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Colormetric Sampling

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ObjectivesDescribe colorimetric science Describe common colorimetric detection

devices Describe the process for detection of known

materials Describe the process for detection of

unidentified materials

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Colorimetric Sampling Colorimetric tubes

Detect known and unidentified gases or vapors

Easy method to narrow down an unidentified material to its chemical family

Can tell you how much of a certain material is present if you know the material

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Colorimetric Sampling One of the most important concepts of

colorimetric sampling

They may not be able to tell you what is present

But they can certainly tell you what is not present

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Colorimetric ScienceReagent filled glass

tubes designed to react with specific gases and vapors

Bellows or piston style pump used to draw contaminated air across reagent

If target gas or vapor is present there is a color change to the reagent

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Colorimetric ScienceThey can usually detect a wide variety of

substances.

Most have some cross-sensitivities and will react in much the same fashion as the target material.

Instructions provide cross-sensitivities list.

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Chip SystemIn addition to tubes,

Dräger has a Chip Measurement System (CMS)

Bar coded strips that function much like the colorimetric tubes, but a reader performs analysis of the tube

With the CMS, a reading is given on a LCD screen and does not need interpretation

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Chip SystemCMS

Good that there is no human interpretation

But it is also bad in that there is no human interpretation

Unable to manipulate the CMS chip, as you can a tube

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Detecting of known materialsMost tubes are

designed to read in parts per million

Some are in percent by volume

Some only indicate presence of a material

For some materials there are a variety of sampling ranges available

Always read instructions for tube

You need to know: Number of pump

strokes Color changes Cross sensitivities Special instructions

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Detecting of known materialsCalibrated for a

certain temperature and humidity

Correction factors provided

Use less pump strokes to decrease sensitivity of tube

Use more pump strokes to increase sensitivity of tube

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Detection of unidentified materials

Detection of unidentified materials is not an easy task

Knowledge of colorimetric sampling, chemistry, and street sense is essential

Most manufacturers provide a flow chart when looking for unidentified materials Use a combined system of flow charts, with

several types of detection tools When looking for unidentified materials, you

are not trying to establish levels of the material You are only trying to see what may be present

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$499

$595

Detection of unidentified materials

If you get a hit on a tube, there is no need to continue pumping air across the tube that is a positive

Move onto the next tube in the system

More than one material may be present

Both Dräger and Mine Safety Appliances company allow for multiple tube use

Tubes are preassembled and placed in manifold to draw air across 5 tubes at one time

Detection times extended due to extra tubes that are drawing air 1212

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Multi-Tube Systems

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Street Smart Tips Major key point - Read the Instructions

Cross sensitivities are very useful in identifying a unidentified material

Book of photocopied instructions works much better than 20 sheets

Use additional pump strokes to increase sensitivity of tube

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Street Smart Tips Humidity plays a

major factor in tube response

Most tubes are calibrated for 50 percent humidity

Correction factors can be calculated using the instructions

Atmospheric pressure also plays a role

Each tube has a specific temperature

Age, light, and storage conditions determine accuracy of tubes

Tubes typically have a 2-3 year shelf life

Consistent storage temperatures are best

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Street Smart Tips More than one gas

may be present Remember cross

sensitivities of tubes Know color of tube

you are sampling and the color it should change to

Keep an unbroken tube with you to compare color changes

Some may be very subtle

Water vapor may be released from pump

Not uncommon for a tube to heat up and release visible vapor Some chemical tubes

create a very hot chemical reaction or ignition source

Some tubes release irritating gases

Clear pump with strokes in between tubes

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Summary Colorimetric sampling can be a valuable tool

if instructions are followed

Colorimetric tubes can establish a level of contaminants present

Colorimetric tubes can help identify or at

least classify an unidentified material