Distillation
When an analyte and interferent are miscible liquids, a separation by distillation is possible if their boiling points are significantly different. The figure below shows the progress of a distillation as a […]
Illustration
Coning and Quartering
For a heterogeneous material consisting of large particulates, the original (or gross) sample may be too large to analyze. For example, a Ni-bearing ore with an average particle size of 5 mm […]
Sample Thief
A sample thief is used for sampling smaller particulate materials, such as powders. A typical sample thief consists of two tubes that are nestled together. Each tube has one or more slots […]
Riffle Sampler
For particulate materials, particle size often determines the sampling method. Larger particulate solids, such as ores, are sampled using a riffle, which is a trough containing an even number of compartments. Because […]
Gravity Corer
This figure shows a schematic diagram of a gravity corer in operation. The corer’s weight is sufficient to penetrate into the sediment to a depth of approximately 2 m. Flexible metal leaves […]
Systematic-Judgmental Sampling
This figure shows a systematic–judgmental sampling plan for monitoring the leaching of pollutants from a landfill. The sampling sites, shown as red dots (•), are on a systematic grid that straddles the […]
Nyquist Theorem: Why Sampling Frequency Matters
According to the Nyquist theorem, to accurately determine a periodic signal’s true frequency, we must sample the signal at least twice during each cycle or period. If we collect samples at an […]
Importance of Sampling to Overall Uncertainty in an Analysis
The overall variance in an analysis, s2, is the sum of the variances arising from the method, (smeth)2, and the variance due to sampling, (ssamp)2. s2 = (smeth)2 + (ssamp)2 The blue curve in […]
Effect of Inert Salt on an Aqueous Equilbrium
The effect of a inert salt on a reaction’s equilibrium position is shown by the solutions in these two beakers. The beaker on the left contains equal volumes of 1.0 mM FeCl3 […]
pH Scale
Scale showing the pH value for representative solutions. Milk of Magnesia is a saturated solution of Mg(OH)2.
Reaction Dynamics: Approaching and Reaching a State of Equilibrium
The figure below shows how the masses of Ca2+ and CaCO3 change as a function of time during the precipitation of CaCO3. The dashed line indicates when the reaction reaches equilibrium. Prior […]
Evaluating a Linear Regression Model
The three plots below show the residual error in the signal, Sstd, as a function of the concentration of analyte, Cstd for an unweighted straight-line regression model. The red line in each […]