Higher production labs get a hugh productivity increase by using an AA finish for gold values rather than gravimetric finish. However, the calibration process is much move involved than most people initially realize.
You cannot just use the stock calibration solutions to make standards as this will produce a bias in almost all results.
One way to overcome this problem is by using a metallic gold standard which travels through the assay process. The method is something like this:
1) Weigh a piece of pure gold on the microbalance. You can record the weight by wrapping the gold in a piece of tape and writing the weight on the tape. This piece of gold should be approximately the correct weight to match your liquid AA standard used for calibration.
2) Assay this piece of gold along with your other assays. Make sure and use a new crucible so there is less chance of contamination.
3) After digesting the dore beads in aqua regia (I will discuss this further in another thread) use the digested gold piece to check the value of the liquid standard. You can note the "actual" value of the liquid standard and use it for further calibration. Example: if your 0.5 ppm standard reads 0.48 ppm against the gold piece, use the value of 0.48 ppm to standardize.
4) Make sure and have at least 2 gold pieces (one of them could be a flyer).
5) You should have a gold piece periodically (every 48 assays?).
6) You can generate the gold pieces from gravimetric finish assays.
You cannot just use the stock calibration solutions to make standards as this will produce a bias in almost all results.
One way to overcome this problem is by using a metallic gold standard which travels through the assay process. The method is something like this:
1) Weigh a piece of pure gold on the microbalance. You can record the weight by wrapping the gold in a piece of tape and writing the weight on the tape. This piece of gold should be approximately the correct weight to match your liquid AA standard used for calibration.
2) Assay this piece of gold along with your other assays. Make sure and use a new crucible so there is less chance of contamination.
3) After digesting the dore beads in aqua regia (I will discuss this further in another thread) use the digested gold piece to check the value of the liquid standard. You can note the "actual" value of the liquid standard and use it for further calibration. Example: if your 0.5 ppm standard reads 0.48 ppm against the gold piece, use the value of 0.48 ppm to standardize.
4) Make sure and have at least 2 gold pieces (one of them could be a flyer).
5) You should have a gold piece periodically (every 48 assays?).
6) You can generate the gold pieces from gravimetric finish assays.