FlashEA 1112 Elemental Analyzer (CHNS): User Guide

Manual Information

User Guide Contents

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Introduction

Carbon, hydrogen, nitrogen, and sulfur (CHNS) are fundamental elemental components that are analyzed on the ship during IODP expeditions. Fluctuations in the concentration and/or content ratio of carbon, nitrogen, and sulfur define the origin, depositional environment, and diagenetic alteration of source materials.
A few options for sample preparation method, instrument settings, and measurement methodology exist. In addition to the pregenerated methods, specific analytical methodology may be required based on the nature of certain sample materials. In this case, new methods will be created by the laboratory technicians working in conjunction with the scientists. Each instrument method is recorded by the USIO and will be associated with the measurements performed under that method.

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Dried and powdered samples are combusted in a tin sample crucible with vanadium pentoxide catalyst, purified by a reactor packed with electrolytic copper and copper oxide, separated on a gas chromatographic column, and analyzed using a thermal conductivity detector (TCD). Addition of the V₂O₅ ensures complete conversion of inorganic sulfur in the sample to sulfur dioxide.
When the tin crucible with sample is dropped into the reactor, the oxygen environment triggers a strong exothermic reaction. Temperature rises to _{1800°C, causing the sample to combust. The combustion products are conveyed across the reactor, where oxidation is completed. Nitrogen oxides and sulfur trioxide are reduced to elemental nitrogen and sulfur dioxide and oxygen excess is retained. The gas mixture containing N}2_{, CO}2_{, H}2_{O, and SO}2~ flows into the chromatographic column, where separation takes place. Eluted gases are sent to the TCD where electrical signals processed by the Eager 300 software provide percentages of nitrogen, carbon, hydrogen, and sulfur contained in the sample.

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Apparatus, Reagents, & Materials

Hardware

Carbon, hydrogen, nitrogen, and sulfur are analyzed on a Thermo Electron Corporation FlashEA 1112 CHNS elemental analyzer (Figure 1) with autosampler (Figure 2).

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_Ref301357189 Figure 1. Elemental Analyzer: (1) Furnace Access Door, (2) Synoptic Panel, and (3) Thermostatic Chamber Access. Dry Sample Autosampler is located on top of furnace.

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Figure 2. Dry Sample Autosampler (red box in Figure 1): (1) Drum, (2) Gas Connection Fitting, (3) Gas Tube, and (4) Reactor Fitting..

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Note that many of these materials are hazardous and before any work is done with them, the user must be familiar with the appropriate Material Safety Data Sheets (MSDS).

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Sample Preparation

Bulk samples are freeze-dried, crushed and homogenized using a mortar and pestle or electric mill, and weighed into a tin sample cup (crucible) with vanadium pentoxide catalyst. The crucibles are then closed (referred to as "wrapping" the sample) and placed in the autosampler for instrumental analysis.

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Drying and Homogenizing the Sample

1. Break clumpy sample into pieces.
2. Fill a freeze-drying chamber with sample pieces and place into freeze dryer.
3. Freeze-dry sample for at least 12 hr until sample is completely dry (may require additional freeze-drying time, up to 3 hr). The sample is dry when there is no more condensate in the cold part of the tube.
4. Note: do not overload the freeze dryer; it will not dry properly.
5. Wipe an agate mortar and pestle with ethanol and allow to dry completely before grinding each sample. Be sure the mortar and pestle are completely dry; ethanol reagent residue can cause false C and H results.
6. Grind and homogenize sediment using the cleaned and dry agate mortar and pestle.
7. Fill a sample bottle with powdered homogenized sediment.
8. Place sample bottle into the desiccator. Many mineral species are hygroscopic (tend to absorb water), so the sample bottles containing the dried samples should be kept in the desiccator until used.

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Sample Volume

Because the balance system is of unknown lower precision aboard ship than in a shore-based laboratory, we recommend 6–9 calibration points to obtain a high CHNS measurement precision. The usual quantities of sample materials and standards used are as follows:
–Vanadium pentoxide: ½ of small spatula for blank, standard, and unknown samples
–Standard (sulfanilamide):

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Wipe spatula, spring tweezers, balance, and other stainless equipment with ethanol between each sample. Be sure these are completely dry before using to avoid contaminating samples.

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Weighing and Wrapping Samples

1. Double-click the Cahn Balance icon.
2. Log into the system by entering LIMS user name and password.
3. Enter 200 as the Count Limit.
4. Place an empty crucible (tin container) on the REFERENCE balance pan (right pan).
5. Place a new crucible into the small hole of the metal plate.
6. Open the upper half of the tin cup and place a crucible on the UNKNOWN balance pan (left pan).
7. Tare the balance using the software. (Do not press the Tare button on the Cahn balance.)
8. Click Start to start weighing.
9. Once the mass volume is acceptable, click Get Mass.
10. Remove the crucible from the UNKNOWN balance pan, place the crucible on the metal plate, and place the appropriate amount of sample material (see Sample Volume) into the crucible.

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1. Place crucible with sample material back on the UNKNOWN balance pan and close door.
2. Click Weigh and Start.
3. Click Get Mass if the mass value is acceptable.
4. Enter any part of a sample ID or Label ID and click Search.
5. Select the sample that was just weighed from the list and click Assign.
6. Enter a container number (sample holder number, not an autosampler number) in the Container# field.
7. Click Save.

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Sample Analysis

Data flow for CHNS sample analysis includes the following:

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• Prepare the instrument for running samples (see Preparing the Instrument).
• Confirm instrument calibration (see Verifying Instrument Calibration).
• Export LIMS file from LabWare for CHNS (see Creating the Sample Table).
• Import LIMS sample table and edit (see Uploading the Sample Table to Eager 300 Software).
• Start sequence (see Running Samples).
• Summarize, edit, and analyze results (see Analyzing Data).
• Export sample data as CSV file and upload to LIMS (see LIMS Integration).

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Preparing the Instrument

The shipboard technician will set up and maintain the reactor and gas chromatographic column. The technician will also instruct the scientist on the operation of the instrument.
Instrument startup and conditioning are conducted by the shipboard technician, who also loads the analytical configuration (method). If a specific analytical configuration is required because of the nature of the samples, scientists should collaborate with the technician to develop the analytical method and run parameters. When the instrument is ready, the Eager 300 CHNS screen displays. To confirm the status of the CHNS analyzer instrument, select View > View Elemental Analyzer Status (see Figure 4, below).(Figure 3). Analytical determination takes approximately 40, 100, 150, and 640 seconds for nitrogen, carbon, hydrogen and sulfur, respectively, for a 2 m long separation column. The integration time should be set to approximately 15 min (900 sec) for runs in which sulfur is measured due to the breadth of the signal peak. Either purchase pre-filled reactor columns or prepare them according to the manufacturer's instructions. The adsorption filter should be filled with fresh magnesium persulfate regularly. The JRSO uses pre-packed reactor columns from CE Elantech and Costech; these have always proved to be of high quality, without gaps or faults in the reagents that could lead to a poorly-reacted gas stream.
If pre-filled reactor columns are not available, follow the instructions in the Flash EA 1112 vendor manual to prepare them. Packing columns is in Chapter 5 of the vendor manual; installing reactor and adsorption columns is discussed in Chapter 6. Note that the JRSO uses CE Elantech 061110 columns for sulfur, loaded with copper and tungsten oxide, but many other options are possible.
A general schematic is shown below in Figure 3.
Prepare the EA reactor, adsorption filter, and chromatographic column for the desired analytical elements according to the following schematic:
Figure 3: Analytical equipment setup based on desired elements.
Properties of reactor materials and adsorption filter: Copper oxide/chromium oxide: Creates an oxidizing environment during combustion of the sample. Vanadium pentoxide: Catalyzes the combustion of S (as sediment ion sulfate/sulfides) to sulfur dioxide. Tungsten oxide (WO₃): Helps complete the oxidation of combustion products to final products.
Electrolytic copper: Reduces potentially formed nitrogen oxides and sulfur trioxide combustion products to elemental nitrogen and sulfur dioxide. Silvered cobaltous/cobaltic oxide: Catalyst used to remove sulfur dioxide and halogens. Magnesium perchlorate (anhydrone): Desiccant which removes water (i.e., combusted H) in the adsorption filter.

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Figure 4. Eager 3000 CHNS Screen.

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Verifying Instrument Calibration

The CHNS instrument is calibrated at the beginning of each expedition (see Quality Assurance/Quality Control). Calibration is verified before running each sample sequence by running a blank and a calibration verification standard against the current calibration curve.

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Calibration method can be changed on this screen. For more information see the FlashEA 1112 Operating Manual (p. 232).
If the calibration factor is acceptable (see Quality Assurance/Quality Control), unknown samples can be run. If the calibration factor is outside of control limits, the laboratory technician will edit the component table and integration parameters and recalculate the calibration factor.

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5. Sample Table.

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6. Calibration Curve.

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Creating the Sample Table

1. Double-click on CHNS.exe.
2. Enter the LIMS user name and password to activate CHNS Loader.
3. Open the Output Sample from LIMS tab.
4. Click column header Container (samples are sorted by container number).
5. Select samples to be run in the next batch or sequence.
6. Adjust row index. Row index number must be the same as the row number that is two rows below the last sample in the current sequence table of the Eager 300 software.
7. Click Export and save file to the folder where you saved the method.
8. Exit the CHNS Loader.

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Uploading the Sample Table to Eager 300 Software

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1. On the CHNS screen, select Edit > Sample table.
2. From the menu at the top of the sample table, select Edit sample > Import sample table from LIMS (Figure 6Figure 7).
3. Select appropriate LIMS file, and click OK to upload file.
4. Click Cancel to escape the window.
5. Make sure sample holder number is correct.

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Figure 7. Edit Sample Menu.

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Running Samples

1. To start

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1. To start running samples, click the green arrow toolbar icon on the CHNS screen.
2. To monitor the acquisition status, select View > View sample being acquired (Figure 7Figure 8).
3. Once samples are run, View Chromatograms shows a single selected chromatogram; Overlay Chromatograms is better suited for comparison of chromatograms (maximum of five).

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8. View Menu.

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Analyzing Data

QA/QC data is captured by LIMS, but the technician should monitor QC values from the calibration verification (CV) standards and determine if corrective action should be taken.
After analyzing the standard and checking the instrument precision, complete the following steps.

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1. On the CHNS screen, select Recalculation > Summarize results (Figure 8Figure 9).
2. Select a group of samples to calculate the standard deviation for by indicating a group number (1) in the Group column of the Summarize results table. For example, in Figure 8 Figure 9 the 6 sulfanilamide standards are grouped (1) for standard deviation analysis.
3. With the mouse, select the first row of a group (Row 2 in Figure 8Figure 9) and select View > Statistical Calculation to see statistical data calculated for that group.

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Figure 9. Summarize Results Screen.

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Quality Assurance/Quality Control

A program of quality assurance/quality control (QA/QC) ensures that a measurement system is performing within control limits and therefore provides high-quality data. The QA/QC program for this system includes instrument calibration and calibration verification, blank verification, and accuracy and precision monitoring.

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A calibration blank run each sequence consists of a tin cup containing only reagent V₂O₅ catalyst to assess the effect that the tin cup and catalyst have on the analysis results. If the blank chromatogram has unexpected peaks or a disturbed baseline, the cause of this problem must be determined before unknown samples can be run. Notify the chemistry technician.

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Calibration Verification

The calibration verification standard, also called the QC check standard, is run with each analytical batch and contains _{0.6–0.7 g of BBOT in a tin cup with V}2_O5~ catalyst. If the calibration factor is within control limits, unknown samples can be run. If the calibration factor is outside of control limits, edit the component table and integration parameters and recalculate the calibration factor.
Poor calibration verification results can also indicate degradation of the reactor. If calibration cannot be verified, notify the onboard laboratory specialist.

Precision

Wiki MarkupPrecision is the degree to which further measurements will show the same or similar results. To analyze for precision on this system, a standard (sulfanilamide, BBOT, or aspartic acid) is run in duplicate or triplicate and the standard deviation of the results calculated for each element: s= i=1N(xi-x)2N-1s.d. = SQR\[(x{~}1~ - _x{_}{~}m{~}){^}2^ + (x{~}2~ - _x{_}{~}m{~}){^}2^ + (x{~}3~ - _x{_}{~}m{~}){^}2{^}\]/({_}n_ - 1), where x _x{_}{~}m~ = average of results, xi and _n_ _N_ = number of data points.

Accuracy

Accuracy is the degree of closeness of a measured value to the actual (true) value. A standard of sulfanilamide in a tin cup with V₂O₅ catalyst is run with each sequence to verify accuracy. Results of the standard must be within ±10% of true values for the system to be considered in control.
Sulfanilamide true values and control limits:

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Sample/Analysis Components

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where   = average of results,  and N = number of data points.

Accuracy

Accuracy is the degree of closeness of a measured value to the actual (true) value. A standard of sulfanilamide in a tin cup with V₂O₅ catalyst is run with each sequence to verify accuracy. Results of the standard must be within ±10% of true values for the system to be considered in control.
Sulfanilamide true values and control limits:

• C = 41.848% (37.663%–46.033%)
• H = 4.685% (4.217%–5.154%)
• N = 16.267% (14.640%–17.894%)
• S = 18.620% (16.758%–20.482%)
• O = 18.582% (16.724%–20.440%)
• Other materials (e.g., USGS reference sediments) can be used to measure accuracy, so long as their values are known.

LIMS Integration

Sample/Analysis Components

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When uploading data enter the term "Rejected" in place of the value for an elemental concentration for a sample or series of samples that followed a running standard in which the analytical error exceeded the QA/QC limits (10% for each element). This displays "Rejected" in LIMS/LORE for only that specific sample element and still keeps intact the excel file containing the raw data which is uploaded to the database.

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Health, Safety, & Environment

Safety

General

• Before using the gases, chemicals, and filling materials required for this procedure, carefully read the MSDS for that material.
• Proper personal protective equipment must be used for handling all apparatus and materials in this procedure.
• The instrument has a safety cutoff feature that cuts power to the furnace heating elements if the instrument malfunctions due to a component failure or abnormal operating conditions. If the red safety LED indicator on the synoptic panel is illuminated, contact laboratory staff immediately.

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Extremely toxic! Always use the appropriate personal protective equipment (PPE) and environmental controls when using this chemical.

• Harmful if swallowed or inhaled

• Causes serious eye damage

• May cause respiratory irritation

• Suspected of causing genetic defects, damaging fertility, and/or harm of the unborn child

• Causes damage to internal organs through prolonged or repeated exposure

• Toxic to aquatic life with long-lasting effects

General

• Before using the gases, chemicals, and filling materials required for this procedure, carefully read the MSDS for that material.
• Proper personal protective equipment must be used for handling all apparatus and materials in this procedure.
• Gas cylinders are pressure hazards and should be changed only by shipboard staff. High-pressure gas lines can be hazardous if there are leaks, particularly the oxygen line.
• The instrument has a safety cutoff feature that cuts power to the furnace heating elements if the instrument malfunctions due to a component failure or abnormal operating conditions. If the red safety LED indicator on the synoptic panel is illuminated, contact laboratory staff immediately.

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