Public Lab Research note


Multi parameter analysis using a DIY Spectrometer

by Frikkie | March 05, 2015 11:30 | 1,980 views | 5 comments | #11655 | 1,980 views | 5 comments | #11655 05 Mar 11:30

Frikkie was awarded the Basic Barnstar by warren for their work in this research note.


A colorimeter, flame photometer and conductivity meter all in one.

A few years back I got fascinated with aquaponic food production. After coming to realize the importance of being able to measure various chemical parameters frequently if one wish to successfully operate an aquaponic system, whether it be on small scale or commercial I started looking into ways of setting up my own water testing laboratory at home. I have a fair background in basic analytical chemistry and have been working in analytical laboratories most of my career. I am well aware of the technologies available to fulfill this need but from my point of view it was way too expensive. After finding this website and a few others I realized that a whole new world of opportunities have opened up to me. I am really thankful for the many contributions many people made over here. I hope that what I have to present here will be useful to others.

Details:

The spectrometer

I build my spectrometer using the very cheap Microsoft LiveCam VX800 with its IR filter removed. It really can’t compete with any of the HD cameras but it is fine for the applications that I will describe here.

Colorimetric Analysis

For colorimetric analysis the spectrometer is setup in the usual way. Light from a LED or other source of light is passed through the sample and the absorbance is measured. I have done some experimentation with the analysis of nitrites in water using the Griess reagent and the analysis of phosphate using the ascorbate- molybdate method. I found the following to be rather important: When developing your own colorimetric methods you must be able to control the intensity of the light source and you should preferably use video software that will give you control over camera’s setting such as gamma, intensity and gain. I power my LED’s from an adjustable power supply and use a simple pot to adjust the intensity. I have also been using Debut video software which is free for personal use.

Flame Emission

The analysis of potassium and sodium is achieved by combining the DIY spectrometer with a DIY nebulizer and gas burner build from mostly hardware store materials. The spectrometer is pointed to the flame and the intensities of spectral lines for potassium and sodium can be measured.

Nebulizer and Burner Design

DIY_NEB___BURNER.jpg

Electrical Conductivity

The DIY electrical conductivity meter is a simple 555 IC oscillator (6.8KHz, 53% cycle) The output pulse is connected in series with a DIY conductivity electrode and an LED. The brightness of the LED will depend on the electrical conductivity of the measured solution. The DIY spectrometer is then used to measure the brightness of the LED. By measuring multiple conductivity standards a calibration cure can be obtained. To obtain some flexibility in term of calibration range I will simply manipulate the supply voltage of the oscillator – for example on low conductivity sample I will supply a higher voltage to the oscillator thus getting the LED to be brighter and so forth.

The Circuit

OSCILLATOR.jpg

Data Handling

To allow quick measurement I created an, excel based tool using some “very basic” visual basic programming (This was rather difficult as I am not a programmer) This tool allow me to quickly perform calibrations and direct measurement of standards and samples. I Hope I can pass this on to anyone who might be able to develop this further for the Public Lab community. It is far from perfect and full of bugs but I believe it can serve as a blueprint of the type of “software” that is needed for DIY analysis. I will explain how to use this tool a video.

The Excel Tool (Don't rename this file, if you do the macro's wont work)

SPECTRA_MEASURE_1.0.xlsm

Example Video's

I apologize for the large file size, I don’t have tool to compress my video’s

(Video1)_Nitrate_calibration_and_analysis.wmv

(Video2)Electrical_conductivity.wmv

(Video3)_Flame_emmision.wmv

General Notes

Linearity of the colorimetric methods is exceptional. With conductivity and flame emission measurements I tend to work with non-linear calibration cures that still display good coloration between standards.

NOTE: IF YOU EVER ATTEMPT TO INVESTIGATE FLAME EMISSION TECHNIQUES YOU DO SO AT YOUR OWN RISK. THIS IS DANGEROUS. I HAVE HAD FLASHBACKS ON MORE THAN ONE OCCASION. ONE RESULTED IN A BROKEN WINDOW. THERE ARE SPECIAL TECHNIQUES IN IGNITING AND ADJUSTING THE FLAME AND I WILL NOT BE DISCUSSING THIS HERE. IF YOU EVER ATTEMPT THIS FIND AN OLD ATOMIC ABSORPTION OR FLAME PHOTOMETER MANUAL AND READ UP ON THIS. ALWAYS HAVE SOME SORT OF A SHIELD BETWEEN THE BURNER AND YOUR SELF.

The inside of my DIY spectrometer

DIY_SPECTROMETER_TOP_VIEW.png

Spectrum of a white LED light. The red dot indicate the “Sweet spot” for nitrite analysis. The pink colour developed in the sample absorbs strongly at this position. This is around 530nm.

WHITE_LED_SPECTRA.png

White LED on a LEGO block. Piece of plastic glued into position in front of the LED to act as a diffuser. LEGO block are great to fix component that must be interchangeable.

WHITE_LED.png

Calibration data for Nitrite Standards

NITRITE_CALIBRATION_DATA.png

Analysis of potassium and sodium in progress.

FLAME_EMISION_SETUP.png

Spectral lines for sodium and potassium

Na___K_EMISION.png

The Nebulizer.

Air flow is supplied from a compressor from a small medical nebulizer. This is a cross flow type, made from a 50ml plastic sample vial. The cross flow tips are 2 disposable 1ml pipette tips. The airflow from the horizontal tip passing over the vertical tip (Sample entry) provides suction on this tip and therefor no sample pump is needed. A small size tubing for sample introduction is glued in to the vertical tip

DIY_NEBULIZER.png

Nebulizer producing a fine mist.

NEBULIZER.png

The burner was made from standard pluming fittings and a thick walled aluminium tube.

BURNER.png

Burner Flame

ADJUSTED_FLAME.png

Analysis data of sodium in my tap water. Non-linear curve

SODIUM_IN_TAP_WATER_DATA.png

Oscillator circuit for conductivity measurements

OSCILLATOR_CIRCUIT.png

Improvised conductivity electrode

DIY_EC_ELECTRODE.png

Untitled.png

In Future I will be experimenting on the colorimetric analysis of Ammonia, Nitrate and Turbidimetric methods for Sulphate, Chloride and Calcium.


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5 Comments

For anyone who wants to try out the excel tool, here is the video’s for the recordings I made for the colorimetric nitrite analysis, the EC and flame emission experiments. The Video name’s indicate the sequence in which I recorded the standards and samples. The flame emission and colorimetric analysis works best with the recording playing when it is being analysed, but you will have to have, careful timing to start the measurement only when the spectra for a given sample appears. If you select too many replicates and a too large measurement area the analysis might be slow and therefor the video will play into the next sample before the given sample is completely analysed.

EC_LED_intensities(DI-water)(75ppm)(150ppm)(224ppm)_(tapwater).wmv

Nitrite(Blank)(2ppm)(4ppm)(6ppm)(8ppm)(10ppm)(Blank).wmv

Sodium_and_Potassium(BLANK)(10ppm)(20ppm)(40ppm)(50ppm)(tapwater).wmv

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This is wicked Stuff! Thanks for sharing!

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Just noticed video1's name show nitrate. Its meant to be nitrite, sorry about that.

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This is very interesting. I am also working towards this kind of analysis, and especially open source accessible, whether fabrication or software/knowledge. Your work is a great step in this direction.

I am a retired chemist of various experience, but a keen sense and desire to measure if it is of use! In this context I a an active volunteer at aquaponicslab.org

working within

incredibleaquagarden.co uk

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Very inspiring nice work!!!

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