Author Archives: Rachel Kohn

About Rachel Kohn

So how did an MIT Ph.D. end up selling refrigerators? When I figured out that a lot more scientists buy lab refrigerators than innovative leading-edge instruments. I hope that my many years of lab experience will help you find the right equipment for your work. Before co-founding Tovatech I worked in business development and project management at Smiths Detection, Photon-X, Cardinal Health, and Hoechst Celanese. And before that I spent 12 years as an R&D chemist at Hoechst Celanese and Aventis working on advanced drug delivery systems, polymer films and membranes, optical disks, and polysaccharides. Some day, eventually, I’ll make enough money to develop an innovative technology that will change the world.

How to Calibrate Precision Scales and Analytical Balances

Control panel for the Kern HCN Hanging Scale

Control panel for the Kern HCN Digital Hanging Scale

Before we describe how to calibrate precision scales and analytical balances we’ll tell you why you need to calibrate these precision weighing devices.  In many instances it’s required by law but in all cases calibrating these instruments, especially those used in R&D labs and other demanding applications, should be conducted on a regular basis as a part of good laboratory practices (GLP).

Calibration exercises apply to other types of scales for many of the same reasons.  Buyers and sellers of products want to get and give “fair measure.”  For the purpose of this post we’ll focus on precision scales and analytical balances where deviations between actual weight and displayed weight can be unacceptable.  Calibration exercises are aimed at making the scales as accurate as possible.  

In addition to explaining how to calibrate these weighing instruments this post first goes into detail … Read the rest

Avoiding Errors with Analytical Balances

Avoiding Errors with Analytical Balances

Avoiding errors when using analytical balances – or for that matter any weighing instrument – involves the coming together of several practices on the part of the user.  This post focuses on assuring accurate weighing results when using analytical balances with readouts (what is displayed on the instrument) to milligrams.    For an analytical balance such as the KERN ABT 120-4M available from Tovatech it is 0.1 milligram.   Semi-micro balances can display to micrograms or 0.01 milligram.

Accuracy is paramount when weighing to these levels with analytical balances and is often subject to regulation by organizations such as the FDA and professional trade associations.  Technicians must institute practices and procedures to avoid weighing errors and to insure that the displayed weight precisely reflects the weight of the sample.

Ultrasonic Cleaners for Flammable Solvents

ultrasonic cleaning using flammable solvent

Ultrasonic cleaners are widely recognized as providing outstanding cleaning action thanks to the cavitation produced by the equipment’s generator powered ultrasonic transducers.  But when cleaning with flammable solvents it is imperative that explosion resistant ultrasonic cleaners are employed in the shop, and that the equipment be located in an area equipped with an adequate exhaust system to vent fumes to an exterior location.

Flammable solvents are often preferred for tough cleaning jobs such as degreasing and removing tenacious contaminants like paint and adhesive residues.  Special care must be exercised when cleaning with flammable solvents under any circumstance, but especially when using an ultrasonic cleaner to both speed the process and improve cleaning results.   Unless they are specially constructed, ultrasonic cleaners present two risks:  sparks from internal electronics igniting spilled solvents and fumes, and vapors from solvent evaporation creating a hazardous area in the vicinity of the unit.   … Read the rest

Selecting and Using Precision Scale Test Weights

Calibrating Scales with Test Weights

Weighing accuracy is a primary criterion for precision scales, analytical balances and moisture analyzers where readout (the smallest weight difference displayed) and linearity (the ± deviation from the actual weight) are governed by GLP, ISO and other standards.  Test weights have a critical role to play when scales  with capacities from milligrams to tons are not automatically internally (see below) calibrated . The type of calibration, whether internal or external, is indicated on scales’ spec sheets.

How to Pick the Best Ultrasonic Cleaner

Selecting the Best Ultrasonic Cleaner

Among the steps to be taken to pick the best ultrasonic cleaner is a thorough understanding of what the process is to accomplish and then identify ultrasonic cleaner features that let you accomplish the task(s) in the most cost-effective way.  While ultrasonic cleaners are available from a variety of manufacturers and across a broad spectrum of prices, your investment must be based on an assurance that it will accomplish your task(s) quickly and efficiently.  When you do this you’ll be able to identify your best ultrasonic cleaner.

In other words, pick the ultrasonic cleaner you need.  Don’t succumb to “keeping up with the Joneses.”

An Important Ultrasonic Cleaner Priority:  Size

You can’t mount a 19-inch tire on a 15-inch wheel.  Similarly the dimensions (length, width, depth) of the ultrasonic cleaner’s tank must be sufficient to accommodate the largest component you plan to clean.  But there’s more:  Because a majority of … Read the rest

Selection Tips for Precision Digital Scales

10 Selection Tips for Precision Digital Scales

Today’s precision digital scales, also referred to as digital balances, perform a broad range of weighing-related functions in R&D, quality control, and similar applications where accuracy and precision are key criteria to meeting government, trade association, and industry-promulgated standards.  For purposes of discussion this post focuses on weighing equipment used in comparatively protected environments vs. scales found on manufacturing floors, shipping and receiving departments.  Let us hasten to add, however, that the need for precision and accuracy is important for any application, and equipment is available to meet required standards regardless of where scales are employed.

Precision and Accuracy Defined

Certain of our posts discussing precision digital scales and analytical balances harp on an important difference between precision and accuracy as selection criteria.  Allow us to cite an example:  A $5,000 wristwatch may be precise, but if the hands are set wrong it does not show the accurate time.  More … Read the rest

Analytical Balance Recalibration – A Critical Exercise

analytical balance calibration

Accuracy and precision (there is a difference) in the performance of analytical balances are crucial when weighing extremely small masses such as to 0.1 or 0.01 mg.  Even the smallest deviation in accuracy can throw off critical measurements when compounding, for example, pharmaceuticals and weighing active pharmaceutical ingredients (API).  For this reason analytical balance recalibration exercises and procedures should be carefully spelled out in a company’s standard operating procedures.

The Effect of Gravity on an Analytical Balance

Manufacturers of analytical balances such as the Kern line available from Tovatech call attention to the importance of calibration and recalibration early in their instruction manuals.  Kern points out, for example, that gravitational pull varies throughout the world due to the fact that the world is not a perfect sphere.  This was demonstrated a few years ago by shipping the Kern Gnome to many locations around the world.  The Kern Gnome was accompanied … Read the rest

Ultrasonic Cleaning Solutions Selection Guidelines


Successful ultrasonic cleaning procedures are most likely achieved when thought is given to ultrasonic cleaning solutions that deliver the desired results.  Just as you notice the plethora of detergent choices on supermarket shelves so too is the vast variety of ultrasonic cleaning solution chemistries available to satisfactorily accomplish your cleaning tasks.

In fact an improper choice of cleaning solution chemistry (just as the wrong ultrasonic frequency*) can damage parts or surfaces being cleaned.

Most but not all ultrasonic cleaning solutions marketed today are in the form of biodegradable concentrates formulated for specific cleaning tasks.  They are shipped with instructions regarding dilution, recommended cleaning temperatures and material safety data sheets (MSDS).   Container volumes vary by manufacturer; 2.5, 10 and 25 liters are typical examples.  Biodegradable formulas eliminate handling, health and disposal concerns associated with trichloroethylene and perchlorethylene solvents formerly used for ultrasonic cleaning.… Read the rest

A Vaccine Refrigeration Specification Guide     

Vaccine Refrigeration - 10 Essential Items to Consider

Proper vaccine refrigeration is not a hit-or-miss proposition.  Each year there are reports on how improper vaccine storage or other mishaps relating to vaccines result in loss of potency.  This necessitates locating and revaccinating those who have received compromised inoculations plus the associated cost and inconvenience.  Proper vaccine storage is also a critical element for complying with government-funded Vaccines for Children (VFC) programs.

Vaccine manufacturers are careful to note the proper storage temperatures for their products along what is called the cold chain of custody between manufacturing and inoculation.  But manufacturers have little influence on the equipment used by healthcare facilities to maintain these temperatures.  The CDC (Centers for Disease Control and Prevention) has stepped into this by issuing its 2016 Vaccine Storage and Handling Toolkit to provide comprehensive information on this vital activity.    The Toolkit also covers in detail the importance of staff training and written standard operating procedures … Read the rest

How to Check Pump System Accuracy for HPLC Analysis

Digital HPLC Liquid Flow Meter At a Glance

Pump system accuracy is crucial for equipment used to conduct high performance liquid chromatography (HPLC) analysis in the pharmaceutical and other industries subject to regulatory oversight by the FDA and similar authorities. Among functions performed by HPLC are included checks for purity, monitoring changes in pharmaceutical intermediates during chemical synthesis scale-up, stability and dissolution tests, and performing ongoing quality control procedures.

A Brief on HPLC Analysis

Identifying an analyte by HPLC is based on accurate and reproducible column retention time as the analyte is pumped through an HPLC system.  Reproducible retention time is critical and depends on accurate, uniform, reproducible HPLC pump flow rates.

Note that it is important to distinguish between accuracy and precision.  These two terms may seem the same but they are not necessarily so.  For example, an HPLC system (or for that matter many other systems such as analytical scales) may test out as precise.  This … Read the rest