Breath Acetone Analysis Using a Porous Glass Sensor Developed By Impregnating with 4-Nitrophenylhydrazine

Abstract

Introduction High concentrations of acetone are typically detected in the air exhaled by patients suffering from diabetes [1]. Therefore, breath acetone analysis is expected to be a non-invasive diagnosis or monitoring method for patients suffering from diabetes, and this method can replace blood tests. Generally, gaseous acetone detection is conducted via gas chromatography/mass spectrometry (GC/MS) [2]. Although this method provides results with low uncertainties, it requires large equipment. Therefore, it does not meet the requirements of clinical applications, which include cost effectiveness and user friendliness. We have previously developed an analytical chip for the simple detection of gaseous acetone using porous glass impregnated with 4-nitrophenylhydrazine (4-NPH) [3]. Porous glass has the advantages of small size, resistance to organic solvents, and large surface area (specific surface area: 200 m2 g−1). The developed chip could detect acetone in 3 h by a passive method that include hanging acetone in a bag containing gaseous acetone. In this study, we evaluated the applicability of chip for the analysis of breath samples and investigated a method to detect gaseous acetone in a short time by combining the chip with an active method. Method Preparation of the analytical chip Porous glass sheets (thickness = 1 mm, Vycor#7930, Corning Co., USA) with an average pore diameter of 4 nm were cut into 8 mm × 8 mm chips and used as a substrate. The porous glass was cleaned with acetone and ethanol using an ultrasonic cleaner (ASU-3, As One Co., Japan), then soaked in 6 mol L−1 hydrochloric acid for 2 h, and finally dried in a nitrogen atmosphere for >20 h. Subsequently, 4-NPH (0.0492 g, Tokyo Chemical Industry Co., Japan) and concentrated HCl (100 µL) were dissolved in methanol (25 mL). The porous glass was soaked in the 4-NPH-methanol solution (1.26 × 10−2 mol L−1) for 24 h and dried in a nitrogen atmosphere for 24 h. Exposure to gaseous acetone To prepare an acetone atmosphere of arbitrary concentration and relative humidity of 50% at 25 °C in a sampling bag, an acetone–water solution (80 µL) and deionized water (498 µL) were injected into a bag filled with 50 L of dry nitrogen. The bag was left to stand at 25 °C for 24 h to volatilize the acetone–water solution. The resulting acetone atmospheres occupied volumes of 50 L at several concentrations (i.e., 1.06, 2.65, 5.30, and 10.6 ppm). Subsequently, the analytical chip was placed in a sensor holder, and the acetone atmosphere flowed through the sensor holder at a gas flow rate of 2.0 L min−1 using a pump (MP-∑300NⅡ, SHIBATA SCIENTIFIC TECHNOLOGY Co., Japan) for an arbitrary time (10, 30, 60, 120, and 300 s). Results and Conclusions The analytical chip exhibited an absorption peak at 314 nm due to its impregnation with 4-NPH. After exposure to an acetone atmosphere, a new absorption peak appeared at 390 nm. This peak can be attributed to the production of 4-NPH derivative (Acetone-4-NPH) resulting from the reaction between 4-NPH and acetone inside the chip. It was found that the absorbance at 390 nm increased with an increase in the acetone concentration or exposure time. The 3 h exposure to 1 L of acetone atmosphere (1.06, 5.30, and 10.6 ppm) by a passive method showed an absorbance difference at 390 nm of 0.322, 1.20, and 2.04, respectively. In contrast, when exposed to an acetone atmosphere (1.06, 5.30, and 10.6 ppm) at a gas flow rate of 2.0 L min−1 for 30 s, it was 0.0183, 0.0540, and 0.133, respectively. The calculated acetone concentration of the 1 L breath samples suggested that the results obtained using analytical chip agreed with those obtained via gas chromatography with a probability of approximately 60%. Additionally, the chip worked cumulatively and could detect gaseous acetone of 1 ppm in 300 s by the active method of using a pump. Based on a kinetic analysis of the reaction between 4-NPH and acetone, the rate constant of the reaction between these two species was calculated as 3.0 × 10−5 ppm−1 min−1.