reagent solution. The mixture is heated for 3 minutes in boiling water. After cooling, 2 ml. of the tetraethylammonium hydroxide solution is added. The solution is diluted to 10 ml. with dimethylformamide. Readings are then taken at 595 mp. SPOT PLATE. One drop of thc aqueous test solution is added to one drop of the p-phenylazoaniline solution. After a 5-minute wait, one drop of the alkali is added. In the prescnce of nitrite ion, blue to green colors are obtained. The identification limit is 0.2 pg. of nitrite. The blank is yellow. SPOT PAPER.One drop of the reagent is added followed by 1 A (0.001 ml.) of the aqueous trst solution. The spot is heated for 1 minute on the metal part of a steam bath. One drop of alkali is then added. In the presence of nitrite ion, a blue to green color is obtained. l h e identification limit is 0.02 pg. of nitrite. The blank is ycllow. Spot Test Procedures. T h e spot plate and spot paper tests reported in this paper for the nitrite ion are not quite as sensitive as t h e benzaldehyde 2-benzothiazolylhydrazone test ( 2 ) . With amounts of nitrite ion greater than 25 pg.. a blue color is obtained; rvith l o w r amounts, a green color is obtained. The colors obtained in either the spot plate or spot paper methods are stable for a t least 24 hours. Spectrophotometric Procedure. T h e effect of variables o n the standard
procedure was investigated. I n t h e diazotization step t h e relative proportions of water and dimethylformamide are critical. Optimum results were obtained with 1 ml. of test solution and 2 nil. of the reagent solution; a lower or higher volume of eithrr test solution or the reagent solution gave lower intensities. Optimum intensities were obtained with 1.3 to 2.0y0 concentrations of p-phenylazoaniline; loner or higher concentrations gave lower intensiticxs. Ilonever, a concentration of 1% n as chosen in the procedure for, although the intensity n as slightly lower, the blank was considerably improved. The amount of acetic acid in the reagwt \\-as not critical except that concentrations Ion-er than 3% gave Ion-er valurs. The optimum intensities n-ere obtained with heating times of 2 to 5 minutes. From 1 to 5 ml. of alkali could be added with no effect on the color intensity. The final dilution could lie made n-ith dirnethylformaiiiide, acetonc. methanol, or water. The effect of thrsc various solvents on the n avclength mavinia and molar absorptivity vias as expected (1). The final chromogen absorbed a t 595, 588, 575, and 575 mp in dimethylformamide, acetone, methanol, and water, respectively. The molar absorptivity also decreased with the decrcasing basicity of the solvents. BPer's laiv ivas not obeyed although a linear relationship was observed between the
absorbance and concentration from 0.2 to 1.5 pg. of NO*- per ml. of final solution. The method is believed capable of further improvement, especially in respect to simplicity of operation and sensitivity. Interferences. -4s in all diazotization methods, sulfite ion interfered. T h e following ions did not appreciably influence the results in t h e spectrophotometric procedure when present in the ratio of 30 to 1chloride, sulfate, cyanide, iedide, nitrate, calcium, magnesium, sodium, potassium, and lithium. Ferric chloride tended to give slightly higher values probably caused by the presence of nitrite ion in the salt. LITERATURE CITED
(1) Sawicki, E., Hauser, T. R., Stanley, T. W., ASAL.CHEM.31,2063 (1959). (2) Sawicki, E., Noel J. L., -4nal. Chim. Acta 2 5 , 166 (1961). (3) ?awicki, E., Stanley, T. W.,Elbert, W . C.. Mikrochim. Acta, to be published. EUGEXE SAWICKI T. IT. STANLEY K.C. ELBERT
Laboratory of Engineering and Physical Sciences Robert *4. Taft Sanitary Engineering Center Cincinnati 26, Ohio PRESEXTED at the 140th Meeting, AC9, Chicago, Ill., September 1961.
Inaccuracy of Dumas Nitrogen Determinations of Certain 1,2,4-Triazoles SIR: The inaccuracy of conventional nitrogen analyses of some azaheterocyclic compounds ( I , S, 4, 8, 10, 11), including 1,2,4-triazoles (i3, has been often observed. I n the case of 1,2,4triazoles, Potts suggests (9) that preparative rather than analytical difficulties account for low nitrogen values. If this were correct, a survey of a substantial body of analytical data lvould correlate errors of nitrogen analyses with those of carbon and hydrogen. Results of analyses [micro-Dumas method for nitrogen (7, 19) from Zimmermann] of if3 new 1,2,4-triazoles (5) are summarized in Table I. The view of Potts is undoubtedly correct in group (a) (Table I), possibly correct in (b), b u t inapplicable to the triazoles in group (c) ; this lends further support to other findings on the interference of bromine with the determination of nitrogen in heterocyclic compounds (3, 8). 298
ANALYTICAL CHEMISTRY
Triazolcs frcc from bromine but containing nitrogroups or acyl hydrazine side chains may also give very low nitrogen analyses. I n some rases the error can be avoided or minimized by slow purging, but nlien the absolute error
Table 1.
Type, of 1,2,4-Triazole (a) 'l'-Unsubstituted
Summary of Elemental Analyses of Some lI2,4-Triazoles
Elelnelita
C(18) H(18) l(20)
(b) A'--4ryl; T o Br
present
( c ) lV--4ryl; Br
present a
is of the order of lye, the method of Spies and Harris (11) should be used (6) instead of the conventional Dumas method, as illustrated in the cases of 1 - p - nitrophenyl - 5 - phenyl - 1,2,4triazole - 3 - carboxylic acid hydrazide:
%\:
?\(45) C(13)
H(13)
h(l1)
Found 56.06 5.05 24.91 67.61 4 76 18.29 52.65 3.26 14.98
Calcd. 56.24 5.11 24.72 67.56 4.85 18.01 52.94 3.38 13.99
Number of samples is given in parentheses.
Averages, yo Deviations Absolute Relative Standard +0.18 +0.32 0.45 +0.06 +1.19 0.02 -0.19 -0.75 0.53 -0.05 -0.07 0.39 $0.09 f1.89 0.17 -0.28 -1.5 0.48 $0 29 +0.55 0.21 $0.12 +3.68 0.18 -0.99 -6 9 1.os
calcd. N, 25.92; found (D) 24.65, (8 and H) 25.69(;?,, and 1 - p - bromophenyl - 5 - phenyl - 1,2,4 - trizole-3carboxylic acid hydrazide : calcd. N, 19.55; found (11) 18.42, (S and H) 19.4070. LITERATURE CiTED
(1) Albert, A,, Quart. Revs. (London) 6 ,
197 (1952).
(2) Atkinson, 11. R., Polya, J. B., J . Chein. SOC.1952, 3418.
(3) Belcher, It., Bhasin, R. L., West, T., Ibad., 1959, 2585. (4) Brancone, L. M., Fulmor, W,,ANAL. C H E l f . 21, 1147 (1949). ( 5 ) Browne, E. J., Polya, J. B , Chem. & Ind. ( L o n d o n ) 1960, 1085, 1086. J. Chem. SOC.1962, to be published. (6) Challen, E., private communication. ( 7 ) Kirsten, ST-., The Dumas Determination of Nitrogen, in “Commehensive Analytical C h k s t r y , ” C. L. Wilson and D. W. Wilson, eds., Vol. 1, b, pp.
467, 471, and 484, Elsevier, Amsterdam, 1960. ( 8 ) Miher, R. T., Sherman, AI. P.,
ED. 8, 331 (1936). 9) Potts, K. T., C h e m Revs. 61, 87 IN[). E N G . CHEJI., h . 4 L .
i1961). \ - - - - I
10) Ronzio, -1.R.,
I Z D . ENG. CHEM., ANAL.ED. 12,303 (1940) 11) Spies, J. R., Harris, T. H., Z b i d , 9 , 304 (1937). 12) Zimmermann. R..Mikrochemie oer Aiikrochim. A c t i 3 1 , 42 (1943).
E. J. BROWNE J. B. POLYA Chemistry Department The University of Tasmania Hobart, Tasmania, Australia
High-Precision Rapid Injection and Automatic Refill Pipet H. V. Malmstadt and H. L. Pardue, Department of Chemistry and Chemical Engineering, University of Illinois, Urbana, 111.
A
PIPET is described which can operate by remote switching to deliver aliquots of reagent in synchronization with other events. A 1-ml, aliquot is delivered with a precision of 0.002 ml. in 0.4 second. By rotating a switch, a preselected number of aliquots can be added. For example, on dialing “10” ten successive aliquots are added before delivery stops. Any multiple of 1 ml. (or other volume increment) can be dialcd. n ith the maximum number of aliquots depending on the available switch positions. Aliquots other than 1 ml. are pasily obtained with interchangeable cams or syringes.
MICROSWTCH 5 5 1 ACTIVATED)
DELIVERY 3- WAY
TEFLON STOPCOCK OPERATED B Y MOTOR M,
RESERVOIR
The rapid addition of a single aliquot has been especially useful for quantitative reaction rate methods where the analytical results are obtained during the early seconds of a reaction. The accurate selection and pipetting of preset quantities of reagent are essential in automating many analytical procedures. I n other cases, such as for back-titrations, it is desirable to add increments of reagent n i t h good accuracy over a wide range until a n indicator shows a small excess of reagent. For these applications a counter has been connected so that the total number of aliquots from the start to the indicator change is read from a dial. The advantages of this pipet over that described by l l a l m s t a d t and Hicks [ANAL.CHEM.32, 445 (1960)l are the greater precision, the continuous recycling feature with direct readout on a counter, the switching device for preselecting delivery of a fixed number of aliquots, faster delivery times, and the use of a n inert Teflon valve. The Teflon cam and the spring were made as previously described.
r.p.m. reversible Slo-Syn motors (Superior Electric Co., Bristol, Conn.) with instant start and stop. Therefore, the entire sequence of ’/4 turn of stopcock, ’/z turn of cam, reversed turn of stopcock, and reversed turn of cam requires 1.25 seconds, with only about 0.4 second for actual delivery of an aliquot. The basic pipet unit also contains the counter and start switch. The start switch can be pushed for single aliquots or turned to lock in for continuous recycling. Delivery of Single Aliquot. T h e operation of t h e injection pipet to deliver a n aliquot of reagent is de-
DESCRIPTION OF PIPET
MICROSWITCH 53 SPRING
MICROSWITCH I ACTIVATED)
S2
w
TEFLON CAM OPERATED BY MOTOR M,
Figure 1. Delivery and refill system for automatic pipet
The pipet unit delivers one aliquot of reagent b y the upward plunger movement with the syringe connected to the delivery tip. The automatic r e a l occurs when the spring-loaded plunger follows the cam back t o its original position with the syringe connected t o the reagent reservoir as shown in Figure 1. The alternate connections between syringe and either delivery tip or reagent reservoir are made b y 90’ rotations of a T-bore Teflon stopcock. The plunger moves b y 180” rotations of a cam. Both the cam and stopcock are driven by 72
Figure 2. pipet
Basic circuit of automatic
K1. s1.
1 15-volt ax. DPST relay Push button switch for relay contacts of K 1 S2, 53, S4, S5. SPDT microswitches Mn M c . 72-r.p.m., reversible Superior Slo-Syn motor C. 3.3-/lfd., 330-volt R. 250-ohm. 25-watt
VOL. 34, NO. 2, FEBRUARY 1962
299
