CHNSO Elemental Analysis – Sample Preparation

CHNSO elemental analysis, also known as organic elemental analysis or elemental microanalysis, determines the amounts of carbon (C), hydrogen (H), nitrogen (N), sulfur (S) and oxygen (O) present in a sample. It is a reliable and cost-effective technique used to assess the purity and chemical composition of compounds and can be used on a wide range of different sample types including solid, liquid, volatile and viscous substances. Knowing the composition of the organic elements also helps analysts to determine the structure of the sample substance. The chemical characterization of organic compounds is used in research as well as for quality control (QC).

Elemental analysis is a highly reliable analytical technique that is used in a wide range of applications across many different industries (see below). The most common technique of CHNSO elemental analysis is based on the combustion of the sample. This can be performed in a dedicated instrument known as an Elemental Analyzer. Upon combustion, the sample generates uniform compound gases of the elements C, H, N and S. These combustion products (e.g. CO2, H2O, NO2, etc.) are measured using gas chromatography and thus the ratio of the elements in the original sample is determined. C, H, N and S can all be determined simultaneously whereas O may be analyzed in a second step by pyrolysis.

Why weighing is important?

Organic elemental analysis requires relatively small sample weights. The actual sample weights vary according to the nature of the substance, the detection limits, the level of accuracy required and the type of elemental analyzer used. As the final amounts of each element are typically given as a percentage of the original sample weight, it is critical that the sample is weighed accurately. Due to the very small sample size, a highly accurate microbalance is recommended.

Excellence Level microbalances are perfect for sample preparation for organic elemental analysis where measurement of very small quantities requires the use of a highly accurate microbalance.

Watch the video and learn about the benefits of using METTLER TOLEDO equipment for CHNS(O) elemental analysis.

For reliable results, samples must be free from contaminants and moisture. To prepare homogenous samples, it may be necessary to dry the substance being investigated to a constant weight and then finely grind it. For further details on the different methods for preparing samples and sample sizes, please see the Know-How section below.

CHNSO elemental analysis requires the samples under investigation to be weighed with a very high degree of precision. If you need any further information on selecting the right balance to meet the needs of your application or want to be sure that your current balance meets your accuracy requirements, our team of experts is here to help. Please do not hesitate to contact us. 

Laboratories performing CHNS(O) analyses handle hundreds of samples on a daily basis. Fast and accurate results are demanded for further processing. Laboratory analysts are under pressure to complete analyses as quickly as possible.

Accuracy

Weighing out very small quantities into minuscule containers is awkward and must be done with care. The skill of the analyst plays an important role in weighing out samples of a consistent size. As the final results of C, H, N and S content are given as a percentage of the initial sample weight, it is critical to weigh the sample accurately and record the weight correctly.

Sample usage

Because many samples of the same substance will be analyzed, using small sample sizes minimizes substance use, reduces the amount of oxygen required for combustion, and decreases waste. A balance with a low minimum weight helps to minimize the amount of substance required.

Number of samples/throughput

Preparing samples for CHNS(O) analysis is a time and labor-intensive process. Microbalances are very sensitive and can take several seconds to settle before releasing the weight result.

Documentation

Transcribing results takes time and is prone to human error, especially when weight results have 6 or 7 decimal places. Traceability of results is important to labs carrying out the analyses as well as to end customers.

METTLER TOLEDO XPR microbalances offer unique accuracy and exceptionally low minimum weights. The weighing method, including target weight, tolerances, and number of samples can be saved on the balance and accessed directly from a shortcut on the balance display. Built-in quality assurance functions ensure weighing results meet defined tolerances and standards.

Meet accuracy requirements

METTLER TOLEDO microbalances have USP minimum weight values as low as 0.82 mg with a readability of 0.001 mg enabling you to easily meet the accuracy requirements of CHNS(O) elemental analyses. Built-in quality assurance features such as StatusLight™, LevelControl and GWP Approved help ensure right-first-time results.

Eliminate manual transcription

Each weight result is saved on the built-in results notepad so there is no need to write results down by hand. The results can be printed out or transferred via multiple connectivity options to a USB stick, PC or another analytical instrument. This eliminates transcription errors and saves a significant amount of time.

Fast and stable performance

The Active Temperature Control (ATC) feature ensures stable balance performance, delivering results considerably faster than a standard microbalance. Automated draft shield doors help to maintain balance stability and make weighing processes faster and more ergonomic.

Space-saving solutions

The compact footprint saves space, which is especially important when working in a fume cupboard. In addition, the secondary SmartView terminal above the weighing chamber has all the basic functions you need as you weigh-in, while the main terminal can be placed wherever is most convenient — even outside the fume cupboard.

Mass percentages of organic elements (C, H, N, O and S) are determined in relation to the original sample weight, making accurate weighing critical. Samples are combusted in a process that uses highly pure oxygen and an inert carrier gas, so small sample sizes (typically well below 10 mg) are preferable.

A balance with high repeatability can significantly reduce the cost per analysis. METTLER TOLEDO’s XPR microbalances offer exceptional performance and the lowest posiible minimum weights to deliver accurate results faster, more conveniently and at a lower cost.

Connect your microbalance to LabX® laboratory software and benefit from a complete data management system for your laboratory. With central control of instruments, tasks and users, SOP guidance on the balance terminal, and elimination of manual transcription, LabX provides high security, increases efficiency and ensures full data integrity.

One-for-all solution

Because the system works via your internal network, you can connect one or more instruments to a single PC — even one located outside your laboratory. All administrative work is automated so your whole process can be digitalized. LabX integrates easily with other lab systems (LIMS, ELNs, LES, SAP) for seamless, fast data transfer.

SOP user guidance

By implementing your SOP in LabX, analysts receive step-by-step instructions on the balance display. The analyst is guided through each step in the process, ensuring that the SOP is followed precisely by everyone. This reduces error potential and ensures better repeatability.

Data integrity

LabX takes care of all data and calculations automatically, making it easier for you to meet ALCOA+ data integrity requirements. There is no longer the need to manually document results and process information as all data is saved securely in a centralized database. Transcription errors are completely eliminated.