William T. Roubal
Bureau of Commercial Fisheries Food Science Pioneer Research Laboratory Seattle, Washington
I
An Earil~ . Constructed Flow Cuvet A modular assembly for automated chemical analyses
Techniques for automated analytical systems using l~quidflow have developed rapidly during the past several years; dozens of routine chemical tests, conducted manually, have been automated.' By use of the same approach, procedures have been developed for the automated monitoring of column eluates.? To monitor flowing streams, the analyst uses flowcuvets as sample containers. Not all of the cells available, however, are satisfactory. Many flow cuvets of commercial design do not work in flow automation. Cylindrical assemblies of more than a few millimeters internal diameter fail to sweep clean when the flow rate is low; cells of rectangular design have proved to be even less ~atisfactory.~In contrast, a very successful cell is the "sweep-through" type consisting of all rounded corners (Technicon Corp.,
Ardsley, N.Y.).' However, this cell is normally used with a special optical system. In the absence of special fabricating equipment, this seemingly simple cell is difficult to construct. This paper describes the fabrication of a horizontal flow cell (either borosilicate or quartz) that, although not having optically flat windows nor all rounded corners with test-tube ends like the sweep-through cell has, does offer advantages over its commercial counterparts~. The cell is readily constructed with the simplest of equipment. No problems are encountered in focusing; its small internal diameter prevents bubble holdup; any convenient length can be used; and the cell rapidly sweeps clean. The simplicity of construction commends this cell in preference to ones previously de~cribed.~Used with a B & 1, Spectronic 20, precise control of wavelength is achieved. Readout is facilitated by employing a VONI-5 recorder. For systems employing organic solvents of low boiling point, a water-cooled brass cell holder, machined to fit the sample chamber, is used. Cell Fabrication and Techniques
With a needlepoint flame, pull a thin-walled point on a length of 2-mm i.d. tubing (Fig. 1A). Using even rotation, heat the sealed end and allow the glass to thicken into a uniform blob (Fig. 1B). If this operation is done correctly, the inside surface of the closure forms a flat face a t right angles to the cell wall. Next, using a wet cut-off wheel or by careful hand grinding, cut away the face of the blob to give a thin window; maiutain careful control in grinding so as to give a cut surface that is parallel to the internal face (Fig. 1C). Attach an inlet sidearm (1-mm i.d. tubing) as close as possible to the closed end. Bend the tube as shown (Fig. ID); the extension is used as a handle in subsequent steps. I n like manner, seal and cut the opposite end of the cell, and attach an outlet sidearm of 2 3 mm i.d. tubing. Polish the windows by momentarily "splashing" a pinpoint flame directly onto the cut surfaces. Bend the inlet and outlet tubes to fit the spectrophotometer used. Figure 1E shows a partial cross section of the water-cooled holder for the Spectronic 20.
1
"Automation in Analytical Chemistry" (American Edition),
The Technioon Corp., Ardsley, N.Y., 1966.
iRousnr, W. T., a m TAPPEL, A. L., Anal. Biochem., 9 , 211 Figure 1. Flow-cuvet construction: tube drown to a thin-wolled point (A), careful fabrication of closed end formation of window attochment of inlet tube (Dl, piocement of Row cuvet in water-cooled holder (El.
IBI,
ICI,
(1964). a
ROWAL,W. T., Anal. Chem., 37,440 (1965). Use of trade names does not imply endorsement. Volume 45, Number 6, June 1968
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439
