Abstract No. 58. Primary Calibration, What is it?

Transcription

1 Abstract No. 58 Primary Calibration, What is it? Svenerik Bäckman, Degerfors Laboratorium AB, Box 54, S Degerfors, Sweden When doing chemical analysis the values are based or validated on certified reference materials. Sometimes, comparable values will not comply with each other due to use of different references which means that something during the process of certification of reference material has got wrong. It could be at that time, when the certification was done, the analytical reference method was not fully updated or the compliance with the existing references were not correct. In such a case, use of uncertainly information in compliance assessment can be difficult when you make the decision. To verify, then a primary standard could be a good tool. Therefore, when the manufacturing of new certified references it should follow a very strict Standard Methods, from ISO or other standardisation organisations. It also means that the standards have to be upgraded so the working range of new instrumentation can be used. It can be seen that references certified during the youth of ICP was not good due to unknown interferences. This paper will give some examples for combustion analysis using primary standards, how to use primary standards in normal work as well the knowledge of how instrument can affect the value due to its construction.

2 Primary Calibration, What is it? Svenerik Bäckman D-LAB, Degerfors Laboratorium AB Cetas, Dϋsseldorf May 2015 D-LAB Instrumentation 2015 Policy: Answer same day as samples arrive to market lowest price 4 XRF/XRF/XRD, Sim/Seq Thermo, /9900, 1 AdvantX 7 OES, 5 Thermo 4460/ , 3 CS, LECO CS-600/2 CS NOH LECO TCH-600, ONH N/NO LECO TN 114, 2 Multiphase analyzers, LECO RC-412 Sample prep. D-lab Grinder, Herzog, Heattech etc Calibration for Steel, Ni-base, Cu-base, Al-Base, Ti, Co, Oxidic, Minerals, Iron Ore, Ferro Alloys Courses XRF, OES, Combustion, from Operator to Supervisor Number of employee 10 NEW!! Starting School/Trainings for new Employed People/Upgrading

3 Content: - Introduction - Questions - Definitions Primary Calibration - Instrument influence - Gas Dose Calibration - Primary Standards - Conclusion Introduction When buying/using an instrument you use for determination of a specimen different ways of calibrations: - Buy a Factory Calibration - Do an own Empirical Calibration - Using Special Software as MultiScat Decipher - Using Fundamental Calibration The first three use reference material in some form: - Own in house references - Certified CRM:s Validation against CRM:s

4 Introduction - Different manufactorers of reference materials does not comply with each other so something during the process of certification has got wrong - A reference can last for long time (Steel) and at time the reference/standard methods was not fully known - New techniques, as ICP, was used with really bad knowledge about interferences of material and lines in the 80-ties - Reference Standards are not updated to ranges, instrument construction fault etc - Some manufactors misuse and say that they use primary calibration when they in reality only makes a secondary reference material by refering to analysis against CRMs - Therefore, The need of using primary calibration is urgent - In this presentation I will examples for Combustion analysis Misuse of primary standard! Misuse of primary standard When using a CRM You check values and how the values are certified. You can find in material certified 2012 with this text:

5 Questions Combustion analysis Gas dose and Primary Calibration How many of you have done a: - Gas Dose Calibration? - Used Primary Standards? - How many of you have or will participate in a certification of new CRMs? What is a Primary Calibration? Primary Calibration A primary calibration is done using primary standards Definitions: - Primary Standards A primary standard is a reagent that is extremely pure, stable, has no waters of hydration, and has as high molecular weight as possible. ie Primary standard is typically a reagent which can be weighed easily, and which is so pure that its weight is truly representative of the number of moles of substance contained. Features of a primary standard include: - High purity - Stability (low reactivity) - Low hygroscopic loss of crystal water - High solubility (if used in titration) - High equivalent weight - Non-toxicity - Ready and cheap availability - Eco-friendliness,

6 Combustion analysis, Instrument Influence For Combustion analysis, instrument have a big influence on the analysis how correct they are. Linear cells are mandatory: - C, very light powder as CaCO 3 can be blown off due to high lance flow. Use tin foil as a packing material and put it in bottom and add after accelerator and iron chips. Dont use any organic material. The burning is to fast! - S, most material OK except organics, SO 4-2 will decompose as SO3? - N, Combined instrument, - - high oxygen causes flow change when it is absorbed by chemicals, which influence measurement of N with TC-cell. Instrument have to be corrected for this. - - Example 1, Using KNO3 as Primary standard for N, will cause to high detector reading - due to O. Calibration Curves linear but analysed values will be too low. - - References in fine cutted forms (higher surface O)will give for same reason to high value - if calibration is done against Gase Dose Single element instrument is not affected. Using Nitrids or/and Gas Dose preferrable to nitrats - O - comes out of the furnace mostly as CO. In low levels, ie <1000 ug/g it is acceptable. - For higher O, especially when you use ramping, ie depending of temperature in the crucible, the formation of CO 2 increases, up to 25 %! This means that you loose whole or half of oxygen of CO 2 formation as the instrument either measure CO or CO 2. - The instrument should have both CO and CO 2 -cells or more cells matched to each other (normally a factor close to 2). - H, - - Most of the levels are very low, except for Ti. Here you have very few Primary standard that works, but Gas Dose excellent

7 Primary Calibration Examples of Primary standards for Combustion techniques in determination of C, S, N, O and H -C; Tungsten Carbide, Carbonates as SrCO 3, CaCO 3 -S; BaSO 4 -N; KNO 3, ZrN, TiN -O; SrCO 3 SiO 2, Dy2O3 -H; KHC8H4O4, Potassiumftalate for high values -And naturally for all: Gas Dose - C ; CO 2 - S; SO 2 - N; N - O; CO 2, CO - H; H 2 -Best of all, gas dose calibration How to do a Gas Dose Calibration: Gas dose Calibration In the manuals from the manufactorer, you will find instruction how to do a gas dose calibration, and if you follow it you often find it will not work, so here are a short version How to Do (N calibration) with TC(H)600: 1. Find a gas container of at least 10L ( too small will not give enough stable gas pressure 2. Set according to manufactors recommendation the pressure, normal psi 3. Connect the gas (N) to Gas Dose A or B (choose A)

8 4. Notify the Known Gas dose value, in this case N= (note that the value are barometric pressure dependant according to the Ideal gas law. Set the barometric pressure according to manual) 5. Go to Standards and set under Gas dose A Nitrogen value to 0, Go to Methods and choose your method or create one 7. Select properties and gas dose parameter 8. Set minimum dose time, nominal 30 sec 9. Select if you want to bypass the furnace or not 10. Select with input you have used (point 1),(A) 11. Set number of cycles, 12. Select Gas dose A from standards 13. Set sample weight for one dose to 1 g, 2 dose 2 g etc 14. Flush the system until repeatable signals by repeatable analysis 15. Analyse with 1 dose, 2 doses, 3 doses, 4 doses and 5 doses (5 is max). Newer instrument unlimited Primary Calibration Primary Calibration

9 16. Mark the runs you have done 17. Go to Config, Calibration and select Nitrogen 18. Save the calibration curve and run your samples 19. Note that the weight and the expected content have to be within calibrated area. 20. Example: - Expected content 9,5 % - 5 doses gives a content for 1 g sample in this case max 0,24 % - 0,02500 g sample will give within calibrated range Primary Calibration Daily Control Instead of using Certified reference material, you can use Gas Dose as control standard. Do like this: 1. Normal weight and range for Nitrogen in your material are: - 0,3-0,5 g sample and 0,0040 to 0,0200 % nominal range - Use 1 dose for your gas dose, which will cover up to around 0,09 % For N normally you have very good references but for H the value in the references are very uncertain. Here are the best use for gas dosing

10 Repeatability, 5 doses, 10 runs Average 0,2364 % Std 0,0009 % Rsd 0,381 N 10 Gas Dose Calibration Summery Gas Dose Calibration is an excellent tool for - Primary Calibration - Daily Control standard or - For Recalibration - And is very cheap Future wishes is that the instrument could have several coils for dosing instead of repeating one coil

11 THANK YOU!