Preparing Titration Samples
Accurate sample weighing for titration
Why Accurate Weighing is Crucial
From the consumption and concentration of the titrant as well as the weight of the sample used in the analysis, the content of the analyte can be calculated. Accurately weighing the substances used to prepare both the titrant solution and the analyte sample solution is highly important. Only with accurate sample preparation you can be sure of accurate titration results.
The SmartSample™ weighing system for titration automation increases sample identification and efficiency with RFID technology.
Preparing Titration Samples Workflow – Summary from a Typical SOP
The classical way to perform a titration is with a graduated glass cylinder (burette) from which the titrant is manually dispensed, by means of a tap, into the beaker containing the analyte. When the technique was first developed, only those titrations which showed a significant color change upon reaching the endpoint were performed. Today, an indicator dye is added to the analyte. The precision achieved depends mainly on the chemist's skills and, in particular, on the ability to perceive different colors. Titration has developed rapidly: manual and, more recently, motor-driven piston burettes allow accurate and repeatable titrant addition. Electrochemical sensors have replaced the color indicators thus achieving higher precision and accuracy of results. With the use of microprocessors, the titration can be controlled and evaluated automatically. The whole process of titration can be made much easier through automation using a dedicated instrument known as a titrator.
The following method describes the process for preparing titration samples and performing the titration with a titrator.
Typical titrations require the titrant and analyte to be in a liquid form (solution). The solid samples are usually dissolved in water, but other solvents, such as glacial acetic acid or ethanol, may be used for specialized applications e.g. in petrochemistry.
Click Here to Read More on Typical Workflow: Quantitative Analysis of a Dissolvable Solid
In preparing for titration, the concentration of the titrant and the weight of the solid analyte must be accurately determined. It is important that all information and measurements are carefully logged, particularly when titrating multiple samples, to avoid any mix-ups between samples and incorrect calculations.
Preparation of the Sample
Place the titration beaker on the balance and tare
Weigh the substance under investigation into the beaker
Add the solvent to the desired quantity e.g. 50 mL
Transfer the beaker with the analyte to the titrator
The titrator adds the titrant to the analyte in an automated process
A sensor monitors the change in the measured potential of the solution and stops the titration when the end-point is reached
The titrator calculates the concentration of the analyte automatically
Q: What is the drying oven method?
A: The drying oven method is a thermogravimetric method (loss on drying) in which the sample is dried for a defined period of time at constant temperature. The moisture content is determined by weighing the sample before and after drying and determining the difference.
Q: How are samples heated in the drying oven and in the moisture analyzer?
A: In the drying oven, samples are heated by convection. This means the samples are at the same temperature as the drying oven. When using a moisture analyzer, the sample heats up and dries by absorbing infrared radiation from the heating element. The sample's temperature and drying time depends on its absorption characteristics.
Q: Isn’t moisture the same as water?
A: This is a common misconception. Everything which evaporates upon heating is named moisture. Water may be a part of this but there may be other substances which also evaporate, such as alcohol or solvents.
Q: I have many different samples (liquid, pasty, solid, powder). Which method should I use for moisture content determination?
A: In general, all kinds of samples are suitable for both the drying oven and the halogen moisture analyzer. Which method is best for you, depends on how fast you need the result or if you need the result using an official method. Sometimes, for example, in goods-in or final product quality control, moisture analyzers are used in parallel with a drying oven. Fast analysis with the moisture analyzer is done to optimize processes and the drying oven is used for official documentation purposes.
Q: We have to use the standard method with the drying oven but using a moisture analyzer would really speed up our processes. Is it possible?
A: Many industry regulations require manufacturers to follow a standard method. However, it is acceptable to use a moisture analyzer if you can prove its results are the same as those from the drying oven procedure and are of the same level of accuracy. This requires developing a drying method for the moisture analyzer and cross-validating it against the drying oven through a series of analyses. METTLER TOLEDO's application database contains over 100 free ready-to-use cross-validated drying methods. Contact us if you don't find what you need.
Q: How can I put the batch number on the printout from my moisture analysis?
A: You can do this either through the ID management functionality on our moisture analyzers or in the differential weighing application on our balances. If your batch number is a barcode, you can even connect a barcode reader to scan it, or any other ID.
Q: I am using the drying oven procedure. How can I avoid errors when I’m recording results and doing calculations?
A: Manual processes are more prone to error so it's best to use the built-in balance application or a software solution (LabX) with a balance to capture all the results and do the calculations automatically. It's not only much faster but it's error-free too. Results can be printed out for your lab journal or saved on a USB stick to be saved electronically. LabX saves everything in a secure database so you can be sure your data is safe. The LabX report generator enables you to create elegant reports with charts which can be printed out or saved electronically.
Q: How can I avoid my crucibles getting mixed up in the drying oven?
A: Good labelling is key. Using barcode labels uniquely identifies each sample. A barcode reader attached to the balance ensures that no mix-ups occur and weighing results are correctly logged against each sample. Use of a barcode reader is fully supported by the differential weighing application on the balance and by LabX.
Q: What is the difference between moisture content, dry content and ATRO moisture?
A: Moisture content is the amount of moisture in the sample given as a percentage of the sample's original (wet) weight. Dry content is the amount of solids which are left after drying given as a percentage of the sample's original (wet) weight. ATRO moisture (AM) is the amount of moisture in the sample given as a percentage of the sample's final (dry) weight. Different industries use different units e.g. in wood or pulp, ATRO is commonly used.