Sample Introduction
For many of the techniques, a nebulizer is the primary means of producing very small droplets of a solution sample or standard that is transported to a high-temperature source where it undergoes desolvation, vaporization, and atomization. While a range of droplet sizes is generated, some means of size discrimination is present to insure that larger droplets (greater than ∼2.5 μm) are kept from the thermal source. Nebulizers come in a variety of different designs, often serving slightly different functions. Some require very small volume uptake rates (e.g., microconcentric and direct injection nebulizers), others are more efficient at producing small droplets (e.g., ultrasonic nebulizers), and still others are capable of handling viscous and particle-laden solutions (e.g., Babington and cross-flow nebulizers).
A variety of other approaches are also used including discrete micropipetting of solutions, production of gaseous hydrides, ablation of solid materials using a laser or electrical spark, and even reduction and direct use of metal vapor in the headspace above a liquid such as in the case of Hg determinations. In addition to ablation, which samples a relatively large mass of material from a solid (∼1 μg per pulse), sputtering processes (e.g., ion beams and various low-pressure discharge processes) have also been used. In general, any approach that permits the introduction of a vapor or small aerosol particles into a source from a solid, liquid, or solution could be considered as a possibility for conducting quantitative analytical atomic spectrometry. Analysis of gaseous samples by direct introduction, of course, can also be done.
Optimizing drug delivery in COPD: The role of inhaler devicesOptimizing drug delivery in COPD: The role of inhaler devices
9 Nebulizers
The nebulizers are useful tools in treatment of respiratory diseases because they can convert solutions or suspensions of drugs into small droplets able to aerosolize high doses of drugs that are not achieved by DPIs or pMDIs [11].
There are different available typologies of nebulizers, such as jet, vibrating, mesh and ultrasonic, mainly used with bronchodilator and/or corticosteroids agents in patients with obstructive airways diseases, and each of them has a different performance [62,63].
The mechanical nebulizers include a compressor, an ampoule, an interface system and some plastic tubes as connectors. This nebulizers produce droplets of 5 μm or less by using mechanical fragmentation of a liquid solution containing the drug [64]. The ultrasonic nebulizers are based on a piezoelectric transductor which converts a difference of potential in vibration at variable frequencies in order to aerosolize the solution containing the drug [65]. A newer generation of nebulizers uses a vibrating mesh disk, powered by a compressor. These more sophisticated nebulizers contain a microchip, which controls the drug delivery to the patient, and have an adaptive aerosol system that is able to pulse the inhaled drug during the inhalation phase. This system reduces the dose wastage and provides detailed feedback on each treatment, improving patient’s adherence [18,21].
Nebulizers may be considered as an effective alternative to inhalers and can be recommended to asthmatic and COPD subjects who are unwilling or unable to use inhaler devices. Newer formulations could possibly offer a relevant advance for a more efficient nebulization of drugs