Lecture 2 (Sampling, Standardization, Calibration)

What is the difference b/w qualitative and quantitative analysis?

qualitative: what is in the sample

quantitative: how much of an analyte is in the sample

What are the specs for macro, semi-micro, micro, and ultra-micro analysis?

macro: >0.1 g

semi-micro: 0.1-0.01 g

micro: 0.01-0.0001 g

ultra-micro: <0.0001 g

What are the specs for major, minor, trace, and ultra-trace constituents?

major: 1-100%

minor: 1-0.01% (100 ppm)

trace: 100 ppm to 1 ppb

ultra-trace: <1 ppb

What is the matrix effect?

When species in the sample contain similar chemical properties to the analyte, react similarly to reagents, and can cause interference

What is the definition of sampling? What is used to draw conclusions about a population using samples?

The process of acquiring a representative fraction of a population

statistics

What are the steps in obtaining a representative sample?

1. identify the population

2. collect a gross sample (collection of sampling units)

3. Reduce gross sample to a lab sample (heterogenous → homogenous)

What defines the results?

The population

What is the equation for the overall standard deviation and what does each variable mean?

S_o² = s_s² + s_m²

s_s is the sampling uncertainty and s_m is the method uncertainty

What is important about the sampling and method uncertainty and how does it affect the overall uncertainty?

S and M are independent of each other and the overall uncertainty (variance) is the sum of the individual variances

What are batch/discrete approaches and continuous flow methods in automated sample handling?

batch/discreet: mimic the steps normally performed by an analyst

continuous flow method: involves inserting a sample into a flow stream where several operations can be performed b4 sample passes through detector

Describe how a segmented flow analyzer works

1. samples are injected w/ reagent and air

2. the gas bubbles act as barriers, confining the sample and preventing cross contamination b/w different samples

3. Once the solution is mixed, it is de-bubbled before running through the detector

Describe how a flow injection analyzer works

1. Sample is loaded onto a sampling loop

2. It is injected into a flowing stream containing 1 or more reagents

3. Disperses in different manners before reaching the detector

What are the 3 forms of dispersion in FIA?

diffusion: natural dispersion → gaussian curve

convection: fluid in center moves faster than walls due to friction → pointy curve

convection and diffusion: mix of both → looks like a gaussian curve

What do dispersion trends depend on?

the concentration of the sample and how it interacts w/ the reagent

What is the definition of a calibration?

Determines the relationship b/w the analytical response and analyte concentration using chemical standards

What is the definition of a concomitant?

constituents in a sample OTHER than the analyte. called interferences if they interfere w/ the analyte

What is a null comparison/isomation method?

Procedure involving the comparison of an analyte’s properties (or product formed from reacting with the analyte) to a standard to determine if properties match “does my sample respond the same as my standard”

What is an external standard calibration?

A series of standard solutions is used to establish the instrument’s calibration function → calibration curve

What does regression analysis provide?

How to determine the best fit line in a calibration curve

What is the method of least squares?

It assumes a linear relationship b/w measured response and a standard’s concentration

When is correlation analysis and weight-least squares analysis applied?

correlation analysis: when there is significant uncertainty in the x data

weight-least squares analysis: when there is significant uncertainty in the y data

Is an ideal blank (identical to the solvent w/out the analyte) possible?

no, often too difficult or impossible

What is the saturation method for minimizing interference?

Adding intereference species to all samples, standards, and blanks to overwhelm the interference. Can degrade sensitivity/detectability of analyte however.

What is a matrix modifier?

A species added to all samples, standards, and blanks to make the analytical response independent of the [ ] of the interfering species

What is a masking agent?

It reacts selectively with the interfering species to form a complex that doesn’t interfere

What is the matrix-matching method?

Adding major matrix constituents to the blank and standard to match the sample matrix

What is an internal standard and how does it affect the internal standard method?

Internal standard: a reference species similar to the analyte (physically and chemically) that is added to sample, standards, and blanks

By adding a known amount of the internal standard added to all 3 solutions, the measured response will be a ratio of the analyte response to the internal standard’s response

What is the method of standard additions?

Adding a known amount of standard into 1 portion of the sample, measuring the responses b4 and after adding the standard to obtain analyte [ ]

What is the difference b/w single point and multiple additions for the method of standard additions?

single point: standard is added to 1 of 2 portions of the sample

multiple additions: standard is added to several portions of the sample → a multiple additions calibration curve

What is calibration sensitivity, analytical sensitivity, and the detection limit?

calibration sensitivity: slope of the calibration curve

analytical sensitivity: ratio of the calibration curve slope to standard deviation at a given point or concentration

detection limit: smallest [ ] that can be reported with confidence

What method is MOST appropriate when the interfering species can be chemically altered to prevent interference?

masking agent

A concentration gradient exists in a solution w/out any fluid flow. the resulting movement is classified as:

diffusion since only [ ] gradient is present without any fluid flow

The upper limit of the linear dynamic range is defined by?

a 5% deviation from linearity