Clinical chemistry sample volume

In many industrial areas, as well as food and agriculture, the amount of sample available to the analyst is not normally a limiting factor. However, in clinical chemistry the opposite applies, as no patient is willing to donate large volumes of blood for analysis Similarly in forensic work, the sample material may also be limited in size. Sample size is linked to the limit of detection. Improved detection levels can sometimes be achieved by taking a larger mass of sample. However,... 

Collison ME, Stout PJ, Glushko TS, Pokela KN, Mullin-Hirte DJ, Racchini JR, Walter MA, Mecca SP, Rundquist J, Allen JJ, Hilgers ME, Hoegh TB. Analytical characterization of electrochemical biosensor test strips for measurement of glucose in low-volume interstitial fluid samples. Clinical Chemistry 1999, 45, 1665-1673. 

This did away with centrifuging. However, possible effects could be that the volume of serum (or plasma) produced from the whole blood sample may be too low, or the erythrocytes may burst or may rub on and haemolyse the sample. Comparison of the methods of the Reflotron system vs. conventional analysis showed that this kind of serum (plasma) separation does not influence the routine methods in clinical chemistry. 

The sample volume, however, is not only influenced by an insufficiently well maintained pipette or by wrong handling of the pipette. The properties of the sample are also involved. Carriers intended for determination from whole blood are influenced by the haematocrit value. This parameter, which had so far been hardly considered as exercising any influence on the data obtained in clinical chemistry, is now an important factor. The bigger the haematocrit value, the smaller the serum or plasma yield, resulting in a lower sample volume. High haematocrit levels occur in the newborn and in patients suffering from polycythaemia. 

Common to all analytical procedures (manual, automatic, etc.) is the initial careful measurement of a volume of fluid (in clinical chemistry usually blood, serum, plasma, or urine) as well as volumes of standardizing solutions the accuracy and precision of this single operation are probably the factors that most affect the reliability of the whole procedure for any particular type of analysis. Several different sorts of error may be introduced at this stage the absolute volume of sample measured for each of a batch of replicate analyses may be incorrect the variation from one member of a batch to another in respect of the volume of sample taken may be outside the limits acceptable for the analysis and, when batches of specimens are analyzed, there may be cross-contamination of one specimen with material remaining in the system from the analysis of another specimen. 

For trace analysis, this means that small bore columns should be used and low retention factors are advantageous if the sample volume is limited, as is often the case in clinical or forensic chemistry. If enough sample is available, e.g. in food analysis, it is not necessary to use small-bore columns and low retention factors. However, the analysis time, solvent consumption and column overload by accompanying substances (not discussed here) need to be kept in mind. 

Sample Aspiration and Dispensing. Clinical chemistry analyzers perform tests mostly on blood serum or plasma, and less often on other body fluids. Precisely metered amounts of the sample have to be aspirated rapidly and without allowing intersample contamination, known as sample carry-over. Typical sample volume aspirated per test ranges between 1 iL and 25 J,L. Generally, pipetting is accomplished by motor-driven syringes connected through a fluid line to a thin aspiration probe (Fig. 1). 

When blood cannot be collected from the central veins of smaller laboratory animals, sites such as the retro-orbital plexus and tail are used. Some of these procedures can be carried out only at termination or may require anesthesia to allow interim sampling. In general, the collection of blood from dogs and most primates does not cause particular problems in terms of the sample volume required for core clinical chemistry tests, but the demand for and inclusion of additional biomarkers may require a compromise in study design. 

Environmental Studies. A review of the contemporary field of air pollution analyses by GC was published in the first volume of Contemporary Topics in Analytical and Clinical Chemistry (11). A book by Grob and Kaiser (12) discussed the use of LC and GC for this type of analysis. Many chronic respiratory diseases (asthma, lung cancer, emphysema, and bronchitis) could result from air pollution or be directly influenced by air pollution. Air samples can be very complex mixtures, and GC is easily adapted to the separation and analysis of such mixtures. Two publications concerned with the adaptation of cryogenic GC to analyses of air samples are References 13 and 14. Chapter 15 covers the application of GC in the environmental area. 

The book covers the entire field of electrochemical (bio)sensor design and characterization and at the same time gives a comprehensive picture of (bio)sensor applications in real clinical, environmental, food and industry-related samples as well as for citizens safety/security. In addition to the chapters, this volume offers 53 step-by-step procedures ready to use in the laboratory. This complementary information is offered on a CD-ROM included with the book in order to facilitate hands-on information on the practical use of electrochemical biosensor devices for the interested reader. It is the first time that the Comprehensive Analytical Chemistry series offers such complementary information with detailed practical procedures. 

Microdialysis sampling has been applied to numerous tissues, especially the brain since the brain is sensitive to alterations in volume and ionic composition. Ultrafiltration has been primarily used for peripheral tissue sampling from subcutaneous tissue since the removal of fluid from the brain is believed to cause alterations in brain chemistry.2 For basic research use, microdialysis sampling devices are typically called microdialysis probes. For clinical studies, the device is called a microdialysis sampling catheter since in clinical medicine a catheter is defined as a small tube that can be implanted. 

There are many oxidases used in clinical and analytical chemistry for the specific determination of constituents of complex samples, based on the generation of hydrogen peroxide by the action of an aerobic oxidase on its substrate. Cholesterol, glucose, galactose and many other analytes are determined that way. These analyses are also important in food analysis. But the volume of oxidases consumed in food processing is primarily based on the protection afforded the food by the removal of either oxygen or the other substrate acted upon. 

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