What is a good control group?

Abstract

There are numerous analytical detection methods available for human breath investigations. The major spectrometric methods used are solid phase micro extraction-gas chromatography coupled to mass spectrometry (SPME-GC/ MS) [1–4], selected ion flow tube mass spectrometry (SIFT-MS) [5–9], proton transfer reaction mass spectrometry (PRT-MS) [10–14], and multi-capillary column coupled to ion mobility spectrometry (MCC/IMS) [15–20]. In all cases mentioned, a non–invasive and an easy method for early diagnosis or therapy monitoring are developed by identifying diseasespecific biomarkers in the breath of patients. IonMobility Spectrometry (IMS) is an analytical technique to determine and discriminate analytes in the gas phase and has been used from the early 70’s, originally for military use and civil protection [21]. But until the 90’s this technique has not begun to develop considerably. Initially it was thought that the modern analytical ion mobility spectrometers would be more suitable for military applications involving chemical agents. Some of the applications adopted during the last decade include: locations security [15, 22–25], airport security [26, 27], customs control [28], forensic examination [29], drugs detection [29–33], and medical applications [34–37]. Metabolomics is the “systematic study of the unique chemical fingerprints that specific cellular processes leave behind” [38], where the IMS has been used for headspace measurements of fungus, bacteria or cell cultures to characterize their volatile metabolome [39–41]. Breath studies with IMS have demonstrated the early diagnostics of lung cancer [42], that different kinds of tumors can also be distinguished [36], the capability for discrimination between different states of chronic obstructive pulmonary diseases (COPD) [43], and also it turned out that even carcinoma in situ can be detected [44]. In addition, the use of IMS for online-monitoring of drug levels in a patient undergoing anesthesia is also possible, for example propofol anesthetic monitoring [45, 46]. In any medical experiment, there is the need to have a control group that is used as a standard of comparison. A control group is a set of items or people that serves as a standard or reference for comparison with an experimental group [47]. A control group is similar to the experimental group in number and is identical in specified characteristics, such as sex, age, annual income, parity, or other factors, but does not receive the experimental treatment or intervention. Therefore, in the present paper the need of using a control group and what is need to consider is presented, focused on Breath Analysis.