Dry chemistry system

The main development in medical diagnostic reagents since the 1960s has been the steady growth of dry (soHd-phase) chemistry systems. Dry chemistry systems have made substantial gains over wet clinical analysis in the number of tests performed in hospitals, laboratories, and homes because of ease, rehabiUty, and accuracy. 

The principles and biochemical reactions involved in diagnostic reagents are described herein. Constmction of dry chemistry systems and advances are also addressed, as are biosensors. 

Polymers and Coatings Advances ia polymer chemistry have resulted ia many successful medical devices, including diagnostic assays (26). Polymers (qv), which can be manufactured ia a wide range of compositions, ate used to enhance speed, sensitivity, and versatiUty of both biosensors and dry chemistry systems to measure vital analytes. Their properties can be regulated by composition variations and modifications. Furthermore, polymers can be configured iato simple to complex shapes. 

Fig. 4. Dose response for blood glucose measurement using a dry chemistry system having a water-borne, tough coating film. The numbers represent...

In some situations measurement of the reflected, rather than the transmitted, radiation may be made to assess the amount of radiation that has been absorbed by the sample. There are two main ways by which radiation might be reflected. Specular reflection is similar to the reflection by a mirror and, for quantitative work, the angles of the incident and the reflected radiation are important. Diffuse reflection is from within the layers of the material and the reflected light is disbursed over a range of 180°. This type of reflection is measured in the thin films used in dry chemistry systems. The term reflectance density is often used, which is defined in a manner comparable to absorbance the logarithm of the ratio of incident to reflected light. 

Wet chemistry methods lor analysis of body analytes, e.g., blood glucose or chulesierol. require equipment and trained analysts. In contrast, dry chemistry systems can be used at home. 

Dry chemistry systems are useful not only to diabetics, but also to patients having other medical problems. These systems arc also used in animal diagnosis, food, fermentation, agriculture, and environmental and industrial mciniloring. 

The reflectometric evaluation procedure of the Ektachem system differs considerably from that of other dry chemistry systems. Ulbricht s sphere is not required in this reflectometric measurement. Measurement is effected from the underside of the slides. The arrangement of the measurement makes it possible to eliminate interfering substances that can influence the reflectometric measurement signal by their colour only. 

E455 Langton, S. and Taylor, T. (1988). Effect of proteins on the quality assurance of enzymes in Kodak dry chemistry systems. Lecture held on the 4th Asian-Pacific Congr. Clin. Biochem., 28 August-2 September, Hong Kong. p. 124, FC16. 

Rl 19 Phillips, S., Wyndham, L., Shaw, J. and Walker, S.F. (1988). How accurately does the Reflotron dry-chemistry system measure plasma total cholesterol levels when used as a community-screening device Med. J. Aust. 149, 122-125. 

As has been shown in the preceding chapters, enormous efforts have been made in recent years to intensively evaluate dry chemistry systems. Table 3 lists the essential results and the specifications of the instrument systems. It is left to the reader to assess the pros and cons of each system in respect of suitability for her or his particular purpose, since no recommendations in favour of a particular system can be given. 

A detailed description of various commercially available dry chemistry systems such as Ektachem, Reflotron, Seraly2er, Cobas Ready, Drichem, Opus and Stratus are also included. 

A dry chemistry system has also been described in which a nonenzymatic approach was used, based on the reaction with 3,5-dinitrobenzoic acid. ... 

Enzymatic methods for the measurement of urea are based on preliminary hydrolysis of urea with urease (urea amidohydrolase, EC 3.5.1.5 main source jack bean meal) to generate ammonium ion, which is then quantified. This approach has been used in end-point, kinetic, conductimet-ric, and dry chemistry systems. ... 

Among variations in approaches for electrolyte measurements with ISEs is the Kodak Potentiometric Dry Chemistry System, where batchwise measurements are made on disposable slides. These are manufactured by coating an appropriate polymeric membrane over an internal reference gel layer on a conductive substrate. Slides for potassium, sodium, chloride and carbon dioxide are available. A drop of sample is placed on one half of the slide and a drop of reference solution on the other half. The drops are connected by an electrolyte bridge and the e.m.f. measured via metallic contacts. 

Dry chemistry systems are very widely used in physician s offices, hospital laboratories and many homes worldwide. They are used for routine urinalysis, blood chemistry determinations, immunolomcal and microbiolo cal testing. Today dry chemistry systems are also used mr assays in applications ranging from chlorine in swimming pools to coolant levds in cars and trucks 12). 

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