Correlation, between analytical methods

To establish the "quality" of the human body, it is necessary to have correct information concerning its environment, and the food and pharmaceutical products administrated within less than 24 hours. With this knowledge, the medical practitioner will be able to request and establish the best correlation between analytical results and illness also, the analyst can select the best method, free of interferences. The sample collection is of major importance in this case, especially when an immunological method is applied. It is well known that the human body is able to synthesize antibodies during the same period of time as sample pickup. It is possible for these antibodies to act as interfering species in analysis and to increase the uncertainty. As a result, an increased value of uncertainty may be recorded when a tourniquet is put on different places around the arm for blood sample collection. It is also important to know the exact time of day a sample has been taken. 

The instrument must be calibrated using reference standards for each of the parameters that are to be analyzed, which is a fundamental step in assuring the quality of the future results. In order to calibrate the instrument correctly it is necessary to analyze a large number of reference standards containing each of the analytes at known concentrations it is considered that up to 150 wines of the same type are needed to establish a good calibration. The concentration of each of the parameters in the reference standards should be determined by a reference method, such as the methods described in this article, and obviously the quality of the calibration is directly related to the accuracy of the results obtained by the reference method. With good quality calibrations, FTTR is capable of excellent repeatability and reproducibility, frequently superior to those obtained with official usual methods and in some cases to official reference methods. There is usually a good correlation between reference methods and FTIR analyses however, if the wine contains a substance for which the instrument was not calibrated the results obtained will differ enormously from those obtained by a standard reference method for that substance. 

In AAS, similar to other spectroscopic techniques, the correlation between analyte concentration or mass and the measured value (in A or Ai t) is established by the use of calibration samples, usually calibration solutions. In the standard calibration method a calibration function (calibration curve) is established using calibration solutions ranging from A = 0 (Ajnt = 0) to the highest (integrated) absorbance expected for the measurement solutions. The standard calibration method can only be applied if interferences by concomitants are absent. The method of additions, where calibration solutions are made by adding increasing masses of the analyte to equal volumes of the sample solution, permits correction for some interferences (see Sec. 1.6). 

Methods for Determining Biomarkers of Exposure and Effect. Besides environmental exposure, exposure to cyanide can also occur from consumption of cyanide-containing food, metabolism of certain drugs, and smoking cigarettes. Since so many factors can influence cyanide exposure, the exact correlation between cyanide concentrations in the body and its level in the environment has not been made. Therefore, measuring cyanide and/or thiocyanate levels in blood and urine cannot be used as a biomarker for exposure to low cyanide concentrations. Analytical methods of required sensitivity and reliability to detect cyanide and thiocyanate in blood, plasma, and urine of both unexposed and exposed persons are available (see Table 6-1 and Table 6-3). Further studies determining biomarkers for exposure to low cyanide concentrations would be useful. 

One interesting paper by Suehara et al. used NIR to measure the cell mass in solid cultures of mushroom.41 Because mushrooms grow in solid matrices, spectroscopic analyses are sometimes difficult to perform. With coffee grounds as the main medium, reflection NIR was used for the determinations. The correlation between the glucosamine (analyte determined) predicted and that found by the conventional method was 0.992 with an SEP of 0.346 mg/g. 

Several chlorophenols, including 2,5-dichlorophenol, have been identified in laboratory animals exposed to lindane. This indicates that the presence of 2,5-dichlorophenol is fairly specific, but not completely specific, for 1,4-dichlorobenzene exposure. Information on the analytical methods commonly used to detect and quantify 1,4-dichlorobenzene in biological samples is presented in Section 6.1. There are currently no data available to assess a potential correlation between the values obtained with these measurements and the toxic effects observed in humans or laboratory animal species. 

Methods for Determining Biomarkers of Exposure and Effect. Exposure to 1,4-dichloro-benzene may be evaluated by measuring the levels of this compound in blood, breath, milk, and adipose tissue, and by measuring the level of 2,5-dichlorophenol, a metabolite of 1,4-dichlorobenzene, in urine (Bristol et al. 1982 Erickson et al. 1980 Jan 1983 Langhorst and Nestrick 1979 Pellizzari et al. 1985). Sensitive analytical methods are available for measurements in blood. Development of methods with improved specificity and sensitivity for other tissues and breath would be valuable in identifying individuals with low-level exposure. Development of standardized procedures would permit comparison of data and facilitate the study of correlations between exposure and measured levels biological samples. Interlaboratory studies are also needed to provide better performance data for methods currently in use. 

---