6020a digestion

Is anyone out there using HCl in their digestion?  If so what volume of HCl are you adding to your 50mL digestion?  If Cr is working well for you with HCl in your digestion, are you using a collision or reaction cell.  I use an Elan 9000 and have found Cr to be unstable with HCl in the digestion.  If I switch to HNO3 only digestion, Cr is stable.  But that would double the work for my lab.  Let me know what you are doing in your lab.  We use a Scott Spray Chamber with cross tip nebulizers.  Thanks.  Craig

Avoid using HCL for digestion of samples if you are running ICP MS. you may preferably use HNO3.

6020A is not a sample preparation method, it is an analytical method to be used in tandem with one of the 3000 series sample prep methods.

If you are using a block digestion system then you need to follow 3050b digestion method, which does not use HCl. Here is that method in a nutshell:

Weigh out 1-2 grams of a well mixed sample into a digestion vial
Add 10 mL of a 1:1 trace metal grade HNO3 in Type I water solution
Place watchlids on vials and reflux for 15-20 minutes on block digestion system set to 95 C
Remove from block and allow to cool
Add 5 mL of concentrated trace metal grade HNO3, replace watchlid and reflux @ 95 C until now brown fumes remain (30 minutes or more depending on samples)
Remove from  block and allow to cool
Add 2 mL of Type I water and 2 mL of ~30% ultra high purity grade (Fisher Optima or JT Baker Ultrex II) hydrogen peroxide and replace watchlids and put back on block at 95 C.
Heat the samples until no more bubbles are present (1-2 hours).  Note that you may need to add additional aliquots of hydrogen peroxide and water depending on the nature of the samples.
Remove from block and allow to cool.
Add about 30 mL of Type I water to each vial, swirl and then filter the digest through a quantitative grade ashless filter paper. 
Bring to a final volume of 100 mL using ASTM Type I water.

Now run the samples using 6020A

If you are not analyzing sludge, solid or soil samples, then you may have to use a little bit of HCl.  For aqueous samples I use the following digestion method:

Shake sample and aliquot 50 mL of sample into vial
Add 1000 uL of 1:1 trace metal grade HNO3 and Type I water solution
Add 500 uL of 1:1 Ultra trace metal grade HCl and Type I water solution
Place watchlids on each vial and place samples on block digestion system set to 85 C for 5-6 hours (until samples are reduced by ~70%)
Remove samples from block and allow to cool
Filter samples using quantitative grade ashless filter papers and then bring to a final volume of 50 mL using Tye I water.

The key here is to use ULTRA trace metal grade HCl and not standard trace metal grade HCl.  I know that it is a lot more expensive, but it makes all the difference, especially is you have an ICP-MS that can only run in standard mode.

What concentration are you acheive? I use 0.5% HCl for aqueous digestion and obtain great results for Cr down to 5ppb. The correction for Cl and O can reduce accuracy on the low end. Make sure your range is not to big i.e I calibrate with a blank, 5ppb, 20ppb, 50ppb and 100ppb. If you calibrate too high you will give up accuracy at the low end.

We calibrate from 0.1 ppb to 200 ppb and report Cr at 1 ppb.  It can be extremely difficult at times, but maybe we should look at calibrating much closer to our RL's.  Thank for the pointer riverbrat.  Our concentration for HNO3 is 2% (v/v) and HCl is 1% (v/v).  We should look at going to 1%/0.5% respectively.  Does anyone see excessive carryover for Tl and Mo?  I look forward to hearing from all of you.

My calibration curve is:
0.5 ppb
10 ppb
50 ppb
100 ppb

This curve has always worked well for me for most elements.

People will think I'm crazy for doing this, but we use 10 ml of concentrated HCl for our solid sample digestions (following 3050B for flame digestions).  It is the last step of our digestion procedure in between adding peroxide  and pulling the samples out of the hotblock.  We filter and dilute the digestate up to 100 ml with deionized water.  Given the nature of our samples, we have the capability of diluting each digestate 1/5.  So far we have not had any problems whatsoever with any of our elements (including Cr).  The reason I did this was because my Antimony and Silver recoveries were low (almost zero for Sb and around 20% or so for Ag).  We passed several ampules and blind studies without any difficulties.  We are using an ELAN 9000 ICP-MS instrument without DRC or collision cell correction.  Our calibration curve is 1 ppb, 10 ppb, 100 ppb, 200 ppb, 500 ppb.  Again, we never ever had any problems performing analyses this way. 

Ha...that is great! Most methods are performance based so you can just add deviations to your SOPs. Most chemists get too caught up in the detains and ignore what actually works.