Editors' Column Blood Components Analyzed by New Film Technology A drop of undiluted blood serum is analyzed within several minutes on a dry thin film of 0.1-mm thickness. Typically, ΙΟ-μί, samples are spotted on a film containing all the reagents necessary to perform clinical analysis by colorimetry. When the develop ment of this technique is finalized and the products are marketed, the meth od may revolutionize the way in which some of the blood constituents are de termined in the clinical laboratory. The company that conceived the idea several years ago and has invested much effort in developing this film technique is none other than Eastman Kodak, the foremost film producer in the world. Apparently its research effort is approaching the last stage of development before marketing, and recently the company's researchers have been describing the technique at various meetings related to clinical chemistry. One such recent forum was the 10th Annual Symposium on Ad vanced Analytical Concepts for the Clinical Laboratory, hosted by Oak Ridge National Laboratory March 16-17, 1978 (page 343 A, March). Ac cording to the two speakers from East man Kodak, Henry G. Curme and Richard W. Spayd, known chemistries have been combined with the solid phase technology developed for use in photographic film to produce a simpli fied analytical technique for the deter mination of a wide variety of clinically important compounds. Advantages of the film technique include ease of op eration, speed of analysis, and low cost, the three most important factors for clinical chemistry applications. In essence, the technique miniaturi zes all of the necessary chemical pro cesses in an element approximately 1 cm 2 in area and 0.1 mm thick. The analysis film is made up of a transpar ent plastic base, one or more reagent (or indicator) layers, and the spread ing layer, in that order from the bot tom to top. On top of a transparent plastic base, the reagent layer(s) con taining all of the necessary reagents for the analysis is coated. Hydrophilic polymers, such as gelatin or agarose, are used as the binder in the reagent layer. On top of the reagent layer, an isotropically porous spreading layer consisting of cellulose acetate pig mented with T i 0 2 is coated. The final thickness of the spreading layer is typ ically 0.1 mm, 10 times the thickness of the dry reagent layer.
When an automatic sampler dis penses a volume of serum sample on the spreading layer, it spreads uni formly and rapidly (5-10 s) through the layer until the capillary pores are filled. The spreading layer is designed to do two things: to deliver the sample evenly so that the concentration of an analyte determined is nearly indepen dent of the volume of the spotted sam ple, and also to screen colored or tur bid components in the serum, from the field of observation in the reagent layer. When the water from the ap plied serum diffuses into the reagent layer, the hydrophilic binder polymer in the reagent layer rapidly swells to several times its dry volume. This in troduction of water into the reagent layer initiates the chemical process that produces colored species which are measured by a reflection densi tometer. The film is illuminated from the bottom against the white back ground of T i 0 2 in the spreading layer. The potential of the technique was demonstrated by the determination of a variety of compounds in sera, in cluding glucose, blood urea nitrogen, amylase, bilirubin, and triglycerides. The results were comparable to those obtained by the established methods of analysis. The general principles in volved in the assay of all five blood components are the same, but each film incorporates chemistries unique to that particular analyte. For exam ple, in the determination of amylase, a chemical reaction is carried out in the spreading layer since amylase, be cause of its size, is unable to diffuse into the indicator layer. After the re action the small soluble species pro duced diffuse into the indicator layer. This principle is of general use in the analysis of bilirubin and triglycerides. These compounds are freed from their respective transport proteins prior to diffusion into the indicator layers. In another case, blood urea is determined by the enzymatic generation of ammo nia, which causes a change in an indi cator layer. An important element here is the layer of cellulose acetate butyrate that permits the diffusion of the gas but rejects the aqueous phase. In all cases, the necessary reactions are complete in approximately 7 min. And the assay method can be selected so that all reactions proceed at one set of conditions. A study on the stability of the film showed no significant changes after storage in the freezer for one year. However, the questions still remaining are: how soon will the prod ucts be available and at what cost? Barbara Cassatt
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ANALYTICAL CHEMISTRY, VOL. 50, NO. 7, JUNE 1978 · 695 A
