Analytical Chemistry concept notes

ANALYTICAL TOOLS RELATED:

Qualitative analysis reveals the identity of the elements and compounds in a sample. Quantitative analysis indicates the amount of each substance in a sample. Analytes are the components of a sample that are determined.

• An interference or interferent is a species that causes an error in an analysis by enhancing or attenuating (making smaller) the quantity being measured.

• The matrix, or sample matrix, is the collection of all of the components in the sample containing an analyte. Techniques or reactions that work for only one analyte are said to be specific. Techniques or reactions that apply to only a few analytes are selective.

Calibration is the process of determining the proportionality between analyte concentration and a measured quantity.

• The two knife edges in a mechanical balance are prism-shaped agate or sapphire devices that form low-friction bearings with two planar surfaces contained in stirrups also of agate or sapphire.

Glassine paper is specially treated through a process called calendering. The process begins with breaking down paper pulp fibers by beating. The beaten pulp is then squeezed into molds and dried into sheets. These sheets are then rolled through an alternating series of hot steel and fiber rollers called a supercalender. This step, which makes the pulp fibers in the sheets lie flat and in the same direction, is repeated several times. The final product is an extremely smooth paper that can be used as barrier protection from many kinds of grease, air, and liquids. Glassine is used as an interleaving paper in bookbinding, especially to protect fine illustrations against contact with facing pages. The paper can be manufactured with neutral pH and can prevent damage from spilling, exposure, or rubbing. It is used in foodservice as a barrier between layers of products: meat, baked goods, and cheese, for example. In chemistry, we use glassine as an inexpensive weighing paper for powdered or granular samples because particles have little tendency to adhere to the paper, it is quite light, and it is inexpensive. Narrow strips of glassine are nearly ideal for handling weighing bottles or any common items that must be transferred by hand to and from a balance pan.

• A buoyancy error is the weighing error that develops when the object being weighed has a significantly different density than the masses.

Drying or ignition to constant mass is a process in which a solid is cycled through heating, cooling, and weighing steps until its mass becomes constant to within 0.2 to 0.3 mg.

Decantation is the process of pouring a liquid gently so as to not disturb a solid in the bottom of the container.

Glassware types include Class A and Class B. Class A glassware is manufactured to the highest tolerances from Pyrex, borosilicate, or Kimax glass . Class B (economy ware) tolerances are about twice those of Class A.

• A meniscus is the curved surface of a liquid at its interface with the atmosphere.

Parallax is the apparent displacement of a liquid level or of a pointer as an observer changes position. Parallax occurs when an object is viewed from a position that is not at a right angle to the object.

• An aliquot is a measured fraction of the volume of a liquid sample.

• SI is the acronym for the French “Système International d’Unités.

• The ångstrom unit Å is a non-SI unit of length that is widely used to express the wavelength of very short radiation such as X-rays (1 Å 5 0.1 nm 5 10210 m). Thus, typical X-radiation lies in the range of 0.1 to 10 Å.


Reference: Skoog, D.A., et. al. (2014). Fundamentals of Analytical Chemistry (9th edition). Belmont: Brooks/Cole, Cengage Learning.

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