During today's call, I will provide you a brief overview of our first quarter operating results as well as an update on our three phase transformation plan focused on; Number 1, beginning our commercial momentum; Number 2, further strengthening our organization with leadership and performance management; and Number 3, aligning our portfolio with growth areas.
Briefly reviewing our operating results, for the first quarter revenue grew 31% as reported, 27% on a constant currency basis, and non-GAAP adjusted earnings per share grew 99% year-over-year.
Our largest market category pharma grew 28% in constant currency, industrial grew 24%, and academic and government grew 29%.
On a constant currency basis; sales in Asia grew 41%, with China up 109%; sales in Americas grew 14%, with US growing 13%; and sales in Europe grew 25%.
From an operating segment perspective, our Waters division grew 26%, while TA grew by 28% on a constant currency basis.
Recurring revenues grew 15%, with services growing 14% and chemistry consumables revenue growing 18%, driven by combined pharma strength and improved industrial demand.
LC instruments grew across all of our major geographies and market categories with more than 40% growth.
Mass spec sales were also strong in the first quarter with growth in excess of 50% as demand in the pharma market remains robust.
Revenue grew 28% as demand rebounded in the core industrial business and strength continued in pharma medical devices and semiconductors.
Our three-phase transformation plan is; Number 1, beginning our commercial momentum; Number 2, strengthening our organization with leadership and performance management; and Number 3, aligning our portfolio with growth areas.
We delivered a significant acceleration in instrument revenue growth to 45%.
Third, our e-commerce initiative has begun to deliver tangible results, search engine optimization and paid search had lead to search impressions that are up more than 40% year-on-year.
This is now especially relevant from one of the structural changes in the sugar pattern of the spike protein of the SARS-CoV-2 virus.
In the first quarter, we recorded net sales of $609 million, an increase of approximately 27% in constant currency.
Currency translation increased sales growth by approximately 4%, resulting in sales growth of 31% as reported.
Our revenue -- our reoccurring revenue, which represents the combination of precision chemistry products and service revenue increased by 15% for the quarter, while instrument sales increased 45%.
Chemistry revenues were up 18% for the quarter, driven by strong pharma market growth and improving industrial demand.
On the service side of our business, revenues were up 14% as customers continue to reopen labs and catch up on performance maintenance, professional services and repair visits.
Breaking first quarter operating segment sales down further, sales related to Waters Division sales grew 26%, while TA Instrument sales grew 28%.
Combined LC and LCMs instrument sales were up 47%, while TA system sales grew 34%.
Gross margin for the quarter was 58.2%, a 350 basis point increase compared to 54.7% in the first quarter of 2020, primarily due to an increase in sales volume and favorable effects.
Operating expenses increased by approximately 9% on a constant currency basis and 11% on a reported basis.
In the first quarter, our effective operating tax rate was 14% an increase from last year, as compared to the comparable period included some favorable discrete items in the prior year.
Net interest expense was $7 million for the quarter, a decrease of about $3 million, as anticipated on lower average outstanding debt balances.
Our average share count came in at 62.6 million shares, flat with the first quarter of last year.
Our non-GAAP earnings per fully diluted share for the first quarter increased 99% to $2.29 in comparison to the $1.15 last year.
On a GAAP basis, our earnings per fully diluted share increased to $2.37 compared to $0.86 last year.
In the first quarter of 2021, free cash flow grew 60% year-over-year to $193 million, after funding $40 million of capital expenditures.
Excluded from free cash flow was $14 million related to the investment in our Taunton precision chemistry operation.
In the first quarter, this resulted in $0.32 of each dollar of sales converted into free cash flow.
In the quarter, accounts receivable days sales outstanding came in at 84 days, down 15 days compared to the first quarter of last year.
Inventory decreased by $16 million in comparison to the prior year quarter on higher sales volumes.
In terms of returning capital to shareholders, we repurchased approximately 600,000 shares of common stock for $173 million in the first quarter.
These capital allocation activities along with our free cash flow results in cash and short-term investments of $810 million in debt of $1.7 billion on our balance sheet at the end of the quarter.
This resulted in a net debt position of $893 million and a net debt to EBITDA ratio of about 1 times at the end of the first quarter.
These dynamics support updated full-year 2021 guidance for constant currency sales growth up 8% to 11%.
At current rates, the positive currency translation to 2021 sales growth is expected to be approximately 1 percentage points to 2 percentage points.
Gross margin for the full year is expected to be between 57.5% and 58%.
Accordingly, we expect 2021 operating margins of between 28% and 29% based on a combination of investments, the normalization of COVID-related cost, and disciplined expense controls.
Moving now below the operating income line, other key assumptions for the full year guidance are as follows; net interest expense of $35 million to $38 million; a full year tax rate in the range of 14.5% to 15.5%; the net impact of our share repurchase program in 2021 that will result in an average diluted 2021 share count of 61.5 million to 62.0 million shares outstanding.
Rolling all this together, and on a non-GAAP basis, full-year 2021 earnings per fully diluted share are now projected in the range of $9.85 to $10.05, which assumes a positive currency impact on full year earnings-per-share growth of approximately 3 percentage points.
We expect constant currency sales growth to be 14% to 16%.
At today's rates, currency translation is expected to increase second quarter sales growth by approximately 3 percentage points.
Second quarter non-GAAP earnings per fully diluted share are estimated to be in the range of $2.15 to $2.25 as the significant prior year COVID cost savings actions start to normalize.
At current rates, the positive currency impact on second quarter earnings-per-share growth is expected to be approximately 1 percentage point.

Summary:
In the first quarter, we recorded net sales of $609 million, an increase of approximately 27% in constant currency.
Our non-GAAP earnings per fully diluted share for the first quarter increased 99% to $2.29 in comparison to the $1.15 last year.
On a GAAP basis, our earnings per fully diluted share increased to $2.37 compared to $0.86 last year.
These dynamics support updated full-year 2021 guidance for constant currency sales growth up 8% to 11%.
Rolling all this together, and on a non-GAAP basis, full-year 2021 earnings per fully diluted share are now projected in the range of $9.85 to $10.05, which assumes a positive currency impact on full year earnings-per-share growth of approximately 3 percentage points.
We expect constant currency sales growth to be 14% to 16%.
Second quarter non-GAAP earnings per fully diluted share are estimated to be in the range of $2.15 to $2.25 as the significant prior year COVID cost savings actions start to normalize.