Chapter 2–7 Key Vocabulary: Precision, Errors, Gravimetry, Absorption, AAS/AES, Chromatography

Vocabulary flashcards covering key terms from precision, errors, gravimetric analysis, absorption, AAS/AES, and chromatography topics.

Population mean

The average of all measurements in a population (often denoted M).

Sample mean

The average of a sample, used as an estimate of the population mean.

Standard deviation

A measure of data spread around the mean; the square root of the variance.

Coefficient of variation (CV)

A relative measure of dispersion: CV = (standard deviation / mean) × 100%.

Spread / range

The difference between the largest and smallest values in a data set.

Absolute error

The absolute difference between a measured value and the true value.

Relative error (ppt)

Absolute error divided by the true value, expressed in parts per thousand (ppt).

Replicate measurements

Multiple measurements of the same quantity to assess precision.

Accepted value

The true or reference value used for comparison.

Gaussian distribution

A normal distribution describing how random errors cluster around the mean.

Standard error of the mean

Standard deviation of the sampling distribution of the mean (SD/√n).

Precision

Reproducibility of measurements; how close repeated measurements are to each other.

Accuracy

Closeness of a measurement to the true value.

Determinant (systematic) error

Biases due to instruments or setup (calibration, temperature, contamination).

Gross error

Large, obvious errors often due to human mistakes; usually corrected or discarded.

Indeterminate (random) error

Unpredictable fluctuations that yield a normal distribution of results.

Calibration

Adjustment of instruments to standard references to reduce systematic error.

Maintenance

Regular servicing of equipment to prevent errors.

Proper instrumentation & method

Using appropriate equipment and procedures to minimize errors.

Personal error

Mistakes due to user misreading, miscalculation, or bias.

Outlier

Data point far from the rest; may be discarded after evaluation.

Gaussian curve

Another term for the normal distribution around the mean.

Gravimetric analysis

An analytical method based on mass determination of a precipitate or product.

Precipitation

Formation of a solid from a solution during gravimetric analysis.

Ostwald ripening

Growth of larger crystals at the expense of smaller ones to improve crystal quality.

Digestion (Ostwald ripening)

Heating precipitate in mother liquor to enlarge crystals and remove imperfections.

Filtration

Separation of a solid from liquid using a filter.

Washing (precipitate)

Removal of surface contaminants from the precipitate.

Drying

Removal of moisture by heating to obtain a stable weight.

Weighing

Measuring mass with a balance or analytical balance.

Interferences (gravimetric)

Substances that affect precipitation or measurement.

Selective precipitating agent

Reagent chosen to precipitate the analyte specifically.

Absorption spectrum

Spectrum of wavelengths absorbed by a substance; acts as a fingerprint.

Internal standard method

Calibration technique using a known added compound to correct for variability; uses peak area ratios.

Peak area

Integrated area under a chromatographic peak; proportional to concentration.

Peak ratio

Ratio of peak areas of analyte to internal standard for quantitation.

Ethanol/Propanol (example)

Compounds used in an internal standard calibration example.

Emission spectrum

Spectrum of light emitted when excited species return to lower energy levels.

Line spectrum

Emission at discrete wavelengths corresponding to specific transitions.

Band spectrum

Molecular emission with multiple closely spaced lines forming bands.

Continuum spectrum

Broad, continuous emission across a range of wavelengths.

Atomic Absorption Spectroscopy (AAS)

Technique measuring absorption of light by ground-state atoms; Beer–Lambert law applies.

Atomic Emission Spectroscopy (AES)

Technique measuring emission from excited atoms returning to ground state.

Absorbance

Logarithmic measure of light absorbed; A = log(I0/I).

Beer–Lambert law

Relationship A = εlc between absorbance, concentration, and path length.

Hollow Cathode Lamp (HCL)

Element-specific light source used in AAS to excite atoms.

Atomizer

Device (flame or graphite furnace) that creates free atoms from a sample.

Monochromator

Optical component that selects a narrow wavelength for detection.

Detector (PMT)

Device (photomultiplier tube) that converts light to an electrical signal.

Readout

Displayed measurement signal from the detector.

Background signals

Unwanted signals from scattering, flame emission, or plasma.

Background correction (D2 lamp, Smith–Hieftje, Zeeman)

Techniques to remove or reduce background contributions in AAS/AES.

Smith–Hieftje method

Background correction using lamp reversal for AAS.

Zeeman effect

Background correction using a magnetic field to separate atomic signal from background.

Chromatography

Separation technique based on differential partitioning between mobile and stationary phases.

Gas Chromatography (GC)

Chromatography using a gas mobile phase to separate volatile compounds.

Mobile phase (GC)

Inert gas (e.g., He, N2) that carries the sample through the column.

Stationary phase (GC)

Liquid or solid coating inside the column that interacts with analytes.

Sample volatility requirement (GC)

Samples must be volatile and thermally stable for GC analysis.

Column types (GC)

Packed columns or capillary/open tubular columns used in GC.

Detectors (GC)

FID, MS, or other detectors used to quantify separated compounds.

High-Performance Liquid Chromatography (HPLC)

Chromatography using a liquid mobile phase to separate nonvolatile or thermally labile compounds.

Mobile phase (HPLC)

Liquid solvent or solvent mixture that transports analytes in HPLC.

Stationary phase (HPLC)

Packed or bonded-phase material inside the column (normal/reversed phase, ion exchange, etc.).

Detectors (HPLC)

UV–Vis, PDA, RI, fluorescence, conductivity, MS, etc., for detection.

Retention time (general)

Time required for a analyte to pass through the chromatography column.

Dead time (tM or t0)

Time for an unretained compound to elute; used to calculate retention factors.

Retention factor (k′)

k′ = (tR − tM) / tM; measures how long an analyte is retained on the column.

Number of theoretical plates (N)

Column efficiency; higher N indicates sharper peaks and better separation.

Resolution

Quantifies the degree of separation between two peaks in chromatography.