ISC-Science Products

PRODUCTS

isotopic standards, isotope standards, certified reference materials, isotope dilution standards, isotope dilution analysis, ICP-MS, isotope reference standards, methylmercury, tributyltin, ethylmercury

ISC-Science produces isotopic standards, Reference Materials (RMs) and Certified Reference Materials (CRMs) of stable elemental isotopes and isotopically enriched compounds for Isotope Dilution and ICP-MS and/or GC-MS applications. ISC-Science produces Certified Reference Materials (CRMs) of elements in waters

marca acreditacion

ISC-Science is a Reference Material Producer accredited by ENAC with accreditation no. 3/PMR004

ENAC is a signatory to the EA and ILAC Multilateral Agreements for Reference Material Producers

The marked activities (*) are neither covered by ENAC accreditation nor its international recognition agreements

Check the Technical Annex here.

CRM-DW · Elements in drinking water (*)

Certified Reference Materials (CRMs) of elements in drinking water. Produced and certified in element concentration according to ISO 17034.

· See more information about CRM-DW

(*) not covered by ENAC accreditation no. 3/PMR004.

CRM · Elemental Isotopic Standards

 

isotopos elementales

Certified Reference Materials (CRMs) of Elemental isotopic standards for Isotope Dilution Analysis (ID-MS). Produced and certified according to ISO 17034.

· See more CRMs of isotopic standards

RM · Isotopically Enriched Organic Compounds

 

compuestos orgánicos

Reference Materials (RMs) of Isotopically enriched organic compounds for Isotope Dilution Analysis. Produced and characterized according to ISO 17034.

· See more RMs of enriched compounds

isotopic standards, isotope standards, certified reference materials, isotope dilution standards, isotope dilution analysis, ICP-MS, isotope reference standards, methylmercury, tributyltin, ethylmercury

About Isotope Dilution Analysis (ID-MS)

Isotope Dilution Analysis is based on the modification of the isotopic composition of a sample by the addition of a known amount of an isotopically enriched element or compound generally called tracer or spike. The general concept of isotope dilution can be explained using a simple analogy: How can we determine the large number of white marbles (Nw) inside a box?

Although, the simplest way is to count all the marbles it is a very time consuming process and we can commit errors. The best way is to resort of a kind of "dilution" using a known amount of black marbles (Nb). The marbles have the same size and properties, the only difference between the white and the black marbles is their colour, which allows us to apply the concept of "dilution" to determine the number of white marbles in the in the box. For that purpose, the black marbles are added to the white marbles in the box. Once black and white marbles are mixed forming a homogenous mixture, a sample of the mixture is taken and the white (W) and black (B) marbles are counted, obtaining this way the relation shown in the figure.

If another sample is taken out of the box, a different number of white (W) and black (B) marbles could be obtained, though the relation W/B will remain the same. The total number of white marbles in the initial sample can be determined according to the following equation:

Nw= Nb(W/B)

This is the basic concept of isotope dilution analysis that uses the existence of isotopes of the elements and the isotope ratio measurements to quantify elements or compounds with very high accuracy and precision. Isotope dilution analysis provides several unique advantages in relation to classical approaches and is considered a primary method directly traceable to the International System of Units (SI).

Isotope dilution mass spectrometry, isotopic standards, methylmercury, enriched methylmercury

The elemental analysis by isotope dilution is based on the intentional modification of the isotopic abundances of the element to be determined in the sample though the addition of a known amount of an enriched isotope of the same element (tracer). The majority of the elements of the periodic table possess more than one isotope, therefore they can be determined by this methodology.


If we consider the number of moles of a poly-isotopic element present in a sample Ns and the number of moles of the same element in the tracer Nt added to the sample, the number of moles of the element in the mixture Nm is given by:

Nm = Ns + Nt

In the same way, we can establish mass balances for the isotopes a and b:

Nma = Nsa + Nta
Nmb = Nsb + Ntb

If we divide the two equations the isotope ratio of the isotopes (a/b) in the mixture (Rm) can be obtained. When taken into account the abundances of the isotopes a and b in the sample (Asa and Asb) and in the tracer (Ata and Atb), the isotope ratio can be expressed as:


                   Nma    Nsa + Nta    NsAsa + NtAta
          Rm = ----- = ----------- = -----------------
                   Nmb    Nsb + Ntb    NsAsb + NtAtb

 where        

          Nsa = NsAsa; Nta = NtAta
          Nsb = NsAsb; Ntb = NtAtb

Rearranging for Ns we obtain:

                        RmAtb - Ata
           Ns = Nt ---------------
                        Asa - RmAsb

This equation expresses the number of moles of the element in the sample as a function of the number of moles of the tracer added and the abundances of both, as well as the measured isotope ratio. If we define Rs and Rt as the isotope ratio of the isotope b/a and a/b for the sample and the tracer, respectively, the number of moles of the element in the initial sample is given by:

                        Atb   Rm-Rt
           Ns = Nt  ---- ---------
                        Asa  1-RmRs

This equation can be transformed as a function of the analyte concentration considering the masses of the sample and the tracer that were taken, ms and mt; the atomic weights of the element in the sample and in the tracer, respectively, Ms and Mt. By substitution, the final isotope dilution equation is obtained:

                       mt   Ms    Atb  Rm - Rt
            Cs = Ct ----- ------ ------ ----------
                       ms   Mt   Asa  1 - RmRs

In this equation the concentration of the element in the initial sample Cs can be determined directly by measuring just the isotope ratio in the mixture Rm, since all other parameters of the equation are known or measurable. If the element has natural isotopic composition the values Ms, Asa and Rs can be obtained from the IUPAC tables of isotopic composition and atomic weights of the elements.

Isotope dilution analysis provides several advantages compared to other analytical techniques that use methodological calibrations. As can be seen in the equation, the isotope dilution equation does not contain any parameters that are dependant of the instrumental sensitivity, therefore posible factors that affect the instrument's sensitivity like signal drift or matrix effects don't affect the final result. Further, once sample and tracer have formed a homogeneous mixture, any loss of the sample during sample preparation does not change the final result, since any aliquot of the sample will have the same Rm during the whole process.  

ISO 17034 ACCREDITATION

ISC Science is a Reference Material Producer accredited by ENAC.

Accreditation no.: 3/PMR004. Check the Technical Annex here.

Savillex products and services different than Reference Material Production are not covered by ENAC accreditation no. 3/PMR004.