tion, the connector, while under water, is disconnected a t least from the large-bore tubing. The condenser will now operate as part of a syphon. The flow of water into the beaker should be adjusted to keep the beaker overflowing a t all times. The volume of water flowing through the condenser depends upon the head employed. T o reduce friction or drag, the lengths of tubing in the syphon portion should be kept to a minimum. Although air bubbles tend to form in the tubing, especially where the water leaves the top of the condenser, they will not stick if the surfaces are clean and smooth. Glass tubing connected directly to the condenser with short pieces of polyethylene tubing proved to be quite satisfactory for long-term operation. One such set-up was operated continuously for over twelve days. To go back to attended operations, the connector is replaced in the line and the water flow adjusted.
RECEIVEDfor review June 13, 1974. Accepted July 8, 1974. Apparatus to control pressure and to prevent flooding when using a water-cooled condenser Figure 1.
The mention of firm names or trade products does not that they are endorsed or recommended Over other firms or similar products not mentioned.
Improved Absorption Tube for Arsenic Determinations. Stanley C. Elliott Department of Agricultural Chemistry, Oregon State University, Corvallis, Ore. 9 733 1
Bobby R. Loper
U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station, Forestry Sciences Laboratory, Corvallis, Ore. 9733 1 5:.n
The standard method for the determination of arsenic (1-3) involves the reduction of arsenic to arsine by use of zinc in an acid solution in a Gutzeit generator. The generated arsine is then passed through a lead acetate impregnated glass wool plug and then to a silver diethyldithiocarbamate pyridine solution in which it is absorbed to produce a red colored solution. The absorbance of the solution is read a t 535 nm, and the arsenic concentration is determined by use of a standard curve. Most publications show two- and three-piece absorption tube apparatus. This laboratory found such apparatus cumbersome and difficult to clean. To solve these problems, this laboratory has improved the design of the absorption tube assembly, producing an apparatus that is easier to handle and occupies less space.
1 \ )I ' y
EXPERIMENTAL APPARATUS T h e apparatus shown in Figure I is constructed by joining a 24/ 40 standard tapered joint t o 36 cm of 3-mm i.d. capillary tubing connected t o a 15-ml centrifuge tube; t h e capillary tubing is bent as in Figure 1. T h e bulb in the capillary tubing is needed t o stop syphoning of solution when the absorption tube is removed from the generating flask. T h e glass beads are added to enhance mixing when generated gas passes through the silver diethyldithiocarbamate solution. T h e lead acetate impregnated glass wool plug is inserted a t the entrance t o t h e capillary over the standard tapered joint. (1) "Standard Methods for the Examination of Water and Waste Water," 13th ed., M. J. Taras, A. E. Greenberg, R. D. Hoak, and M. C. Rand, Ed., American Public Health Ass., Washington, D.C.. 1971, pp 62-64. (2) V. Vasak and V. Sedivec, Chem. Listy, 46, 341 (1952); Chem. Absb., 47, 67e (1953). (3) H. K. Hundley and J. C. Underwood, J. Ass. Offic. Anal. Chem., 53, 1176-78 (1970).
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2%s
5
3 \ T
1
i d
Figure 1. Schematic diagram of arsine absorption apparatus
DISCUSSION In use, a measured amount of silver diethyldithiocarbamate solution is added to the 15-ml centrifuge tube portion of the apparatus, usually between 5 to 10 ml, an amount less than enough to cover the glass bead bed will make it hard to remove solution for spectrometric measurement, too large an amount will cause solution to be lost when generated gas is passed through the apparatus. Enough glass beads are added to the apparatus to cause a good dispersion of bubbles; in this laboratory the conical portion of the apparatus is filled. Glass beads should be larger than 3 mm
A N A L Y T I C A L C H E M I S T R Y , VOL. 46, NO. 14, DECEMBER 1974
or they will lodge in t h e capillary tubing. A piece of lead acetate impregnated glass wool is in t h e standard tapered joint end of t h e apparatus (see Figure 1). T h e absorption tube is then p u t on top of t h e generating flask and any generated arsine collected. After t h e arsenic determinations have been carried out, t h e absorption apparatus is easily cleaned by placing in a test tube rack and t h e solution forced out by use of a rubber bulb being placed on the 15ml centrifuge end of the apparatus. We have found t h e apparatus t o be easier to handle t h a n
two- and three-piece absorption tubes, and it can be easily constructed.
RECEIVED for review July 12, 1974. Accepted August 7, 1974. Published with approval of t h e Director of t h e Oregon S t a t e Experimental Station, Technical Paper Number 3855. Work supported in part by supplement No. 96 to t h e Master Memorandum of Understanding between the U.S. Forest Service a n d Oregon S t a t e University.
S pect romet ry No mencl at u re W e have compiled the following list of terms, their definitions, and abbreviations, which occur most frequently in papers on spectrometry. The list indicates our preferred usages in an attempt to obtain some consistency in a field where much discrepancy exists. Sources used in this compilation w e r e ASTM Committee E-1 3 on Molecular Spectroscopy (1 9 6 6 revision of tentative definitions); H. K. Hughes et a/. [Anal. Chem., 24, 1 3 4 9 ( 1 952)l; and Chemical Abstracts. This list is approved by the Nomenclature Committee of the ACS Division of Analytical Chemistry. Absorbance, A .
( S o t optical density, absorbancy, or extinction.) Logarithm t o t h e base 10 of the reciprocal of the transmittance A = loglo ( l / T ) .
(Xot k ) . (Kot absorbancy index, specific extinction, or extinction coefficient.) Absorbance divided by the product of t h e concentration of t h e substance a n d t h e sample p a t h length,
Absorptivity, a.
A bc
a = -
( S o t molar absorbancy index, molar extinction coefficient, or molar absorption coefficient.) Product of t h e absorptivity, a, and t h e molecular weight of the substance.
Absorptivity, Molar, E.
d. Unit of length equal t o 1/6438.4696 of wavelength of red line of Cd. F o r practical purposes, it is considered equal to lo-* cm.
Angstrom,
(Representing Beer-Lambert law.) Absorptivity of a substance is a constant with respect t o changes in concentration.
Beer's Law.
Quantity of t h e substance contained in a unit quantity of sample. ( I n absorption spectrometry it is usually expressed in grams per liter.)
Concentration, c.
Frequency.
Number of cycles per unit time.
T h e region of t h e electromagnetic spectrum extending from approximately 0.78 to 300 micrometers.
Infrared.
Unit of length equal to 10-6 meter. (Do not use micron.)
Micrometer, pm. Nanometer, nm.
Unit of length equal to 10-9 meter.
(Do not use millimicron.) (Xot I or d.) Internal cell or sample length, usually given in centimeters.
Sample Path Length, b.
Instrument with a n entrance slit and dispersing device t h a t uses photography t o obtain a record of spectral range. The radiant power passing through t h e optical system is integrated over time, and t h e quantity recorded is a function of radiant energy. Spectrometer, Optical. Instrument with a n entrance slit, a dispersing device, and with one or more exit slits, with which measurements are made at selected wavelengths within the spectral range, or by scanning over the range. The quantity detected is a function of radiant power. Spectrometry. Branch of physical science treating t h e measurement of spectra. Spectrophotometer. Spectrometer with associated equipment, so t h a t i t furnishes t h e ratio, or a function of the ratio, of t h e radiant power of two beams as a function of spectral wavelength. These two beams may be separated in time, space, or both. Transmittance, T . (Not transmittancy or transmission.) T h e ratio of the radiant power transmitted by a sample t o the radiant power incident on t h e sample. Ultraviolet. The region of the electromagnetic spectrum from approximately 10 to 380 nm. The term without further qualification usually refers to the region from 200 to 380 nm. Visible. Pertaining to radiant energy in the electromagnetic spectral range visible t o the human eye (approximately 380 t o 780 nm). Wavelength. (One word.) The distance, measured along the line of propagation, between two points t h a t are in phase on adjacent waves-units A., pm, and nm. Wavenumber. (One word.) S u m b e r of waves per unit length. The usual unit of wavenumber is the reciprocal centimeter, cm.-' I n terms of this unit, the wavenumber is t h e reciprocal of the wavelength when t h e latter is in centimeters in vacuo. Spectrograph.
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