Measurement Skills and Spectrophotometry Laboratory

Vocabulary flashcards covering measurement consistency, accuracy, precision, standard deviation, micropipetting techniques, serial dilutions, spectrophotometry, and the Beer-Lambert law.

Precision

The degree of mutual agreement or reproducibility among repeated independent measurements of the same item under identical conditions.

Accuracy

The closeness of an individual measurement or the mean of a series of measurements to the true or desired target value.

Standard Deviation ($S.D.$)

A statistical metric that describes the dispersion or variability of values around their sample mean, calculated as the square root of the sum of squared deviations divided by $n - 1$.

Coefficient of Variation ($C.V.$)

A standardized measure of relative dispersion calculated as the standard deviation divided by the sample mean ($C.V. = \frac{S.D.}{\text{mean}}$, often expressed as a percentage), used to compare variability across different datasets.

Serological Pipette

A calibrated glass or plastic tube with volume graduations used in laboratories to dispense moderate liquid volumes, typically between $1\,ml$ and $50\,ml$.

Micropipettor

A precision handheld instrument featuring an adjustable volume readout used to aspirate and deliver microliter ($\mu l$) quantities of liquid accurately.

First Stop

The initial point of resistance felt when depressing a micropipettor plunger, used to measure and aspirate the precise volume dialed into the display.

Second Stop

The final plunger position reached by depressing completely past the initial resistance, used to blow out residual liquid and overcome surface tension during sample ejection.

Micropipette Volume Display

The numerical readout window on a pipettor indicating volume: on a P1000 the red digit denotes thousands of $\mu l$, on a P200 digits represent whole $\mu l$, and on a P20 the red digit represents tenths of a $\mu l$.

P20 Micropipette

A micropipettor designed for volumes ranging from $2\,\mu l$ to $20\,\mu l$, where the top digit indicates tens of $\mu l$, the middle indicates ones, and the bottom red digit indicates tenths of a $\mu l$.

P200 Micropipette

A micropipettor designed for volumes ranging from $20\,\mu l$ to $200\,\mu l$, where the display directly indicates the number of microliters to be dispensed.

P1000 Micropipette

A micropipettor designed for volumes ranging from $200\,\mu l$ to $1000\,\mu l$, where the top red digit denotes thousands of $\mu l$, the middle denotes hundreds, and the bottom denotes tens.

Spectrophotometer

An optical laboratory instrument that measures the concentration of solutes or cells in a liquid by projecting light through a sample and determining how much light is absorbed.

Absorbance

A measure of the quantity of light absorbed by a dissolved chemical or cellular suspension rather than transmitted through the solution.

$$\lambda_{\max}$$

The specific wavelength of light at which an absorbing solute or substance reaches its highest absorbance.

Beer-Lambert Law

The physical law stating that the absorbance of a solution is directly proportional to the solute concentration at a given wavelength, predicting that doubling concentration doubles absorbance.

Standard Curve

A reference graph plotting known solute concentrations against their measured absorbances, fitted with a best-fit line to estimate the unknown concentration of a sample.

Serial Dilution

A stepwise series of uniform dilutions performed to systematically reduce the concentration of a stock solution, ensuring convenience, accuracy, and precision for very low concentrations.

Blank

A cuvette containing only the solvent or growth medium without the absorbing analyte, used to calibrate the spectrophotometer to zero absorbance by subtracting background optical effects.

Cuvette

A small, optically transparent straight-sided container designed to hold liquid samples inside the light path of a spectrophotometer.

Luria Broth

A liquid nutrient medium used for cultivating bacteria, which serves as the blank solution when quantifying bacterial density using spectrophotometry.

Dilution Factor

The ratio of solute or aliquot volume to the final total solution volume, such as a $1/4$ dilution formed by adding $0.25\,ml$ of stock to $0.75\,ml$ of diluent.

Vernier Caliper

A handheld precision measuring tool equipped with adjustable jaws and a digital or graduated scale, used in the lab warmup to record morphological skull widths at their widest point.