Automated Solvent Dispensing

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Automated Gravimetric Solvent Dispensing


The Challenges of Preparing Samples


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1. What is gravimetric sample preparation?

Gravimetric sample preparation is weighing the sample, either manually or automated, and then delivering the required amount of solvent to achieve the desired concentration. The solvent amount is calculated automatically based on the actual amount of sample weighed, and measured by weight. Gravimetric dosing is referenced in USP chapter 1251 Weighing on an analytical balance as a type of weighing typically used for sample or standard preparation.


2. How can I prepare stock solutions more efficiently?

Stock solutions can be prepared more efficiently by gravimetric weighing of the solvent because the sample or standard is weighed into a vessel on the balance, and the solvent can then be added directly to container without the need to transfer it elsewhere. An accurate concentration is therefore prepared efficiently, without any transfer between containers or different areas of the workbench.


3. How can I ensure that my standard solutions are traceable?

Standard solutions are traceable when prepared on the XPR Automatic Balance because the amount of standard weighed and the amount of solvent added is recorded automatically. The resulting concentration is also calculated automatically. This information, along with all relevant metadata, is stored electronically or exported as required, making the standard preparation process fully traceable.


4. How can I ensure that all the steps in my analytical procedures meet compliance regulations or guidelines?

If you consider USP requirements for analytical weighing and data integrity by following the ALCOA+ framework, it is important to ensure that the balance you are using is appropriate for the amount you need to weigh out. You must respect the minimum weight specification and keep within the safe weighing range for your laboratory environment. The GWP Approved function on the XPR Automatic Balance will show you whether the minimum weight requirement is adhered to or not. For data management, the powder weighed is identified by the RFID chip in the dosing head to avoid errors, and the weight dispensed into each vial is recorded automatically and can be exported with all necessary metadata if required using LabX laboratory software. All this data is included in the audit trail for full compliance with regulations.


5. How do I switch from concentrations from mg/ml to mg/g?

A concentration in mg/g can be converted to mg/ml, and vice versa, using a simple density conversion (density = mass/volume). However, if a standard calibration curve is generated in mg/ml to start with, then the conversion is unnecessary because the sample concentration is measured relative to the calibration curve.