quiz 3 Flashcards
what are three methods to obtain TDS?
- Evaporation/weighing
- Conductivity
- Ion Analysis
Methods to obtain TDS (explain, +/-) : evaporation/weighing
- Place known volume of sample in pre-weighed container -> in oven at 105*C -> dry until constant weight achieved
- Calculate mg/L TDS: (final weight - initial)/initial
+/-
+ cheap: standard lab equipment and man power
+ time saving: obtain values in a few hours
- volatile substances change form when heated, can confuse TDS with DO
Methods to obtain TDS (explain, +/-) : Conductivity
- measure sample conductivity -> compare to NaCl standard -> report TDS as sample made up of NaCl
+/-
+ conductivity meters are cheap and easy to use
- values are approximate
Methods to obtain TDS (explain, +/-) : Ion analysis
- analyze individual ions ($$$ICP to $ISE) -> each ion mg/L -> sum of all ions is TDS mg/L
+/-
+ thorough and very accurate
- time consuming and expensive
Ways to obtain ion concentrations relevant to TDS (5)
- titrations
- IC - ion chromatography
- AA - atomic absorption
- ICP - atomic emission
- ISE - potentiometric analysis
Obtain [ion] relevant to TDS (explain + example) : titrations
What.
- A solution of known concentration is reacted with a solution of unknown concentration to an end point.
- Since reaction is stoichiometric, titration information is used to determine unknown concentration.
Examples.
- acid/base - p and m
- redox - residual chlorine
- precipitation - chloride
- complex formation - EDTA
Obtain [ion] relevant to TDS (explain + example) : IC
What.
- Use of an ion exchange column to analyze for anions, usually involve conductivity detector.
- Can be used for all anions except for HCO3- and CO32-
Examples.
Cl-, SO42-
Obtain [ion] relevant to TDS (explain + example) : AA
What.
- Light is directed through a sample and the attenuation of the intensity is used to determine unknown concentration after a calibration curve has been obtained.
- One unknown at a time
- Unknown must have a suitable lamp
Examples.
Na+, Ca2+, Zn, Cu
Obtain [ion] relevant to TDS (explain + example) : ICP
What.
- atomic emission
- sample causes light -> wavelength and intensity used to determine unknown identity and concentration after a calibration curve has been obtained.
Examples.
Most cations, just not NH4+
Obtain [ion] relevant to TDS (explain + example) : ISE
What.
- potentiometric analysis
- electrode is designed that measures the activity (ie. concentration) of a particular ion via a reaction at an anode or cathode
- potential relative to reference electrode on calibration curve to obtain unknown concentration
Examples
chloride, ammonium
Equation for frequency
v = c/wavelength
photon energy equation
E = hv
Describe how molecules absorb different wavelengths (4)
- microwave: molecule rotates
- IR: molecules vibrate
- VIS: electronic excitation
- gamma: inner shell electrons excited
What is T
Transmittance
measurement of light that has passed through the sample
= I/Io
What is T%
T x 100
equation for absorbance
A = 2-log10%T
Schematics for the different spec analysis (3)
- absorption
light -> sample -> detector - emission
sample -> detector - scattering
light -> sample ->
|
v
detector
analyte
components of a sample that are being determined
blank solution (def and use)
solution containing all analysis reagents and solvents, but no analyte.
takes into parameters of analysis that are being affected by outside factors that are not analyte -> equipment, matrix
standard solution (def and use)
concentration of solute known with high reliability
used to plot calibration curve and solve for concentration of analyte in unknown
advantages of ICP (4)
- obtain many elements in one analysis
- large linear range and low detection limit
- very few interferences
- can detect elements that resist decomposition during FAA
What is linear range
Range of values where output signal is a direct, linear function of input signal - line of best fit follows a straight line
detection limit
when a reading is below this limit -> absorbance signal is less than background noise
intrapolation and extrapolation
Both involve drawing line of best fit to obtain non-measured values.
- intrapolation: line between highest and lowest data points
- extrapolation: line extends past highest and lowest data points
