FAQ Frequently asked questions

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White from  field:

These are bottles filled in the field with distilled water (for metal analysis) or mineral water (for organic analysis) which are exposed to the sampling environment for the same period as the sample.  

The field blank is analyzed with the same methodology used for the sample, and if any contamination is found, then probably the same occurred with the sample during collection or processing in the laboratory.   

What are quality controls (QC)?  

Quality control (QC) is a set of technical activities – including sampling, calibration and analytical procedures – which are adopted to evidence and promote the production of data with known accuracy and precision.  

For the sampling of water, effluents, soils, solid waste and sediments, one of these quality controls is the white one, used to signal if there was contamination of the sample with any foreign material from the collection stage, through transportation, to the analysis.   

What is LD?  

The method’s detection limit is the lowest concentration of the analyte that can be detected, but not necessarily quantified under the conditions employed during the analysis. A concentration below LD may not be detected by the method.  

O que é LD?  

O limite de detecção do método é a mínima concentração do analito que pode ser detectada, mas não necessariamente quantificada sob as condições empregadas durante a análise. Uma concentração abaixo do LD pode não ser detectada pelo método.    

What is LQ?  

Limit of quantification is the lowest concentration of an analyte that can be determined with acceptable accuracy and precision under the conditions used during the analysis.  

What is rush time? 

Rush time is any time of analysis inferior to the ALS standard.  

Does ALS reuse bottles?  


Do I pay for the bottles?  


Can I use the same type of bottle for all analyses?  

No, since each matrix requires a specific type of bottle.    

What is Holding Time? 

Holding time is the maximum period indicated between the collection of the sample – maintained under specific conditions – and its analysis, without significant degradation of analytes or their properties. This period depends on the characteristics of the analyte, the type of matrix and the specific constituents of the sample.  

The holding time is established due to the possibility of certain sample constituents suffering degradation or volatilization over time, which would result in an inaccurate measurement of these compounds.   

In order to avoid the degradation of analytes, some samples require preservation by chemical and/or physical means, such as pH adjustment and temperature control, respectively. Thus, it is more likely that the results obtained through the analyses will express the real state of the object studied, whether it is an effluent, water, soil, sediment, industrial waste, gas, indoor air, outdoor air, etc.   

What is environmental analysis and why should I do it? 

Environmental analysis is the characterization and evaluation of the quality of the environment used to determine the degree of impact of any human activity on the level of quality of soil, water and air, as well as the verification of the effectiveness of effluent treatments and the classification of waste.   

What is the validity of my oil sample?

The oil sample is not valid but because it is a predictive maintenance it is not recommended to stock. So after the collection should be sent immediately.

How should I collect the oil?

After the kits have arrived, follow the step-by-step instructions for collecting all the maintenance plan compartments. For a perfect oil collection, the equipment must be moved and all of its implements must be activated so that the oil circulates through the parts, keeping the particles in suspension.

It is important to remember that if the equipment has been out of operation for more than 30 minutes, it should be moved again. Follow step-by-step to collect all maintenance plan compartments.

For collection, simply cut the hose approximately one hand wider than the dipstick. In the case of the filling nozzle, the size must be sufficient to reach a maximum of 5 cm from the level of the reservoir oil.

The next step is to attach the hose to the pump, so that the tip does not enter the collection bottle. Tighten the nut to secure the hose and uncap the collection bottle, storing the cap in the bag and securing the bottle to the pump. To ensure that the pump is not in contact with the oil, always keep it in an upright position.

Insert the hose into the bottom of the filler neck or dipstick tube and pump. If the oil is not filtered, lower the hose a little more into the tank. As soon as the vial is full, loosen the pump nut to let air in and the oil stop being pulled. Carefully pull the hose from the reservoir, then carefully remove the bottle from the pump and immediately plug it.

With the pump upright, push the hose down and wipe it clean. Turn pump with hose tip up and clean again. Then just pull the hose down. It is important to note that the hose must not be reused and should be discarded in an appropriate place. Watch the step by step here.

Do I need any tools to perform fluid collection?

Yes, at the time of collection it is necessary to have a pump or a collection valve that will aid the flow of the fluid and prevent external contamination.

Should I do oil analysis on stationary machines?

Stationary machines are also subject to possible contamination as a result of problems of different origins. They may arise from inconsistency in the lubricating oil itself, in the equipment or by external factors. Oil analysis on stationary machines enables equipment to be always available if your company needs to use them.

Why should I opt for PQI analysis?

The PQI enables the anticipation of severe wear problems that may not be detected early by traditional atomic emission spectrometry techniques.

How often should I perform fluid collection on my equipment?

Although the original equipment manufacturer’s recommendations provide a good starting point for the development of preventive maintenance practices, sampling intervals can vary easily. The importance of a piece of equipment for production is an important consideration in determining collection frequency, as well as environmental factors such as hot and dirty operating conditions, short trips with heavy loads and excessive idle times.

What is oil analysis and why should I do it?

Oil analysis is a diagnostic, predictive maintenance tool that has the primary purpose of monitoring and evaluating lubricant and equipment conditions. It enables you to maximize asset performance and reliability by identifying small issues before they become major failures. You can safely extend oil drain intervals and, ultimately, the life of your equipment – saving time and money.

Why don’t the results from ALS match results from other methods? Why do results for a given sample vary among the various sampling and analytical approaches?

The challenge presented when comparing methods containing so many variables involved has led this issue to be an oft-debated question at both technical conferences and in literature. Some variables in question may include:

  • Sampling media: tubes, bags, canisters, oil and solutions are all currently used by the various methods.
  • Analytical instrumentation: GC/MS, GC/ICP and GC/AED.
  • Calibration standards: some methods use liquid standards, while others use vapor-phase standards.
  • Target analyte list: Varies from 5 to 22 siloxane compounds.
  • Reporting limits: vary greatly.
  • Results calculations and reporting formats: some methods report total siloxanes but do not speciate them, others speciate them in various units: mg/m3, mg Si/m3, ppmV, ppmV as Si or µg Si/m3 CH4.

Given these factors, it is not unexpected that there could be variability observed in the results obtained by the various methods.

Can the results be reported in units of “ppmV as Si” or “µg Si/m3 CH4”?

Yes, the lab can report results in µg/m3, ppmV as Si or µg Si/m3 CH4. The default report unit is µg/m3, and the standard report also includes a “total Si” value listed at the bottom of each report. Other units/report formats should be requested prior to sample submission. To report µg Si/m3 CH4, the methane concentration needs to be determined by EPA method 3C, which requires the submission of a separate Tedlar bag or summa canister. Please note that methane cannot be collected with the siloxane sorbent tube.

Are the samples considered “dangerous goods”?

Siloxane tubes are neither flammable nor toxic, so they can be shipped via standard shipping methods (UPS/FedEx). If samples are collected with Tedlar bags, however, and the sample contains flammable concentrations of methane, then the bag may be characterized as dangerous goods or hazardous goods. It is the shipper’s responsibility to adequately characterize their sample and ship them in compliance with
DOT regulations.

Can volatile organic compounds be determined from the siloxane sampling tube?

While this sampling and analytical approach is suitable for a limited list of VOCs, most of the VOCs typically reported by EPA TO-15 or TO-17 are not available with this analysis.

What is the sample hold time?

Sorbent tubes are stable for up to fourteen days after sampling and may be stored at room temperature prior to analysis. Tedlar bags may be stored for 72 hours prior to analysis.

Are there advantages in one collection method over the other?

Since both methods yield comparable data, the selection of sampling media can be a function of parameters such as sampling preference/familiarity, field time, reporting limits, shipping requirements, and hold time.

What about inclement weather?

In cases of extreme cold, lower recoveries have been observed due to siloxane adherence to the sample tubing. Recommendations to improve recoveries in cold weather include making the sample train as short as possible to minimize losses, using insulated tubing, or sampling with a Tedlar bag.

Will high humidity affect the sample results?

Since some of the siloxane compounds are soluble in water (most notably Trimethylsilanol and D3), high humidity (>90%) may hinder the overall siloxane recovery. Appreciable water build up inside the tubes may also reduce the performance of the sorbent, so in cases where there are visible water droplets it is recommended that a Tedlar Bag be used for collection.

Can the samples be collected and submitted in a Tedlar bag instead of sampling with a tube?

Yes, a Tedlar bag may be used to collect the samples for this analysis. Note, the standard hold time for a Tedlar bag sample is 72 hours from sample collection to analysis. Reporting limits for samples collected with a Tedlar bag will be higher than those for samples collected on a sorbent tube, due to a smaller sample size.

What quality control criteria is followed once a sample is received?

The laboratory follows QA/QC criteria established by the National Environmental Laboratory Accreditation Program(NELAP), which includes, but is not limited to: instrument tuning, internal calibration (ICAL), second source standards verification, continuing calibration verification (CCV), laboratory control standards and duplicates (LCS and LCSD) and method blanks.

How did the lab arrive at a nine-compound target siloxane list?

The analytes are those most frequently referenced in literature as the primary constituents in landfill gas and biogas.

What are the most common siloxanes found in LFG/biogas?

Our field research has consistently detected trimethylsilanol, octamethylcyclotetrasiloxane (D4), and decamethylcyclopentasiloxane (D5) in landfill gas. Similarly, D4 and D5 have been observed in biogas, while trimethylsilanol is not typically a significant factor.

How did you validate your in-house developed method?

The laboratory adhered to OSHA’s Organic Chemicals Air Sampling and Analysis Guideline for validating sorbent-based methods. This guideline was followed to validate method parameters such as sampling rate, sample volume, breakthrough studies, sample recoveries, sample hold time, relative humidity, gas-phase standards, field samples and field sample “over-spikes.”

Are there any established standards for siloxane monitoring?

There are currently no state or federal promulgated methods for the sampling and analysis of siloxanes, because currently siloxanes are not subject to regulation under current air quality standards. Rather, monitoring of siloxanes is typically performed to characterize gas streams used in combustion applications (waste to energy applications), or for performance criteria for turbines. There are numerous commercially available siloxanes sampling and analytical methods.

Why couldn’t a uniformly mixed bed of multiple sorbents be used for passive sampling? Wouldn’t you be able to capture more compounds?

If a passive sampler were comprised of a mixed bed of different sorbents, contaminants would preferentially adsorb to the strongest sorbent in the mix. Unlike active sampling, where contaminants travel through each bed in increasing sorbent strength (and only the most volatile compounds are trapped on the strongest sorbent bed), it is likely that many or all compounds would adsorb irreversibly on the strongest sorbent in the mixture.

For example, if a client was sampling a mixture of PCE and breakdown products to vinyl chloride, during active sampling (passing a sample stream through a beds of increasing strength) the PCE and TCE would likely be trapped by the first (weaker) sorbent, mid- range compounds would be trapped by both the weakest and the middle sorbent, and the vinyl chloride would travel through all sorbents until it reached the strongest sorbent in the back of the tube. If everything adsorbed onto the strongest sorbent (as in the case of the mixed-sorbent bed), only the very volatile compounds would be recovered off of the tube.

If multi-sorbent tubes can be used for active sampling to get a longer compound list, why aren’t they used for passive sampling?

Most multi-sorbent tubes are packed such that there are a few centimeters of each material bed packed in the tube sequentially, from weakest to strongest. When thermal desorption tubes are used in a passive mode (called “axial diffusive samplers”), one end of the tube  is capped off (the outlet) and a diffusion cap is placed on the other end of the tube (the inlet). With this configuration, air enters the tube through the diffusive end only, and interacts with approximately just the first one to two centimeters of the first sorbent bed.

Over time, it is possible that once the tube is capped contaminants may come to equilibrium within the tube (meaning some compounds will be released from that “weaker” first bed of sorbent and then will preferentially migrate to the other “stronger” beds); generally speaking, however, passive sampling will only yield interaction with the first few centimeters of sorbent, rendering the unexposed sorbent beds virtually  useless in passive applications.

What if I want to analyze a compound on the sampler that does not have an established uptake rate?

In many cases this can be done; however, only the mass of the target analyte can be determined and reported. The uptake rate is required, along with the laboratory-quantified mass value (μg/sample), to calculate the average concentration (μg/m3 or ppbV) over the sampling interval.

Are all passive samplers ready to go off-the-shelf or should the laboratory QC them prior to field use?

Laboratory QC of the samplers depends on vendor specifications. Some recommend cleaning and QC prior to deployment, others do not. Consult with the laboratory for vendor recommendations for the sampler selected for your project.

What are the types of passive samplers? For what families of compounds do you have samplers?

There are many types of commercially available samplers for many different families of compounds. ALS routinely offers analysis using the samplers listed below in Table 1 (Reverse side).

Are all samplers the same?

Although all passive samplers operate on the same principle, the housing materials, shapes and sorbent options differ and therefore lend variability. Each sampler has been optimized for an ideal sampling time, relative humidity level, target analyte list, and reporting limits, which also varies among sampler types.

Why do I need to record and provide sampling duration to the laboratory?

The laboratory can merely determine the mass collected on the sorbent for a given analyte unless the sampling duration is provided and an uptake rate is available. In order to convert mass/sampler to mass/volume (µg/m3 or ppbV), the sampling duration must be provided.

Why do you ask that I record the average ambient temperature on the chain of custody? Do humidity or wind speed affect the sampling rate?

Since the uptake rates are established at ambient temperature (298K, or 25°C), a correction factor can be applied for samples collected under non-ambient conditions. In order to apply this correction factor, field conditions should be noted on the chain of custody, otherwise the ambient uptake rates will be used.

How long do I deploy a passive sampler for?

Deployment time depends on the both the type of sampler used and the required reporting limits. Typical sampling rates vary anywhere from eight hours to four weeks. The laboratory can provide you with the vendor-recommended sampling intervals for your project-specific target analyte list.

How do passive samplers for air applications work?

Unlike active sorbent sampling, which requires a sampling pump and has a definitive sample volume, passive sampling involves the collection of organic vapors by way of diffusion. Samplers are deployed near a point of interest (ex. clipped on a garment in the breathing zone, hung in a room, etc.) and left for a specified period of time. Compounds adsorb to the sorbent material by means of diffusion. The respective masses of the target analytes are then converted to time-weighted average concentrations (in units such as µg/m3 or ppbV) using an experimentally derived variable called an “uptake rate.” Uptake rates are a function of both the sorbent material being used and the geometry of the particular sampling device. Each target analyte requires its own established uptake rate, and the variable is expressed as milliliter of compound adsorbed by the sampler sorbent per minute (mL/min). Not every compound has an established uptake rate for a given sampling device. Consult with the laboratory for the most current list of uptake rates for the available sampling devices.