Maintenance of Graphite Furnace Atomization Atomic Absorption Spectroscopy Systems

Graphite Furnace assembly in sampling position

Graphite Furnace Atomization assembly is optionally available along with the flame version for analysis of trace metals on Atomic Absorption Spectroscopy systems. Graphite Furnace Atomic Absorption Spectroscopy highlights the features and benefits of this option. In order to get highest levels of reliability of results regular maintenance is an absolute must. An earlier article – Tips to ensure high uptime of your Atomic Absorption Spectrometer proposes some guidelines on maintenance of flame AAS systems.

Low-level trace metal determinations require use of graphite furnace atomization assembly. The present article makes some suggestions for maintenance of graphite furnace systems. The overall maintenance of graphite systems can be carried out routinely by you but for some tasks expert handling by service engineer of instrument supplier becomes necessary.

Routine Maintenance

Routine maintenance involves mostly visual observation which can be made easily before making use of the assembly. It can take at the most about 10 – 15 minutes but it is worth the time spent as you can rest assured on the reliability of reported results.

Graphite Tube

The graphite tube is the most critical component in the furnace assembly. Visually inspect daily for cracks, deformations, pitting or deposits around the injection hole. In case such damage is observed tube replacement is the best option.

Gas Supply

Ensure the supply of argon gas is adequate before utilizing the facility. The output supply pressure should be maintained between 50 – 60 psig.

Light Source

The hollow cathode lamp or electrodeless discharge lamp should have sufficient remaining life before it is put to use. After the lamp is switched on it should be given sufficient time to stabilize. Hollow cathode lamps can take half an hour to give a stable output and electrodeless discharge lamps can take longer stabilization time. Lamp energy status should be reviewed for stable output before the sample is introduced into the graphite tube.

Contact Rings

Like the graphite tubes the contact rings should also be inspected for damage due to pitting or cracks. It is time to replace the rings if any such damage is noticed.

Autosampler Tubing and Probe

The tubing should be inspected for any bends or kinks. The tube should be clean and if any blockages are observed or kinks develop the best solution is to replace the tubing. Similarly the probe should be cleaned or replaced if it gets blocked.

Expert Maintenance

Expert attention is required at least once or twice a year depending on usage and nature of samples analyzed. Such recommendations include:

• Cleaning of the mechanical assembly
• Cleaning of optical windows of any solid deposits
• Checking of sensitivity by means of calibration against traceable standards
• The cooling system should be inspected for blockages, if any, and the filters if found choked should be cleaned. If cleaning is not possible the filter should be replaced

Graphite furnace assembly is required for low level determinations in the ppb range of concentrations. At such levels reproducibility of results can be influenced by several factors depending on contamination from reagents, sampling and errors in analytical methods. However, preventive maintenance, as a bottom line, helps you ensure reliability of results over the useful lifespan of the facility.

Filed Under: AAS

Comparative evaluation of sample digestion techniques for Atomic Absorption Spectroscopy

Trace metals analysis by Atomic Absorption Spectroscopy requires the introduction of the sample into the system as a homogeneous liquid. It is necessary to digest solids for complete extraction of analyte(s) of interest into the solution. Commonly used practices are:

• Acid digestion
• Fusion
• Ashing

The technique adopted should be safe, reproducible and afford to save time. The article discusses the advantages and disadvantages of these popular techniques.

Samples ready for digestion in sealed tubes

Acid Digestion

Acid digestion is the most popular of the three techniques. Such digestions are classified into two categories, namely, open digestions and closed digestions. Open digestions are conducted in fume hoods using hot plates whereas closed digestions are carried out using microwave digestion systems.

Characteristic	Open Digestion	Closed Digestion
Corrosive fumes	Evolved- Need to be ventilated	Pose no harm
Digestion temperature	Limited by the boiling point of acid	Pressurised digesters permit higher temperatures
Sample size	For low concentrations larger sample sizes can be handled	Large sample sizes not required
The number of acids	Requires large quantities	Smaller quantities are sufficient
Loss of volatile analytes	Yes –Possibility exists	No loss of volatile elements
Risk of contamination	Yes from surrounding environment	No contamination risk
Time is taken for digestions	Long- hours to days	Less than an hour for even difficult to digest samples

Open acid digestions are in common use in most laboratories but closed system microwave assisted digestions are cost-effective and are gaining popularity.

Fusion

Fusion with alkali metal salts is popular. Such methods find the use for digestion of inorganic materials such as minerals, clays, silicates, and refractories.

Fusions can lead to clogging of nebulizer tubing if suspended solids are not removed completely from solutions. Further, the concentrations could be high and further dilutions may become necessary thereby increasing chances of errors due to dilutions.

Ashing

 Heating the material to non- combustible ash for analyzing its elemental composition is known as ashing. The advantages and disadvantages of ashing are briefly mentioned.

Advantages:

Large sample sizes can be taken if concentrations are low.

 Saving on the cost of reagents in sample preparation

Disadvantages:

Loss of volatile analytes on heating

Contamination from crucible material

Contamination from inside muffle furnace during heating

Material loss due to air currents when the muffle furnace door is opened or closed

Evolution of toxic vapors during ashing

It can be seen that microwave digestion offers distinct advantages over other contemporary techniques both in terms of complete quantitative digestion and time-saving. However, both ashing and fusion still find use even today when other techniques are not feasible.

Prevention of accidents in Laboratory Stores

Laboratory stores play a significant role in the efficient working of laboratories. Stores maintain stocks of chemicals, utilities, and consumables which are required by chemists. It is true that not all items pose hazards but materials that have hazard potential include:

• Toxic and poisonous chemicals
• Flammable solvents
• Corrosive liquids including strong acids
• Compressed Gases
• Highly reactive chemicals and explosive materials
• Dangerous microbiological specimens
• Radioactive materials

The list can include other hazardous items depending on activities of the laboratory. An earlier article covered the responsibilities of stakeholders for implementing laboratory warehouse safety.  In the present article, suggestions are being offered for the prevention of accidents in warehouses.

Well maintained laboratory stores

Types of accidents

Accidents in stores can prove to be even more damaging than in laboratories primarily because storage is in bulk quantities. Generally, accidents result from the following factors:

• Fires
• Electrical short circuits and shocks
• Leaks and spills
• Unplanned storage
• Use of defective material handling equipment
• Careless handling of containers

Fires

Fires can result in stores maintaining stocks of flammable liquids and gases.

• Provide adequate numbers of fire extinguishers in vulnerable locations. In addition, smoke detectors and fire hoses should also be additionally provided. Such devices should be periodically inspected to confirm their proper functioning.
• Basic firefighting training should be provided to all warehouse workers.
• Stocks of flammable liquids and gases should be kept in specially designated areas away from other routine supplies. The areas should be well ventilated and protected from sunshine and rain. Gas cylinders should be inspected periodically for freedom from leakages.
• Only sufficient stocks should be maintained and replenished from time to time in line with laboratory requirements.

Electrical short circuits and shocks

Electrical shocks and short circuits are next common cause of accidents

• Ensure electrical utilities are properly earthed
• Electrical points are not overloaded
• Inspect wirings for damages so that there are no exposed cables
• Entry to high tension areas should be allowed only with safety shoes and gloves.

Leakages and Spillages

• Inspect containers and packets  for physical damage and leaks before stocking in designated spaces
• Inspect gas cylinders periodically for leaks and store them in well-ventilated rooms
• Maintain spill management kits
• Spillage areas should be cordoned off immediately and spills should be attended to on priority
• Move solvent bottles in trays or trolleys

Unplanned storage

• Do not stock material in passages and galleries as it can lead to blockage of escape routes during emergencies
• Incompatible materials should not be stored in the close vicinity of one another
• Before stacking plastic carboys and metal drums ensure that base pallets are not damaged, cracked or deformed
• Highly toxic and poisonous materials should be stocked in special cabinets under lock and key

Defective material  handling  equipment

• Ensure proper functioning of material handling equipment such as trolley and forklifts before using them
• Do not operate the material handling equipment in reverse as this can lead to unexpected accidents
• Never overload trolleys and forklifts

Careless handling

• Do not carry solvent bottles from the neck alone. Place the other hand below for additional support
• Do not place corrosive liquids on overhead shelves. The best option is to place them on the floor.
• Keep the storage area well illuminated at all times
• Make use of protective clothing and gloves when handling corrosive liquids
• Gas cylinders should be kept properly secured to walls and should not be rolled on the floor or down the ramps.

Safety in the stores can be ensured through a contribution from all concerned as it is a joint responsibility. Safety instructions should reach all through training sessions. On observation of any damages or flaws, corrective action should be taken proactively to prevent mishaps in future.

Prevention of contamination in trace metal analysis laboratories

Protective laboratory clothing for safety and freedom from contamination

Today advanced sophisticated analysis techniques are capable of providing trace metal analysis in ppm, ppb or even ppt levels. The most popular techniques are Atomic Absorption Spectroscopy, ICP – MS and ICP – OES. Determinations at low levels can be reliable only if adequate precautions are taken at different stages of analysis such as sampling, storage, and sample handling under controlled environmental conditions. Practices that should be adopted for minimization of contamination at various stages of analysis are briefly covered in the article.

Analysis Stages

Sampling

Proper sampling practices and precautions should be taken to ensure reliability of analysis in the first stage of testing itself:

• Samples should be representative of the whole. The sample should be homogeneous in nature. In most cases the original sample is found to be inhomogeneous. Such samples abound in nature and range from minerals and rocks, water bodies likes lakes, rivers, oceans, soils, etc. In such cases representative lots are obtained by drawing larger sample quantities on the basis of established sampling procedures and after thorough homogenization sample should be drawn for analysis.
• The sampling vessels should be cleaned and rinsed with the sample at least 2 to 3 times before sample collection
• The sample container should be sealed airtight and packed securely in case it is to be transported to the analysis site.

Sample Storage

• Analysis samples requiring storage should be stored under recommended conditions of storage such as temperature, humidity, exposure to light,etc
• The time between sample collection and analysis should be kept to the minimum to avoid any degradation or decay

Sample preparation and treatment

Trace metal analysis in samples such as water does not require much sample preparation. In case of solid samples or biological specimens additional steps such as fusion with flux materials or ashing or acid digestion would be necessary for extraction of trace metals from complex matrices. In such cases high purity grade reagents and acids should be used so that they do not contribute metallic impurities to the sample.

• Clean volumetric glassware should be used always
• The analyst should use clean graduated cylinders, spatulas and other items for transferring of reagents and sampling media.
• Do not keep sample longer than required in the fume hood chamber as this increases risk of contamination. It is preferable to use microwave digestion systems over open-air acid digestions.
• The analyst should avoid sample contamination from self by making use of disposable gloves, head covers and face masks while handling samples and carrying out dilutions

Environmental controls in the laboratory

• The sample preparation area should be isolated from the sophisticated instrument facilities
• Entry to the sample preparation and analysis areas should be restricted. All authorized visitors should adhere to the required dress code to prevent ingress of external contaminants
• The test area should be isolated and provision made for cleaning the air using HEPA filters
• Flooring of trace metal analysis laboratory should be vinyl coated and mopped periodically during the day
• Analyst should be allowed inside test area after changing to laboratory footwear so that outside contamination does not enter the laboratory.

The greater the precautions taken the greater will be reliability of trace metal analysis. The required environmental controls are even more stringent when ultra trace level determinations are required to be made.

EXTREME WEATHER EVENTS IN THE MONTH OF AUGUST-KAKINADA

KAKINADA

EXTREME WEATHER EVENTS IN THE MONTH OF AUGUST

Year	Temperature(oC)		Rainfall (mm)
	Highest Maximum(Date)	Lowest Minimum(Date)	24 Hours Highest (Date)	Monthly Total
2018	36.3(5)	23.4(9)	29.4(14)	125.7
2017	36.2(2)	24.2(30)	26.9(3)	105.8
2016	36.6(21)	24.2(24)	39.2(24)	53.2
2015	36(25)	24.3(4)	65.6(17)	184.1
2014	36.7(9)	24.5(13)	37(29)	101.1
2013	36(31)	21.7(1)	22(14)	69.4
2012	35.2(17,18)	23.6(4)	55.4(30)	278.8
2011	35.4(13)	23.6(3)	68(3)	232.2
2010	36.4(11)	23(31)	49(13)	241.1
2009	38.4(4, 7)	24.2(20)	44(31)	141.8
ALL TIME RECORD	38.4(4,7/2009)	21.7(19/1955 & 01/2013)	155.8(08/1983)	374.8(1983)

CLIMATOLOGICAL TABLE

PERIOD: 1981-2010

Month	Mean Temperature(oC)		Mean Total Rainfall (mm)	Mean Number of Rainy Days	Mean Number of days with
	Daily Minimum	Daily Maximum			HAIL	Thunder	FOG	SQUALL
Jan	20.3	29.2	12.6	0.9	0	0.1	0.1	0
Feb	21.7	31.2	10.3	1.1	0	0	0	0
Mar	24.0	34.0	7.5	0.5	0	0.7	0.1	0
Apr	26.2	36.2	16.4	1.1	0	2.1	0	0
May	27.8	37.5	42.3	2.8	0	5.2	0	0
Jun	27.3	35.8	122.8	7.1	0	5.4	0	0
Jul	26.2	32.9	175.4	10.9	0	5.2	0	0
Aug	25.9	32.2	176.9	10.2	0	4.7	0	0
Sep	25.9	32.7	199.4	9.1	0	7.5	0	0
Oct	24.8	31.9	243.4	9.0	0	6.8	0	0
Nov	22.5	30.4	98.8	3.8	0	1.3	0	0
Dec	20.3	29.2	10.7	0.9	0	0	0	0
Annual	24.4	32.8	1116.6	57.5	0	39	0.1	0

Local Weather Report and Forecast For: Kakinada    Dated :Jul 31, 2019

Past 24 Hours Weather Data Maximum Temp(oC) (Recorded. on 31/07/19) 33.5 Departure from Normal(oC) 1 Minimum Temp (oC) (Recorded. on 31/07/19) 26.3 Departure from Normal(oC) 0 24 Hours Rainfall (mm) (Recorded from 0830 hrs IST of yesterday to 0830 hrs IST of today) NIL Relative Humidity at 0830 hrs (%) 80 Relative Humidity at 1730 hrs (%) (Recorded. on 31/07/19) 66 Todays Sunset (IST) 18:35 Tommorows Sunrise (IST) 05:41 Moonset (IST) 17:00 Moonrise (IST) 03:31

7 Day's Forecast Date Min Temp Max Temp Weather 31-Jul 26.0 33.0 Generally cloudy sky with Light rain 01-Aug 26.0 32.0 Generally cloudy sky with moderate rain 02-Aug 26.0 32.0 Generally cloudy sky with moderate rain 03-Aug 26.0 32.0 Duststorm or Thunderstorm with squall or hail 04-Aug 27.0 33.0 Generally cloudy sky with Heavy rain 05-Aug 26.0 32.0 Rain 06-Aug 26.0 32.0 Rain