As aquarists, we are masters of artificial environments we have created, and maintenance of water quality should be more than just a passing notion – it is everything to our captive animals. Their very existence depends upon your skills as the manager of their life support system and your ability to prevent or troubleshoot water quality issues. Your decisions should be informed ones, and to this end, devices to analyze various water parameters are important.
Various test ‘kits’ are available to hobbyists, and most deliver acceptable results. However, interpretation of results based on color perception of the human eye can be difficult, and are subject to observer’s bias. It is here that colorimeter instruments excel – results are based on absorption of light. If proper laboratory technique and protocol are followed, instruments will deliver sound and repeatable results.
Recently, while looking through a catalog from a pet supply company, I noticed instruments capable of analyzing for single-point parameters (such as nitrate and phosphorus). These were colorimeters – instruments capable of measuring changes in transmission (or absorption) of light, as caused by the addition of a reagent to a sample gathered from an aquarium (or other body of water. See ‘Theory of Operation’ below).
These meters, individually, were about $200 each. If a single-point colorimeter meet your needs, then these instruments will likely be quite suitable. However, there are options available that offer advantages to serious hobbyists and professional aquarist. This month, the LaMotte Smart 2 colorimeter is the focus of review.
In 2002, LaMotte Company (Chestertown, MD) introduced their Smart 2 colorimeter using LED (light-emitting diode) and microprocessor technologies. By replacing expensive optical components with LEDs, LaMotte is making general purpose water analyses relatively affordable and regulates full-blown spectrometers to critical applications usually found in medical or research laboratories. The beauty of LED colorimeters, besides their reduced cost, is ease of transport for field research as well as multi-parameter analyses capabilities.
The Smart 2 colorimeter comes factory calibrated for testing of 65 chemical or physical parameters (LaMotte’s ‘official’ list describes 61 parameters, but absorbance capabilities for each of the 4 LED lamps makes 65). Various ranges of parameters (such as high-range, or low-range, nitrate) expand the parameter list to 100. The user can also program in 10 custom tests (such as nitrate corrected for interference of chlorides).
I’ll make the assumption that most hobbyists are interested in testing for these parameters: Ammonia, nitrite, nitrate, phosphorus and possibly pH, ozone, iodine and copper. The LaMotte Smart 2 meter can perform all of these as well as a few others. Table 1 is a partial list of tests.
|Suitable for seawater with dilution|
|Requires optional adapter, Order Code 5-0086|
|Works with seawater, but better methods are available|
|Alkalinity ¹||0-200||X||Unit Dose Vial ²|
|Aluminum||0.00-0.30||X||X||Eriochrome Cyanine R|
|Ammonia Nitrogen, Low Range||0.00-1.00||X||X||Salicylate|
|Ammonia Nitrogen, High Range||0.00-4.00||X||X||Nesslerization|
|Bromine Low Range||0.00-9.00||X||X||DPD Tablets|
|Bromine||0.00-22.00||X||X||Unit Dose Vial|
|Chlorine (Liquid DPD Method)||0.00-4.00||X||X||DPD|
|Color||0-1000||X||X||Platinum Cobalt Units|
|Copper, Low Range||0.00-3.50||X||X||Bicinchoninic Acid|
|Dissolved Oxygen (DO)||0.0-12.0||X||Winkler Colorimetric|
|Hardness, Total: Sum Ca & Mg ³||10-500||X||Unit Dose Vial|
|Hydrogen Peroxide, Low Range||0.00-1.50||X||DPD Tablets and KI|
|Manganese, Low Range||0.00-0.70||X||PAN|
|Manganese, High Range||0.0-15.0||X||Periodate|
|Nitrate, as Nitrogen Low Range||0.00-3.00||X||X||Cadmium Reduction|
|Nitrite, as Nitrogen Low Range||0.00-0.80||X||X||Diazotization|
|Ozone, Low Range||0.00-0.40||X||Indigo Trisulfonate|
|pH (Chlorphenol Red)||5.0-7.0||X||X||Colorimetric|
|pH (Phenol Red)||6.6-8.4||X||X||Colorimetric|
|pH (Thymol Blue)||8.0-9.5||X||X||Colorimetric|
|Phosphate, Low Range||0.00-3.00||X||X||Ascorbic Acid Reduction|
|Phosphorus, Total Low Range||0.00-3.50||X||X||Ascorbic Acid & Persulfate Digestion|
|Silica, Low Range||0.00-2.50||X||X||Heteropoly Blue|
|Silica, High Range||0-50||X||X||Silicomolybdate|
|Sulfide, Low Range||0.00-1.00||X||Methylene Blue|
|Zinc, Low Range||0.00-3.00||X||Zincon|
Colorimeters – Theory of Operation
Colorimeters are able to determine concentrations of various substances by monitoring absorbance of certain wavelengths of light, and colorimetry is simply a ‘measure of color’. Colorimeters exploit the ability of colored sample water to absorb certain light wavelengths. For example, if we add DPD (N,N-Diethyl-p-Phenylenediamine) to a water sample containing chlorine, a red color develops. Since water colored red absorbs green light efficiently, a comparison of absorption of green light by the red sample to the absorption of green light through a clear ‘blank’ sample allows for estimation of chlorine concentration when compared to an absorption curve (don’t worry, LaMotte has all this programmed into the instrument, and a few keystrokes and ‘cookbook’ chemistry allows rapid determination of a number of elements of interest to an aquarist).
The Smart2 colorimeter is easy to use. Once a 9V battery is installed (or when the included power supply is attached), the instrument is ready to go. However, reagents are not included and must be purchased separately.
An instruction manual is included and provides comments on proper use and care of the instrument as well as directions for every chemical test. The directions are well written and understandable – only a general knowledge of chemistry is required. It would be helpful to have rudimentary laboratory equipment available, such as a graduated cylinder and/ or pipette. In their absence, it is possible to use a measuring cup and liquid medicine measure (a small graduated cylinder used to measure and deliver accurate doses, and found in any well stocked drug store. Make sure you devote these items to your laboratory use only!). Since some reagents can be harmful (or even fatal) if ingested, it is critically important to follow instructions carefully and have a healthy respect for chemicals (if you have a reef aquarium, you probably have this respect already – you’re already dealing with lots of salts and metals that can harm you). I don’t mean to beleaguer this point. Just accurately assess your needs and skills when considering the purchase of any laboratory instrument.
I have not used all testing reagents, and have no need to, so I can comment on only a few.
Testing chemicals I have used are liquids (in dropper bottles) or powders (delivered with a small measuring spoon). These are added to a 10 milliliter sample contained within a glass vial, or cuvette (four cuvettes are included with the colorimeter).
The instruction manual provides guidance on sample collection and proper storage if the sample can not be analyzed immediately (some such as pH and dissolved oxygen – this particular test applicable to freshwater samples only – and other dissolved gasses must be analyzed immediately). Others can be stored for various lengths of time if the samples are ‘fixed’ (usually by adding an acid).
Once the meter is directed by the user to perform a certain test, a vial containing the ‘blank’ sample (one without reactive reagents) is placed within the Smart 2 meter and absorbance is determined (an automatic wavelength function determines which LED to use. LED outputs are at 430nm, 520nm, 570nm & 620nm).
Reagents are added to the sample, and after a prescribed reaction time, the operator directs the meter, via a couple of keystrokes, to perform an analysis. Within seconds, the meter displays the result. An internal data logger can store up to 350 test results for later review (or download to a computer – Windows-based only – using a RS232 port and optional Smart Link 2 software).
There are several optional items you may want to consider when making your purchase. The Smart2 colorimeter does not come with a carrying case. These items are essentially all profit for a company. Consider buying a case elsewhere (Lowe’s home improvement stores carry a large, padded case made of aluminum for about $30.)
There are a couple of items that must be purchased from LaMotte, such as adapters (such as the UVD adapter, used in some alkalinity, chlorine, bromine, copper and other tests).
As mentioned earlier, the Smart Link 2 software is necessary to download information from the data logger to a computer (although manual data entry is certainly possible).
Consider purchase of extra test vials (4 are supplied). These are handy to have if you’re doing multiple tests simultaneously, want to devote vials to particular tests, or have butterfingers (like me) or somehow manage to break lab glassware on a regular basis.
As with any equipment, the LaMotte Smart 2 colorimeter has its strong and weak points.
I’ll list these along with quick comparative notes on a similar instrument (Hach’s DR 890 colorimeter).
- The price of the Smart 2 meter is as much as $240 less than its competition ($779.10 vs. $1,020.00 for Hach’s DR890 colorimeter. Sources: USABlueBook Lab Catalog #L118 and Hach’s website).
- It is a compact unit, and is smaller and lighter than the DR 890.
- Operates on batteries or 110v (with the included transformer. The DR 890 is battery-operated only).
- Operator entered tests can be named (by using an easy-to-master scrolling function, much like programming a cell phone. The Hach DR 890, or any of the 800 series colorimeters, does not offer this option).
- Low Battery Indication (standard on most battery-operated devices).
- Test sequences can be altered to bundle favorite tests. This naturally minimizes time required to scroll through testing options. This feature is easier to use than Hach’s method of selecting a test, where a Program Number is used to identify a procedure and must be entered.
- Iodine is a programmed test, no conversions needed (the DR 890 I have requires that a chlorine test be performed, and a manual conversion factor is used). Alternatively, the Hach meter can be programmed to test for Iodine, but requires data from a user performed calibration curve, requiring standards of known concentrations.
- The data logger stores 350 points (Hach meters store 99 points).
- A programmable Power Saver function shuts down the instrument after a predetermined length of time.
- Data are time stamped by an internal clock, an important consideration in Good Laboratory Practices (GLP).
- Updates (new test calibrations) can be downloaded as they become available (a special cable is required for a Windows-based computer. Order LaMotte part number Code 1771).
- Instrument complies with CE mark of compliance for electromagnetic compatibility and safety.
- The Smart 2 meter does not have a timer. For the price, this device should have this convenience. An inexpensive kitchen timer can be used instead. (The Hach 800 series colorimeters have timers, and the appropriate time for each step of a test is programmed into memory).
- Oddly, the directions do not mention the impact of seawater chloride content on nitrate analyses. Nitrates will read low if no correction is applied.
- The instrument is not particularly weather proof (the directions implicitly state that condensed moisture must not enter the testing chamber. Compare this to Hach’s waterproof 800 series it can be dropped in water momentarily and still function).
- Reports only one chemical species (such as Nitrate as Nitrogen, or NO3-N, or simply as Nitrate). Conversion to other species is performed manually by the user. (Hach meters allow for a simple keystroke to choose chemical species.)
- LaMotte’s Instruction Manual and website do not specify a temperature operating range.
- Direct transmittance analyses are not programmed into memory.
- And not really a fault of the device – LaMotte’s website is not really friendly in that it doesn’t post prices and does not allow for on-line ordering. Instead you are directed to a local distributor – I hate that! Compare this to Hach’s global website where ordering directly is encouraged.
The major long term operational cost for the Smart 2 meter is the price of reagents. Table 2 compares prices* of LaMotte and Hach reagents.
|**Winkler method, for freshwater only.|
As we can see, in most cases, the cost per test is often lower than that of the competition.
Source: Laboratory catalog #L118, USABlueBook, Gurnee, Illinois.
Reagent Shelf Life
LaMotte reagent containers are labeling with a date of manufacture, though their code obscures this fact. However, this information is readily available on their website:
This site also lists anticipated shelf life of each reagent (generally a year or more).
General Impression and Conclusion
The LaMotte Smart 2 colorimeter is a powerful tool for advanced hobbyists. Many results generated by this instrument are acceptable to the US Environmental Protection Agency. Its accuracy and precision is remarkable for a relatively inexpensive device.
This colorimeter’s low price is evidenced in size and apparent robustness. Although its performance is not hampered by these attributes, it has the look and feel of an instrument made for indoor use, as opposed to the environmental extremes of field work.
My advice is to protect the instrument from the insults associated with a saltwater environment. Keep it clean, dry, and properly stored and it should last for many years.
Also consider that initial purchase price and regent costs are less than those of at least one competitor.
The Smart 2 meter is worthy of your consideration when contemplating the purchase of an analytical colorimeter.
I have made every effort to present accurate and timely information. However, typographical errors can occur, and reagent and instrument specifications are subject to change. I strongly recommend use of the following websites.
For further details on reagents, see: www.LaMotte.com/pages/wawa/smart2/html
For general information, see: www.lamotte.com
Questions? Comments? Reach me at: [email protected]