Determination of Formaldehyde by Conversion to Hexahydrooxazolo[3,4-a]pyridine in a Denuder Tube With Recovery by Thermal Desorption, and Analysis by Gas Chromatography–Mass Spectrometry†

Abstract

The implications for formaldehyde analysis arising from a recent study where the inter-laboratory relative standard deviation for formaldehyde [CAS Registry number: 50-00-0] monitoring was reported to fall in the range 20 to 60% are discussed. A thermal desorption approach is proposed as a possible way to address the requirement for less intensive sample processing in formaldehyde analysis; as well as meeting other important criteria such as reduced sample handling and increased overall sensitivity. A denuder tube coated with 2-hydroxymethylpiperidine [CAS Registry number: 3433-37-2] and connected to an adsorbent sampler packed with Tenax TA was used to derivatise formaldehyde vapour. The volatile derivative, hexahydrooxazolo[3,4-a]pyridine [CAS Registry number: 274-50-0], was retained on the adsorbent trap. Analysis of the derivative was accomplished using a thermal desorption technique coupled to gas chromatography–mass spectrometry. To test the approach a test atmosphere generator based on a permeation tube containing α-polyoxymethylene was constructed. A dilution chamber heated to 80 °C was used to prevent repolymerisation of the released formaldehyde. Gravimetric measurements indicated that formaldehyde was generated at a rate of 1.9 × 10^–4 g h^–1 (95% confidence limits = ± 1 × 10^–6 h^–1) and atmospheres of formaldehyde at concentrations of 5.92, 3.35 and 1.79 mg m^–3, with a water concentration less than 17 mg m^–3 at 20 °C and 1.013 kPa were validated using NIOSH Method 3500 for formaldehyde determination. Formaldehyde masses in the range 0.1 to 16 µg were sampled using the system described. The contents of the adsorbent trap were then analysed. The data obtained supported the hypothesis that formaldehyde derivatives could be recovered in an analytically useful way by thermal desorption. Mass spectrometric data confirmed previous assignments for hexahydrooxazolo[3,4-a]pyridine and that thermal decomposition did not occur to a detectable extent during desorption. The relationships between mass sampled and instrument response were linear up to the point of breakthrough, with limits of detection in the range 0.03 to 0.51 mg m^–3 formaldehyde in air.