Qualitative Analysis of Microgram Samples General Technique and Confirmatory Tests A. A. BENEDETTI-PICHLER' A N D IklICHAEL CEFOL.42 Washington Square College, New York University, New York, N. Y. The technique of working in the capillary cone has been extended to permit the performance of confirmatory tests after the separation of constituents. The tests are carried out on a circular plateau of 0.03- to 0.2-sq. mm. area obtained by cutting a glass thread of 0.2- to 0.5-mm. diameter. The thread is drawn out from the end of a short glass rod of 5-mm. diameter, which serves at the same time as condenser for concentration of the light in the plateau. The identification of approximately 0.001 microgram of the more common ions of the hydrogen sulfide group is assured in this manner. The cell for the performance of the operations has been modified to accommodate a greater variety of tools, and better control of the operation of the micropipet has been obtained with the use of a plunger adianced by means of a screw with fine thread.
A
PRECEDIXG paper ( 2 ) described a general working
teclinique, which can be applied to the qualitative analysis of samples of 1 microgram mass or less. The procedure employed in separating the constituent ions was outlined, hut the performance of confirmatory tests was not mentioned. This report may be considered a n extension of the first paper, dealing with confirmatory tests and some niodifications of the working technique. Various changes in the design of apparatus are in part required to facilitate the performance of confirmatory tests and in part suggested by the accumulation of experience in work of this kind.
liminary experiments (Z),was found unsatisfactory for two reasons: (1) It does not provide ample room to accommodate a condenser rod and a capillary carrier of the above-specified dimensions which would comfortably hold as many as six or seven capillaries without crowding; (2) it causes difficulties in manipulations, especially in removing and introducing capillaries. The new chamber shown in Figure 1 has been found entirely satisfactory. The sides, a, consist of pieces of brass 67 mm. in length, 6 mm. in thickness, and 11 mm. in height. Four grooves run lengthwise, and, in addition, each bar has a vertical groove, f,a t one end. The two pieces forming the side of the chamber are attached with screws t o a brass frame, b, which in turn is mounted by means of De Khotinsky cement on a glass plate, h (68 mm. x 60 mm.), serving as the bottom of the chamber. The brass frame is 1 mm. thick and made to fit plate h, so as to give a border 5 mm. wide all around. This leaves an area approximately 48 X 57 mm. through which light can pass. A piece of glass slide, c , which fits the vertical grooves, f, forms the back of the cell. The top plate, d, is cut from an old projection slide, so that it can be freely moved when inserted into the uppermost of the horizontal grooves of the brass bars. Thus, the dry chamber resembles a chess box with the cover sliding in and out and one end open. To convert it into a moist chamber, the remaining horizontal grooves of the brass bars are Iined with cotton, e , which, if slightIy moistened with water, produces a damp atmosphere in the cell. FORCEPS. .4t least two forceps, one of which should be corktipped, are required. They should be made of stainless steel and have smooth (not corrugated or toothed) parallel tips. Cork-
Apparatus CARRIER.To enable the mounting of a larger number of reagent capillaries, capillary cones, etc., the dimensions of the carrier slide have been changed to 35 X 25 X 7 mm. It may be cut from plate glass, or microscope slides of the proper dimensions may he cemented together to give the thickness desired. The thick slide is easier to handle and has the further advantage that it supports the capillaries in approximately the level in which the platform of the condenser rod is located. P~~OIST ASD DRYCHAMBER. The all-glass chamber, recommended for biological work by Chambers ( 5 ) and used in the pre-
* Present address, Queens College, Flushing, N. Y. Present address, Metallurgical Laboratory, University of Chicago,
FIGURE1. MOISTCHAMBER
Chicago, 111.
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
tipped forceps are necessary, for they prevent the loss of capillaries which often slip the grasp of plain forceps. The loss of a espillaw cone may mean the untimely end of an investication
flected heht
1s
hanging from the tip of the buret. The micropipet is introduced into the hanging drop, and suction is applied with the plunger. When enough liauid has been taken in t o fill shaftlet and taoer. the pipet is'witlidrawn from the drop of cleaning liquid and it;
most convenientlv ohGined hv means of two mi-
aontardirection thr&h
the rear w i d o w (c. Figure 1) into the
by side withi; easy reach of the experinienter. MICROPIPETS.Micropipets having a bore of approximately Ip a t the opening were used a t t h e outset and operated by means of a hypodermic syringe according to the directions of Chambers (6). It was found more convenient in work with capillary cones t o give the micropipet B wider opening and t o control the flow of
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as axis. The buret wi'th the cleaning fluid is placed so that it is only necessary t o withdraw the micropipet from the moist chamher and rotate the manipulator through 90 degrees t o get the uimt to the tiu of the buret.
n e
iraduallv tapering fine tip was snipped off with a
