We are analyzing the metal at PPB level through Analytik Zena AAS ZEEnit 700 instrument
Recently we have observed the absorbance value of sodium and potassium ion, 0.826 and 0.752 respectively at the scale of PPB( Parts per billion) in well processed double distilled water.( Blank water)
Even we have detected more value in HPLC ultra pure grade water which showed 1.21 and 0.742 absorbance value for Na and K ion which is too much exceed.
According to principle the absorbance value should be in 0.00xxx range, not to be exceed than this range in PPB level. Like for copper metal it is showing 0.0042 value for absorbance in blank double distilled water .
Can any one help to describe the possible least value in double distilled water or triple distilled water?
And is it possible to avoid this range at PPB level detection?
Dear Dr Gupta
Distillation is the best method in this case.
I remember that in the late seventies geologists at the department of earth science at ETH, Zurich, used double "quartz" distilled water followed by a surface evaporation step for their isotope studies. Unfortunately, I don't have any information on the remaining impurities, but maybe you can find something in the literature.
Your HPLC water came from a glass bottle. Glass exchanges ions with water. As Michael Päch and Parisa Ziarati said, you will need to distill the water from a PFA or other fluoropolymer or quartz vessel, collect and store it in PFA or high purity polypropylene in order to maintain low Na and K levels.
Sodium and potassium are ubiquitous elements so the contamination may be coming from anywhere. We have struggled with similar problem in capillary electrophoresis of cations long ago.
First, you need "Na/K free" water. It is best obtained by distillation from quartz, silver or fluoropolymer apparatus as Richard and Michael mentioned. You may also try hight quality cation exchange resin, of course the column should be made of quartz or quality plastic.
Second, every grain of dust, sweat aerosol, or other particulate matter usually contains "tons" of sodium and potassium, so you have to work at best under laminar flow hood (NOT in conventional fume hood) and transfer the samples to the instrument in closed containers.
Third, you should use quartz or polymer labware and sample containers as any glass item contains a lot of alkali metals as mentioned earlier.
Last, but not least, please be aware that any piece of labware, i.e. the still, volumetric flasks, pipettes, sample contaimers, and the like should be properly cleaned with "Na/K free" hydrochloric or nitric acid, washed with "Na/K free" water, and kept protected from the dust. When sufficiently "good" acid cannot be obtained from commercial source, you can make your own by isothermal distillation.
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