Quantitative Validation of the n-Butanol Sniffin’ Sticks Threshold Pens

Melanie Y. Denzer 1 2 Stefan Gailer 1 2 David W. Kern 1 2 L. Philip Schumm 1 2 Norbert Thuerauf 1 2 Johannes Kornhuber 1 2 Andrea Buettner 1 2 Jonathan Beauchamp 1 2 0 ) Department of Sensory Analytics, Fraunhofer Institute for Process Engineering and Packaging IVV , Giggenhauser Strasse 35, 85354 Freising, Germany 1 L. P. Schumm Department of Health Studies, The University of Chicago , 5841 South Maryland Ave., MC2007, Chicago, IL, USA 2 D. W. Kern Department of Comparative Human Development, and The Institute for Mind and Biology, The University of Chicago , 940 E 57th St., Chicago, IL, USA Odorant pens are used by medical practitioners and researchers to assess olfactory dysfunction. Despite their routine use, there are currently no data on the gas-phase odorant concentrations released from the pen tips or whether these concentrations scale linearly with the aqueous-phase concentrations inside the pens. The commercially available Sniffin' Sticks odor threshold test containing n-butanol was chosen for evaluation. The gas-phase concentration of n-butanol at the tip of each pen was measured directly in a new set of pens via proton-transfer-reaction mass spectrometry (PTR-MS). Measurements were additionally made on the same pens after 6 months and two older pen sets, namely a 3-year-old (used) and 4-year-old (new) set. Furthermore, application-related tests were made to determine the performance of the pens during routine use and under stress. These data demonstrate that the gas-phase n-butanol concentrations of the threshold pens are linear over the entire set, both for brand-new pens and 6 months later; this reflects the expected performance that was previously only assumed. Furthermore, the application-simulation tests demonstrated a good performance of the pens when used according to their intended protocol. Measurements of the older pen sets suggest that storage conditions are more critical than usage for pen stability. The present findings confirm that the nbutanol odorant pens are an appropriate tool for threshold testing, provided they are stored and handled correctly. - Abbreviations PTR-MS Proton-transfer-reaction mass spectrometry UPSIT University of Pennsylvania Smell Identification Test CCCRT Connecticut Chemosensory Clinical Research Test VOCs Volatile organic compounds GC-MS Gas chromatographymass spectrometry v/v Volume per volume ppmv Parts per million, by volume ID Inner diameter OD Outer diameter m/z (Ion) mass-to-charge ratio PFA Perfluoroalkoxy (Teflon) cps Counts per second LOD Limit of detection VMR Volume mixing ratio sccm Standard cubic centimeters per minute SEM Secondary electron multiplier Olfactory dysfunction is a condition in which the sense of smell is impaired or even completely lost and can accompany or manifest after illness, head trauma, or diverse pathologies such as Alzheimer s, Parkinsons, and Huntingtons diseases, multiple sclerosis, amyotrophic lateral sclerosis, epilepsy, and schizophrenia (Doty 1997; McKeith et al. 2003; Zaccai et al. 2006; Haehner et al. 2009a), as well as mild cognitive impairment (Djordjevic et al. 2008; Lehrner et al. 2009; Sohrabi et al. 2012). It has been estimated to affect some 20 % of populations (Brmerson et al. 2004; Vennemann et al. 2008) and can lead to a marked reduction in quality of life, as well as being linked to depression and obesity (Hoover 2010). Accurate evaluation and diagnosis of a loss in the sense of smell is therefore imperative to enable treatment or counseling, as necessary. Several tests have been designed to identify olfactory dysfunction on an objective basis. Simmen and co-workers developed a test based on diskettes containing a range of different odorants that are released upon opening and reported its applicability for screening olfactory dysfunction (Simmen et al. 1999). Doty and others (1984) developed the UPSIT based on scratch-and-sniff odor panels that can be used for testing a wide variety of olfactory disorders. The CCCRT consists of an identification test that includes ten test substances and an n-butanol threshold test for the examination of olfactory dysfunctions (Cain et al. 1988). Hummel and colleagues (1997) created a test battery based on odorant pens, known as Sniffin Sticks. The Sniffin Sticks include a threshold test, a discrimination test, and an identification test to assess multiple components of olfactory dysfunction. The n-butanol odor threshold test is widely used for the evaluation of olfactory sensitivity and has been successfully employed in multiple research fields to investigate the influence of age and gender on olfactory sensitivity (e.g., Hummel et al. 2007; Markovic et al. 2007; Thuerauf et al. 2009). The Sniffin Sticks test battery has been validated from a clinical approach (Kobal et al. 2000; Albrecht et al. 2008; Tekeli et al. 2013), but the pens have not been comprehensively evaluated on a chemicalanalytical basis to date. Although routinely used to assess dysfunction, the linearity of the odor concentrations emitted from the pen tips of the n-butanol threshold pens is currently unknown. The aim of the present work is to investigate the linearity of the n-butanol gas-phase concentrations released from the tips of the Sniffin Sticks threshold pens and thereby evaluate the applicability of this test for olfactory sensitivity testing. Materials and Methods Three different threshold evaluation sets of n-butanol Sniffin Sticks (Burghart Messtechnik GmbH, Wedel, Germany) were assessed: (1) a new, unused set (referred to as new), (2) a 3year-old set that had been used previously in a research setting (3 years, used) (Kern et al. 2010), and (3) a 4-year-old unused set (4 years, new). Each set consisted of 16 different pens in a 1:2 volume per volume (v/v) aqueous dilution series at concentrations ranging from 4 % (designated as pen no. 1) to 1.2 ppmv (parts per million, by volume) (pen no. 16) (Hummel et al. 1997). The full concentration series is listed in Table 1. In addition, the new and 3 years, used sets each had an 8 % v/v nbutanol pen (pen no. 0), which was a special fabrication from the manufacturer for a large population study (Kern et al. 2014). n-Butanol is a substance with a low vapor pressure (6.6 hPa at 20 C) (Eickmann 2008) that is soluble in water up to 7.9 g per 100 g water at 20 C (Rauscher et al. 1996). The volatility of n-butanol relative to water is 0.7 (Eickmann 2008), which means that water evaporates at a slightly faster rate than n-butanol. Analytical Tools and Sampling Setup A high-sensitivity proton-transfer-reaction mass spectrometer (PTR-MS; IONICON Analytik GmbH, Innsbruck, Austria) was used for the present assessments. The operating principles of the instrument have been described in detail in the literature (Hansel et al. 1995; de Gouw et al. 2003; de Gouw and Warneke 2007) and will not be repeated here. In brief, the technique is based on soft chemical ionization via proton transfer reactions from h (...truncated)