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Precipitate Formation and Particle Size Control

Precipitate Formation and Particle Size Control

In precipitation gravimetry, the precipitating agent should react specifically or selectively with the analyte. While a specific reagent reacts with the analyte alone, a selective reagent can react with a limited number of chemical species.
The obtained precipitate should be either a pure substance of known composition or easily converted to one by a simple process, such as ignition or drying. In addition, the precipitate should be insoluble and easily filterable. In general, filterability...

Precipitation of Ions

Precipitation of Ions

Predicting Precipitation
The equation that describes the equilibrium between solid calcium carbonate and its solvated ions is:

Types of Coprecipitation

Types of Coprecipitation

Coprecipitation is the contamination of a precipitate by otherwise soluble species and occurs via different processes. In colloidal precipitates, coprecipitation occurs via surface adsorption. For instance, barium sulfate has a primary layer of adsorbed barium ions and a secondary layer of nitrate counterions. This results in contamination of the precipitate by barium nitrate.
Sometimes, ions in a crystal lattice can undergo isomorphous replacement by inclusions of similar charge and size. For...

Precipitation Titration: Endpoint Detection Methods

Precipitation Titration: Endpoint Detection Methods

In argentometric precipitation titrations, endpoints can be detected visually by the Mohr, Volhard, and Fajans methods. In the Mohr method, adding a soluble chromate indicator gives an initial yellow color to the analyte solution. As the titrant is added, the first excess of silver ions forms a red silver chromate precipitate, marking the endpoint. The solution pH should be maintained at about 8 by adding solid CaCO3.
In the Volhard method, a standard excess of AgNO3 is first added to the...

Washing, Drying, and Ignition of Precipitates

Washing, Drying, and Ignition of Precipitates

After filtration, the precipitate is washed to remove coprecipitated impurities and any remaining mother liquor. Colloidal precipitates, such as silver chloride, are washed with an electrolyte (such as dilute nitric acid) to prevent the peptization of the precipitate. In the case of slightly soluble precipitates, the wash solution contains a common ion to reduce solubility. Lead sulfate, which is slightly soluble in water, is washed with dilute sulfuric acid. Similarly, wash solutions may be...

Colloidal precipitates

Colloidal precipitates

The high insolubility of some precipitates can result in an unfavorable relative supersaturation. This can lead to colloidal particles with a large surface-to-mass ratio, where adsorption is promoted. For instance, in the precipitation of silver chloride, silver ions are adsorbed on the surface of the colloidal particles, forming a primary layer. This layer attracts ions of opposite charge (such as nitrate ions), forming a diffuse secondary layer of adsorbed ions. This electric double layer...

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Related Experiment Video

Updated: Oct 6, 2025

Capillary-based Centrifugal Microfluidic Device for Size-controllable Formation of Monodisperse Microdroplets

Capillary-based Centrifugal Microfluidic Device for Size-controllable Formation of Monodisperse Microdroplets

Published on: February 22, 2016

OsciDrop: A Versatile Deterministic Droplet Generator.

Shun Ye¹, Caiming Li^1,2, Xu Zheng³

¹State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China.

Analytical Chemistry

|January 21, 2022

Summary

This summary is machine-generated.

OsciDrop generates size-tunable droplets on demand using a chip-free method. This versatile droplet generator enables precise control for miniaturized molecular diagnostics and assays.

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Last Updated: Oct 6, 2025

Capillary-based Centrifugal Microfluidic Device for Size-controllable Formation of Monodisperse Microdroplets

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Published on: February 22, 2016

Glass-Based Devices to Generate Drops and Emulsions

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Published on: June 20, 2020

Area of Science:

Biotechnology
Microfluidics
Molecular Diagnostics

Background:

Droplet generation is crucial for miniaturized analytical systems.
Existing methods often require complex microfluidic chips.

Purpose of the Study:

To introduce OsciDrop, a novel chip-free droplet generator.
To demonstrate its capability for producing size-tunable droplets on demand.

Main Methods:

OsciDrop segments fluid from a disposable pipette tip using oscillation.
Investigated effects of flow rate, oscillation parameters, and waveform.
Identified a Weber number-dominated regime for droplet generation.

Main Results:

Achieved robust, deterministic generation of monodisperse droplets.
Programmable droplet sizes ranged from 200 pL to 2 μL.
Validated with digital loop-mediated isothermal amplification and digital polymerase chain reaction assays.

Conclusions:

OsciDrop offers a versatile, chip-free approach to droplet generation.
Enables miniaturization, integration, and automation in molecular diagnostics.
Demonstrates accessibility for digital molecular diagnostics.