[FSH SPECIAL TOPICS] Types of Gravimetry - Analytical Chemistry

Summary

This video script provides a detailed overview of three types of gravimetric methods: particulate gravimetry, volatilization gravimetry, and precipitation gravimetry. It explores their applications, such as measuring total suspended solids in wastewater, determining crude fat content in chocolate, and assessing ash content in polymers. The script emphasizes the importance of techniques like filtration, drying, and precipitation in accurate mass measurements. While some methods, like precipitation gravimetry, are less commonly used today, they remain valuable for verification and qualitative analysis in various fields, including environmental science and pharmaceuticals.

Takeaways

• 😀 Particulate gravimetry is a method where the analyte is already in particulate form, making it easier to separate from the sample matrix using filtration or extraction.
• 😀 A common application of particulate gravimetry is determining total suspended solids (TSS) in treated wastewater, using a glass fiber filter to retain solids and drying them to a constant weight.
• 😀 Another application of particulate gravimetry is measuring crude total fat in chocolate, where the sample is extracted with an organic solvent and then dried to measure fat content.
• 😀 Particulate gravimetry can also be used to measure suspended particles in the atmosphere by collecting air samples with pre-weighed filters and determining the mass of particles after 24 hours.
• 😀 Volatilization gravimetry involves decomposing the sample using thermal or chemical energy, and then measuring the mass of the residue or volatile products.
• 😀 A key application of volatilization gravimetry is determining the inorganic ash content of polymers like pululan, where the sample is hydrolyzed and ignited at high temperatures, with the remaining ash weighed.
• 😀 The loss on drying test for drug substances is another application of volatilization gravimetry, where tablets or capsules are crushed and dried under vacuum to determine moisture content.
• 😀 Precipitation gravimetry involves adding a precipitating reagent to a solution containing the analyte, and then filtering and weighing the resulting precipitate.
• 😀 A typical example of precipitation gravimetry is determining the percentage of barium in a barium nitrate solution by adding potassium chromate to form a yellow barium chromate precipitate.
• 😀 Precipitation gravimetry is less commonly used today due to more advanced techniques but still has applications for verifying other analytical methods and identifying inorganic and organic analytes.

Q & A

What are the three types of gravimetry discussed in the transcript?

The three types of gravimetry discussed are particulate gravimetry, volatilization gravimetry, and precipitation gravimetry.

How does particulate gravimetry work and what is a common application?

Particulate gravimetry involves the separation of analytes in a particulate form, typically through filtration or extraction. A common application is the determination of total suspended solids in treated wastewater, using a glass fiber filter to retain solids followed by drying at 103-105°C.

What is the standard method for determining total suspended solids in wastewater using particulate gravimetry?

The standard method for determining total suspended solids in wastewater is method 2540D, published in the Standard Methods for the Examination of Water and Wastewater.

Can you explain the process of determining crude total fat in chocolate using particulate gravimetry?

In particulate gravimetry, the process for determining crude total fat in chocolate involves extracting the sample with an organic solvent for 16 hours, then evaporating the extract to dryness at 95-100°C and weighing the residue.

How is particulate gravimetry used to measure suspended particles in the atmosphere?

Particulate gravimetry measures suspended particles in the atmosphere by collecting air samples using a high-volume sampler with a pre-weighed filter. After collecting the sample for 24 hours, the filter is weighed to determine the mass of suspended particles.

What is volatilization gravimetry and what does it measure?

Volatilization gravimetry involves the thermal or chemical decomposition of a sample containing the analyte. It measures the mass of residue remaining after decomposition, the mass of volatile products, or the change in mass due to material loss during volatilization.

What is the residue on ignition test used for in volatilization gravimetry?

The residue on ignition test is used to determine the inorganic ash content of polymers, such as pullulan, by hydrolyzing the sample with sulfuric acid and then igniting it at high temperatures (500-600°C) to burn off organic material. The remaining ash is then weighed.

What other application of volatilization gravimetry is mentioned in the transcript?

Another application of volatilization gravimetry is the loss on drying test for drug substances, where samples like capsules or tablets are dried under vacuum, and the mass loss is used to estimate moisture content and other volatile substances.

What is the principle behind precipitation gravimetry?

Precipitation gravimetry involves the addition of a precipitating reagent to a solution containing the analyte, leading to a double displacement reaction. The analyte forms a precipitate, which is then filtered, dried, and weighed to determine its concentration.

What is a specific example of precipitation gravimetry given in the transcript?

A specific example of precipitation gravimetry in the transcript is the determination of barium in a solution of barium nitrate. The solution is mixed with potassium chromate, resulting in the formation of a yellow precipitate, barium chromate, which is then weighed.

How has precipitation gravimetry been replaced, and what are its current uses?

Precipitation gravimetry has been largely replaced by more advanced analytical techniques. However, it is still used for verifying the composition of standard reference materials, performing qualitative tests for inorganic and organic analytes, and assessing the accuracy of other analytical methods.