Archive for the ‘Chemistry’ Category

Cilantro: What makes it taste so good or so bad?

Thursday, January 6th, 2011

The leaves of the coriander plant are referred to as cilantro and are widely used in Mexican, Asian and Indian foods. Over the years I’ve frequently heard friends comment on the taste of cilantro. Most have said they like it, adds a fresh citrus taste, etc. But every once in a while I hear people say they can’t stand even a small amount. The taste is described mostly as soap but I’ve also heard metallic, moldy, and that it even tastes like stink bugs, although I for one have never tasted a stink bug. A quick search yields a number of blogs and postings where the detractors pull no punches about their hatred for these innocent little leaves. And surveys claim the percentage of people who dislike the taste ranges between 30% and 50%.

So I was wondering why there can be such a disparity of opinions. A number of references attribute this to genetic differences between people and that the people who really hate the taste are “Super Tasters”.   These super tasters seem to have a higher number of taste receptors on their tongues. I think my taste has been ruined by too many days spent around smelly chemicals since I feel cilantro has very little flavor.

In the ripe coriander fruits, or seeds, the content of essential oil is low (typically, less than 1%). The oil consists of about 55% linalool (50 to 60%) and about 20% terpenes (pinenes, γ-terpinene, myrcene, camphene, phellandrenes, α-terpinene, limonene, cymene).

It is believed that the cilantro aroma (from the leaves) is created by about a half-dozen aldehydes which are fragments of fat molecules. Similar aldehydes are also found in soaps and lotions and, interestingly, bugs. The taste of the fresh herb leaves and unripe seeds is due to an essential oil (0.1%) that is almost entirely made up of aliphatic aldehydes of 10 to 16 carbon atoms. There are both saturated (decanal) and α,β unsaturated (trans-2-tridecenal) aldehydes.

So there you have it. Aliphatic aldehydes are what makes cilantro taste like soap, mold or stink bugs. Me, I’m fat, dumb and happy being a not-so-super taster.

SPEX CertiPrep offers a full range of organic Certified Reference Materials.


Gourmet Salt…What’s in it?

Sunday, May 2nd, 2010

I’m sure you have seen those appealing bottles of gourmet salt for sale in gourmet food stores. They come from all around the world in a variety of colors and types of crystals. Did you ever wonder what makes one pink, another gray and yet another brown? Probably not, but I did. Yea, I know, pretty geeky, but table salt, NaCl, is colorless. So I bought a dozen different brands, then we dissolved about 0.14gm in 50ml of 2% nitric acid and analyzed by ICPMS for metal content, in particular heavy metals that might be harmful to one’s health. The tables below list the salts tested and the results. Oh, we also tested normal table salt and reagent grade sodium chloride, NaCl.

Gourmet Salts analyzed

Cyprus Black SaltMed. SeaSeaDark Grey2-10mm crystals
Mediterranean Sea SaltMed. SeaSeaWhite2-3mm crystals
Sel Gris De GuerandeFrance?Light Grey1-3mm crystals
Alaea Hawaiian Sea SaltHawaiiSeaRed Brown2-3mm crystals
Hawaii Kai Black SaltHawaiiSeaBlack1-3mm crystals
Murray River Pink Flake SaltAustraliaRiverLight Pink/Beige<2mm Flakes
HimalaSalt Primordial Sea SaltHimalayas?Pink to white2-10mm crystals
Sel de MerIsrael?White3-5mm crystals
Murray River Pink Flake SaltAustraliaRiverLight Pink/Beige<2mm Flakes
Kala Namak Black Mineral SaltIndiaMineralLight Brown/BlackFine powder
Chardonnay Oak Smoked SaltFranceSeaGrey/BrownSmall crystals
Himalayan Pink Mineral SaltHimalayasMineralLight pink/whiteFine crystals

Toxic Metals in Gourmet Salts (parts per million by weight)

MetalHIJKLTable SaltReagent NaCl

Effect of Toxic Metals on Adults

As you can see the levels of heavy metals in these samples were very low. The concentration was only about one ppm for lead in several of the samples and the other heavy metals were generally at least an order of magnitude lower. But one has to watch out even at these low levels as heavy metals tend to be difficult for the body to eliminate and therefore they can accumulate over time.

  • Lead: Is a cumulative poison and causes cancer reproductive problems.
  • Cadmium: Causes hypertension, bone and joint aches and pains and damages the kidneys and liver.
  • Mercury: Is the most toxic of all the heavy metals. Causes tiredness, loss of appetite and brain damage.
  • Arsenic: Causes skin cancer, kidney and liver failure

So how much is too much? It is a very tough question so I’ll give you some information and let you decide. A number of sources list the allowable concentrations of heavy metals. But the key is the total quantity or weight of the heavy metal one takes in since one person might consume much more or less of a food, supplement or in the case here gourmet salt. Current recommendations are for one to limit their intake of sodium to 2400mg per day which equates to about a teaspoon, or 6gm of table salt. So our calculations will be based 6gm of salt, which is probably low for most people.

The table below lists the Allowable Daily Limit (ADL) of four heavy metals in micrograms per day, one microgram = 0.000001gm. We also list the maximum weight found of these metals equated to a 6 gm sample of the salt. Based on this, the last column shows the percent of the daily allowance that one would get from the 6gm intake of salt. As you can see salt would contribute low percents of these daily intakes but bear in mind this is only one source and all sources add up, so one must minimize each source as much as possible.

Allowable Daily Intake (ADL) of Heavy Metals (ug) (6 g Daily Serving)

ElementMax Wt (ug) found in 6g sampleADL% ADL per Serving

Sample Preparation for ROHS/WEEE Directive Analysis

Tuesday, June 9th, 2009

ROHS/WEEE directives require that product components of electrical equipment imported into a number of countries, notably the European Common Market, contain less than 1000ppm of Bromine, Br, Chromium, Cr, Lead, Pb, Mercury, Hg, and less than 100ppm of Cadmium, Cd. Direct-reader, hand-held X-Ray Fluorescence, XRF, instruments have become the choice for quick, efficient screening of products for these elements.

For these analyses the handheld XRF instrument is simply pressed against the surface of the product. The XRF technique only “sees” the very thin, top layer of the sample. Further, the XRF technique is very dependent on calibration with a matrix matched reference material prior to the analysis.

The purpose of this study is to determine if this method is applicable for the directive. This study examines the accuracy and reproducibility of XRF analysis of various electrical components both as received (heterogeneous) and when ground and blended (homogeneous).

For one investigation three circular samples were cut from populated circuit boards and the front and back sides of the samples were analyzed by XRF. The samples were then cut into small pieces and copper parts were removed followed by cryogenic grinding and pressing at 30 tons onto boric acid substrates prior to XRF analysis. The results are shown below, reported as parts per million:


Sample Front Back Pellet
1 0 0 32
2 0 0 1166
3 0 0 0


Sample Front Back Pellet
1 7726 8323 7287
2 8853 8853 5504
3 8305 8305 10626


Sample Front Back Pellet
1 305 128 1903
2 181 485 1654
3 261 525 308

As can be readily seen the analytical results of the heterogeneous and homogeneous samples are very different.

  1. In samples 1 and 2 chromium was not detected prior to grinding but found after grinding. Cr levels in sample 2 were very high.
  2. Lead levels were significantly higher in ground samples 1 and 2.
  3. Bromine exceeded the RHOS/WEEE limits in all cases.
  4. Cadmium and mercury were not detected in any of the samples.

A more complete discussion and results from the analysis of additional types of samples, such as connectors and electrical components, can be found in the applications section of the SPEX SamplePrep website:

Chemicals Responsible for the Oak Aromas in Wine

Wednesday, May 6th, 2009

I like red wine, I admit it.  But I’ll also admit that I have trouble identifying the individual tastes and aromas in wine.  I can always tell if I like a wine or not, I just can’t say “It’s spicy with hints of almond and cedar”….or whatever.  I guess my nose isn’t what it should be after too many years in the lab.  But that certainly doesn’t stop me from enjoying a glass.  Being a chemist, I can appreciate the analytical approach of identifying the source and chemical compounds responsible for at least some of the aromas from a nice, heavy red.  I believe that red wine should be aged in oak barrels.  The oak is responsible for a lot of the character of the wine.  “Obie’s Out of Bounds” performs the primary fermentation, perhaps 95%, in a large plastic tub then the very, very young wine is pressed and pumped into French oak barrels to age.

The species and source of the oak itself can be a major factor in the variation in the aroma profile of a wine. Oak species differ greatly.  The French Pedunculate Oak (Quercus pedunculata = Q. robur) is known for its relatively faint aromas compared to French Sessile Oak (Q. sessilis and Q. petraea). American White Oak (Q. alba) can have a strong, distinctive aroma, sometimes considered overpowering in certain wines.  In contrast, Oregon White Oak (Q. garryana) seems to have more similarities to the French oaks than to American White Oak.

Other factors are geographic origin, hybridization, growing conditions, age and genetic variation. The stave’s position on a trunk can influence its aroma composition as well as stave seasoning and kiln versus air drying.  The cooperage process adds additional variability with barrel to barrel and even stave to stave variations from toasting.

Toasting: Lighter toasting aromas are usually attributed to oak lactones. As toasting increases, vanilla and caramel aromas associated with vanillin, furfural and 5-methylfurfural increase. At even higher toast levels these compounds decrease and are replaced by spicy (eugenol, isoeugenol, 4-methylguaiacol) and smoky characters (guaiacol, 4-methylguaiacol).

Fermentation in barrel: When fermentation is done in the barrel aldehydes such as vanillin, furfural, and 5- ethylfurfural can be partially transformed by yeast into non-aromatic alcohols.

Synergistic effects: Compounds with chemical similarities are often released from oak together (such as eugenol, isoeugenol, or other volatile phenols). The combination of similar molecules can result in perceived synergistic sensory effects even when they are below their individual sensory thresholds. This can even occur between unrelated volatiles; for example oak lactone’s sensory threshold has been found to be 50-fold lower in the presence of vanillin.

Piney, resin, cedar  and dill aromas: These aromas are often associated with American White Oak Quercus alba, and can be linked to high levels of cis oak lactone.  Quercus alba can also contain relatively high amounts of terpenes; however, key compounds have not been identified.

Nutty, roasted almond and roasted hazelnut aromas: Nutty aromas may arise at least partially from the combined sensory effect of known  volatiles coming from wine or oak.  These include diacetyl (fatty, butter), free fatty acids (fatty, rancid), furfural  and 5-methylfurfural (caramelized tones).

Cinnamon and nutmeg aromas: Cinnamon and nutmeg have both woody and spicy aromas and can be attributed to the combination of woody, coconut oak lactones and spicy compounds such as eugenol and isoeugenol.

Bread crust, toast and gingerbread aromas: Bread crust or toast character can be described as a yeasty flavor (from yeast byproducts in bread as well as in wine), or caramel aromas from carbohydrate byproducts such as furfural and 5-methyl-furfural, or smoky aromas from guaiacol, 4-  ethyl-guaiacol.  A gingerbread aroma, which may be less yeasty, can have additional contributions from spicy flavored compounds such as eugenol.

Disagreeable dusty or cardboard aromas: Chloroanisoles (TCA, TeCA and PCA) are powerful odorants with a musty, moldy odor generally referred to  the “corked” smell.  If wine seems “corked”, even prior to bottling, oak is one possible source of chloroanisole.  Of course cork is the usual source.

Pharmaceutical, band-aid or horsy, sweaty aromas: Compounds responsible for these odors are 4-ethylphenol (4EP) and 4-ethylguaiacol  and are byproducts of the yeast Brettanomyces.  One should periodically screen for Brettanomyces activity during oak aging.

The information above was obtained largely from ETS laboratories, 899A Adams St., St. Helena CA 94574, 707 963-4806.
ETS analyzes oak aromas using solid phase microextraction headspace technology for sampling (HS/SPME) followed by analysis by gas chromatography/mass spectroscopy (GCMS).

SPEX CertiPrep sells a selection of single and multi-component wine standards (pdf) for GC, GC/MS, HPLC, and HPLC/MS analysis.

BPA and Phthalates in Laboratory and Consumer Water Sources

Tuesday, March 24th, 2009

Patricia Atkins, Thomas Mancuso,
Vanaja Sivakumar and Ralph Obenauf

Spex CertiPrep, Metuchen, NJ 08840


The study examined the phthalate and bisphenol A (BPA) levels of several popular commercial bottled waters, municipal tap water, various samples of laboratory water from commercial sources, well water, and water from  de-ionized filtration systems.  In addition, the study attempted to discover whether the phthalate and BPA levels increased after being heated under conditions comparable to temperatures reached inside an automobile during the summer.  Samples were extracted then tested for phthalate and BPA levels by GC-MS.  The concentration of phthalates and BPA found in all the commercially bottled water samples and the municipal water sources were below EPA RfD (oral reference dosage) guidelines.  The EPA, defines the RfD as:  ‘…an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. The RfD is generally expressed in units of milligrams per kilogram of bodyweight per day (mg/kg/day).’  In addition, the exposure of bottled water to heat did not significantly increase the concentration of phthalates.  BPA was not detected in any of the bottled water or municipal water sources.  The water samples taken from consumer Point-of-Use (POU) systems varied greatly in the level of phthalates and BPA depending on the type of system and the amount of water flushed from the system prior to the samples being taken.  Samples taken from a stationary POU system had increased levels of phthalates compared to samples taken after the stationary water was flushed from the system.  Samples taken from one of the POU systems were found to contain small amounts of BPA, well under the guidelines of the EPA’s RfD.

To request a full copy of this very informative white paper, please visit the SPEX CertiPrep website.

Flux Fusion Energy Costs: Electricity versus Gas

Tuesday, December 23rd, 2008

When comparing the benefits of electric powered fusion units versus gas fired units, one factor that is often overlooked is the running costs. Obviously the costs go beyond just the raw price of the gas and electricity, but here we will just focus on the cost of electricity consumption of the KATANAX K2 Electric Fluxer versus that of a typical 3 or 4 unit gas burner.

The K2 electric unit:
The instrument takes about 15 minutes to heat up to a hold temperature of 1000oC. At a power of 2750W (i.e. the max power) we have a ramp-up energy of 2750 W x 15 min / (60 min / hr) = 688 W/hr = 0.688 kWh (maintaining the holding temperature of 1000oC uses 1.38 kWh).

The typical “oxide” fusion method lasts 20 minutes from start to finish and uses 2065W of energy.
2065W x 20 min / (60 min) = 688 W/hr = 0.688 kW/hr (same as heat-up)

There are three different ways one can use the instrument and each has a different energy usage:

    1.  Start from cold state then run only one fusion:

Energy = (ramp-up) + (fusion cycle) = 0.688 + 0.688 = 1.38kWh per fusion

    1. Continuous fusions:

24/7:Daily = (average power) x (hours per day) = 2065W x 24 = 50 kW per day

    1. Instrument always on, but fuses only a fraction “f” of the time:

Power = (f %) x (average fusion power) + (1-f %) x (standby power)
Daily eg: fusion 30% (f=30%) avg power = 1577 W; Daily=1577W x 24h=38kWh

The typical gas unit:
For this discussion we will focus only on consumption/cost of gas.

From internet information it appears the maximum gas consumption is approximately 19L of propane gas per minute.  The expansion ratio of LPG is approx 250:1, therefore 1 liter of LPG yields 250L of propane gas.
At a consumption rate of 19 L/min (maximum), 1 liquid liter of LPG will last 250/19 = 13 minutes, meaning the unit uses about 5 liters of liquid LPG per hour.

For comparison to the three cases above:

    1. Not applicable for gas units
    2. Continuous fusions, 24/7

(Liters per hour) x (hours in day) = 5 x 24 = 120L/day

    1. Fusions only a fraction “f” of a day

(Liters per hour) x (hours in day) x (f /100)
Example: fusions 30% of the day (f=30%) = 5 x 24 x 0.3 = 36L/day

The calculations for the gas unit are not as concise as for the electric unit, as the average consumption of gas in an approximation.

The Relative Costs:

Obviously the costs of LPG and electricity vary all round the world and are dependent on the time of year, economic factors, etc.  The costs below, for the discussion here, were from recent UK rates.

Case 2, Continuous fusions:

  • Electrical unit uses 50kW per day.  In the UK a domestic kW costs approx 12p, therefore the total cost would be 50 x £0.12 = £6.00
  • LPG unit uses 120L per day.  In the UK LPG costs 55p/L so the total cost would be 120 x £0.55 = £66.00

Case 3,  30% of time spent doing fusions:

  • Electrical unit uses 38kW/h per day.  1 kW costs approx 12p in the UK, so the total cost would be 38 x £0.12 = £4.56.
  • LPG unit uses 36L/day.  LPG costs 55p/L in the UK, so the total cost would be 36 x £0.55 = £19.80

I would stress again that these calculations use a number of assumptions and therefore are not completely accurate.  However it appears that the energy costs are approximately 4 to 10 times higher for a gas burner unit compared to the electric the K2 unit.

Cork Taint in wine

Thursday, October 30th, 2008


Cork Taint in Wine  If you ever opened a bottle of wine and immediately were hit with a pungent odor (not vinegar) you know what I want to discuss here: “ Cork Taint” or wine that is “Corked”.  The term “Corked” is a broad term that people use to describe many undesirable smells and tastes in wine arising from spoilage to storage conditions to wooden barrels to just bad grapes.     However the chief cause is believed to result from the compound, 2,4,6-trichloroanisole, TCA.  The human threshold for TCA is in the single-digit parts per trillion, varying by several orders of magnitude depending on an individual’s sensitivity.  The smell has been described as mold, wet dog, phenol, chlorine, and others.  While harmless, TCA can make a wine undrinkable, except perhaps by me.   SPEX CertiPrep has been working on detection limits and the development of reference materials for 2,4,6-Trichloroanisole.  As you may know most cork comes from cork trees grown in Portugal.  The production is mostly from mom and pop business where the bark is striped, spread out to dry and treated with a chlorine containing chemical.  The chlorine chemicals are believed to react with phenolic compounds in the cork resulting in cork taint, i.e. 2,4,6-Trichlorophenol.  Some people believe these phenolic compounds come from fungi in the cork or in the air.   A number of vintners are beginning to use twist off caps for white wines, as un-classical a way of sealing wine as it is, because it provides a great seal.  For reds, synthetic corks are not as good as they should be, but they are improving and will eventually compete with natural cork, especially if cork taint continues to be a problem.

Caffine and calories in beverages and energy drinks

Thursday, October 30th, 2008

Caffeine in Beverages

Beverage / Drink Calories (kcal) Carbs (g) Sodium (mg) Volume (oz) Caffeine/Vol (mg) Caffeine/12oz (mg)
Water 0 0 0 na 0 0
Gatorade 50 14 110 8 0 0
Gatorade Endurance 50 14 200 8 0 0
Powerade 64 17 53 12 0 0
Coke Classic 140 39 50 12 35 35
Sunkist 190 52 45 12 41 41
Pepsi 100 27   12 38 38
Dr. Pepper 150 39   12 41 41
Mountain Dew 110 31   8 37 56
Brewed Coffee (avg) 0 0 0 8 150 225
Decaf Coffee 0 0 0 8 6 9

Caffeine in Energy Drinks

Beverage / Drink Calories (kcal) Carbs (g) Sodium (mg) Volume (oz) Caffeine/Vol (mg) Caffeine/12oz (mg)
Amp 114 30   8.4 75 107
SoBe Adrenaline 120 31   8.3 79 114
Red Bull 106 27 193 8 80 116
Full Throttle 220 58   16 144 108
Monster 200 52   16 160 120
Hi Ball Energy 4     8 60 90
Hype Energy Drink 114 27   8 77 116
Fixx       20 500 300
Wired X505       24 505 253


Monday, October 8th, 2007

ISOTOPE DILUTION FOR THE ANALYSIS OF METALS IN PLASTICS  Ralph Obenauf, Vanaja Sivakumar, Laszlo Ernyei, Bill Driscoll, SPEX CertiPrep, Inc. 203 Norcross Avenue, Metuchen, NJ 08840,

     The European Directive, Restriction of Hazardous Substances (RoHS) & Waste Electrical and Electronic(WEEE) restricts the use of hazardous substances such as  lead, cadmium, chromium(VI), mercury and brominated polybihphenyl ethers  in electronic and other equipment.  The RoHS & WEEE directives set only a minimum standard.  Different countries have set their own regulations and requirements.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             Various analytical methods are employed to determine the concentration of restricted substances.  Most methods require some sample preparation such as digestion or extraction.  Many of the methods currently used are not appropriate for all products tested, and results differ from method to method.  It is vital to develop standard methods that produce reliable results that can be implemented by all laboratories.  We have developed a method for accurate analysis of the above metals in plastic.       Methods based on direct analysis of solid samples by XRF and Laser Ablation ICP-MS are limited due to the lack of calibration standards for various complex plastic matrices.  Methods based on destructive sample preparation usually employ heating the polymers with mineral acids or dissolution in organic solvents [1].  However, heating with acids may lead to the loss of analytes due to volatilization and many polymers are sparingly soluble in organic solvents.  Here we employed two techniques for sample preparation, namely, conventional ashing and microwave digestion.       Isotope dilution Mass Spectrometry (IDMS) is based on the addition of a known quantity of an enriched isotope to a sample. Equilibration of the spike isotope with the natural element in the sample alters the isotope ratio that is measured. Knowing the isotopic abundance of both spike and sample, the amount of spike added to the known amount of sample, the measured concentration of the spike added and the altered isotope ratio, then the concentration of the element in the sample can be calculated [2].  Since elements of interest such as Cd, Cr and Pb in the RoHS directive have two or more naturally occurring isotopes, the isotope dilution technique presents an interesting solution for the determination of these elements.       Ashed polyethylene polymer dissolved in nitric acid was analyzed for cadmium, chromium and lead. The polymer was spiked with a known amount of cadmium enriched with Cd-106, chromium enriched with Cr-50 and lead enriched with Pb-206; then ashed.  Both spiked and un-spiked polyvinyl chloride and polyethylene polymers were also digested in a combination of nitric, hydrochloric, hydrofluoric acid along with hydrogen peroxide.     The IDMS technique results in higher accuracies in the determination of lead, chromium and cadmium than conventional calibration methodology.   Partial loss of analyte due to sample preparation or the complexity of the matrix did not affect the accuracy of determination.   References: 1. Digestion of Plastic Materials for the Determination of Toxic Metals with a Microwave Oven for Household Use: Hiroki Sakurai et al, Analytical Sciences, February 2006, Vol.2.2. USEPA Method 6800: Elemental and Speciated Isotope Dilution Mass Spectrometry. 

Matrix Effects in ICP-OES Analysis

Friday, August 17th, 2007

Matrix effects in ICP-AES analysis

Ralph Obenauf and Vanaja Sivakumar

SPEX CertiPrep, Metuchen, NJ

The sample “matrix” is the bulk composition of the sample such as water, organic compounds, acids, dissolved solids and salts, etc. Matrix effects can influence the ability of an analytical method, to qualitatively identify and quantitatively measure target compounds in environmental and other samples, by indirectly affecting the intensity and resolution of observed signals. To obtain defensible results the analyst must account for all matrix effects. In ICP-OES analysis the ionic-to-atomic line intensity ratio can be used as an indicator for determining plasma related matrix effects. Elements such as sodium and calcium, which are ubiquitous in nature, have low ionization potentials and as a consequence are some of the most easily ionized elements. In this study the influence of sodium as well as the acid concentration on the ionic-to-atomic intensity ratio of chromium, cadmium and lead has been investigated.

Effect of Sodium concentration:

We observed a considerable change in the recovery of cadmium and chromium, which exhibits a profound influence on these analytes by varying the concentration of Sodium. The relative intensity of chromium and cadmium atom lines were much higher than the respective ionic lines for these analytes. The effect is significant even at 50 ppm sodium. The lead concentration is affected, relatively, less by the change in the sodium concentration.

Effect of acid concentration:

The matrix effect due to changes in the acid concentration was very significant for cadmium and lead in nitric acid, While the chromium atomic line was unaffected, a decrease was observed in the in intensity for the chromium ionic line. The higher the acid concentration, the lower the intensity for lead and cadmium, and therefore resulting in poorer detection limits. We observed much smaller changes in analyte recoveries for increases in hydrochloric acid concentrations when compared with comparable nitric acid concentration changes.Matrix effects have a profound effect on the accuracy of trace elemental analysis by ICP. Excess acid from acid digestion can be a source of error in the analysis. Because of the different behavior of the atomic and ionic lines, at least two internal standards are needed to compensate for matrix effects. It is absolutely essential to match the sample matrix to the standard to assure accurate and defensible data.