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91

The Technical Working Group for 3D Toolmark Technologies (TWG3D2T) is soliciting public comments on their draft “Best practice guide for the calibration and quality control of 3D surface topography measurement instruments used for Virtual Comparison Microscopy (VCM) of toolmarks.” Please review the document and provide any comments you may have. All comments will be adjudicated by the Quality Assurance task group after the public comment period has closed. Thanks!

Please visit www.twg3d2t.org to download the document and public comment form if you’re interested. The public comment period will start on November 1, 2023 and end on November 30, 2023. For more information or help with accessing the files, please email alan.zheng@nist.gov.
92
Technical Assistance / Re: GSR Nitrite Swab control issues
« Last post by Holli Worden on October 26, 2023, 01:20:59 PM »
Travis, I have also noticed the weakness of the pre-prepared nitrite swabs over time. Ours are stored in a plastic container, such as one for pencils/pens. I think others suggestions make sense as far are just wetting a swab with nitrite solution day of.
93
Technical Assistance / Re: GSR Nitrite Swab control issues
« Last post by Chris Gunsolley on October 26, 2023, 09:54:55 AM »
We've seen the same thing with regard to nitrite swabs not lasting forever and, since we rarely even perform this testing, prepare them fresh for each exam.  Another thing of note... we had a jar of alpha-napthol that was decades old that, while a preparation of sheets using it passed Q.C. tests (using nitrite swabs), it performed poorly in casework.  That is, its sensitivity was diminished.  Because the nitrite swabs were *loaded* with nitrite, it seemed fine but even processing test fired panels produced poor results.  Because of that experience, I think there's some room for improvement regarding the Q.C. process.  Maybe perform a serial dilution of the nitrite swab solution to see that which most closely mimics that seen in casework? Or just use known/test panels as part of the actual Q.C. process?
94
Technical Assistance / Re: GSR Nitrite Swab control issues
« Last post by Stacey Phetteplace on October 26, 2023, 07:44:33 AM »
Nice, Evan, but he still needs nitrite test swabs for controls :D  We recently validated QF and I love it!


Our SOP states to follow the procedure you have for storing dried swabs, but all of us have all switched to making fresh the day of use for that very reason. One of our examiners published our method validation and he describes the limitations of prepared & stored versus prepared fresh.

One of the observations he noted was the dried swabs took longer to produce a positive result (30-45 seconds versus 10 second with a freshly made swab).




95
Technical Assistance / Re: GSR Nitrite Swab control issues
« Last post by Evan Thompson on October 25, 2023, 10:38:51 PM »
Consider Quantofix from CTL scientific.  Certified, stable paper, for the detection of nitrites.


https://www.ctlscientific.com/cgi/search.cgi
96
Technical Assistance / Re: GSR Nitrite Swab control issues
« Last post by Justine Kreso on October 25, 2023, 03:10:48 PM »
We have not had that issue, but they are stored in a bag, in a box, in a drawer.


We do put a year expiration on them, however so they never sit longer than that.


It could also be your photo paper potentially?  Have you tried a new batch of photo paper?
97
Technical Assistance / Re: GSR Nitrite Swab control issues
« Last post by Julie Knapp on October 25, 2023, 02:51:25 PM »
I have never really like the swabs because I have found them to be not as reactive over time, but never had a problem with the solution being kept and just using it on clean swabs as I need it.  I have never tested that though - just personal observation. 
98
Technical Assistance / Re: GSR Nitrite Swab control issues
« Last post by Greg Laskowski on October 25, 2023, 02:50:10 PM »
I ran into that problem years ago.  My solution was to seal the swabs in Kapak and store them at laboratory temperature.
99
Technical Assistance / Re: GSR Nitrite Swab control issues
« Last post by Travis Melland on October 25, 2023, 02:26:40 PM »
Doug, yeah we have been forced to make a new batch basically every time we need to perform the test. Which we don't get a frequent amount of requests, so they tend to sit. The new batches always work...for a while?


Julie, we may have to look into changing out method/SOPs and keep the solution. Has your lab found that keeping nitrite swabs over time tended to lessen the potency? Or have you always made fresh swabs prior to testing?


Thank you both for a response!
100
Technical Assistance / Re: GSR Nitrite Swab control issues
« Last post by Julie Knapp on October 25, 2023, 01:18:24 PM »
I recommend not making/storing the swabs, but making and storing the solution of Sodium Nitrite.  When you are doing the case, just pour some into a small beaker and dip your clean swabs into the solution, mark your corners, or whatever your procedure is...etc. 
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