Innovations in Metals Digestions Article
Monday, 29 January 2018 07:35

Check out an article by our very own David Smith on the many innovative products for metals digestions that Environmental Express has to offer. These products help make metals digestions safer, more efficient, more accurate, and save you valuable time and money.

You can read the article in Labcompare.

ProWeigh® filters – A Novel Approach to Solids Testing

Standard Methods for the Examination of Water and Wastewater requires that the 1.5 µm, glass fiber filter used for solids determinations be prepared by rinsing with distilled or deionized water, oven drying, cooling, and then weighing to the nearest 0.1 milligram. ProWeigh® filters. a product designed to eliminate the labor and time involved in the preparation of the filter, meet all the method requirements found in Standard Methods 2540D and 2540E.

This product is novel in that it is simply a machine-produced duplication of the tasks necessary for Total Suspended Solids (TSS) testing, and not a new test method. Since the product is a replication of present laboratory efforts, only routine blank testing is required and no equivalency testing needs to be done. ProWeigh® meets all of the EPA requirements for a TSS filter, thereby meeting with EPA approval.


ProWeigh® filters are laser cut to ensure accuracy and smooth edges. Traditionally, filters have been cut using a click press. This can fray the filter material which can be lost during testing, thereby affecting the final weight. The 1.5µm, borosilicate glass fiber filters are vacuum rinsed with three aliquots of deionized water, which removes any loose fibers to provide consistent blanks. After washing, the filters are oven dried at 105°C for 90 minutes in a horizontal flow mechanical convection oven, and then transferred to a desiccating cabinet to cool for 24 hours. After preparation, the filters are weighed robotically to the nearest 0.1 mg using a certified, computer-interfaced balance. Each filter is placed in an aluminum dish that has the weight of the filter and the filter identification number printed on a heat-resistant Mylar® label which are automatically affixed to the aluminum planchet. As a continuing quality check, 8 percent of all filters are redried and reweighed, assuring filter weight stability and reproducibility.


To perform a TSS sample evaluation, the analyst takes the filter from its aluminum dish and places it in a vacuum filtration apparatus. The sample is filtered across the ProWeigh® and the filter is then returned to its aluminum weigh pan. The pan is placed in a 105°C oven for one hour and then cooled to balance temperature in a desiccator. The filter is weighed and then returned to its pan. The pan is returned to the 105°C oven for one hour and then cooled to balance temperature in a desiccator once more. The filter is weighed a second time and the two final weights must be within a 0.5 mg of each other. If not, the cycle of heating, cooling, and weighing must be repeated until two, consecutive weights are within the specified tolerance of 0.5 mg.

To address a frequently voiced concern regarding this product, the initial recorded weight indicated on the pan label is not affected by absorbed moisture. The filter tare weight is captured when the filter is completely dried and desiccated. The testing laboratory's final weighing is performed after drying and desiccating. Therefore, all interim air moisture absorbed by the filter while in transit or on the stock shelf of the laboratory is a nonfactor and will be removed before the final filter weight is measured.

In addition, the use of different balances should not affect accuracy. Balances must be calibrated routinely to ensure correct results. Environmental Express balances are repeatedly certified with NIST weights and are calibrated internally several times during each working day.


Current users of the fully-prepared ProWeigh® filters enjoy the improved accuracy, time and cost savings, and convenience that this product provides. Laboratories enjoy the benefit of half the turnaround time on a TSS sample. Also, because TSS analysis routinely sells for $8.00 to $16.00 and is, therefore, generally of low value to the laboratory, the technician can perform additional and more revenue generating tasks.

When the filter cost was added to actual labor cost, one customer found that by switching to ProWeigh® filters, they were able to save about 10 percent in the total cost of performing a single TSS. With over 20 TSS sample tests performed each day in this busy municipal lab, an extra 30 minutes per day is now productively redirected to the performance of other pressing requirements.

ProWeigh® is a standard 47 mm filter that is used with any common 47 mm filter funnel. Crucible users who do not use a filter funnel for TSS have found three distinct advantages in changing to this product:

  • Most crucible filters measure less than 25 mm in diameter, so thick, sludgy samples filter 3-4 times quicker because of the vastly increased surface area.
  • Solids routinely adhere to the sides of crucibles and are then baked on. Great difficulty is encountered in scouring and scrubbing afterwards. With ProWeigh®, little washing is required because solids adhering to the sides of the filter funnel are washed onto the filter using a squirt bottle of deionized water.
  • Finally, 99 percent of all labs using crucibles already possess at least one 47mm filter funnel of some design. Therefore, new equipment does not need to be purchased to switch over to this product. It is important, however, for crucible users to fully understand that only the filter will be weighed when using ProWeigh® as the crucible method requires that both the filter and crucible be weighed in tandem.


ProWeigh® filters are also available for fixed or volatile solids. After washing the filter, these filters are heated in a muffle furnace to 550°C to drive off any potential volatiles present on the glass fiber. As with all ProWeigh® products, they are desiccated to balance temperature, weighed to the nearest 0.1 mg and quality checked for accuracy.


We all know how auditors can be very meticulous in their findings. Standard Methods 2540D states that during the filter preparation, the filter must be weighed twice and these two weights must be consistent and within the 0.5 mg tolerance. Our ProWeigh® filters meet these requirements but only the first weight is recorded. Some auditors and regulatory bodies require that the second weight is documented to prove method compliance. Environmental Express has a solution to this requirement, The ProWeigh® DoubleWeigh filter. The DoubleWeigh filters are prepared the same way as the ProWeigh® filters except that both weights are recorded.

In summation, the ProWeigh filter family of products saves you valuable time, money, and resources by eliminating the need for TSS/VSS filter prep. On average, you can save up to 3+ hours of prep time that can be utilized on more productive, revenue-generating tasks.

I’ve got 99 problems, but METALS aren’t one!!
Thursday, 14 September 2017 06:10

Not with the new innovative additions to our Metals Digestion product line that is!!  Our newest metals digestion products are designed to help save you time, money, and improve the consistency and accuracy of your results.

Not enough hours in the day??  Our new AutoBlock Fill may be just what you’re looking for.  The AutoBlock Fill automates the most dangerous steps of metals digestion – reagent addition.  With the push of a button the AutoBlock Fill will save you from countless nasty pipetting thumb cramps and best of all TIME!!  The unit allows the user to add an existing HotBlock of any size and lock it into the system creating an automated Metals Digestion Unit at a fraction of the price of a traditional automated unit.  The AutoBlock Fill holds five 1-Liter reagent bottles in the on-board reagent rack and a 5-way valve system allows for easy switching between reagents.  The unit utilizes Masterflex® pumping technology to accurately dispense reagents and software can be controlled via an on-board touchscreen or using a laptop.  The user simply picks a digestion method, presses Start and walks away…AutoBlock Fill does the rest.

If you’re looking to get more out of your HotBlock, check out our new HotBlock 200 & soon to be released HotBlock 300.  These new HotBlocks are everything you love about the original version, but can now reach maximum temperatures of 200°C & 300°C.  These new HotBlocks use an external controller that can control up to 2 independent blocks at a time.  Each controller comes in a unique Kydex® housing that can be mounted to the side of your fume hood via magnets, placed on the countertop, or installed in an empty receptacle on the fume hood.  These new HotBlocks are available from 25-96 wells and cup sizes of 15mL, 50mL, and 100mL or request a custom unit.

If you haven’t heard, we’ve redesigned our 50mL digestion cup to bring you the Ultimate Cup!  This new cup is molded from the same polypropylene resin you’ve come to trust and comes certified for 68 elements, still the most on the market today.  Our new design features include:  increased wall strength for more durability, graduation lines on both sides, a new linerless cap option, redesigned screw thread profile for a tighter seal, and a deeper dimple on the bottom adding extra stability.  The new Ultimate Cup provides premium performance.

Is your lab in need of an ultimate low level metals digestion cup? Well look no further!  I present to you the Ultimate Clean Cup, our newest addition to the line of metals digestion cups.  Further utilizing the improvements of the Ultimate Cup this premium cup is specifically designed for trace metals analysis, certified for 68 elements at part-per-billion and part-per-trillion levels.  It’s the most robust certification on the market today.  Each cup is carefully handled and specially packaged to avoid common means of contamination and ready to use in any clean environment setting.

How antidepressants are ending up in Great Lakes fish
Monday, 04 September 2017 09:25

A new study might depress anyone concerned with Great Lakes water quality.

Antidepressant drugs, making their way through an increasing number of people's bodies, getting excreted in small amounts into their toilets, and moving through the wastewater treatment process to lakes and rivers, are being found in multiple Great Lakes fish species' brains, new research by the University of Buffalo has found.

Read more here.

Chemists Say You Should Add A Little Water To Your Whiskey. Here's Why
Friday, 18 August 2017 09:37

Chemists Say You Should Add A Little Water To Your Whiskey. Here's Why

It's a common refrain from whiskey enthusiasts: Adding a few drops of water to a glass opens up the flavors of the drink. Chemists in Sweden provide a molecular explanation for why this works.

Click here for the full article from NPR 

Updates to Standard Methods and the newly signed Method Update Rule
Thursday, 17 August 2017 06:39

The newest edition of Standard Methods is in print and available for purchase; part number EE1550400. The 23rd edition contains updates to multiple methods (45+) as well as additional clarification and consistency on QC requirements for each method. Of particular interest for us is in the revision for SM2540 Solids. Our very own David Smith was part of the Joint Task Group for this section and helped draft the language that expanded the allowed materials used for evaporating dishes. The StableWeigh™ vessels are included as an example of an accepted alternate material. Also, after more than a decade of operating under an EPA acceptance letter, we are excited that the disposable BOD bottle has been included in this edition of Standard Methods. Both of these products originated from ideas brought to us by lab personnel. Keep the ideas coming so that we can keep making your job easier.

The long awaited Method Update Rule (MUR) was signed by the EPA administrator on August 7th. Be sure to check your method citations, especially from Standard Methods or ASTM, as many methods have been revised. We are very excited about the enzymatic Nitrate Reductase method from NECi for nitrate/nitrite analysis for Clean Water Act (CWA) reporting that was included. If you haven't already started to familiarize yourself with the new MDL procedure, now is the time. It will become mandatory before you know it.

The Science of Water Chemistry
Thursday, 20 July 2017 09:10

The Science of Water Chemistry

Concerned about water pollution and water testing? It’s been on the minds of the people in the Mt. Pleasant community, the home of Environmental Express. To help the community better understand the water monitoring process, our Technical Director David Smith wrote a very informative article for our local paper about the science of water chemistry. You can read the entire article at

An Alternative to Total Dissolved Solids and Total Solids Analysis
Tuesday, 11 July 2017 11:34

An Alternative to Total Dissolved Solids and Total Solids Analysis

by Joe Boyd 


TDS Filling StationAn alternative to preparing, weighing, cooling and cleaning dishes and crucibles for total dissolved solids (TDS) and total solids (TS) analysis uses disposable prepared vessels, eliminating hours of manual labor and increasing efficiencies.

The basics of TDS testing

TS are the materials left in a vessel after a sample is evaporated at a defined temperature. TDS are the portion of the total solids that pass through a 2.0-μm (or smaller) nominal-pore-size filter. For TS, the liquid sample is evaporated at a temperature of 104 °C; for TDS, the filtrate is first evaporated and the evaporating dish is then transferred to a 180 °C oven for at least one hour. In both analyses, the evaporating dish is cooled in a desiccator to balance temperature and is then weighed. These heating, cooling and weighing steps are repeated until a constant weight of ±0.5 mg is achieved. The difference between the post- and preweight is the amount of TS or TDS in milligrams for the sample.

The key to successful TS and TDS analysis is the container from which the filtrate is evaporated. Approved analytical methods such as Standard Methods 2540B and 2540C have specific instructions regarding preparation of the container to achieve the most accurate results possible; the evaporation dishes must hold at least 100 mL and be constructed of porcelain, platinum or high-silica glass. The dish must be washed with soapy water to remove residue, rinsed with deionized water and then dried for one hour at 104 °C for TS or 180 °C for TDS. It should then be stored in a desiccator until ready for use (the dish should be weighed immediately prior to use).1,2

Vessels for TDS

StableWeigh vessels from Environmental Express are an alternative to traditional dishes or crucibles. They are constructed of a proprietary blend of high-temperature plastics and arrive at the laboratory as prepared vessels, ready to use for TS or TDS analysis. Each vessel meets the preparation requirements of Standard Methods and is preweighed, with the weight and ID printed on the vessel. This saves several hours that would be spent manually cleaning and weighing dishes. The vessels are also disposable. 

StableWeigh vessel advantages

Traditional dishes used for TS and TDS analysis weigh around 80 g, and the sample residue range per Standard Methods is 10 to 200 mg. This creates sensitivity issues in the analysis that can lead to erroneous results and difficulties establishing weight stability. StableWeigh vessels weigh between 3 and 4 g, giving much better resolution on lower TS/TDS ranges and helping to achieve weight stability faster. 

One of the most widely used evaporating dishes is the porcelain crucible. These are shipped to the laboratory with a glaze that helps decrease moisture absorption from the atmosphere, which is important when establishing dish preweights and weight stability at the end of analysis. Over time, the glaze wears off from washing the crucibles to remove residue from previous analyses. Porcelain is a porous material that draws moisture from the atmosphere, affecting weights. This leads to data uncertainty and adversely affects results. StableWeigh vessels are constructed of a proprietary blend of high-temperature plastics that will not absorb moisture from the atmosphere. Because the vessels are disposable, there is also no risk of altering their composition by washing. 

Unique properties of vessel material and design greatly reduce cooling times. While dishes or crucibles constructed of porcelain or glass typically require about one hour in a desiccator to cool down after a process conducted in a 104 °C or 180 °C oven, StableWeigh vessels require only 10 to 15 minutes. 

Method acceptance

Although StableWeigh vessels are not constructed of one of the materials stated in Standard Methods, they are covered under the method flexibility allowed in U.S. EPA Rule 40 CFR Part 136.6, which sets out the requirements for a modified analytical method to be considered equivalent to a promulgated analytical method:3 

The March 12th Methods Update Rule promulgated 136.6 which allows the regulated community more flexibility that includes:

  1. If the underlying chemistry and determinative technique in a modified method are essentially the same.
  2. The modified method must be sufficiently sensitive and meet or exceed performance of the approved method. 

Data generated by Environmental Express and independent laboratories has proven that StableWeigh vessels meet or exceed the performance of Standard Methods for both TS and TDS (see Tables 1 to 5). Standard Methods is also actively working to update Methods 2540B and 2540C to include StableWeigh as an acceptable evaporating dish. 


1.      Rice, E.W.; Baird R.B. et al., Eds. Standard Methods for the Examination of Water and Wastewater; vol. 22, 2012; APHA, AWWA, WEF: Washington, D.C.

2.      Baird, R.B.; Eaton A.D. et al. Standard Methods for the Examination of Water and Wastewater; online edition, 2016; APHA, AWWA, WEF.


Table 1 – Method blank data for StableWeigh shows results within method acceptance criteria*

Table 1

*Laboratory Reagent Blank (LRB)


Table 2 –LFB, inorganic material for StableWeigh shows results within ±4% of the true value and obtaining weight stability in 10 out of 10 samples on first try*

Table 2

*LFB, laboratory fortified blank.


Table 3 –LFB, inorganic material for porcelain evaporating dishes shows results within ±6% of the true value and obtaining weight stability in 6 out of 10 samples on first try

Table 3


Table 4 – Biosolids (high organic content) sample results using StableWeigh shows weight stability in 10 out of 10 samples on first try

Table 4


Table 5 – Biosolids (high organic content) sample results using porcelain evaporating dishes shows weight stability in 0 out of 10 samples and weight stability never being achieved in 6 out of 10 samples after two tries

Table 5

Figure 1 – A StableWeigh vessel fits easily inside a StableWeigh single-place filling station, a design similar to a bell jar, to aid in filtration of the sample directly into the StableWeigh vessel.


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