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  • Stephen Biss

BAC Analysis in a Lab Without Bracketing Controls is at Best Qualitative not Quantitative


Purpose:

To obtain an admission that when government scientists conduct quantitative analysis to determine blood alcohol concentration using blood, urine, or serum, they use positive and negative controls.

To obtain an admission from the government scientist that when they conduct such quantitative analysis they use a low control, an expected midpoint control, and a high control.

To obtain an admission from the government scientist that they would never use just one control at 100 mg/100mls.

To obtain an admission from the government scientist that using just one midpoint control would be unacceptable laboratory practice.

To suggest that use of only one mid-point control in a laboratory does not assist in checking linearity.

To suggest that use of only one mid-point control in a laboratory to obtain a quantitative analysis in a laboratory would not be in compliance with ASCLD/LAB accreditation.

To obtain an admission that if the bracketing controls failed then the result is at best qualitative rather than quantitative.

Q. Now I want to ask you, you said before that you do analysis of alcohol and other things, well, alcohol specifically, with respect to blood, urine, serum? A. Yes, that’s correct. I’m a designated analyst. Q. And when you are conducting such an analysis you use positive controls? A. And negative controls, yes. Q. What’s the difference between a positive control and a negative control? A. A negative control is simply a blank. Q. Right. A. So, there’s nothing in it other than internal standard and you’re seeing whether or not that – the procedure that you’ve used has caused contamination of any of the samples or any of the parameters or any of the controls that you’ve been analysing. Q. And the – when you run those kinds of quantitative analysis, and it is quantitative analysis, I take it? A. Yes, it is. Q. Unless of course, you’re unable to report and you – you just give a – a qualitative, detected/not detected, I take it, sometimes? A. Well, not detected means it’s not there, or it’s below the limit of detection. Q. All right. A. A qualitative result would occur if you had a control that failed. So, all samples are run between

controls, and if the positive control on either side passes, then every sample that was analysed between those two samples, would be acceptable and would be reported quantitatively but if you had a positive control that passed and the bracketing one failed... Q. Yes. A. ...then the results reported between those two would be qualitative only. So, it’s be ethanol detected, but not a concentration, if it was, again, above the limit of detection. Q. Then between controls, so you’ve got maybe a low control in relationship to the expected concentration, a high control in relationship to the expected concentration. A. And a midpoint control as well.

Q. Right. A. Right at 80 milligrams of alcohol in 100 millilitres of blood. Q. So, you’ve got three data points to – as part of your measurement? Run those controls with every one of those quantitative analysis? A. That's correct. Q. Not one, not just at 100 milligrams to 100 mils, but at three, right? A. That's correct. Yes. Q. And that’s way – your way of spot checking to make sure that the linearity of the instrument – is called a Hamilton Diluter?

A. Well, the diluter is what you use to put internal standard in, and to do the sample with. Q. Oh, I see. All right. A. Yes. Q. What’s the instrument that you actually use

for a measurement? A. It’s a gas chromatograph. Q. But in using that gas chromatograph, you use a low control, a medium control and a high control? A. Yes. Q. You would never just use one control of 100 milligrams per 100 mils? A. No. Q. Because that would be unacceptable laboratory practice A. That would be unacceptable for the purposes of accreditation for doing alcohol analysis according to ASCLD/LAB, yes. But the parameters for doing breath testing are different. Same restraints aren’t placed on breath testing as it does for laboratory analysis. Q. Is that true around the world? A. You would have to ask the rest of the world. I don’t know. Q. I want to see.... A. I’m familiar with some of the United States where they do testing where they don’t even do calibration checks. They just simply do an air blank and a breath test and an air blank.

#linearity #calibration #accreditation #bestpractices

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