Category Archives: Lab

Chickens and the Unbroken Chain of Calibration

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A recent discussion in the LinkedIn group, Metrology & Test Measurement, on the “unbroken chain of calibration” has driven me to hone in on my personal understanding of measurement uncertainty. I am ashamed to say that I know virtually nothing (0 ±0.0031415929) about calibration despite having worked as an electronics technician in the ’90’s. My excuse is that ISO 9xxx only hit the repair floor in the ’90’s. (Well, that’s why it was called ISO 9000.)  But the National Bureau of Standards (NBS), which predates the National Institute of Standards and Technology (N.I.S.T.) by 87 years, has been around since 1901.

logo of National Institute of Standards and Te...

Logo of National Institute of Standards and Technology (Photo credit: Wikipedia)

And the NBS was predated by the International Bureau of Weight and Measures (BIPM in French). In any case, I’m not quite sure how to connect ISO 9xxx with calibration. It must come into it somewhere. All I remember was what kind of shoes to wear and grounding rules. I guess you could say that my uncertainty around these topics is not measurable or traceable!

How do we arrive at an unbroken chain when it comes to metrology? Let’s go to the start of the chain. We will use N.I.S.T. for discussion purposes but really it applies to any of the international organizations that set standards for metrology.

  1. We start with a reference point. This is a universally known measurement value of a particular measurable event. For example, the melting point of ice. (N.I.S.T uses a thermometer as an example on their website.)
  2. This reference is used as a standard by N.I.S.T. I assume that means that a correctly calibrated thermometer will measure – well, I’m not sure exactly what it will measure. It is close to 0 degrees Centigrade. There are various factors that can determine the temperature, such as atmospheric pressure and the purity of the actual water that the ice is composed of. The point is – a standard is set that will be used to begin the chain. This standard is the reference that all other measurements down the chain are going to be traced back to.
  3. Going down the chain, we compare the measurements of the next instrument to be checked against the N.I.S.T. measurement , then document the differences in the results. Depending on the conditions of the measurement, we can make the necessary adjustments needed to arrive at the most accurate measurement but can never be absolutely certain of a true value. Like much of life, we do our best. The “best” is a range of values that approximates the value of the N.I.S.T standard. This range of values is the range of uncertainty. You know that somewhere in this range, lies the true value and if you calibrate an instrument to show results within this range, you should be able to certify your instrument as calibrated according to the standard. If along the way, you lose the reference, your instrument cannot be considered to be calibrated according to the N.I.S.T. standard.

I know! This is a rather crude, simplistic explanation of the process. I “did my best”!

I got further confused after my visit to the supermarket today. They had fresh whole chickens on sale with a limit of 6 Kg per customer. For the customer’s convenience, a scale was placed near the chickens, allowing the customer to verify the total weight of his selection. The trick was to see whether you could get four chickens for 6 Kg, despite the average weight of 1.55 Kg per chicken. You do the math now. It seemed a shame to buy only three chickens and thus not take full advantage of this special sale. Four chickens were over 6 Kg and three were under by quite a bit.


Photo credit: P. Naumann

Well, I came pretty close. I managed to find two smaller looking birds and my total weight on the scale (when last was it calibrated, I wonder?) was 6.14 Kg. I went over to the poultry supervisor and told him that I was a little over the maximum weight allowed, and with a smile on his face, he said, “That’s fine.”

<!–Here’s the moral of my little story–>: The more accurate our measurements are, the more honest we can be in our relationships with customers, clients, and other businesses. However, sometimes in life a little uncertainty goes a long way when it comes to give-and-take with others. <!–End of moralizing–>

Of interest:


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Where Can I Find a Clintec Automix 3+3 Compounder?

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Probably not at a Walmart store.

And why would I want a Clintec Automix Compounder?

Well, personally, I don’t actually need one – but – according to the stats on Used-Line, quite a few of our users do.

Before we look at the statistics, let’s try to describe what a Clintec Automix Compounder is. It is not a gas chromotograph, which was discussed in our most recent blog about the Agilent 5975. After doing your compounding thing with the Clintec Automix, you could then use the Agilent 5975 to separate and analyze what you compounded, but why would you want do to that? You would be reversing the process, wouldn’t you?

The Clintec Automix Compounder is a parenteral nutrient compounding system. If I understand this correctly, parenteral nutrient compounds are compounds that are administered by circumventing the digestive system. The compound is often fed intravenously.

Saline solution for IV

Saline solution for IV (Photo credit: Wikipedia)

Most of us are familiar with IV (intravenous) lines, but are less familiar with the processing of the mixtures that are inserted into the IV lines. This is where  compounding systems come into the picture. The Clintec Automix 3+3 Compounder is one such system. It is an automated system, and it can handle the processing of large volume ingredients, such as water and glucose.

Now let’s move on to the statistics.

Last month, July 2013, the terms, “clintec automix” were used in Used-Line searches 199 times. These two terms used together took up position number three in the top 100 search terms entered by visitors. Similarly, Google Analytics revealed that “clintex automix” was used in 72 Unique Searches on Used-Line, placing the terms in position number one for the month of July.

July 2013 Stats for search term, "Clintec + Automix"

AnalyticsCountUnique SearchPosition
Google 721

So where can you find a Clintec Automix 3+3 Compounder? On Used-Line, of course!

If you are in the market for a Clintex Automix compounder (you may be one of the 72 unique searchers who contributed to our July statistics), Toronto Surplus & Scientific has listed a Clintec 2M8286 Automix pump module on Used-Line. Toronto Surplus & Scientific Inc. has provided the following specifications on their own website:

  • Delivery Volume Range: 10 – 5000 ml
  • Specific Gravity Range: 0.50 – 3.00
  • Dimensions: 20.5″ W x 12.5″ D x 21.5″ H

If the pump module is not specifically what you want, you can post your own want list in the Used-Line Wanted System, which sends out a daily list of wanted items to all registered dealers. We will be talking about the ULWS soon! Watch for it!

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Agilent 5975 Gas Chromatograph Analyzes Vegemite Yeast Extract

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I know this is a cliche, but either you love it or you hate it. We’re talking about Vegemite. Actually, I’ve never tasted Vegemite, but I love to eat Marmite, a British and South African almost-clone of the Australian Vegemite. The rest of my family hates it. How can you kill a piece of toast with that extremely salty, hard-to-smear, strong smelling stuff, they ask?! In answer, I tell them that the trick is to spread a generous helping of butter on your toast, followed by a thin layer of Marmite. (If you’re avoiding either fat or salt, forget about it.)

But there is no need to convert the converted and I doubt I’ll be able to sway those diehard Marmite/Vegemite objectors.

I have to “import” Marmite from South Africa, where it is kosher. I hope my cousin does not have to pay for the extra weight of her luggage when she brings me my little jars of Marmite, but the good news is that it lasts FOREVER, so she does not have to satisfy my yeast extract fix too often.

Here are two of my current jars of Marmite.


Marmite in my kitchen.









So where does Agilent come into this culinary discussion? Well, I don’t know if the recipe for Vegemite has been as closely guarded a secret as the recipe for Coca Cola, but Renée Webster, an Australian pursuing her doctorate, has analyzed the contents of Vegemite to find the distinct chemical compounds that produce the unique odor of the much-loved (or much-rejected) yeast extract. The Agilent 5975 gas chromatograph played a major role in the Vegemite analysis by breaking up this smelly (but delicious) mass that smells distinctly of – well – Vegemite – into more than 35 compounds that smell of everyday items such as flowers, wine, and leather, and which seem to have no connection to the smell of the yeast extract itself. I’m not sure if I really needed to know what Vegemite (and possibly Marmite) is composed of. You would not normally catch me spreading anything that smells of wax – or rancid fat (yes, rancid fat really is one of the detected odors) – or sweat – on my toast!

Renée Webster conducted her analysis in three stages:

  1. Sampling: Using a kitchen knife, a Solid Phase Microextraction (SPME) sampler, and a lab oven. I wonder if she regrets sacrificing to science the sample of Vegemite she needed for her experiment – never to be spread on a piece of toast!
  2. Separation: Using an Agilent 5975 GC/MSD (gas chromatograph with mass spectrometer) to separate the Vegemite compound into its multiple chemical components for individual analysis. The 5975 is built with 7890 GC technology. The gas chromatograph is responsible for the separation part of the process.
  3. Analysis: Using the mass spectrometer that, together with the included software, analyzes the detected chemicals. Hmm, couldn’t she simply use her olfactory system, that is, her nose, instead of the mass spec? Well, that might not be ideal if you want exact measurements, percentages, and specific odor descriptions.

According to the article, Agilent Helps Uncover Vegemite Mystique, on the Agilent News Hub, the GC performs the separation, and the mass spec does all the detection work. I’m guessing that with over 35 compounds and odors to detect, the 5975 GC/MSD is ideal because it allows for quick column changing; thus speeding up the detection and analysis process.

Here are a few of the top chemicals that were found in Vegemite, including their accompanying odors.

Vegemite Compound Analysis (Top three by percentage)

Percentage of TotalChemical CompoundAssociated Odor
43.8ethyl decanoatefruit, oil, sweet, wax
16.6ethyl trans-4-decenoatewax, leather, pear
12.5octanoic acid, ethyl esterfruity, fatty, floral, green, menthol, anise

To see the complete results of the separations and each component’s odor, you can read the Guardian’s Australia FoodBlog on the Vegemite analysis. As well, for details on the process Renée used to conduct her analysis, view her own blog.

If you are now inspired by the 5975’s work on Vegemite, take a look at the list of 5975’s currently available on Used-Line.

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