REPORT FOR ANALYTICAL CHEMISTS

original sample. While this proce­dure serves for materials like sugar, urea, creatine, creatinine, and phos­phate, and many other materials, methods of concentrating the sub­stance sought must be used. Often, this eliminates need to precipitate the original protein.

For volatile materials like am­monia, steam micro distillation was first resorted to (65). This process is still used by some, particularly for protein bound iodine estimations (70). This has the weakness tha t only one sample can be processed at a time. This was followed by de­velopment of micro aeration setups (79) and finally by the use of diffu­sion techniques (20). At first, mi­cro diffusion setups consisted of a small container holding absorbant, suspended in a flask containing the sample to be diffused (29, 83). This evolved to a special dish with concentric chambers, the so called Conway diffusion dish (21). These dishes presented problems in clean­ing, especially because the cover plate had to be greased to avoid leakage. A movement back to the original setup then followed. Wha t evolved was a glass rod held in a one-hole rubber stopper (see Figure 1). The rod, after dipping in the absorbant, is put into a bottle containing the sample. After diffu­sion takes place, the rod is then washed into the color reagent—e.g. Nessler's reagent for ammonia. This permits control of the final sample volume. Amounts of am­monia of the order of fractions of micrograms can be assayed (63). Evolution toward simplicity and convenience has resulted in return­ing to essentially the original de­sign. In the modern clinical chem­istry laboratory ammonia, carbon monoxide (34), volatile alcohols (23), aldehydes (formaldehyde, acetaldehyde), and acetone (84) are determined by microdiffusion.

Gases such as carbon dioxide and oxygen are estimated by the micro-gasometer (see Figure 1) capable of measuring from 5 to 15 μ\. of gas (42, 60). Arsenic is separated by volatilizing it as either the chloride or arsine, and determined by stain or colorimetrically. Amounts of the order of 1 7 or less may be deter­mined (8).

Figure I . Compact instrumentation is used to analyze volati le materials in the clinical laboratory. The rota­tor ( lef t ) turns at 100 r.p.m. to mix reagents and expose the surface for microdiffusion. The shaft is bent so that a rocking motion adds to the ro­tary motion. The hand holds the rod which is dipped in the absorbent. This is inserted into the bott le prior to rotat ion. The microgasometer (r ight) is used for analysis of such gases as carbon dioxide and oxygen. (Scientific Industries, Springfield, Mass.)

Lipides are separated by extrac­tion into an organic solvent. Ex­traction into organic solvents is also used to concentrate certain elements for assay. Practical examples are lead as dithizone (10), calcium as the alizarinate (62), and iron as the thiocyanate (60). In the examples cited, amounts of the order of 1 to 2 γ are determined. Extraction into . organic solvents is of particular value in tha t it permits concentra­tion into a small final volume so tha t reasonably high absorbances are obtained with a small amount of material being analyzed.

Paper electrophoresis (2) is rou­tine in many clinical chemistry laboratories. With amounts of serum or blood of the order of 2 to 10 μ\., partition of the proteins, lipide- and carbohydrate-carrying proteins, and hemoglobins (47, 50) is carried out routinely. In some laboratories, electrophoresis on starch blocks is also utilized for this purpose (31).

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VOL. 3 1 , NO. 3, MARCH 1959 · 1 9 A

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