Measurement of internal diameters of capillaries and glass syringes using gravimetric and optical methods for microflow applications.

OBJECTIVES: Microflow measurement devices are used in several science and health applications, mainly drug delivery. In the last decade, several new methods based on optical technology were developed, namely the front tracking and interferometric method, in which the knowledge of the inner diameter of the syringe or the capillary used is critical. Only a few National Metrology Institutes (NMIs) can perform inner diameter measurements below 1 mm, which requires expensive technology. Therefore, IPQ, in cooperation with CETIAT, CMI and UNIDEMI, under the EMPIR project 18HLT08 MeDDII - Metrology for Drug Delivery, developed new measurement methods for small inner diameter tubes based on the gravimetric principle and optical methods in order to simplify the apparatus used for this type of measurements without increasing uncertainty. METHODS: The gravimetric experimental setup consists of measuring the liquid volume on a specific length of the glass tube. The optical method used is based on the front track principle that uses a high-resolution camera and ImageJ software, to determine the diameter at both ends of each capillary. RESULTS: To validate the developed methods, a comparison was performed between CETIAT, CMI and IPQ and the results obtained were all consistent. CONCLUSIONS: This work allowed the determination of inner diameter of syringes or capillaries using two different methods with relative expanded uncertainties from 0.1 to 0.5% (k=2), that can be applied for flow measurements using optical technology.

Assessment of drug delivery devices working at microflow rates.

Almost every medical department in hospitals around the world uses infusion devices to administer fluids, nutrition, and medications to patients to treat many different diseases and ailments. There have been several reports on adverse incidents caused by medication errors associated with infusion equipment. Such errors can result from malfunction or improper use, or even inaccuracy of the equipment, and can cause harm to patients' health. Depending on the intended use of the equipment, e.g. if it is used for anaesthesia of adults or for medical treatment of premature infants, the accuracy of the equipment may be more or less important. A well-defined metrological infrastructure can help to ensure that infusion devices function properly and are as accurate as needed for their use. However, establishing a metrological infrastructure requires adequate knowledge of the performance of infusion devices in use. This paper presents the results of various tests conducted with two types of devices.

Narrow stack emissions: Errors in flow rate measurement due to disturbances and swirl.

European legislation continues to drive down emission limit values, making the emission measurement of narrow stacks of increasing importance. However, the applicable standards (EN ISO 16911-1 and EN 15259) are poorly validated for narrow stacks, and the effect of flow disturbances on the described methods are largely unknown. In this article, measurement errors are investigated in narrow stacks with flow disturbances and swirl, both experimentally and through computational fluid dynamics (CFD) simulations. The results indicate that measurement errors due to misalignment of the flow with typical measuring probes (pitot tubes) are small compared to errors resulting from the positioning of these probes in the measurement plane. Errors up to 15% are reported using the standardized methods, while the measurement error is both smaller and more predictable when using additional measurement points. Implications: Current international standards provide methods to measure emissions from industrial stacks. With increasingly small emission limit values, the accuracy of these measurements is becoming considerably more important. The data from this study can be used to inform revisions of these standards, in particular with respect to flow disturbances in narrow stacks, and can help law- and policy-makers to obtain insight into the uncertainties of emission measurements in these specific situations.

Primary standard for liquid flow rates between 30 and 1500 nl/min based on volume expansion.

An increasing number of microfluidic systems operate at flow rates below 1 µl/min. Applications include (implanted) micropumps for drug delivery, liquid chromatography, and microreactors. For the applications where the absolute accuracy is important, a proper calibration is required. However, with standard calibration facilities, flow rate calibrations below ~1 µl/min are not feasible because of a too large calibration uncertainty. In the current research, a traceable flow rate using a certain temperature increase rate is proposed. When the fluid properties, starting mass, and temperature increase rate are known, this principle yields a direct link to SI units, which makes it a primary standard. In this article, it will be shown that this principle enables flow rate uncertainties in the order of 2-3% for flow rates from 30 to 1500 nl/min.