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Handling, Calculations, Preparation and Storage of Standards

ICP Operations Guide: Part 3 By Paul Gaines, Ph.D.• Overview• Handling• Calculations• Preparation• Storage• Further Reading• View as one page

Overview

This section contains basic information on the handlin , preparation and stora e of standards, as !ell as basic

calculations and nomenclature.

Handling

Obser"in the follo!in recommendations !ill sa"e considerable time, money, and frustration:

1. Never put solution transfer devices into the standard solution. This precaution avoids possi le

conta!ination fro! the pipette or transfer device.

". #lwa$s pour an ali%uot fro! the standard solution to a suita le container for the purpose of

volu!etric pipette solution transfer and do not add the ali%uot re!oved ac& to the original standard

solution container. This precaution is intended to avoid conta!ination of the stoc& standard solution.

'. Perfor! volu!etric pipette solution transfer at roo! te!perature. #%ueous standard solutions

stored at (lower( te!perature will have a higher densit$. )eight solution transfers avoid this pro le!provided the densit$ of the standard solution is &nown or the concentrations units are in wt.*wt. rather

than wt.*volu!e.

+. Never use glass pipettes or transfer devices with standard solutions containing HF. Free HF

attac&s glass ut it is so!eti!es considered safe to use glass when the HF is listed as trace and*or as

a co!ple,. However- !an$ uorinated co!pounds will attac& glass /ust as readil$ as free HF.

0. on(t trust volu!etric pipette standard solution transfer. )eigh the ali%uot of the standard

ta&en. This can e easil$ calculated provided the densit$ of the standard solution is &nown. There are

too !an$ possi le pipetting errors to ris& a volu!etric transfer without chec&ing the accurac$ $

weighing the ali%uot.

2. 3ncap $our stoc& standard solutions for the !ini!u! ti!e possi le. This is to avoidtranspiration concentration of the anal$tes as well as possi le environ!ental conta!ination.

4. Replace $our stoc& standard solutions on a regular asis. Regulator$ agencies reco!!end or

re%uire at least annual replace!ent. Why is this precaution taken in view of the fact that the

vast majority of inorganic standard solutions are chemically stable for years? This is due to

the changing concentration of the standard through container transpiration and the possi ilit$ of an

operator error through general usage 5 !ore info 6. # !ista&e !a$ occur the 7rst ti!e $ou use the stoc&

standard solution or it !a$ never occur with the pro a ilit$ increasing with use and ti!e. 8n addition-

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the transpiration concentration e9ect occurs whether the standard solution is opened * used or not and

increases with use and increased vapor space 5transpiration rate is proportional to the ratio of the

circu!ference of the ottle opening to vapor space6.

Calculations

The concentration units for chemical standard solutions used for ICP applications are typically e#pressed in $ %m&

'micro rams per milliliter( or n %m& 'nano rams per milliliter(. )or e#ample, a *+++ $ %m& solution of Ca :" contains

*+++ micro rams of Ca :" per each m& of solution and a * $ %m& solution of Ca :" contains *+++ n of Ca :" per

milliliter of solution. To con"ert bet!een metric concentration units the follo!in con"ersions apply:

Table 3.1: ass portion of concentration unit where g ! gram

"re#$ %cienti#c&otation

'ecimale(uivalents

)$ample *nits

&ilo; 5&6 < 1= ' < 1=== g &ilogra! 5&g6

!illi; 5!6 < 1= ;' < =.==1 g !illigra! 5!g6 !icro; 5>6 < 1= ;2 < =.=====1 g !icrogra! 5>g6

nano; 5n6 < 1= ;? < =.========1 g nanogra! 5ng6

pico; 5p6 < 1= ;1" < =.===========1g

picogra! 5pg6