper plot. IMPORTANCE OF pH
pH is one of the most important controls in color processingfor example, in the first developer the control tolerances are 10.05 pH. Beckman Laboratory Model G instruments are used with the Type E Blue Tip electrode and a wick-type calomel electrode, A rather detailed manual on pH measurements has been written to assist the control laboratories. National Bureau of Standards borax buffer is used as the primary standard. The meter and electrodes are cross-checked using a calcium hydroxide-calcium chloride buffer (1) of p H approximately 12. This cross check is used prior to making p H measurements of developers. No difficulty is encountered in the use of the borax
1565
+0.4
-
C
~ o , ---H-E-" e 08
z - 0 . 2 &A
8-o., 0 0
&
0,s-
LI
0.4
Groups
0.1
s
of 3
Anolyses
I
I
1
e
+
New Type
E Electrode
t* New Calomel Electrode
e
* *
0
I
I
Average Range
e
i
3
2
I
DAYS
20 U.C.L.
0.3 0.1
T
D D
w
Q
0
-
nv co
etc.
-
: - 0.70.5
e
-------_----__ 2_--_-___-----__-_--Letters: Analyst A,B,C, 2u L.C.L.
1.00.9
In 0.8 a
d
__--
e
0
w
The data plotted in Figure 10 indicate several electrodes which showed deterioration with time and the replacement of those A 20 U.C.L. K electrodes with rejuvenated electrodes. On the third day, one I ----a-----~----_------
4
-
Standard
Figure 10. Glass Electrode Control Chart
e
Calcium hydroxide-calcium chloride buffer
e
I
I
0
I
I
point fell above the upper tolerance; that proved to be a faulty calomel electrode and not a faulty Tvpe E. This action is typical of calomel electrodes which become plugged a t the hick. Whereas the Type E electrode gradually becomes sluggish, thus resulting in a skexed distribution of the data, a control chart is used successfully as a basis for deciding whether or not to report pH values using a given electrode. SU3l\lARY
I n summary, unstable standard samples are of value:
As an aid in understanding the chemical reactions occuriirig dui ing the decomposition of various solutions. Inspection of plotted records of the analyses indicates whether the analysis is near enough to the expected value to warrant 1 eporting answers on production samples. Improved keeping conditions have been found for standard samples and have also been adopted for production solutions. I n cases in which the decomposition rate is linear the 2u control limits have been calculated and used to decide whether the analyses are within control. The accuracy of the individual analyst's results is determined objectively by his analyzing unknown standard samples. His average values are compared with the group grand average. The precision of the individual analyst's results are ap raised by plotting the range of his three successive analyses. 8ontrol limits are calculated and used to appraise his work statistically. Type E glass electrodes, though unstable, are used successfully by making frequent checks upon their sluggishness using a high pH buffer. LITERATURE CITED
(1) Tuddenham, W. If.,and Anderson, D. H., * 4 ~ . 4 ~CREM., . 22, 1146 (1950).
RECEIVED hugust 9 , 19.51.
4th Annual Summer Symposium-Standards
Standardization of Microchemical Methods and Apparatus C . 0. WILLITS,'Eastern Regional Research Laboratory, Philadelphia 18, P a .
S
TAKD.~RDIZATIOSis not new in macrochemistry, but it is new in microchemistry. Ncrochemistry is a mere child by comparison with macrochemistry, being only 40 years old. The growth and popularity that niicrochemistry has enjoyed in this country are justified, for it has met a great need in analytical chemistry. B t first the procedures and apparatus adhered closely to those of the leaders in this new field of chemistry, but some microchemists have had no contact with the pioneers, and modi-
fications have crept into both the microprocedures and the apparatus. This is a healthy trend, but i t also presents a problem, because many of the new or modified procedures or apparatus give the desired results only in the hands of those who proposed them. Why, no one knows, except that the specificationsof some empirical condition have been omitted. There is nothing new in such an occurrence; it had been experienced in nearly every branch of chemical analyses. I n macroanalysis, this problem has been re-
