All analyzers are not created equal, just as all methods depend on the quality of the analyst more than the quality of the analyzer. The preceding statement is a little known fact.

Years of environmental analysis at environmental laboratories have implanted into the minds of the consumer of methods that all are equal, and competition by price is fair. This price competition has lead to cutbacks in laboratories resulting in a scale down of technician pay and gradual reductions in staff. Laboratory managers have compensated for the staff reductions and “dumbing down” through heavy reliance on automated equipment believed to generate equivalent results regardless of operator skill. Instrument manufacturers have propagated the problem by marketing instrumentation as easy to use with canned methodology. To make matters worse, competition between laboratories and between manufacturers generally comes down to specifications of who is faster or can detect smaller quantities. Quality is always assumed and it is assumed to be equal.

Not all analyzers are equal, and not all analysts are either. The type of instrument purchased for a particular task depends as much on the quality of the analyst as it does on the type of task the instrument will be used for. The more routine the task the simpler the analyzer can be. Some key questions are:

1. How many samples will there be to analyze per day?

2. How many tests are needed per sample?

3. What is the matrix of the samples?

4. What is the skill level required for the analysts?

5. Is sample pretreatment necessary? Will the analyzer pretreat samples?

6. What are the operating costs?

7. Will it meet my detection limit, accuracy, and precision requirements?

Question 7 is asked more often followed by question 6 as a close second. What needs to be asked are questions 1 – 5.

How many samples per day is the number one limiting factor that decides what type of wet chemistry analyzer is used. The next most important, and closely tied, question is the number of tests that will be done per sample. Throughput of the laboratory is limited by the number of tests processed per day. It is, however, very important to be realistic. I have worked at, and visited, numerous laboratories that do not have a handle on the average number of samples processed per day. Without this knowledge an intelligent decision on what analyzer to purchase cannot be made.

The number of samples per day, tests per sample, and variety of samples must be known as well as the degree of analyst skill the laboratory is willing to devote to it. Segmented flow analyzers (SFA) are capable of automating all wet chemistry tests, of high throughput, high accuracy/precision, with very low detection limits. These significant advantages come at a high cost and that cost is the high skill required of the analysts. A multiple channel, efficient, well designed segmented flow analyzer with an experienced user is capable of analyzing up to six tests simultaneously at speeds of 90 samples per hour, or 540 tests per hour. The segmented flow analyzer can automate dilutions, filtrations, digestions, distillations, and many other laboratory operations that are limited only by the imagination and skill of the operator.

Flow injection analyzers (FIA) are a simpler form of SFA and require slightly less operator skill in routine analysis. Flow injection analyzers are well suited for chemical analysis not requiring multiple operations such as in – line sample preparation. They are excellent tools for nutrient analysis and range, or detection limits, are more easily adjusted than by SFA. A multiple channel flow injection analyzer is capable of the same sample throughput as multiple channel SFA instruments, however, FIA tends to use more reagent and require larger sample aliquots that SFA.

Both SFA and FIA instruments limit sample throughput by the number of active channels. Each channel is capable of one test. Tests are analyzed simultaneously after the instruments sampler picks up sample and passes it through chemical reactors where reagents are merged into a flowing stream. Each channel is essentially a detector, and a cartridge that consists of mixing loops, heaters, and reaction zones where the chemical reactions that produce a measurable color takes place.

Discrete analyzers are newcomers to the environmental market. Discrete analyzers are not limited by channels. Chemicals are combined with reagent in discrete sample reaction cuvettes where mixing, incubation, and final color measurement all occurs. The limiting factor on a discrete analyzer is the number of incubated mixing chambers instead of the number of channels. Since there is no tubing, discrete analyzers can perform multiple methods all using the same detector. Discrete analyzers require less analyst training than is required for flow methods.

Choosing the correct analyzer is not as simple as a fad, or buying on cost. What is to be analyzed, the level of operator skill available, and the expected number of tests per day are all important. This article touches briefly on the differences between the major varieties of commercial automated wet chemistry analyzers. The differences go far beyond what is mentioned here. The laboratory should examine both short term and long term needs before making financial commitments.

William Lipps
http://www.oico.com
(979) 690-1375 ext. 230
wlipps@oico.com

One Extraction, One Dilution, One Injection, Automation solutions.
Segmented Flow, Flow Injection, Discrete Analyzers, TOC Analyzers, Sample Introduction, Gas Chromatography, Gel Permeation, Purge & Trap

Expert Methods Consulting
http://www.williamlipps.com

Classical Wet Chemistry, HPLC, IC, GC, GC/MS, SFA, FIA, Discrete, TOC, TOX, UV-VIS, IR, Osmometry, Petroleum, Proximate Analysis, Extractions, Digestions

Author: William Lipps
Article Source: EzineArticles.com
Provided by: Guest blogger