ICP / OES

Inductively Coupled Plasma/ Optical Emission Spectrometry (ICP/OES)

LabEquipment01

ICP/OES is one of the most powerful and popular analytical tools for the determination of trace elements in a myriad of sample types (listed in Table 1). The technique is based upon the spontaneous emission of photons from atoms and ions that have been excited in a radio-frequency discharge. Liquid and gas samples may be injected directly into the instrument, while solid samples require extraction or acid digestion so that the analyses will be present in a solution. The sample solution is converted to an aerosol and directed into the central channel of the plasma. At its core the ICP/OES sustains a temperature of approximately 10,000K (more than 9,700˚C), so the aerosol is quickly vaporised. Analyst elements are liberated as free atoms in the gaseous state. Further collisional excitation within the plasma imparts additional energy to the atoms, promoting them to excited states. Sufficient energy is often available to convert the atoms to ions and subsequently promote the ions to excited states. Both the atomic and ionic excited state species may then relax to the ground state via the emission of a photon. These photons have characteristic energies that are determined by the quantised energy level structure for the atoms or ions. Thus, the wavelength of the photons can be used to identify the elements from which they originated. The total number of photons is directly proportional to the concentration of the originating element in the sample.

Table 1: Survey of elemental application areas of ICP/OES

Categories Examples of samples
Agricultural and food Animal tissues, beverages, feeds, fertilizers, garlic, nutrients, pesticides, plant materials, rice flour, soils, vegetables, wheat flour
Biological and clinical Brain tissue, blood, bone, bovine liver, feces, fishes, milk powder, orchard leaves, pharmaceuticals, pollen, serum, urine
Geological Coal, minerals, fossils, fossil fuel, ore, rocks, sediments, soils, water
Environmental and water Brines, coal fly ash, drinking water, dust, mineral water, municipal wastewater, plating bath, sewage sludge, slags, seawater, soil
Metals Alloys, aluminium, high-purity metals, iron, precious metals, solders, steel, tin
Organic Adhesives, amino acids, antifreeze, combustion materials, cosmetics, cotton cellulose, dried wood, dyes, elastomers, epoxy, lubricant, organometallic, organophosphates, oils, organic solvent, polymers, sugars
Other materials Acids, carbon, catalytic materials, electronics, fiber, film, packaging materials, paints and coatings, phosphates, semiconductors, superconducting materials

 

The instrumentation associated with an ICP/OES system is relatively simple. A portion of the photons emitted by the ICP/OES is collected with a lens or a concave mirror. This focusing optic forms an image of the ICP/OES on the entrance aperture of a wavelength selection device such as a monochromator. The particular wavelength exiting the monochromator is converted to an electrical signal by a photodetector. The signal is amplified and processed by the detector electronics, then displayed and stored by a personal computer.

The characteristics of the ICP/OES as an analytical atomic emission source are so impressive that virtually all other emission sources [such as the flame, Microwave-Induced Plasma (MIP), Direct Current Plasma (DCP), Laser-Induced Plasma (LIP), and electrical discharge] have been relegated to specific, narrowly defined application niches. Indeed, even much of the application field originally assigned to Atomic Absorption Spectrometry (AAS), using both the flame and Graphite Furnace Atomic Absorption Spectrometry (GFAAS), has been relinquished to the ICP/OES. Compared to these other techniques, ICP/OES enjoys a higher atomisation temperature, a more inert environment, and the natural ability to provide simultaneous determinations for up to 70 elements. This makes the ICP/OES less susceptible to matrix interferences and better able to correct for them when they occur. In cases where sample volume is not limited, ICP/OES provides detection limits as low as, or lower than its best competitor, GFAAS, for all but a few elements. Even for these elements, the simplicity with which the ICP/OES instrument is operated often outweighs the loss in sensitivity.

 

Characteristics

The main analytical advantages of the ICP/OES over other excitation sources originate from its capability for efficient and reproducible vaporization, atomisation, excitation, and ionisation for a wide range of elements in various sample matrices. This is mainly due to the high temperature, 6000±7000K, in the observation zones of the ICP/OES. This temperature is much higher than the maximum temperature of flames or furnaces (3300K). The high temperature of the ICP/OES also makes it capable of exciting refractory elements, and renders it less prone to matrix interferences. Other electrical-discharge-based sources, such as alternating current and direct current arcs and sparks, and the MIP, also have high temperatures for excitation and ionisation, but the ICP/OES is typically less noisy and better able to handle liquid samples. In addition, the ICP/OES is an electrode less source, so there is no contamination from the impurities present in an electrode material. Further-more, it is relatively easy to build an ICP/OES assembly and it is inexpensive, compared to some other sources, such as a LIP. The following is a list of some of the most beneficial characteristics of the ICP/OES source.

  • high temperature (7000±8000 K)
  • high electron density (1014 ±1016 cm 3)
  • appreciable degree of ionisation for many elements simultaneous multi element capability (over 70 elements including P and S)
  • low background emission, and relatively low chemical interference
  • high stability leading to excellent accuracy and precision
  • excellent detection limits for most elements (0.1± 100ng mL 1)
  • wide Linear Dynamic Range (LDR) (four to six orders of magnitude)
  • applicable to the refractory elements cost-effective analyses.

 

Analytical Figures of Merit

For ICP/OES, the analytical figures of merit include the number of elements that can be determined, selectivity, reproducibility, long-term stability, susceptibility to matrix interferences, LOD, and accuracy. The number of elements that can be measured by ICP/OES is often more than 70 out of a total of 92 naturally occurring elements, as listed in Table 2. Routine determination of 70 elements can be accomplished by ICP/OES at concentration levels below 1mg L1. Almost all naturally occurring elements, with the exception of hydrogen, oxygen, fluorine, and inert gases, can be determined by ICP/OES. The elements that are not usually determined by ICP/OES fall into three basic categories. The first category includes those elements that occur either as trace contaminants in the argon gas used in the ICP/OES (C from CO2), constituents of the sample solvent (C, O, H), or as contaminants from the environment or atmosphere (N for example). The second category encompasses those elements that require high excitation energy, such as the halogens. These elements could be determined with poor LOD, however. The third category is the family of short-lived radioactive elements that are commonly determined by g-ray spectrometry.

Table 2:  A list of elements that can be determined by ICP/OES

Alkaline

and

Alkaline earth

Rare Earth

Transition Metal

Others

Li, Na, K, Rb, Cs, Be, Mg,

Ca, Sr, Ba

Ce, Pr, Nd, Sm, Eu, Gd, Tb,

Dy, Ho, Er, Tm, Yb, Lu,

Th, U

Sc, V, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y,

Nb, Zr, Mo, Ru, Th, Pd, Ag, Cd, La,

Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg

B, C, N, Al, Si, P, S, Cl, Ga,

Ge, As, Se, Br, In, Sn,

Sb, Te, I, Tl, Pb, Bi



Why we need to know?

  • ICP/OES is also widely used in the field of radiometric dating, in which it is used to analyse relative abundance of different isotopes. ICP/OES is more suitable for this application than the previously used Thermal Ionization Mass Spectrometry, as species with high ionization energy such as Osmium (Os) and Tungsten (Hf-W) can be easily ionized.
  • In the field of flow cytometry, a new technique uses ICP/OES to replace the traditional fluorochromes. Briefly, instead of labelling antibodies (or other biological probes) with fluorochromes, each antibody is labelled with a distinct combination of lanthanides. When the sample of interest is analysed by ICP/OES in a specialized flow cytometer, each antibody can be identified and quantitated by virtue of a distinct ICP/OES "footprint". In theory, hundreds of different biological probes can thus be analysed in an individual cell, at a rate of ca. 1,000 cells per second. Because elements are easily distinguished in ICP/OES, the problem of compensation in multiplex flow cytometry is effectively eliminated.
  • The ICP/OES allows determination of elements with atomic mass ranges 7 to 250. This encompasses lithium (Li) to Uranium (U). Some masses are prohibited such as 40 due to the abundance of argon in the sample. Other blocked regions may include mass 80 (due to the argon dimer), and mass 56 (due to ArO), the latter of which greatly hinders Fe analysis unless the instrumentation is fitted with a reaction chamber.
  • A typical ICP/OES will be able to detect in the region of nanograms per litre to 10 or 100 milligrams per litre or around 8 orders of magnitude of concentration units. ICP/OES is a method of choice for the determination of cadmium in biological samples.
  • Unlike atomic absorption spectroscopy, which can only measure a single element at a time and ICP/OES has the capability to scan for all elements simultaneously. This allows rapid sample processing. A simultaneous ICP/OES that can record the entire analytical spectrum from Lithium,Li to Uranium,U in every analysis won the Silver Award at the 2010 Pittc Editors’ Awards.
  • Application of ICP/OES includes the determination of metals in wine, arsenic in food, and trace elements bound to proteins.
  • ICP/OES is widely used in minerals processing to provide the data on grades of various streams, for the construction of mass balances.
  • ICP/OES is often used for analysis of trace elements in soil, and it is for that reason it is often used in forensics to ascertain the origin of soil samples found at crime scenes or on victims etc. Taking one sample from a control and determining the metal composition and taking the sample obtained from evidence and determine that metal composition allows a comparison to be made. While soil evidence may not stand alone in court it certainly strengthens other evidence.
  • It is also fast becoming the analytical method choice for the determination of nutrient levels in agricultural soils. This information is then used to calculate the amount of fertilizer required to maximize crop yield and quality.
  • ICP/OES is used for motor oil analysis. Analysing used motor oil reveals a great deal about how the engine is operating. Parts that wear in the engine will deposit traces in the oil which can be detected with ICP/OES. ICP/OES analysis can help to determine whether parts are failing. In addition, ICP/OES can determine what amount of certain oil additives remain and therefore indicate how much service life the oil has remaining. Oil analysis is often used by fleet manager or automotive enthusiasts who have an interest in finding out as much about their engine’s operation as possible. ICP/OES is also used during the production of motor oils (and other lubricating oils) for quality control and compliance with production and industry specifications.


Metal In Oil

Metal in general oil can come from various sources, such as wear, contamination and additives. Wear metals result from friction or corrosion of the engine components, for example, pistons, and bearings, during operation. Contamination can come from dirt, leaks or residual metal pieces. Additives used as detergents, anti-oxidants, and anti-wear agents, are added in order to reduce engine wear.

Like blood, lubricating oil contains a good deal of information about the envelope in which it circulates. Wear of metallic parts, for example, produces many minute particles, which are carried by the lubricant.

Regular monitoring of wear metals in oil can diagnose engine wear, so that preventive maintenance procedures can be performed, increasing equipment reliability. The analysis of oil for trace metals is routinely carried out as an equipment maintenance program for engines of various types.


Metal Element in General Oil:

Element

Symbol

Element

Symbol

Aluminium

AI

Molybdenum

Mo

Antimony

Sb

Mercury

Hg

Arsenic

As

Nickel

Ni

Barium

Ba

Phosphorus

P

Boron

B

Silicon

Si

Cadmium

Cd

Silver

Ag

Calcium

Ca

Sodium

Na

Chromium

Cr

Titanium

Ti

Copper

Cu

Tin

Sn

Iron

Fe

Total Halogen

-

Lead

Pb

Vanadium

V

Manganese

Mn

Zinc

Zn

Magnesium

Mg

 

 



STANDARD AND SPECIFICATION OF RECOVERED WASTE OIL IN MALAYSIA

Waste oil may contain physical and chemical impurities that can induce variety of illness and diseases in human and living organisms through inhalation, ingestion or skin contact. Table 1 below shows the main contaminants in waste oil:

Table 1: Principal Contaminants in Waste Oil

Metals and Inorganics

Chlorinated Hydrocarbons

Other organics

Aluminium

Antimony

Arsenic

Barium

Cadmium

Calcium

Chromium

Cobalt

Copper

Lead

Magnesium

Manganese

Mercury

Nickel

Phosporus

Silicon

Sulphur

Zinc

Dichlorodifluoromethane

Trichlorodifluoromethane

1,1,1 –Trichloroethane

Trichloroethylene

Tetrachloroethylene

Total chlorine

Polychlorinated biphehyls

 

Benzene

Toluene

Xylene

Benza(a)anthracene

Benzo(a)pyrene

Napthalene

Other PAHs

In Malaysia, waste oil is classified as scheduled wastes under the First Schedule of the Environmental Quality (Scheduled Wastes) Regulations 2005, with the following codes and descriptions:

  • SW305  –  Spent lubricating oil
  • SW305  –  Spent hydraulic oil
  • SW307  –  Spent Mineral oil-water emulsion
  • SW308  –  Oil tanker sludge
  • SW309  –  Oil-water mixture such as ballast water
  • SW310  –  Sludge from mineral oil storage tank
  • SW311  –  Waste oil or oily sludges
  • SW312  –  Oily residue from automotive workshop, service station oil or  grease interceptor
  • SW314  –  Oil or sludge from oil refinery or petrochemical plant

Waste oil should be managed properly according to the requirements of the Environmental Quality (Scheduled Wastes) Regulations 2005. For waste oil that still has an economic value, it can be recovered by waste oil recovery facilities that are licensed by Department of Environment. The recovered, recycled or reconstituted processes of waste oil that does not meet the standard and specification set, it still categorised as scheduled waste.

Waste oil that has been processed by recovery facilities and met the standard and specification of recovered waste oil as in Table 2 below can be considered as non-scheduled waste. For waste oil that has been processed but does not meet the standard and specification of recovered waste oil as in Table 2 below still categorised as scheduled waste.

 

Table 2: Standard and Specification of Recovered Waste Oil

Parameters / Constituent

Allowable Limit

Arsenic

5 ppm maximum

Cadmium

2 ppm maximum

Chromium

10 ppm maximum

Lead

100 ppm maximum

Total Halogen (as chlorine)

1000 ppm maximum

Flash Point

37.7 ˚C or higher

Appearance

The recovered waste oil must have a clear and bright appearance

Table 3: ICP/OES Oil Analysis Report

Elements

Symbol

DOE Spec

Unit

Diesel

Petrol

Base Oil

New Engine Oil

Tyre Oil

Light Fuel Oil 

(80 cSt)

Medium Fuel Oil (180 cSt)

Bunker Fuel

Waste Engine Oil

Aluminium

AI

ppm

<1

<1

<1

<1

<1

<5

<8

<100

<15

Antimony

Sb

ppm

<1

<1

<1

<1

<1

<1

<1

<1

<2

Arsenic

Ar

5 ppm Max

ppm

<1

<1

<1

<1

<1

<1

<1

<1

<1

Barium

Ba

ppm

<1

<1

<1

<1

<3

<2

<20

<3

<4

Boron

B

ppm

<1

<1

<1

<5

<1

<1

<1

<20

<220

Cadmium

Cd

2 ppm Max

ppm

<1

<1

<1

<3

<3

<3

<3

<3

<4

Calcium

Ca

ppm

<1

<1

<1

<600

<25

<10

<10

<2000

<1200

Chromium

Cr

10 ppm Max

ppm

<1

<1

<1

<2

<2

<3

<2

<6

<4

Copper

Cu

ppm

<2

<1

<1

<3

<3

<4

<3

<7

<20

Iron

Fe

ppm

<1

<1

<1

<2

<20

<20

<20

<220

<80

Lead

Pb

100 ppm Max

ppm

<1

<1

<1

<1

<3

<1

<3

<4

<8

Magnesium

Mg

ppm

<1

<1

<1

<900

<4

<4

<4

<20

<250

Mangasene

Mn

ppm

<1

<1

<1

<1

<4

<4

<4

<6

<1

Mercury

Hg

ppm

<1

<1

<1

<1

<2

<3

<1

<2

<2

Molybdenum

Mo

ppm

<1

<1

<1

<3

<3

<4

<4

<4

<40

Nickel

Ni

ppm

<1

<1

<1

<1

<1

<30

<30

<30

<4

Phosphorus

P

ppm

<1

<1

<1

<950

<30

<25

<2

<150

<700

Silicon

Si

ppm

<3

<1

<1

<10

<55

<15

<10

<90

<65

Silver

Ag

ppm

<1

<1

<1

<1

<6

<5

<8

<5

<7

Sodium

Na

ppm

<1

<2

<1

<1

<4

<1

<15

<80

<75

Tin

Sn

ppm

<1

<1

<1

<1

<2

<2

<1

<2

<5

Titanium

Ti

ppm

<1

<1

<1

<1

<5

<5

<8

<6

<5

Total Halogen

-

1000 ppm Max

ppm

<150

<150

<150

<500

<800

<200

<200

<7500

<600

Vanadium

V

ppm

<1

<1

<1

<3

<3

<90

<45

<110

<3

Zinc

Zn

ppm

<2

<1

<1

<1100

<25

<6

<4

<80

<800

* ppm – parts per million

 

Light metals are metals of low atomic weight. The cut-off between light metals and heavy metals varies. Lithium, beryllium, sodium, magnesium and aluminium are almost always included. Additional period 4 element metals up to nickel are often included as well. Metals heavier than nickel are usually called heavy metals. Light metals are generally less toxic than heavy metals. Beryllium is toxic, but it is rarely found in large concentrations. Vanadium, not always counted as a light metal, is also toxic. Other light metals are toxic in large amounts.

A heavy metal is a member of a loosely defined subset of elements that exhibit metallic properties. It mainly includes the transition metals, some metalloids, lanthanides, and actinides. Many different definitions have been proposed-some based on density, some on atomic number or atomic weight, and some on chemical properties or toxicity. The term heavy metal has been called a "misinterpretation" in an IUPAC (International Union of Pure and Applied Chemistry) technical report due to the contradictory definitions and its lack of a "coherent scientific basis". There is an alternative term toxic metal, for which no consensus of exact definition exists either. As discussed below, depending on context, heavy metal can include elements lighter than carbon and can exclude some of the heaviest metals. Heavy metals occur naturally in the ecosystem with large variations in concentration. In modern times, anthropogenic sources of heavy metals, i.e. pollution, have been introduced to the ecosystem.

Metal

Elements

Non-ferrous metals

Copper, aluminium, lead, zinc, tin, nickel, magnesium, antimony, cobalt, mercury

Black Metal

Iron, manganese, chromium

Light non-ferrous

Aluminium, magnesium, sodium, potassium, calcium, strontium, barium

Heavy non-ferrous metals

Copper, nickel, lead, zinc, cobalt, tin, antimony, mercury, cadmium, bismuth, osmium

Precious metals

Lithium, rubidium, beryllium, cesium, titanium

Scattered metals

Gallium, indium, thallium, germanium

Scattered radioactive metals

Radium, uranium, plutonium

Rare earth metals

Lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium

Semi-metallic

Silicon, selenium, tellurium, arsenic, boron