sampling and sample preparation

proper sampling

process of obtaining a portion of a material that will represent the subject under study

gross sample

consists of several portions of the material to be tested

laboratory sample

small portion of the sample that is actually analyzed

aliquot

measured portion of the volume of a liquid sample taken for the analysis

bulk, ton; gross, kg; laboratory, <1g; analytical sample; aliquot

representative sample

a sample that is typical of the parent material for the characteristic under inspection

static system

compositionoftheparentmaterialispermanentwith respect to position in space and stable in time

dynamic conditions

the parent material is changing with respect to time; removal of a portion at any instant represents only a snapshot of that moment in time and in that particular location

composite sample

consists of two or more portions of material (collected at the same time) selected so as to represent the material being investigated

in situ sample

allows monitoring the target population without removing individual grab samples

grab sample

a portion of the target population is collected at a specific time or location, providing a “snapshot” of the target population

grab sample

1/50th of the total bulk

grab sample

easiest but less reliable

grab sample

type of sample that is only satisfactory for homogenous sample

grab sample

best and easy time for sampling is during transportation

random sampling

any portion of the material has an equal and known chance of being chosen

random sampling

leas biased approach to sampling

selectove (judgemental) sampling

a sample which is deliberately chosen by using a sampling plan that screens out materials with certain characteristics and/or selects only material with other relevant characteristics (directed/focused sampling)

convenience sampling

a sampling plan in which samples are collected because they are easily obtained

systematic sampling

the sample is taken according to a previously arranged regular intervals in time or space.

Systematic–judgmental sampling

a prior knowledge about a system to guide a systematic sampling plan

Stratified (judgmental–random) sampling

population being sampled is divided into segments (or strata) and a simple random sample is selected from each

sampling, sample preservation, sample preparation, analysis

method for taking appropriate sample

siphoning, decanting, or by using a pipet or syringe

homogenous samples are easily sampled by?

grab

what type of sampling method is alright with sampling liquids?

serum

fluid separated from clotted blood

plasma

fluid separated from unclotted blood

plasma

fluid separated from clotted blood

naf, anticuagulant (heparin)

use preservatives such as ___ for glucose and ___

vacutainers

evacuated tubes with rubber cap for storing biological fluids

flow rate and depth

the chem comp of surface waters such as streams, rivers, lakes, and estuaries are influeced by?

grab samples

type of sample used in natural water

submerge the capped bottle below the surface, then remove cap. After the sample bottle is filled, cap is replaced then bottle removed.

how to collect natural water?

glass containers

natural waters - used for collecting samples for the analysis of pesticides, oil and grease, and organic

plastic bottles

natural water - used for collecting samplesfor the analysis of trace metals

control ph and temperature, limiting its exposure to light or to the atmosphere, or by adding a chemical preservative

how to preserve natural waters?

displacement of liquids (not reacting with or solubilizing the sample)

sampling method for gases

cryogenic cooling

changes the sample from gaseous to a liquid state (>150 K using He, H2, or N2).

in situ

type of smapling that the reaction between the gas and the reagent takes place ???

sampling with enrichment

gas is adsorbed onto a solid collection phase or adsorbed into a solution

sampling without enrichment

used for determining organic gases that occur permanently in the air or workplace

direct sampling: a gas storage vessels, gas-tight syringes, or gas sample bags pumped at 1-3 L/min flow rate

sampling of gases generally uses?

impingers (bubblers)

special glass tubes designed to collect airborne contaminants by bubbling the sample air at a high flow rate onto a specific absorbing liquid inside.

solid sorbent, filter, cryogenic cooling

sample preservation for gases

grab samplers

pair of jaws that close when they contact the sediment, scooping up sediment in th process.

tendency to lose finer particles

disadvantage of grab samplers

cylindrical coring device

maintains their vertical profile when collecting sediment samples

small surface area is sampled

disadvantage of cylindrical coring device

soil punch

thin-walled steel tube, may be used, which retains the core sample when it is pushed into the soil and removed

scooping, thieving, cone & quartering

3 static sampling for powder

table sampling, chute splitting, spin riffling

3 dynamic sampling for powder

scoop sampling

widely used and consists of plunging a scoop into a heaped batch

thieving

plunging a capture devise

cone & quartering

combination of crushing and grinding the gross sample

table sampling

powder flow along incline table

chute-splitting

v-shaped

spin riffling

uses mechanical energy

sawing, milling, or drilling

how to obtain metal alloys

sampling spears (sack samplers) (40-45 cm)

most commonly used for taking samples from bags. what sould be the length?

distilled water; methanol, chloroform, or toluene

sample dissolution used for inorganic salts uses ___, while ___ for organic materials

acid/base

With samples that are difficult to dissolve, the first approach is usually to try digesting the sample with ____

higher temperatures (200–300 °C) and pressures (40–100 bar) and consequently, may be accomplished in less than 30 min.

microwave digestion must be at?

large excess of alkali metal selt (flux)

• Inorganic samples that resist decomposition by digestion with acids or bases often can be brought into solution by fusing with a?