Chapter 6: Sampling, Standardization, and Calibration Flashcards by Clint Anthony Arcilla

are traditionally classified as gravimetric methods, volumetric methods, or instrumental methods

quantitative methods

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an analysis used for samples whose masses are greater than 0.1 g

macro analysis

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is performed on samples in the range of
0.01 to 0.1 g

semi-micro analysis

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is performed on samples in the range of
10^-4 to 10^-2 g

micro analysis

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is performed on samples in less than 10^-4 g

ultramicro analysis

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TRUE or FALSE
Techniques for handling very small samples are quite different from those for treating macro samples.

TRUE

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species present in the range of 0.01 to 1% are usually termed

minor constituents

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species present in the
range of 100 ppm (0.01%) and 1 ppb are called

trace constituents

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Components present in amounts lower than 1 ppb are usually considered to be

ultratrace constituents

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The analysis of real samples is complicated by the presence of the

sample matrix

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can contain species with chemical properties similar to the analyte. can react with the same reagents as the analyte, or they can cause an instrument response that is not easily distinguished from the analyte.

Matrix

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If the interferences are caused by
extraneous species in the matrix, they are often called

matrix effects

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The process of acquiring a
representative fraction is termed

sampling

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is often the most difficult
aspect of an analysis.

sampling

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TRUE or FALSE
The composition of the gross
sample and the laboratory
sample must closely resemble
the average composition of
the total mass of material to be
analyzed

TRUE

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Steps in obtaining a lab sample

identify the population
collect a gross sample
reduce the gross sample to a laboratory sample

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representative portion of a whole analytical sample, which with further treatment, becomes the laboratory sample

gross sample

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The items chosen for analysis are often called

sampling units or sampling increments

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chemists usually call
the collection of sampling units or increments the

gross sample

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gross sample is usually reduced in size and
homogenized to create the

laboratory sample

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Statistically, the goals of sampling process are

obtain a mean analyte concentration for an unbiased estimate of population mean
obtain a variance in the measured analyte concentration for an unbiased estimate of the population variance

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can reveal whether the between
samples variation (sampling variance plus measurement variance) is significantly
greater than the within samples variation (measurement variance).

analysis of variance

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TRUE or FALSE
Errors due to invalid sampling
are unique in the sense that they are not controllable by the use of blanks and
standards or by closer control of experimental variables. For this reason, sampling errors are usually treated separately from the other uncertainties associated with an analysis

TRUE

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is a miniature replica of the entire mass of material to be analyzed. It should correspond to the bulk material in chemical composition and in particle-size distribution if the sample is composed of particles.

gross sample

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gross sample is acquired by

1. uncertainty that can be tolerated 2. degree of heterogeneity of the whole 3. level of particle size, which heterogeneity begins

is a state intermediate between a suspension and a solution.

colloid

intermediate between heterogeneity that develops in particles that may have dimensions on the order of a centimeter or more and maybe several in grams are called

colloidal materials and solidified metals

the constant Ks is called the

Ingamells sampling constant

is a container that can be opened and filled at any desired location in the solution.

sample thief

TRUE or FALSE With large volumes of solutions, mixing may be impossible. It is then best to sample several portions of the container with a “sample thief,”

TRUE

What is used to collect vapor samples

gas-tight syringe or stainless steel canister

TRUE or FALSE The laboratory sample should have the same number of particles as the gross sample.

TRUE

samples of metals are obtianed by

sawing milling drilling

TRUE or FALSE With some materials, a representative sample can be obtained by sawing across the piece at random intervals and collecting the “sawdust” as the sample.

TRUE

the steps in sampling a particulate solid includes

crushing grinding seiving mixing dividing the sample to reduce its mass

can lead to higher throughput (more analyses per unit time), higher reliability, and lower costs than manual sample handling.

automated sample handling

two different methods for automated sample handling

batch or discrete approach continuous flow approach

A method where Automated instruments that process samples in a discrete manner often mimic the operations that would be performed manually.

Discrete methods

In continuous flow methods, the sample is inserted into a flowing stream where a number of operations can be performed prior to transporting it to a flow-through detector. Hence, these systems behave as automated analyzers in that they can perform not only sample-processing operations but also the final measurement step.

continuous flow methods

discrete methods do

dilute filter partition grind centrifuge homogenize extract treat samples with reagent

continuous flow method do

reagent addition dilution incubation mixing dialysis extraction

2 different types of continuous flow systems

segmented-flow analyzers flow injection analyzers

divides the sample into discrete segments separated by gas bubbles

segmented-flow analyzer

is a more recent development, samples are injected from a sample loop into a flowing stream containing one or more reagents

flow injection analysis

is a band-spreading or mixing phenomenon that results from the coupling of fluid flow with molecular diffusion.

dispersion

is mass transport due to a concentration gradient.

diffusion

the sample and reagent are both injected into carrier streams and merged at a tee mixer.

merging zones flow injection analysis

sample dispersion is controlled by the sample size, the flow rate, and the length and diameter of the tubing. It is also possible to stop the flow when the sample reaches the detector to allow concentrationtime profiles to be measured for kinetic methods

flow injection analysis/ merging zone FIA

determines the relationship between the analytical response and the analyte concentration

calibration

the relationship of analytical response and the analyte concentration (calibration) is determined by

chemical standards

Constituents of a sample other than the analyte are called

concomitants

Concomitants that interfere with the determination of an analyte may be referred to as

interferences or interferents

needs to indicate whether the threshold has been exceeded

comparator

Some analytical procedures involve comparing a property of the analyte (or the product of a reaction with the analyte) with standards such that the property being tested matches or nearly matches that of the standard are called as

null comparison or isomation methods

are among the most accurate of all analytical procedures, the analyte reacts with a standardized reagent (the titrant) in a known stoichiometric manner.

titration

a type of calibration process in which a series of standard solutions is prepared separately from the sample, The standards are used to establish the instrument calibration function, which is obtained from analysis of the instrumatrment response as a function of the known analyte concentration.

external standard calibration

A plot of instrument response versus known analyte concentrations is used to produce a

calibration curve or working curve

provides the means for objectively determining such a line and also for specifying the uncertainties associated with its subsequent use

regression analysis

Least squares method two assumptions

linear relationship between the measured response y (absorbance in Figure 6-10) and the standard analyte concentration x any deviation of the individual points from the straight line results from error in the individual measurements

The vertical deviation of each point from the straight line is called a

residual

simple least-squares analysis may not be appropriate when the uncertainties in the y values vary significantly with x. In that instance, it may be necessary to apply different weighting factors to the points and perform a

weighted least square analysis

is a rough measure of the magnitude of a typical deviation from the regression line.

SD abour regression/ standard error of the estimate/ standard error

measures the fraction of the observed variation in y that is explained by the linear relationship and

coefficient of determination R^2

The process of relating multiple instrument responses to an analyte or a mixture of analytes is known as

multivariate calibration

The least-squares procedure just described is an example of a

univariate calibration

The use of multivariate statistical methods for quantitative analysis is part of the subdiscipline of chemistry called

chemometrics

involves adding the interfering species to all the samples, standards, and blanks so that the interference effect becomes independent of the original concentration of the interfering species in the sample

saturation method

is a species, not itself an interfering species, added to samples, standards, and blanks in sufficient amounts to make the analytical response independent of the concentration of the interfering species

matrix modifier

is added that reacts selectively with the interfering species to form a complex that does not interfere

masking agent

can sometimes be used if the interfering species produces no significant effect below a certain concentration level.

dilution method

attempts to duplicate the sample matrix by adding the major matrix constituents to the standard and blank solutions

matrix-matching method

a type of calibration method in which a known amount of a reference species is added to all the samples, standards, and blanks

internal standard method

We use the _______________ when it is difficult or impossible to duplicate the sample matrix. a known amount of a standard solution of analyte is added to one portion of the sample

method of standard additions

additions of known amounts of standard analyte solution are made to several portions of the sample, and a multiple additions calibration curve is obtained.

multiple additions method

is a general term that applies to many fields including analytical chemistry. It is a numerical expression representing the performance or efficiency of a given device, material, method, or procedure.

figures of merit

Analytical procedures are characterized by a number of figures of merit

accuracy precision sensitivity detection limit dynamic range

the change in the measured quantity per unit change in analyte concentration. slope of the calibration curve

calibration sensitivity

Scatter in the response is also called as

noise

is the smallest concentration that can be reported with a certain level of confidence

detection limit

TRUE or FALSE A k value of 2 corresponds to a confidence level of 92.1%, while a k value of 3 corresponds to a 98.3% confidence level

TRUE

of an analytical method most often refers to the concentration range over which the analyte can be determined using a linear calibration curve

linear dynamic range

is a sequentialplot of some characteristic that is a criterion of quality.

control chart

if the value is within the upper control limit and lower control limit, the balance is said to be in

statistical control

determines the suitability of an analysis for providing the sought-for information and can apply to samples, to meth odologies, and to data

validation

is the final step before release of the results

data validation

a known amount of a standard solution of analyte is added to one portion of the sample

method of standard additions/ standard addition method

This standard additions method assumes a linear response

multiple additions method

is a rough measure of the magnitude of a typical deviation from the regression line

standard deviation about regression, also called the standard error of the estimate or just the standard error

is identical to the sample but without the analyte.

ideal blank

Most often a real blank is either a ___________, containing the same solvent in which the sample is dissolved

solvent blank

containing the solvent plus all the reagents used in sample preparation.

reagent blank

contains the solvent or the solvent plus all the reagents used to prepare the samples.

blank

is the ratio of the calibration curve slope to the standard deviation of the analytical signal at a given analyte concentration.

analytical sensitivity