Although N-nitrosodimethylamine (NDMA) has been the most prevalent N-nitrosamine detected in disinfected waters, it remains unclear whether NDMA is indeed the most significant N-nitrosamine or just one representative of a larger pool of N-nitrosamines. A widely used assay applied to quantify nitrite, S-nitrosothiols, and N-nitrosamines in biological samples involves their reduction to nitric oxide by acidic tri-iodide, followed by chemiluminescent detection of the evolved nitric oxide in the gas phase. We here describe an adaptation of this method for analyzing total N-nitrosamine (TONO) concentrations in disinfected pools. Optimal sensitivity for N-nitrosamines was obtained using a reduction solution containing 13.5 mL glacial acetic acid and 1 mL of an aqueous 540 g/L iodide and 114 g/L iodine solution held at 80 degrees C. The method detection limit for N-nitrosamines was 110 nM using 100 microL sample injections and NDMA as a standard. N-nitrosamines featuring a range of polarities were converted to nitric oxide with 75-103% efficiency compared to NDMA. Evaluation of potential interfering species indicated that only nitrite and S-nitrosothiols were a concern, but both interferences were effectively eliminated using group-specific sample pretreatments previously employed for biological samples. To evaluate the low TONO concentrations anticipated for pools, 1 L samples were extracted by continuous liquid-liquid extraction with ethyl acetate for 24 h, and concentrated to 1 mL. N-nitrosamine recovery during extraction ranged from 37-75%, and there was a potential for artifactual nitrosation of amines during solvent reflux in the presence of significant nitrite concentrations, but not at the low nitrite concentrations prevalent in most pools. Using the 1000-fold concentration factor and 56% average extraction efficiency, the method detection limit would be 62 pM (5 ng/L as NDMA). The TONO assay was applied to six pools and their common tap water source in conjunction with analysis for specific nitrosamines. Even accounting for the range of N-nitrosamine extraction recoveries, NDMA accounted for an average of only 13% (range 3-46%) of the total nitrosamine pool.

Recent advances in manufacturing techniques have opened up new interest in rapid prototyping at the microscale. Traditionally microscale devices are fabricated using photolithography, however this process can be time consuming, challenging, and expensive. This paper focuses on three promising rapid prototyping techniques: laser ablation, micromilling, and 3D printing. Emphasis is given to rapid prototyping tools that are commercially available to the research community rather those only used in manufacturing research. Due to the interest in rapid prototyping within the microfluidics community a test part was designed with microfluidic features. This test part was then manufactured using the three different rapid prototyping methods. Accuracy of the features and surface roughness were measured using a surface profilometer, scanning electron microscope (SEM), and optical microscope. Micromilling was found to produce the most accurate features and best surface finish down to ∼100 μm, however it did not achieve the small feature sizes produced by laser ablation. The 3D printed part, though easily manufactured, did not achieve feature sizes small enough for most microfluidic applications. Laser ablation created somewhat rough and erratic channels, however the process was faster and achieved features smaller than either of the other two methods.

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Recent developments in microfluidics have opened up new interest in rapid prototyping with features on the microscale. Microfluidic devices are traditionally fabricated using photolithography, however this process can be time consuming and challenging. Laser ablation has emerged as the preferred solution for rapid prototyping of these devices. This paper explores the state of rapid prototyping for microfluidic devices by comparing laser ablation to micromilling and 3D printing. A microfluidic sample part was fabricated using these three methods. Accuracy of the features and surface roughness were measured using a surface profilometer, scanning electron microscope, and optical microscope. Micromilling was found to produce the most accurate features and best surface finish down to ∼100 μm, however it did not achieve the small feature sizes produced by laser ablation. 3D printed parts, though easily manufactured, were inadequate for most microfluidics applications. While laser ablation created somewhat rough and erratic channels, the process was within typical dimensions for microfluidic channels and should remain the default for microfluidic rapid prototyping.