Nutrient Analysis Using Colorimetry

Torrey LindboSWRP, PSU-ESR

Safety Equipment

GlovesGogglesMaterial Safety Data Sheets

Other Considerations: Alcohol Hand Wash Table or Tarp (spill prevention)

Colorimetry

Colorimetry: method for quantifying the concentration of a chemical constituent by analyzing change in color Based on color change for standard

solutions of known concentration Light usually filtered to specific

wavelength

Visible Light Spectrum = ROYGBIV Red ~ 700 nm Violet ~ 400 nm

Colorimeter

Color change measured using colorimeterColorimeter determines amount of transmitted light absorbed by sample

Transmitted Light Detector

Light sourceTungsten Lamp

Lens Sample VialFilter

Light Paths

Refracted

Absorbed

Transmitted

Reflected

Absorbance (A) is logarithmically related to transmittance (T)A = - log T

Beer’s Law

A = εLcWhere,A = absorbanceε = absorptivity; experimentally

derived constant for each substrateL = path length of light through samplec = concentration of substance in

solution

Beer’s Law

Concentration (c)

A = εLc

Absorbance (A)

Slope = εL

Hach DR/850 Colorimeter

Has pre-programmed filters and calibration curvesCap doubles as light coverSample color change compared to “blank” – what ZERO looks likeBlank may be stream sample with no reagent added, or it may be deionized water with reagent

7 9

4 5

1

I/0

2

8

6

3

0 READ

DR/850 Colorimeter

TIMER Enter

Hach DR/700 Colorimeter

Each test requires a “module” that needs to be turned to the correct program number. Example: Nitrate module = 50.01 Low range procedure = program 50.07.1 High range procedure = program 50.05.1

Need to perform Lamp Intensity AdjustmentUse film canister as light cover

“Zeroing” the Colorimeter

Concentration (c)

Beer’s LawA = εLc

c = εL / A

A

Slope = εL(constant)

SampleAbsorbance

BlankAbsorbance

Other DR/850 Features

Timer Beeps when reaction periods for tests are

over Limits colorimeter use; no other tests can

be run while timer is running

Store Can store up to 99 readings

Download Hach makes infrared computer interface

Hach Glassware

Cleaning is crucial first stepAcid Washing Soak in ~10% acid bath Choose acid depending upon

tests (i.e., don’t use nitric acid if you’re testing for nitrate)

Rinse thoroughly with DI water Etching on Hach glassware

may erode after long soaks10 mL

20 mL

25 mL

Colorimetric Analyses

Soluble Reactive Phosphorus (SRP)Total PhosphorusAmmonia NitrogenNitrate NitrogenChlorine

Phosphorus

Clean glassware crucialSRP test is quick and easy (2 minute reaction time) – good for flexibility with colorimeter sharingTotal Phosphorus requires digestion Hot plate Strong Acid and Base Requires fume hood This test should be run in the lab

Phosphorus

Equipment Needed 3-5 vials for samples + 1 for blank PhosVer3 reagent powder pillows Non-toxic waste container DR/850 Colorimeter

Procedure Overview 10 mL sample + reagent in each sample 10 mL sample and no reagent for blank Shake and wait 2 minutes

The Meniscus

Meniscus: the curved, lens-like surface of water in glassGlass has a negative charge that attracts the positive H from waterRead volumes from bottom of meniscus

10 mL

Nitrate Nitrogen

Vigorous Shaking2 Procedures: Low (< 0.5 mg/L) and High (0.6 – 20 mg/L) RangeToxic waste – Cadmium (heavy metal) used to reduce nitrateTime requirement (i.e., Low Range takes 20+ mins.) Shake 3 min, wait 2, add reagent 2,

shake, wait 15 min.

Low Range Nitrate Procedure

Equipment Needed: 6-10 vials for samples + 1 for blank NitraVer6 and NitriVer3 reagent

powder pillows

Low Range Procedure: 30 mL sample + NitraVer6 in each

sample (shake 3 mins) 10 mL treated sample + NitriVer3 10 mL sample and no reagent for

blank

High Range Nitrate Procedure

Equipment Needed: 3-5 vials for samples + 1 for blank NitraVer5 reagent powder pillows Toxic waste container

High Range Procedure: 10 mL sample + NitraVer5 in each

sample 10 mL sample and no reagent for blank

Ammonia Nitrogen

Timing – measure each sample immediately after reaction time Time table; stagger reagent addition

to each vial by 1 minute

Blank is deionized water + reagents (only need 1 blank) DI water source must be PURE

Ammonia Nitrogen

Equipment Needed: 3-5 vials for samples + 1 for blank Ammonia Salicylate and Ammonia

Cyanurate reagent powder pillows Toxic waste container

Procedure Overview: 10 mL sample + reagents in each

sample 10 mL DI water + reagents for blank

Chlorine

Sample needs to be collected in glassBest measured immediately in field

Chlorine

Equipment Needed 3-5 vials for samples + 1 for blank DPD chlorine reagent powder pillows Non-toxic waste container DR/850 Colorimeter

Procedure Overview 10 mL sample + reagent in each sample 10 mL sample and no reagent for blank Shake and wait 2 minutes

Waste Management

Appendix A, pages 1-3Collection Plastic Bottles work fine Clearly Labeled Non-Toxic, Ammonia and Nitrate all

should be stored separately

Organization “Callister Carrier” = cardboard 6-pack

container

Non Toxic Waste

DO, pH, Alkalinity, SRP, ChlorineDisposal Neutralize pH (baking soda) Pour down drain with excess water

Ammonia Waste

Several constituents of concern Maximum concentrations in manual

No way to safely reduce volumeMust be disposed of at a hazardous waste facility METRO or PSU Waste Consortium Talk to your local waste handler,

administrator or local college for other disposal sites

Nitrate Waste

Cadmium is only constituent of concernManual has instructions for precipitating heavy metalsMost teachers bring entire waste container to hazardous waste facility